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NORWEGIAN JOURNAL OF GEOLOGY <strong>Provenance</strong> <strong>characteristics</strong> <strong>of</strong> <strong>the</strong> <strong>Brumunddal</strong> <strong>sandstone</strong> <strong>in</strong> <strong>the</strong> <strong>Oslo</strong> Rift<br />

<strong>Provenance</strong> <strong>characteristics</strong> <strong>of</strong> <strong>the</strong> <strong>Brumunddal</strong> <strong>sandstone</strong><br />

<strong>in</strong> <strong>the</strong> <strong>Oslo</strong> Rift derived from U-Pb, Lu-Hf and trace element<br />

analyses <strong>of</strong> detrital zircons by laser ablation ICMPS<br />

Tom Andersen, Ayesha Saeed, Roy H. Gabrielsen & Snorre Olaussen<br />

Andersen, T., Saeed, A., Gabrielsen, R.H. & Olaussen, S.: <strong>Provenance</strong> <strong>characteristics</strong> <strong>of</strong> <strong>the</strong> <strong>Brumunddal</strong> <strong>sandstone</strong> <strong>in</strong> <strong>the</strong> <strong>Oslo</strong> Rift derived from<br />

U-Pb, Lu-Hf and trace element analyses <strong>of</strong> detrital zircons by laser ablation ICMPS. Norwegian Journal <strong>of</strong> Geology, vol. 91, pp 1-19. Trondheim<br />

2011. ISSN 029-196X.<br />

The 800 m thick <strong>Brumunddal</strong> <strong>sandstone</strong> is partly an eolian, partly a fluvial <strong>sandstone</strong> deposited <strong>in</strong> a fault-bounded bas<strong>in</strong> <strong>in</strong> <strong>the</strong> nor<strong>the</strong>rn part <strong>of</strong> <strong>the</strong><br />

<strong>Oslo</strong> Rift <strong>in</strong> Permian time.The <strong>sandstone</strong> is <strong>the</strong> youngest rift-related deposit <strong>in</strong> <strong>the</strong> nor<strong>the</strong>rn part <strong>of</strong> <strong>the</strong> <strong>Oslo</strong> Rift. Well rounded detrital zircons are<br />

common accessory m<strong>in</strong>eral gra<strong>in</strong>s <strong>in</strong> <strong>the</strong> <strong>sandstone</strong>. U-Pb dat<strong>in</strong>g <strong>of</strong> detrital zircon from a sample <strong>of</strong> <strong>the</strong> <strong>Brumunddal</strong> <strong>sandstone</strong> by LAM-ICPMS<br />

gives a range <strong>of</strong> ages from (rare) late Archaean ages to Permian (283±4 Ma). The age and <strong>in</strong>itial εHf pattern <strong>of</strong> zircons <strong>in</strong> <strong>the</strong> sediment match <strong>the</strong><br />

ma<strong>in</strong> rock- form<strong>in</strong>g events <strong>in</strong> Fennoscandia from Archaean to Phanerozoic time. This k<strong>in</strong>d <strong>of</strong> diverse provenance was most likely obta<strong>in</strong>ed by<br />

repeated recycl<strong>in</strong>g <strong>of</strong> clastic sediments <strong>of</strong> Fennoscandian orig<strong>in</strong>, with Silurian, cont<strong>in</strong>ental <strong>sandstone</strong>s as <strong>the</strong> most probable direct precursors. Trace<br />

element distributions show a conspicuous absence <strong>of</strong> patterns with <strong>the</strong> high level <strong>of</strong> U and Th enrichment typical <strong>of</strong> zircon from granitic rocks.<br />

This is consistent with a complex transport and redepositional history: High U-Th, metamict zircons were selectively removed by abrasion dur<strong>in</strong>g<br />

repeated transport-deposition-erosion cycles. In addition to recycled material, Caledonian syn-orogenic <strong>in</strong>trusions and Permian <strong>in</strong>termediate to<br />

felsic plutonic rocks <strong>in</strong> <strong>the</strong> <strong>Oslo</strong> Rift itself were m<strong>in</strong>or, but still significant sources <strong>of</strong> detrital zircon.<br />

Tom Andersen & Roy H. Gabrielsen, Department <strong>of</strong> Geosciences, University <strong>of</strong> <strong>Oslo</strong>, PO Box 1047 Bl<strong>in</strong>dern, NO-0316 <strong>Oslo</strong>, Norway (tom.andersen@geo.<br />

uio.no). Ayesha Saeed, GEMOC, Macquarie University, NSW-2109, North Ryde, Australia. Snorre Olaussen, The University Centre <strong>in</strong> Svalbard, P.O. Box<br />

156, N-9171 Longyearbyen, Norway<br />

Introduction<br />

The <strong>Brumunddal</strong> <strong>sandstone</strong> (<strong>in</strong>formal name) is <strong>the</strong><br />

uppermost preserved member <strong>of</strong> <strong>the</strong> late Paleozoic, riftrelated,<br />

volcanosedimentary succession <strong>in</strong> <strong>the</strong> nor<strong>the</strong>rn<br />

part <strong>of</strong> <strong>the</strong> <strong>Oslo</strong> Rift. It was deposited on a substrate <strong>of</strong><br />

rhomb porphyry lava, and is preserved <strong>in</strong> a ca. 6.5 km by<br />

2.5 km, downfaulted block, <strong>the</strong> Narud halfgraben (Fig.<br />

1). The <strong>Brumunddal</strong> <strong>sandstone</strong> consists <strong>of</strong> red and yellow,<br />

cross-bedded, eolian dune deposits and fluvial channel<br />

and floodpla<strong>in</strong> deposits (Rosendal 1929, Larsen et al.<br />

2008). Its maximum depositional age is constra<strong>in</strong>ed by<br />

a Rb-Sr m<strong>in</strong>eral isochron age <strong>of</strong> <strong>the</strong> underly<strong>in</strong>g rhomb<br />

porphyry lava at 279±9 Ma (Sundvoll et al. 1990). The<br />

absence <strong>of</strong> overly<strong>in</strong>g, datable rocks leaves <strong>the</strong> younger<br />

limit for <strong>the</strong> age <strong>of</strong> deposition unconstra<strong>in</strong>ed. Larsen et<br />

al. (2008) regarded <strong>the</strong> <strong>sandstone</strong> as a remnant <strong>of</strong> graben<br />

fill that formed dur<strong>in</strong>g <strong>the</strong> ma<strong>in</strong> rift<strong>in</strong>g stage <strong>of</strong> <strong>the</strong> <strong>Oslo</strong><br />

Rift, which is characterized by widespread plateau lavas<br />

<strong>in</strong>tercalated by cont<strong>in</strong>enal deposits.<br />

Through <strong>the</strong> U-Pb and Lu-Hf isotope systems and trace<br />

element distribution patterns, detrital zircon gra<strong>in</strong>s<br />

<strong>in</strong> a <strong>sandstone</strong> reta<strong>in</strong> a robust memory <strong>of</strong> <strong>the</strong> age,<br />

petro genetic history and compositional <strong>characteristics</strong><br />

<strong>of</strong> <strong>the</strong> magmatic or metamorphic rock(s) <strong>in</strong> which <strong>the</strong>y<br />

formed, i.e. <strong>of</strong> <strong>the</strong> protosource (e.g. Fedo et al. 2003,<br />

K<strong>in</strong>ney & Maas 2003, Belousova et al. 2002, 2006). As<br />

<strong>the</strong> youngest pre-Quaternary sedimentary deposit <strong>in</strong> <strong>the</strong><br />

nor<strong>the</strong>rn part <strong>of</strong> <strong>the</strong> <strong>Oslo</strong> Rift, this <strong>sandstone</strong> may have<br />

sampled a range <strong>of</strong> Precambrian and Paleozoic protosources<br />

<strong>in</strong> <strong>the</strong> Fennoscandian Shield, <strong>the</strong> Caledonian<br />

nappes and with<strong>in</strong> <strong>the</strong> <strong>Oslo</strong> Rift itself. However, detrital<br />

zircons <strong>in</strong> a sedimentary rock may have been recycled<br />

through one or more <strong>in</strong>termediate reservoirs by erosion<br />

and redeposition <strong>of</strong> older sedimentary rocks (e.g. Røhr<br />

et al. 2010).<br />

In this paper, we present <strong>the</strong> results <strong>of</strong> an analytical study<br />

apply<strong>in</strong>g laser ablation <strong>in</strong>ductively coupled mass spectrometry<br />

(LAM-ICPMS) and electron microprobe analysis<br />

to detrital zircon <strong>in</strong> <strong>the</strong> <strong>Brumunddal</strong> <strong>sandstone</strong>.<br />

Data <strong>in</strong>clude s<strong>in</strong>gle-zircon U-Pb ages, Lu-Hf isotope<br />

ratios and trace element distribution patterns, which<br />

provide new <strong>in</strong>sights <strong>in</strong>to <strong>the</strong> sources and recycl<strong>in</strong>g patterns<br />

<strong>of</strong> clastic material <strong>in</strong> Fennoscandia <strong>in</strong> late Paleozoic<br />

time, and which help to ref<strong>in</strong>e <strong>the</strong> position <strong>of</strong> <strong>the</strong> <strong>sandstone</strong><br />

with<strong>in</strong> <strong>the</strong> evolutionary history <strong>of</strong> <strong>the</strong> <strong>Oslo</strong> Rift.<br />

1


2 T. Andersen et al. NORWEGIAN JOURNAL OF GEOLOGY<br />

Figure 1<br />

a) Simplified geological map <strong>of</strong> <strong>the</strong> sou<strong>the</strong>rn part <strong>of</strong> <strong>the</strong> Rendal graben segment <strong>in</strong> <strong>the</strong> <strong>Oslo</strong> Graben, Norway (after Høy and<br />

Bjørlykke 1980). Legend: i: <strong>Brumunddal</strong> <strong>sandstone</strong> (Mauset Fm), ii-iv: Permian lavas and volcaniclastic sediments (Bjørgeberg<br />

Fm.), v: Bruflat Fm. (Upper Silurian), vi: Ekre shale (Silurian). vii: Pentamerus limestone (lower Silurian), viii:<br />

Mjøsa limestone (middle Ordovician), ix: Fluberg Fm (middle Ordovician), x: Cambrian shale and <strong>sandstone</strong>, xi: R<strong>in</strong>gsaker<br />

quartzite (Neoproterozoic). The broken l<strong>in</strong>e is an <strong>in</strong>ferred, unexposed fault.<br />

b) Ma<strong>in</strong> geological features <strong>of</strong> <strong>the</strong> <strong>Oslo</strong> Rift, after Larsen et al. (2008). Legend: SG Skagerrak Graben, VG: Vestfold Graben,<br />

AG: Akershus Graben, RG: Rendal Graben. 1: Mesoproterozoic basement, 2: Hedemark Bas<strong>in</strong> (Neoproterozoic). 3: Cambrian<br />

to Silurian sedimentary rocks, 4: Permo-Carboniferous volcanic and sedimentary rocks. 5: Permian <strong>in</strong>trusive rocks.<br />

6: Central volcanoes (cauldrons), 7: Transfer zones, 8: Brittle faults. The red rectangle marks <strong>the</strong> position <strong>of</strong> Fig. 1a.<br />

c) The outl<strong>in</strong>e <strong>of</strong> <strong>the</strong> <strong>Oslo</strong> Rift system, <strong>the</strong> preserved parts <strong>of</strong> <strong>the</strong> Permian deposits (red and deep purple; after Larsen et al.<br />

2008) and its relation to <strong>the</strong> tectonostratigraphic units mentioned <strong>in</strong> <strong>the</strong> text: Legend: C: Caledonian nappes, H: Hedemark<br />

Bas<strong>in</strong> (Neoproterozoic), D: Dala-Trysil bas<strong>in</strong> (Mesoproterozoic). TIB: Transscand<strong>in</strong>avian Igneous Belt (Late Paleoproterozoic).<br />

O: Orsa <strong>sandstone</strong> (Silurian), Ö: Öved <strong>sandstone</strong> (Silurian). On-shore lower Paleozoic sediments <strong>in</strong> <strong>the</strong> <strong>Oslo</strong> Rift are<br />

shown <strong>in</strong> pale blue.<br />

To evaluate <strong>the</strong> potential <strong>of</strong> post-Caledonian cont<strong>in</strong>ental<br />

sediments outside <strong>of</strong> <strong>the</strong> rift area as <strong>in</strong>termediate repositories<br />

for detritus <strong>in</strong> <strong>the</strong> <strong>Brumunddal</strong> <strong>sandstone</strong>, we have<br />

also analysed U-Pb and Lu-Hf isotopes <strong>in</strong> detrital zircons<br />

from a sample <strong>of</strong> <strong>the</strong> Silurian cont<strong>in</strong>ental <strong>sandstone</strong> from<br />

Orsa <strong>in</strong> central Sweden.


NORWEGIAN JOURNAL OF GEOLOGY <strong>Provenance</strong> <strong>characteristics</strong> <strong>of</strong> <strong>the</strong> <strong>Brumunddal</strong> <strong>sandstone</strong> <strong>in</strong> <strong>the</strong> <strong>Oslo</strong> Rift<br />

Geological background<br />

The late Paleozoic <strong>Oslo</strong> Rift (Fig. 1) encompasses four<br />

separate graben units. The sou<strong>the</strong>rnmost unit (<strong>the</strong><br />

Skagerrak Graben) is entirely situated <strong>of</strong>fshore and features<br />

a symmetrical geometry. In contrast, <strong>the</strong> three onshore<br />

units (Vestfold, Akershus and Rendalen grabens)<br />

are half-grabens <strong>of</strong> contrast<strong>in</strong>g polarities. The graben<br />

units are separated by NNW-SSE- and NNE-SSE-strik<strong>in</strong>g<br />

transfer zones (Fig. 1b). Volcanic rocks and batholiths<br />

dom<strong>in</strong>ate <strong>the</strong> <strong>the</strong> Vestfold and Akershus grabens,<br />

whereas <strong>the</strong> Rendalen Graben is devoid <strong>of</strong> batholiths.<br />

Still, some lava flows exist here, albeit m<strong>in</strong>or <strong>in</strong> volume<br />

as compared to <strong>the</strong> sou<strong>the</strong>rn graben units (Larsen et al.<br />

2008).<br />

The rift evolution can be divided <strong>in</strong>to several dist<strong>in</strong>ct<br />

stages (Ramberg and Larsen 1978, Neumann et al. 2004,<br />

Larsen et al., 2008). The proto-rift stage is characterized<br />

by alluvial and m<strong>in</strong>or mar<strong>in</strong>e deposits <strong>of</strong> Pennsylvanian<br />

age, <strong>the</strong> Asker Group (Olaussen et al., 1994, Larsen et<br />

al. 2008). Volcanism dur<strong>in</strong>g <strong>the</strong> ma<strong>in</strong> rift<strong>in</strong>g stage produced<br />

basaltic lava (B1) which form thick sequences<br />

<strong>in</strong> <strong>the</strong> Vestfold Graben, th<strong>in</strong>n<strong>in</strong>g northwards and to<br />

zero around <strong>Oslo</strong>. These lavas are <strong>of</strong> late Carboniferous<br />

to earliest Permian age (300 ± 1Ma, Corfu & Dahlgren<br />

2008). Graben subsidence cont<strong>in</strong>ued and large volumes<br />

<strong>of</strong> rhomb porphyry lava (latite) and m<strong>in</strong>or basalt erupted<br />

through large fissure volcanoes. Also, thick volcanoclastic<br />

and sedimentary units were deposited dur<strong>in</strong>g this<br />

stage. The composite Larvik pluton <strong>in</strong> <strong>the</strong> Vestfold graben<br />

<strong>in</strong>truded <strong>in</strong> this stage, and has been dated to 298-292<br />

Ma by ID-TIMS U-Pb on zircons (Dahlgren et al., 1996,<br />

1998, Dahlgren 2010). In <strong>the</strong> subsequent central volcano<br />

stage, volcanic activity was concentrated <strong>in</strong> dist<strong>in</strong>ct<br />

volcanic centres with local trends <strong>of</strong> magmatic evolution,<br />

term<strong>in</strong>at<strong>in</strong>g <strong>in</strong> caldera collapse. The central volcanoe s<br />

are preserved as between 15 and 20 cauldron structures,<br />

represent<strong>in</strong>g sections through sub volcanic magma<br />

chambers , r<strong>in</strong>g-dike systems and downfaulted blocks <strong>of</strong><br />

volcanic rocks. U-Pb ages are not yet available for <strong>the</strong><br />

rocks that formed dur<strong>in</strong>g this stage, but Rb-Sr ages suggest<br />

a relatively long duration (ca. 280-240 Ma, Sundvoll<br />

et al. 1990). The f<strong>in</strong>al stages <strong>of</strong> rift evolution were characterized<br />

by emplacement <strong>of</strong> <strong>in</strong>termediate to felsic batholiths,<br />

rang<strong>in</strong>g <strong>in</strong> composition from larvikite through syenite to<br />

granite. U-Pb ages on zircons from different <strong>in</strong>trusions<br />

suggest emplacement ages between 272 Ma and 286 Ma<br />

(Pedersen et al. 1995, Haug 2007, Andersen et al. 2009c),<br />

but Rb-Sr isochron ages range down to 241 Ma (Sundvoll<br />

et al. 1990).<br />

The Rendalen Graben is del<strong>in</strong>eated eastwards by <strong>the</strong><br />

westerly fac<strong>in</strong>g extensional Rendalen fault and is superseded<br />

to <strong>the</strong> north by several smaller sub-graben <strong>of</strong> vary<strong>in</strong>g<br />

polarity. One <strong>of</strong> <strong>the</strong>se, <strong>in</strong>formally termed <strong>the</strong> Narud<br />

halfgraben, occupies <strong>the</strong> <strong>Brumunddal</strong>en area, its Permian<br />

sequence be<strong>in</strong>g preserved <strong>in</strong> <strong>the</strong> rotated hang<strong>in</strong>g wall<br />

fault block <strong>of</strong> <strong>the</strong> westerly dipp<strong>in</strong>g Gråkvern fault (Fig.<br />

1a). The fill <strong>of</strong> <strong>the</strong> Narud halfgraben is subdivided <strong>in</strong>to<br />

two formations, namely a lower 250 m thick volcanic<br />

unit, <strong>the</strong> (Bjørgeberget formation) <strong>of</strong> Early Permian age<br />

(Sundvoll et al. 1990), and <strong>the</strong> upper, conformable c.750<br />

m thick undated <strong>Brumunddal</strong> <strong>sandstone</strong> unit, which has<br />

been suggested by Eliassen et al. (<strong>in</strong> prep.) to be renamed<br />

<strong>the</strong> “Mauset formation” (Fig. 2).<br />

The Bjørgeberg formation rests unconformably on folded<br />

Cambro-Silurian sediments and consists <strong>of</strong> four rhomb<br />

porphyry lava flows (RPx-u; Rosendal 1928), <strong>in</strong>tercalated<br />

with up to 30m thick, volcanoclastic conglomerates<br />

and <strong>sandstone</strong>s. The conglomerates consist entirely<br />

<strong>of</strong> rhomb porphyry lava clasts while <strong>the</strong> <strong>sandstone</strong>s<br />

conta<strong>in</strong> 63-65% quartz, 30-32 % feldspar (mostly plagioclase)<br />

and 4-6% lava fragments and hence classify as an<br />

arkosic arenite. The volcanoclastic rocks are <strong>in</strong>terpreted<br />

as alluvial fans derived from evolv<strong>in</strong>g bas<strong>in</strong>-bound<strong>in</strong>g<br />

fault escarpments or local highs. Deposition <strong>of</strong> <strong>the</strong>se fans<br />

took place ei<strong>the</strong>r <strong>in</strong> <strong>in</strong>terludes between extrusive activity,<br />

or represent contemporaneous, lateral variations <strong>of</strong> <strong>the</strong><br />

volcanic-sedimentary sequence (Eliassen et al. <strong>in</strong> prep.).<br />

The Mauset formation (<strong>in</strong>formally <strong>the</strong> <strong>Brumunddal</strong> <strong>sandstone</strong>)<br />

is dom<strong>in</strong>ated by red and yellow <strong>sandstone</strong>s with<br />

subord<strong>in</strong>ate mudstones and carbonates. The rocks <strong>of</strong> <strong>the</strong><br />

Mauset formation can be subdivided <strong>in</strong>to three units.<br />

The lowermost unit (c. 200 m thick) consists <strong>of</strong> red <strong>sandstone</strong><br />

with a m<strong>in</strong>eralogical composition and texture similar<br />

to that <strong>of</strong> <strong>the</strong> arkosic arenites <strong>in</strong>terlayered with <strong>the</strong><br />

lavas <strong>in</strong> <strong>the</strong> Bjørgeberg formation. They are <strong>in</strong>terpreted<br />

as wadi deposits characterized by a stable high watertable.<br />

This unit is superseded by a 500 m thick sequence<br />

<strong>of</strong> texturally mature, f<strong>in</strong>e to medium gra<strong>in</strong>ed subarkosic<br />

arenite with up to 77% quartz, 21% feldspar and less<br />

than 2% lava fragements. The lowermost 250 m <strong>of</strong> this<br />

unit is <strong>in</strong>terpreted as eolian dune, <strong>in</strong>terdune and sandflat<br />

deposits <strong>in</strong>terbedded by fluvial stream and alluvial<br />

pla<strong>in</strong> <strong>sandstone</strong>s and siltstones with evaporite pseudomorphs.<br />

The upper 250 m <strong>of</strong> <strong>the</strong> middle unit consists<br />

entirely <strong>of</strong> eolian sands. The Mauset formation is topped<br />

by a 50 m thick sequence <strong>of</strong> texturally and m<strong>in</strong>eralogically<br />

im mature <strong>sandstone</strong>s somewhat similar to <strong>the</strong><br />

lower unit, but which may have more than 40% feldspar<br />

and less lava fragments. This arkosic arenite is <strong>in</strong>terbedded<br />

by siltstones and carbonates that <strong>in</strong>clude fresh-water<br />

stromatolites. It was deposited <strong>in</strong> ephermal lakes, ponds<br />

and sabkhas typical <strong>of</strong> a mixed playa and alluvial environment<br />

and is <strong>in</strong>dicative <strong>of</strong> a second event marked by<br />

high water-level (Eliassen et al., <strong>in</strong> prep.).<br />

Taken collectively, <strong>the</strong> Mauset formation is a typical<br />

eolian/fluvial wadi deposit (Rosendahl, 1929, Olaussen<br />

et al 1994, Eliassen et al. <strong>in</strong> prep.) much like what has<br />

been described for <strong>the</strong> Upper Rotliegendes <strong>in</strong> <strong>the</strong> Nor<strong>the</strong>rn<br />

and Sou<strong>the</strong>rn Permian Bas<strong>in</strong>s <strong>in</strong> nor<strong>the</strong>rn Europe<br />

(e.g Glennie 1990). The limited outcrops do not allow<br />

<strong>in</strong>terpretation <strong>of</strong> eolian dune types (e.g as barchans,<br />

transverse, seif or dras), nor can reliable determ<strong>in</strong>ations<br />

3


4 T. Andersen et al. NORWEGIAN JOURNAL OF GEOLOGY<br />

<strong>of</strong> paleo-w<strong>in</strong>d direction be made. A similar uncerta<strong>in</strong>ty<br />

exists for <strong>the</strong> sediment transport directions <strong>of</strong><br />

<strong>the</strong> ephemeral alluvial stream deposits, which are likely<br />

to have been determ<strong>in</strong>ed by local dune topography and<br />

structural gra<strong>in</strong> as developed by graben marg<strong>in</strong> fault<strong>in</strong>g<br />

(e.g. Gabrielsen et al. 1995). Still, it is considered<br />

unlikely that <strong>the</strong> 750 m thick eolian/wadi deposit <strong>of</strong> <strong>the</strong><br />

Mauset Formation was constra<strong>in</strong>ed to <strong>the</strong> 6.5 x 2.5 km<br />

half graben <strong>in</strong> <strong>the</strong> Brumundal area alone. It is more likely<br />

that <strong>the</strong> Narud halfgraben is one preserved fragment <strong>of</strong><br />

a wider desert area that covered most <strong>of</strong> <strong>the</strong> nor<strong>the</strong>rn<br />

part <strong>of</strong> <strong>the</strong> <strong>Oslo</strong> Rift and its vic<strong>in</strong>ity. Hence <strong>the</strong> deposits<br />

<strong>of</strong> <strong>the</strong> Brumundal <strong>sandstone</strong> might be <strong>in</strong>terpreted as<br />

a nor<strong>the</strong>rn arm or extension <strong>of</strong> <strong>the</strong> Rotliegendes <strong>of</strong> <strong>the</strong><br />

Nor<strong>the</strong>rn Permian Bas<strong>in</strong> (Olaussen et al. 1994, McCann<br />

1998, Larsen et al. 2008, Eliassen et al. <strong>in</strong> prep). Consistent<br />

with this <strong>in</strong>terpretation is <strong>the</strong> occurrence <strong>of</strong> up to 1<br />

m thick beds <strong>of</strong> red coloured, cross-stratified <strong>sandstone</strong><br />

with well-sorted and well-rounded gra<strong>in</strong>s <strong>in</strong>terpreted as<br />

Figure 2: Stratigraphy <strong>of</strong> <strong>the</strong> <strong>Brumunddal</strong><br />

<strong>sandstone</strong><br />

eolian or reworked eolian deposits (Olaussen et al 1994).<br />

These beds occur with<strong>in</strong> <strong>the</strong> volcanoclastics <strong>in</strong>terbedded<br />

with <strong>the</strong> lava pile <strong>in</strong> <strong>the</strong> Akershus and Vestfold Graben<br />

fur<strong>the</strong>r south <strong>in</strong> <strong>the</strong> <strong>Oslo</strong> Rift. In a reconstructed paleogeographic<br />

sett<strong>in</strong>g, <strong>the</strong> provenance for <strong>the</strong> Mauset Formation<br />

is suggested to be both <strong>of</strong> local orig<strong>in</strong> and from<br />

<strong>the</strong> bas<strong>in</strong> fill <strong>of</strong> <strong>the</strong> rift fur<strong>the</strong>r south.<br />

The Orsa <strong>sandstone</strong> is an erosional remnant <strong>of</strong> Silurian<br />

cont<strong>in</strong>ental <strong>sandstone</strong> preserved with<strong>in</strong> <strong>the</strong> Siljan impact<br />

structure <strong>in</strong> central Sweden (“O” <strong>in</strong> Fig. 1c). It is <strong>the</strong><br />

youngest preserved member <strong>of</strong> <strong>the</strong> lower Paleozoic sedimentary<br />

sequence <strong>in</strong> <strong>the</strong> area, unconformably overly<strong>in</strong>g<br />

limestones and shales <strong>of</strong> Llandowery to Wenlock age<br />

(Thorslund 1960). The deposit consists <strong>of</strong> a cross-bedded,<br />

conglomeratic to coarse sandy lower part, overla<strong>in</strong><br />

by a ma<strong>in</strong> sequence <strong>of</strong> loosely consolidated, f<strong>in</strong>e-gra<strong>in</strong>ed<br />

quartz arenite, which is locally carbonate cemented and<br />

<strong>in</strong>terlayered with clay-rich units (Hjelmqvist 1966). A


NORWEGIAN JOURNAL OF GEOLOGY <strong>Provenance</strong> <strong>characteristics</strong> <strong>of</strong> <strong>the</strong> <strong>Brumunddal</strong> <strong>sandstone</strong> <strong>in</strong> <strong>the</strong> <strong>Oslo</strong> Rift<br />

sample was <strong>in</strong>cluded <strong>in</strong> this study to evaluate <strong>the</strong> potential<br />

<strong>of</strong> post-Caledonian sediments as <strong>in</strong>termediate hosts<br />

for detrital material, ra<strong>the</strong>r than to establish a detailed<br />

provenance history. The Orsa <strong>sandstone</strong> was chosen as<br />

an example ra<strong>the</strong>r than o<strong>the</strong>r Silurian cont<strong>in</strong>ental <strong>sandstone</strong>s<br />

(e.g. <strong>the</strong> Öved <strong>sandstone</strong> <strong>in</strong> Scania (Jeppson &<br />

Laufeld 1986), “Ö” <strong>in</strong> Fig. 1c; <strong>the</strong> R<strong>in</strong>gerrike group <strong>in</strong> <strong>the</strong><br />

<strong>Oslo</strong> Rift) because it is situated between <strong>the</strong> site <strong>of</strong> deposition<br />

<strong>of</strong> <strong>the</strong> <strong>Brumunddal</strong> <strong>sandstone</strong> and potential Paleoproterozoic<br />

and older protosources <strong>in</strong> <strong>the</strong> Svec<strong>of</strong>ennian<br />

and Archaean doma<strong>in</strong>s <strong>of</strong> Fennoscandia. The sample<br />

studied is a f<strong>in</strong>e-gra<strong>in</strong>ed, red, friable <strong>sandstone</strong> without<br />

clay or carbonate (Hjelmqvist 1966).<br />

Zircon petrography<br />

The present study was based on a sample <strong>of</strong> red, friable<br />

<strong>sandstone</strong> from <strong>the</strong> upper part <strong>of</strong> <strong>the</strong> Mauset formation<br />

(N 60° 54.59’, E 10° 58.89’). The sample is a carbonate-cemented<br />

quartz <strong>sandstone</strong> pigmented by f<strong>in</strong>ely<br />

dissem<strong>in</strong>ated iron oxide and conta<strong>in</strong><strong>in</strong>g m<strong>in</strong>or to accessory<br />

amounts <strong>of</strong> detrital zircon. Most detrital zircon<br />

Figure 3. Backscattered electron (BSE)<br />

images <strong>of</strong> detrital zircon from <strong>the</strong><br />

<strong>Brumunddal</strong> <strong>sandstone</strong>. Each image<br />

is identified by analysis number <strong>in</strong><br />

tables <strong>of</strong> <strong>the</strong> Supplementary Material,<br />

U-Pb age and ε Hf at <strong>the</strong> U-Pb<br />

age. Each image is identified by analysis<br />

number, U-Pb age and eHf at <strong>the</strong><br />

U-Pb age. Rare Archaean gra<strong>in</strong>s (a)<br />

are well-rounded and show little <strong>in</strong>ternal<br />

structure, except for a weak, BSE<br />

bright overgrowth (lower part). Paleo-<br />

to Mesoproterozoic gra<strong>in</strong>s (b, c, d)<br />

have well developed, more or less complex<br />

oscillatory zon<strong>in</strong>g patterns typical<br />

for magmatic zircon, and are commonly<br />

well rounded. Permian gra<strong>in</strong>s<br />

(e, f) vary <strong>in</strong> shape from angular to<br />

well-rounded gra<strong>in</strong> shapes, <strong>the</strong>y show<br />

fa<strong>in</strong>t oscillatory zon<strong>in</strong>g struc tures, and<br />

conta<strong>in</strong> abundant, BSE-dark <strong>in</strong>clusions<br />

(feldspar, apatite).<br />

gra<strong>in</strong>s are well rounded, suggest<strong>in</strong>g significant abration<br />

dur<strong>in</strong>g transport (Fig. 3). A few gra<strong>in</strong>s giv<strong>in</strong>g Permian<br />

U-Pb ages are less well-abraded (Fig. 3e), but lack<br />

<strong>of</strong> round<strong>in</strong>g is not a universal feature <strong>of</strong> <strong>the</strong> youngest<br />

group <strong>of</strong> detrital zircons <strong>in</strong> <strong>the</strong> <strong>sandstone</strong> (compare Fig.<br />

3e with Fig. 3f). Most gra<strong>in</strong>s show <strong>the</strong> low-amplitude,<br />

short-wavelength oscillatory zon<strong>in</strong>g <strong>in</strong> backscattered<br />

electron (BSE) <strong>in</strong>tensity that is characteristic <strong>of</strong> magmatic<br />

zircons (Fig. 3b, c, d). Complex <strong>in</strong>ner structures<br />

seen <strong>in</strong> some gra<strong>in</strong>s suggest that <strong>the</strong>y are fragments <strong>of</strong><br />

tw<strong>in</strong>s or <strong>in</strong>tergrown groups <strong>of</strong> crystals (Fig. 3b). BSEbright<br />

overgrowths occur <strong>in</strong> some gra<strong>in</strong>s (e.g. Fig. 3a,c);<br />

<strong>the</strong>se are generally too th<strong>in</strong> to allow separate analysis<br />

by LAM-ICPMS. M<strong>in</strong>eral <strong>in</strong>clusions <strong>in</strong> zircon (e.g. Fig.<br />

3c) were avoided dur<strong>in</strong>g U-Pb and Lu-Hf analysis, but<br />

a few were penetrated dur<strong>in</strong>g trace element ablations.<br />

Inclusions which were large enough to be <strong>in</strong>tegrated<br />

separately showed elevated phosphorus and middle or<br />

light REE, and have <strong>the</strong>refore been tentatively identified<br />

as apatite and monazite, respectively.<br />

5


6 T. Andersen et al. NORWEGIAN JOURNAL OF GEOLOGY<br />

Analytical methods<br />

Sample preparation was done at <strong>the</strong> Department <strong>of</strong> Geosciences,<br />

University <strong>of</strong> <strong>Oslo</strong>, and analysis <strong>of</strong> zircon by<br />

LAM-ICPMS at <strong>the</strong> GEMOC National Key Centre, Macquarie<br />

University and at <strong>the</strong> Department <strong>of</strong> Geosciences,<br />

University <strong>of</strong> <strong>Oslo</strong>. Zircon gra<strong>in</strong>s were separated from<br />

rock samples by standard crush<strong>in</strong>g and m<strong>in</strong>eral separation<br />

techniques, followed by hand-pick<strong>in</strong>g under a b<strong>in</strong>ocular<br />

microscope. Selected gra<strong>in</strong>s from <strong>the</strong> two least<br />

magnetic fractions (magnetic and non-magnetic at 1.5<br />

A magnet current <strong>in</strong> <strong>the</strong> Franz separator at 15º standard<br />

tilt and slope) were cast <strong>in</strong> epoxy disks for LAM-ICPMS<br />

analysis. The mounts were ground and polished to expose<br />

<strong>the</strong> zircons, and thoroughly cleaned before analysis. Zircons<br />

were exam<strong>in</strong>ed <strong>in</strong> transmitted and reflected light,<br />

and by electron backscatter imag<strong>in</strong>g <strong>in</strong> a Cameca SX50<br />

electron microprobe. Each imaged zircon was assigned a<br />

number, which also serves to identify analyses <strong>in</strong> Tables<br />

2, 3 and 4 <strong>of</strong> Supplementary Material. Standards were<br />

mounted <strong>in</strong> separate epoxy disks.<br />

LAM-ICPMS U–Pb dat<strong>in</strong>g.<br />

U–Pb dat<strong>in</strong>g <strong>of</strong> <strong>the</strong> <strong>Brumunddal</strong> <strong>sandstone</strong> sample<br />

was made with a HP 4500 series 300 <strong>in</strong>ductively coupled<br />

plasma quadrupole mass spectrometer (QICPMS),<br />

attached to a Merchantec/New Wave LUV213 Nd-YAG<br />

laser microprobe at GEMOC. Analytical procedures<br />

were as described by Jackson et al. (2004). The analytical<br />

protocol allows accurate correction for U/Pb fractionation<br />

by sample-standard bracket<strong>in</strong>g. Standard zircon<br />

GJ-1 (608 Ma, Jackson et al. 2004) was used for calibration,<br />

while standard zircons 91500 (Wiedenbeck et<br />

al. 1995) and Mud Tank (Black and Gulson 1978) were<br />

run frequently as unknowns to provide an <strong>in</strong>dependent<br />

control on reproduci bility and <strong>in</strong>strument stability.<br />

The GLITTER s<strong>of</strong>tware (Griff<strong>in</strong> et al. 2008) was used for<br />

data reduction and calculation <strong>of</strong> <strong>in</strong>dividual U–Th–Pb<br />

ages. The contents <strong>of</strong> common lead were estimated from<br />

<strong>the</strong> 3D discordance pattern <strong>in</strong> 206Pb/ 238U – 207Pb/ 235U –<br />

208 232 Pb/ Th space, and corrected accord<strong>in</strong>gly (Andersen<br />

2002).<br />

Additional U-Pb analyses <strong>of</strong> detrital zircon from <strong>the</strong> <strong>the</strong><br />

Orsa <strong>sandstone</strong> were made with a Nu Plasma HR multicollector<br />

ICPMS and a NewWave LUV213 laser microprobe<br />

at <strong>the</strong> Department <strong>of</strong> Geosciences, University <strong>of</strong><br />

<strong>Oslo</strong>, us<strong>in</strong>g protocols for data acquisition and standardization<br />

described by Rosa et al. (2009).<br />

Lutetium-hafnium isotopes.<br />

Lu-Hf analyses <strong>of</strong> zircon from <strong>the</strong> <strong>Brumunddal</strong> <strong>sandstone</strong><br />

were made with a NuPlasma multicollector ICPMS<br />

attached to a LUV213 Nd-YAG laser microprobe at<br />

GEMOC, us<strong>in</strong>g protocols described by Griff<strong>in</strong> et al.<br />

(2000) and Andersen et al. (2002b). Ablation conditions<br />

were: Beam diameter: 55 μm (aperture imag<strong>in</strong>g mode),<br />

pulse frequency: 5 Hz, beam energy density: ca. 2 J/cm 2 ,<br />

static ablation. Each ablation was preceded by a 30 seconds<br />

on-mass background measurement. Masses 172 to<br />

180 were measured <strong>in</strong> Faraday collectors, us<strong>in</strong>g <strong>the</strong> standard<br />

collector block <strong>of</strong> <strong>the</strong> NU Plasma mass spectrometer.<br />

The total Hf signal obta<strong>in</strong>ed was <strong>in</strong> <strong>the</strong> range 1.5-<br />

3.0 V. Under <strong>the</strong>se conditions, 120-150 seconds <strong>of</strong> ablation<br />

are required to obta<strong>in</strong> an <strong>in</strong>ternal precision <strong>of</strong> ≤ ±<br />

0.000020 (1SE). Isotopic ratios were calculated us<strong>in</strong>g <strong>the</strong><br />

Nu Plasma time-resolved analysis s<strong>of</strong>tware. The raw data<br />

were corrected for mass discrim<strong>in</strong>ation us<strong>in</strong>g an exponential<br />

law, <strong>the</strong> mass discrim<strong>in</strong>ation factor for Hf was<br />

determ<strong>in</strong>ed assum<strong>in</strong>g 179 Hf/ 177 Hf= 0.7325, <strong>the</strong> observed<br />

2 SE uncerta<strong>in</strong>ty <strong>of</strong> <strong>the</strong> Hf mass discrim<strong>in</strong>ation factor<br />

was better than 0.5%, and was propagated through to<br />

<strong>the</strong> error <strong>of</strong> <strong>the</strong> f<strong>in</strong>al result. The isobaric <strong>in</strong>terferences<br />

on 176 Hf by 176 Lu and 176 Yb were corrected from measurements<br />

<strong>of</strong> <strong>in</strong>terference-free 172 Yb and 175 Lu. The observed<br />

mass discrim<strong>in</strong>ation for Hf was used as a proxy for those<br />

<strong>of</strong> Lu and Yb. 176 Lu/ 175 Lu= 0.02669 was used for correction<br />

<strong>of</strong> Lu <strong>in</strong>terference on mass 176 (DeBievre & Taylor<br />

1993). The 176 Yb/ 172 Yb ratio used <strong>in</strong> <strong>the</strong> correction procedure<br />

(0.5870) was determ<strong>in</strong>ed from multiple runs <strong>of</strong><br />

Yb-doped JM475 Hf standard solutions. Lu-Hf analyses<br />

<strong>of</strong> zircon from <strong>the</strong> Orsa <strong>sandstone</strong> were made with<br />

<strong>the</strong> Nu Plasma HR <strong>in</strong>strument <strong>in</strong> <strong>Oslo</strong>, us<strong>in</strong>g procedures<br />

described by Andersen et al. (2009a) and He<strong>in</strong>onen et al.<br />

(2010).<br />

A value for <strong>the</strong> decay constant <strong>of</strong> 176 Lu <strong>of</strong> 1.867 x 10 -11<br />

a -1 has been used <strong>in</strong> all calculations (Söderlund et al.<br />

2004; Scherer et al. 2001, 2007). For <strong>the</strong> calculation <strong>of</strong><br />

ε Hf values we used present-day chondritic 176 Hf/ 177 Hf =<br />

0.282785 and 176 Lu/ 177 Hf = 0.0336 (Bouvier et al. 2008).<br />

We have adopted <strong>the</strong> depleted mantle model <strong>of</strong> Griff<strong>in</strong><br />

et al. (2000), modified to <strong>the</strong> λ 176 Lu and chondritic composition<br />

used, which produces a present-day value <strong>of</strong><br />

176 Hf/ 177 Hf (0.28325, εHf = +16.4) similar to that <strong>of</strong> average<br />

MORB over 4.56 Ga, from chondritic <strong>in</strong>itial hafnium at<br />

176 Lu/ 177 HfDM = 0.0388.<br />

Trace elements.<br />

Trace elements <strong>in</strong> zircon were analysed us<strong>in</strong>g an Agilent<br />

7500 quadrupole ICPMS and a New Wave Research<br />

LUV213 laser microprobe at GEMOC. Ablation<br />

conditions were: Beam diameter: 40 μm (aperture imag<strong>in</strong>g<br />

mode), pulse frequency: 5 Hz, beam energy density:<br />

ca. 5 J/cm 2 , giv<strong>in</strong>g a laser energy at <strong>the</strong> sample <strong>of</strong> 0.07 mJ.<br />

A fast scann<strong>in</strong>g protocol was employed, analys<strong>in</strong>g masses<br />

from 29 (Si) to 238 (U), with 10 ms dwell times on all<br />

masses analysed except 206 (15 ms), 207 (30 ms) and 238<br />

(15 ms). Ablations lasted for 120 seconds, and each was<br />

preceded by a 60 seconds background measurement with<br />

<strong>the</strong> laser <strong>of</strong>f. NIST 610 silicate glass was used as external<br />

standard, with 29 Si as <strong>the</strong> <strong>in</strong>ternal standard, assum<strong>in</strong>g<br />

a stoichiometric composition for zircon with 32.78<br />

weight % SiO 2 . Data reduction was made <strong>of</strong>f-l<strong>in</strong>e us<strong>in</strong>g<br />

<strong>the</strong> s<strong>of</strong>tware package GLITTER 4.4 (Griff<strong>in</strong> et al. 2008).


NORWEGIAN JOURNAL OF GEOLOGY <strong>Provenance</strong> <strong>characteristics</strong> <strong>of</strong> <strong>the</strong> <strong>Brumunddal</strong> <strong>sandstone</strong> <strong>in</strong> <strong>the</strong> <strong>Oslo</strong> Rift<br />

Figure 4. U-Pb data for detrital zircon<br />

from <strong>the</strong> <strong>Brumunddal</strong> <strong>sandstone</strong>.<br />

a: Tera Wasserburg diagrams show<strong>in</strong>g<br />

data for zircon crystals <strong>in</strong> <strong>the</strong> magnetic<br />

and non-magnetic fractions from<br />

<strong>the</strong> Franz magnetic separator at 1.5 A<br />

separately. Note that Permian zircons<br />

occur only <strong>in</strong> <strong>the</strong> magnetic fraction.<br />

b: Conventional concordia diagram<br />

show<strong>in</strong>g <strong>the</strong> Permian fraction. The<br />

three gra<strong>in</strong>s represented by white<br />

fill def<strong>in</strong>e a concordia age at 285±4<br />

Ma, <strong>the</strong> fraction as such a weighted<br />

average 206 Pb/ 238 U age at 283±4 Ma,<br />

which is <strong>the</strong> preferred estimate <strong>of</strong><br />

<strong>the</strong> crystallization age <strong>of</strong> <strong>the</strong> source<br />

rock(s).<br />

Accuracy and external precision <strong>of</strong> <strong>the</strong> <strong>in</strong>dividual elements<br />

estimated from repeated analyses <strong>of</strong> reference zircon<br />

GJ-1 are given <strong>in</strong> Table 1 <strong>of</strong> Electronic Supplement.<br />

Results<br />

0.20<br />

2800<br />

0.16<br />

0.12<br />

0.08<br />

Uranium-lead ages <strong>of</strong> detrital zircons <strong>in</strong> <strong>the</strong> <strong>Brumunddal</strong><br />

<strong>sandstone</strong>.<br />

Of a total <strong>of</strong> 105 gra<strong>in</strong>s dated by U-Pb (Table 2 <strong>of</strong> Electronic<br />

Supplement), 94 were concordant or less than 10<br />

% normally discordant (central discordance). The zircons<br />

yield a large range <strong>of</strong> U-Pb ages, from late Archaean<br />

207 Pb/ 206 Pb<br />

a<br />

2000<br />

1200<br />

0 4 8 12 16 20 24<br />

Non-magnetic fraction<br />

400<br />

0.04<br />

0 4 8 12 16 20 24<br />

b<br />

206 Pb/ 238 U<br />

0.052<br />

0.047<br />

2800<br />

2000<br />

1200<br />

238 U/ 206 Pb<br />

280<br />

300<br />

400<br />

Concordia Age =285 ±4 Ma<br />

(2 , decay-const. errs ignored)<br />

MSWD <strong>of</strong> concordance and equivalence = 1.6<br />

Magnetic fraction<br />

320<br />

0.042 260<br />

Weighted average<br />

0.037<br />

240<br />

0.26 0.28 0.30 0.32 0.34 0.36 0.38<br />

206 Pb/ 238 U age:<br />

283±4 (95% conf.), 9<strong>of</strong>10 gra<strong>in</strong>s<br />

Wtd by data-pt errs only, 1<strong>of</strong>10 rej.<br />

MSWD = 1.7<br />

207 Pb/ 235 U<br />

0.20<br />

0.16<br />

0.12<br />

0.08<br />

0.04<br />

(2.6 Ga) to Permian (Fig. 4a), with a pronounced frequency<br />

maximum at ca. 1 Ga, and subord<strong>in</strong>ate maxima<br />

at ca. 1400 Ma, 1600 Ma, 1800 Ma and <strong>in</strong> <strong>the</strong> Phanerozoic,<br />

with marked hiatuses <strong>in</strong> <strong>the</strong> Neoproterozoic and<br />

early Paleoproterozoic (Fig. 5a). Although <strong>the</strong> magnetic<br />

and non-magnetic zircon fractions show largely similar<br />

age distribution patterns, a dist<strong>in</strong>ct group <strong>of</strong> late Paleozoic<br />

zircons (270-310 Ma) has been observed only <strong>in</strong><br />

<strong>the</strong> magnetic fraction (Fig. 4a). Of eleven zircons <strong>in</strong> this<br />

group, eight are 10 % or more discordant. The three concordant<br />

zircons give a concordia age <strong>of</strong> 285±4 Ma, and 9<br />

zircons def<strong>in</strong>e a weighted average 206 Pb/ 238 U age <strong>of</strong> 283±4<br />

Ma (Fig. 4b, 5b), <strong>in</strong>dist<strong>in</strong>guishable from <strong>the</strong> concordia<br />

age. Ano<strong>the</strong>r group <strong>of</strong> similar size (9 gra<strong>in</strong>s) give ages<br />

7


8 T. Andersen et al. NORWEGIAN JOURNAL OF GEOLOGY<br />

Number<br />

Number<br />

20<br />

15<br />

10<br />

5<br />

between 526 and 398 Ma, with a peak at 440 Ma, which<br />

is compatible with igneous or metamorphic source rocks<br />

<strong>in</strong> Caledonian nappes (e.g. Gee et al. 2008). Two analyses<br />

give ages <strong>of</strong> 346±4 Ma and 361±4 Ma. These gra<strong>in</strong>s do<br />

not differ from <strong>the</strong> Caledonian fraction <strong>in</strong> terms <strong>of</strong> trace<br />

element distributions and Lu-Hf <strong>characteristics</strong> (below),<br />

and it is <strong>the</strong>refore suggested that <strong>the</strong>y are Caledonian<br />

gra<strong>in</strong>s which have suffered sufficient lead-loss <strong>in</strong> Permian<br />

or recent time to modify <strong>the</strong>ir ages, while rema<strong>in</strong><strong>in</strong>g<br />

concordant with<strong>in</strong> error.<br />

Orsa <strong>sandstone</strong>, Sweden (Silurian)<br />

<strong>Brumunddal</strong> <strong>sandstone</strong><br />

0<br />

200 600 1000 1400 1800 2200 2600 3000<br />

5<br />

4<br />

3<br />

2<br />

1<br />

a<br />

Detrital zircon age, Ma<br />

b Weighted average 206Pb/ 238U<br />

age: 283±4 Ma<br />

0<br />

250 260 270 280 290<br />

300 310<br />

Zircon 206 Pb/ 238 U age, Ma<br />

Relative probability<br />

Relative probability<br />

Figure 5. Accumulated probability distribution<br />

diagrams show<strong>in</strong>g:<br />

a): The whole population <strong>of</strong> dated zircons<br />

( 207Pb/ 206Pb ages for t> 600<br />

Ma, 206Pb/ 238U ages for t< 600 Ma),<br />

analyses with more than ± 10 %<br />

discordance excluded. The colourfilled<br />

background histogram shows<br />

<strong>the</strong> age distribution <strong>of</strong> detrital zircons<br />

<strong>in</strong> <strong>the</strong> Silurian Orsa <strong>sandstone</strong>,<br />

Sweden (Table 5a <strong>of</strong> Supplementary<br />

material).<br />

b): Permian zircons (n=11, <strong>in</strong>clud<strong>in</strong>g<br />

discordant gra<strong>in</strong>s). Broken outl<strong>in</strong>e<br />

<strong>in</strong>dicates zircons that are not used to<br />

calculate ages.<br />

Lutetium-Hafnium isotopes <strong>of</strong> detrital zircon <strong>in</strong> <strong>the</strong><br />

Brumund dal <strong>sandstone</strong><br />

In Fig. 6 (data from Table 3 <strong>of</strong> Electronic Supplement),<br />

<strong>in</strong>itial 176 Hf/ 177 Hf for 82 concordant or near-concordant<br />

zircons are plotted at <strong>the</strong> preferred U-Pb age (i.e.<br />

207 Pb/ 206 Pb ages for zircons older than 600 Ma, 206 Pb/ 238 U<br />

ages for younger zircons).<br />

The late Paleozoic zircons form a coherent group with<br />

dist<strong>in</strong>ct <strong>in</strong>itial Hf character. When zircons that are more<br />

than 10% discordant <strong>in</strong> U-Pb are <strong>in</strong>cluded <strong>in</strong> <strong>the</strong> calculation,<br />

n<strong>in</strong>e zircons give a weighted average 176 Hf/ 177 Hf=


NORWEGIAN JOURNAL OF GEOLOGY <strong>Provenance</strong> <strong>characteristics</strong> <strong>of</strong> <strong>the</strong> <strong>Brumunddal</strong> <strong>sandstone</strong> <strong>in</strong> <strong>the</strong> <strong>Oslo</strong> Rift<br />

Initial Hf/ Hf<br />

176 177<br />

0.2835<br />

DM<br />

0.2830<br />

CHUR<br />

0.2825<br />

0.2820<br />

0.2815<br />

0.2810<br />

0.2805<br />

+10<br />

0<br />

-10<br />

<strong>Oslo</strong> Rift<br />

magmas<br />

TIB crust<br />

Age range <strong>of</strong> Caledonian<br />

magmatism<br />

Sveconorwegian granites<br />

Inherited zircon <strong>in</strong><br />

Sveconorwegian<br />

granites<br />

Inherited zircon <strong>in</strong> TIB,<br />

Intrusions <strong>in</strong> <strong>the</strong><br />

Archaean Doma<strong>in</strong><br />

0.28272±0.00004 (95% confidence) or ε Hf =4.2±1.5, with<br />

no rejections. The spread <strong>of</strong> <strong>in</strong>itial 176 Hf/ 177 Hf <strong>in</strong> this<br />

group is comparable to <strong>the</strong> analytical error, suggest<strong>in</strong>g<br />

that <strong>the</strong>se zircons orig<strong>in</strong>ated from one or more protosource<br />

rocks with<strong>in</strong> <strong>the</strong> rift with homogeneous Lu-Hf<br />

<strong>characteristics</strong>.<br />

Zircons older than <strong>the</strong>se show considerable variation <strong>in</strong><br />

<strong>in</strong>itial 176 Hf/ 177 Hf, rang<strong>in</strong>g from well below CHUR (i.e.<br />

ε Hf


10 T. Andersen et al. NORWEGIAN JOURNAL OF GEOLOGY<br />

could be analysed for Hf isotopes, and yielded nearchondritic<br />

176 Hf/ 177 Hf at its 207 Pb/ 206 Pb age.<br />

Trace element compositions <strong>of</strong> detrital zircon <strong>in</strong> <strong>the</strong> <strong>Brumunddal</strong><br />

<strong>sandstone</strong><br />

The trace element distribution patterns observed <strong>in</strong><br />

<strong>the</strong> analysed samples are typical for magmatic zircon<br />

(Hosk<strong>in</strong> and Schaltegger 2003, Belousova et al. 2002),<br />

with positive anomalies for Hf, U, Th and Ce (Fig. 7, data<br />

from Table 4 <strong>of</strong> Electronic Supplement). Hf concentrations<br />

range from ca. 0.6 to ca. 2.4 percent, and total REE<br />

from 33 to 2000 ppm. Source-dependent trace element<br />

comb<strong>in</strong>ations spread from <strong>the</strong> less U and LREE enriched<br />

part <strong>of</strong> <strong>the</strong> field <strong>of</strong> variation <strong>of</strong> zircon from granitoids<br />

towards that <strong>of</strong> zircon from mafic rocks (Fig. 8, fields<br />

from Belousova et al. 2002). This is reflected by <strong>the</strong><br />

CART classification algorithm <strong>of</strong> Belousova et al. (2002),<br />

which gives a dom<strong>in</strong>ance <strong>of</strong> “dolerite” and different types<br />

<strong>of</strong> “granitoids” as suggested source rocks (Table 1). A few<br />

zircon analyses <strong>in</strong>dicate source rock types such as “kimberlite”<br />

and “carbonatite”. Although both rock types<br />

are known to exist <strong>in</strong> Fennoscandia (e.g. O’Brien et al.<br />

2005, Rukhlov & Bell 2010), <strong>the</strong>y are rare, and unlikely<br />

to have yielded significant amounts <strong>of</strong> detrital material<br />

to <strong>the</strong> <strong>Brumunddal</strong> <strong>sandstone</strong>. Zircon gra<strong>in</strong>s <strong>in</strong>dicat<strong>in</strong>g<br />

uncommon source rock types show anomalous REE patterns<br />

with low HREE and /or HREE / LREE ratios, comb<strong>in</strong>ed<br />

with Eu/Eu* > 0.5 (NM15A-02, 04, 17, 21, 29, 32,<br />

45, 66, Fig. 9) and probably formed by crystalli zation<br />

from hydro<strong>the</strong>rmal solutions or dur<strong>in</strong>g metamorphism<br />

ra<strong>the</strong>r than from magma; <strong>the</strong> relatively flat HREE pattern<br />

<strong>in</strong> NM15A-32 suggests coexistence with garnet (e.g.<br />

Hosk<strong>in</strong> & Schaltegger 2003).<br />

Chondrite normalized REE distribution patterns are<br />

strongly enriched <strong>in</strong> <strong>the</strong> heavy REE, as is common <strong>in</strong> zircon;<br />

all gra<strong>in</strong>s analysed have a marked positive Ce anomaly<br />

and a variable, negative Eu anomaly (Fig. 9). A majority<br />

<strong>of</strong> <strong>the</strong> analyses have (Yb/Sm) CN = 30 to 200, and deep,<br />

negative Eu anomalies (Eu/Eu* < 0.4). With <strong>the</strong> exception<br />

<strong>of</strong> a few gra<strong>in</strong>s with apparent LREE enrichment due<br />

to <strong>the</strong> presence <strong>of</strong> solid <strong>in</strong>clusions (see below), none <strong>of</strong><br />

<strong>the</strong> zircons analysed from <strong>the</strong> <strong>Brumunddal</strong> <strong>sandstone</strong><br />

show <strong>the</strong> characteristic flatten<strong>in</strong>g <strong>of</strong> <strong>the</strong> LREE pattern<br />

observed <strong>in</strong> zircons from “granitoids” by Belousova et al.<br />

(2002), and <strong>the</strong> patterns <strong>in</strong> general resemble those <strong>of</strong> zircon<br />

from “dolerite” and “basaltic” sources (Fig. 9).<br />

Anomalous LREE-enrichment seen <strong>in</strong> a few analyses<br />

(e.g. NM15A-57 and -67) are from ablations that<br />

have picked up m<strong>in</strong>or amounts <strong>of</strong> LREE-rich <strong>in</strong>clusions<br />

(monazite?) <strong>in</strong> <strong>the</strong> zircon. O<strong>the</strong>r anomalous analyses<br />

show relative enrichment <strong>of</strong> middle REE and a shallow<br />

Eu anomaly (e.g. NM15A-37, Fig. 9). Aga<strong>in</strong>, this is due<br />

to accidental ablation <strong>of</strong> small <strong>in</strong>clusions <strong>in</strong> <strong>the</strong> zircon, <strong>in</strong><br />

this case most probably <strong>of</strong> apatite.<br />

The zircons <strong>of</strong> late Paleozoic age form a consistent<br />

group with relatively low HREE enrichment (Yb/Sm) CN<br />

= 20-30). Of <strong>the</strong> 11 gra<strong>in</strong>s <strong>in</strong> this group, four have dist<strong>in</strong>ctly<br />

shallower Eu anomalies than <strong>the</strong> rest (Eu/Eu*>0.4,<br />

compared to Eu/Eu*≤ 0.3, Fig. 9). The patterns <strong>of</strong> <strong>the</strong><br />

latter resemble those <strong>of</strong> <strong>Oslo</strong> Rift larvikite analysed by<br />

Belousova et al. (2002) <strong>in</strong> terms <strong>of</strong> pattern curvature<br />

and Eu anomaly, but at an overall lower REE enrichment<br />

level. The differences <strong>in</strong> concentration level may,<br />

however, be an effect <strong>of</strong> <strong>the</strong> different methods <strong>of</strong> <strong>in</strong>ternal<br />

standardization used <strong>in</strong> <strong>the</strong> two studies (assumed<br />

stoichiometric SiO 2 value <strong>in</strong> this study vs. Hf analysed by<br />

electron microprobe).<br />

U-Pb and Lu-Hf <strong>characteristics</strong> <strong>of</strong> Silurian <strong>sandstone</strong><br />

The age pattern <strong>of</strong> detrital zircon <strong>in</strong> <strong>the</strong> Silurian Orsa<br />

<strong>sandstone</strong> mimics that <strong>of</strong> <strong>the</strong> <strong>Brumunddal</strong> <strong>sandstone</strong><br />

with age maxima <strong>in</strong> <strong>the</strong> late Paleoproterozoic, at ca. 1500<br />

Ma and <strong>in</strong> <strong>the</strong> late Mesoproterozoic (Fig. 5a, data from<br />

Table 5a <strong>of</strong> Electronic Supplement). There is also a small<br />

contribution <strong>of</strong> Phanerozoic zircon, presumably from a<br />

Caledonian source. The variation <strong>of</strong> <strong>in</strong>itial Hf isotope<br />

character also overlaps that <strong>of</strong> <strong>the</strong> <strong>Brumunddal</strong> <strong>sandstone</strong><br />

(Fig. 6, data from Table 5b <strong>of</strong> Electronic Supplement<br />

l). The clearest difference between <strong>the</strong> two distribution<br />

patterns is due to a s<strong>in</strong>gle, highly U-Pb discordant<br />

zircon with ε Hf =-21 at 1376 Ma (Orsa-38, Table 4); this<br />

is most probably a late Archaean or Paleoproterozoic zircon<br />

that has lost a significant amount <strong>of</strong> lead <strong>in</strong> a <strong>the</strong>rmal<br />

event <strong>in</strong> Mesoproterozoic time.<br />

Discussion<br />

U-Pb, Lu-Hf and potential protosources <strong>of</strong> detrital zircon<br />

<strong>in</strong> <strong>the</strong> Brumundal <strong>sandstone</strong>.<br />

The detrital zircon ages from <strong>the</strong> <strong>Brumunddal</strong> <strong>sandstone</strong><br />

range from late Archaean to Phanerozoic, with <strong>in</strong>itial Hf<br />

istope signatures from near depleted mantle to crustal<br />

ratios. The distribution <strong>of</strong> age and <strong>in</strong>itial 176 Hf/ 177 Hf or ε Hf<br />

<strong>in</strong> Fig. 6 is, however, far from random, and can be related<br />

to known crustal evolution events <strong>in</strong> Fenno scandia.<br />

Precambrian protosources. The near-CHUR <strong>in</strong>itial<br />

176 Hf/ 177 Hf <strong>of</strong> <strong>the</strong> s<strong>in</strong>gle late Archaean detrital zircon analysed<br />

for Lu-Hf falls with<strong>in</strong> <strong>the</strong> age and 176 Hf/ 177 Hf range<br />

<strong>of</strong> late Archaean granitoids from eastern Fennoscandia<br />

(Patchett et al. 1981, Lauri et al. 2011). Archaean rocks<br />

are exposed only <strong>in</strong> E F<strong>in</strong>land, NE Sweden N Norway<br />

and NW Russia, at considerable distance from <strong>the</strong>ir sites<br />

<strong>of</strong> deposition.<br />

The Precambrian rocks <strong>of</strong> <strong>the</strong> Fennoscandian shield<br />

immediately border<strong>in</strong>g <strong>the</strong> <strong>Oslo</strong> Rift (Fig. 1c) belong<br />

to <strong>the</strong> late Paleoproterozoic Transscand<strong>in</strong>avian Igneous<br />

Belt (TIB, Högdahl et al. 2004) and <strong>the</strong> early Mesoproterozoic<br />

(“Gothian”) magmatic arc fragments (Andersen<br />

et al. 2004). The TIB was formed by multiple episodes


NORWEGIAN JOURNAL OF GEOLOGY <strong>Provenance</strong> <strong>characteristics</strong> <strong>of</strong> <strong>the</strong> <strong>Brumunddal</strong> <strong>sandstone</strong> <strong>in</strong> <strong>the</strong> <strong>Oslo</strong> Rift<br />

Figure 7. Spider diagrams<br />

show<strong>in</strong>g <strong>the</strong> overall<br />

variation <strong>of</strong> zircon<br />

compositions <strong>in</strong> <strong>the</strong><br />

<strong>Brumunddal</strong> <strong>sandstone</strong>,<br />

normalized to chondritic<br />

values <strong>of</strong> McDonough<br />

and Sun (1995). The<br />

shaded background field<br />

is <strong>the</strong> <strong>in</strong>terquartile range<br />

<strong>of</strong> zircon compositions <strong>in</strong><br />

granitoids (Belousova et<br />

al. 2002).<br />

Hf ppm<br />

Y ppm<br />

25000<br />

20000<br />

15000<br />

10000<br />

5000<br />

1<br />

0<br />

10 6<br />

10 5<br />

10 4<br />

10 3<br />

10 2<br />

10<br />

ppm <strong>in</strong> zircon / ppm <strong>in</strong> chondrite<br />

Mafic rocks<br />

1.0 6<br />

1.0 4<br />

1.0 2<br />

1.0<br />

1.0 -2<br />

Pb La Ce Pr Nd Sm Eu Gd Th Dy Y Ho Er U Yb Lu Hf Nb Ta Ti P<br />

Granitoids<br />

Y ppm Y ppm<br />

1<br />

1 10 10 1 10<br />

Y ppm U ppm<br />

2<br />

102 10-2 10-1 103 103 104 104 105 105 0.1 1 10 100<br />

Nb/Ta<br />

10 6<br />

10 5<br />

10 4<br />

10 3<br />

10 2<br />

10<br />

10 6<br />

10 5<br />

10 4<br />

10 3<br />

10 2<br />

10<br />

1<br />

1 10 100<br />

Yb/Sm<br />

Figure 8. Source-<strong>in</strong>dicat <strong>in</strong>g element and element -ratio plots show<strong>in</strong>g that a significant proportion <strong>of</strong> <strong>the</strong> detrital zircons analysed<br />

falls between <strong>the</strong> ma<strong>in</strong> fields <strong>of</strong> zircon derived from granitoid and mafic (i.e. basalt, dolerite) sources (reference fields<br />

from Belousova et al. 2002).<br />

11<br />

10 3


12 T. Andersen et al. NORWEGIAN JOURNAL OF GEOLOGY<br />

ppm zircon / ppm chondrite<br />

10 4<br />

10 3<br />

10 2<br />

10<br />

1<br />

10 -1<br />

10 4<br />

10 3<br />

10 2<br />

10<br />

1<br />

10 -1<br />

10 4<br />

10 3<br />

10 2<br />

10<br />

1<br />

10 -1<br />

10 -2<br />

La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Lu La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Lu<br />

< 320 Ma<br />

Larvikite,<br />

<strong>in</strong>terquartile range,<br />

Belousova et al. (2002)<br />

900-1250 Ma<br />

M15A-01<br />

NM15A-67<br />

NM15A-57<br />

1400-1500 Ma<br />

NM15A-26<br />

NM15A-62<br />

NM15A-29<br />

320-900 Ma<br />

900-1250 Ma<br />

Basalt Dolerite Granitoids<br />

> 1600 Ma<br />

NM15A-04<br />

NM15A-37<br />

NM15A-35: <strong>in</strong>clusion<br />

NM15A-21<br />

NM15A-32<br />

La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Lu La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Lu<br />

Figure 9. Chondrite normalized REE patterns for zircon from <strong>the</strong> <strong>Brumunddal</strong> <strong>sandstone</strong>, divided <strong>in</strong>to six groups (1600 Ma,<br />

see text for fur<strong>the</strong>r explanation). Reference fields for all except <strong>the</strong>


NORWEGIAN JOURNAL OF GEOLOGY <strong>Provenance</strong> <strong>characteristics</strong> <strong>of</strong> <strong>the</strong> <strong>Brumunddal</strong> <strong>sandstone</strong> <strong>in</strong> <strong>the</strong> <strong>Oslo</strong> Rift<br />

<strong>of</strong> magmatic <strong>in</strong>trusion <strong>in</strong> <strong>the</strong> period 1.88 to 1.68 Ga; <strong>the</strong><br />

TIB <strong>in</strong>trusions close to <strong>the</strong> <strong>Oslo</strong> Rift belong to <strong>the</strong> youngest<br />

part <strong>of</strong> <strong>the</strong> belt, known as TIB3, with <strong>in</strong>trusive ages<br />

around 1.68-1.67 Ga (Larson and Berglund 1992, Heim<br />

et al. 1996, Andersen et al. 2009a). Despite <strong>the</strong> large size<br />

and long time <strong>of</strong> emplacement <strong>of</strong> <strong>the</strong> TIB prov<strong>in</strong>ce, <strong>the</strong><br />

<strong>in</strong>itial Hf signature <strong>of</strong> magmatic zircon from TIB granitoids<br />

shows little variation, which can be represented<br />

by <strong>in</strong>itial ε Hf = +2±3 at 1.88 Ga and 176 Lu/ 177 Hf≈ 0.015<br />

(Andersen et al. 2009a). Given <strong>the</strong> short distance to<br />

potential source rocks with<strong>in</strong> <strong>the</strong> TIB, <strong>the</strong> low abundance<br />

<strong>of</strong> TIB-like detrital zircons <strong>in</strong> <strong>the</strong> <strong>Brumunddal</strong> <strong>sandstone</strong><br />

(Fig. 5a, 6) is somewhat surpris<strong>in</strong>g. On <strong>the</strong> o<strong>the</strong>r hand,<br />

a small group <strong>of</strong> Paleoproterozoic zircons with negative<br />

ε Hf overlaps <strong>the</strong> field <strong>of</strong> <strong>in</strong>herited zircon <strong>of</strong> possible<br />

Archaean orig<strong>in</strong> <strong>in</strong> a TIB <strong>in</strong>trusion at <strong>the</strong> eastern marg<strong>in</strong><br />

<strong>of</strong> <strong>the</strong> belt <strong>in</strong> Sweden (Andersson et al. 2006, Andersen<br />

et al. 2009a). Fur<strong>the</strong>rmore, Paleoproterozoic zircons with<br />

such <strong>in</strong>itial Hf <strong>characteristics</strong> are found <strong>in</strong> Paleoproterozoic<br />

granites with<strong>in</strong> <strong>the</strong> Archaean doma<strong>in</strong> <strong>of</strong> F<strong>in</strong>land<br />

(Patchett et al. 1981, Andersen & Lauri 2010). Paleoproterozoic<br />

crust with Lu-Hf properties similar to <strong>the</strong> rocks<br />

<strong>of</strong> <strong>the</strong> Transscand<strong>in</strong>avian Igneous Belt or <strong>the</strong>ir source <strong>in</strong><br />

<strong>the</strong> deep crust has contributed source material to most <strong>of</strong><br />

<strong>the</strong> Mesoproterozoic crustal magmatic events that can be<br />

recognized <strong>in</strong> southwestern Fennoscandia, even far west<br />

<strong>of</strong> <strong>the</strong> present TIB outcrop area (Andersen et al. 2001,<br />

2002a, 2009b, Andersen 2005, Pedersen et al. 2009).<br />

Detrital zircons <strong>of</strong> early Mesoproterozoic age with <strong>in</strong>itial<br />

176 Hf/ 177 Hf approach<strong>in</strong>g <strong>the</strong> DM curve resemble zircons<br />

from both Mesoproterozoic cont<strong>in</strong>ental marg<strong>in</strong> arc complexes<br />

(Andersen et al. 2002b, 2004) and those from felsic<br />

rocks from <strong>the</strong> Telemark block, which are still poorly<br />

constra<strong>in</strong>ed by Lu-Hf data. A small, coherent group<br />

<strong>of</strong> 1.45-1.50 Ga zircons with ε Hf = -3 to -8 can ei<strong>the</strong>r be<br />

derived from a coeval, crustal source, or <strong>the</strong>y can be TIBderived<br />

zircons that have lost lead <strong>in</strong> a Mesoproterozoic<br />

tectono<strong>the</strong>rmal event.<br />

Dur<strong>in</strong>g <strong>the</strong> Sveconorwegian period, southwestern Fennoscandia<br />

was affected by several episodes <strong>of</strong> mafic and<br />

felsic magmatism <strong>in</strong> different tectonic sett<strong>in</strong>gs, rang<strong>in</strong>g<br />

from ca. 1300 Ma to 920 Ma (B<strong>in</strong>gen and van Breemen<br />

1998, Andersen et al. 2001, 2002a,b, 2007, 2009b,<br />

Vander Auwera et al. 2003, Pedersen et al. 2009). Magmatic<br />

events <strong>in</strong>volv<strong>in</strong>g crustal underplat<strong>in</strong>g with mafic<br />

material with a depleted mantle Hf isotope signature<br />

(ε Hf ≈ +12) at 1.3 and 1.22 Ga have been documented <strong>in</strong><br />

<strong>the</strong> Telemark block; after each <strong>of</strong> <strong>the</strong>se events, <strong>the</strong> <strong>in</strong>itial<br />

Hf isotope composition <strong>of</strong> zircon from magmatic rocks<br />

evolved towards less radiogenic compositions due to<br />

<strong>in</strong>creas<strong>in</strong>g effects <strong>of</strong> crustal source components (Andersen<br />

et al. 2007, Pedersen et al. 2009). Initial ε Hf <strong>of</strong> <strong>the</strong><br />

large group <strong>of</strong> Sveconorwegian zircons overlaps well<br />

with <strong>the</strong> comb<strong>in</strong>ed range <strong>of</strong> magmatic and <strong>in</strong>herited zircon<br />

from Sveconorwegian granitoids (Andersen et al.<br />

2002a, 2007, Pedersen et al. 2009).<br />

13<br />

Caledonian protosources. Synorogenic <strong>in</strong>trusions <strong>in</strong> <strong>the</strong><br />

nappes <strong>of</strong> <strong>the</strong> Scand<strong>in</strong>avian Caledonides that could be<br />

sources <strong>of</strong> early Paleozoic detrital zircon have been dated<br />

to 430-500 Ma (Gee et al. 2008 and references <strong>the</strong>re<strong>in</strong>).<br />

The Caledonian mounta<strong>in</strong> cha<strong>in</strong> was ma<strong>in</strong>ly levelled<br />

by mid-Carboniferous time (Gabrielsen et al. 2005,<br />

2010), but late Permian – Triassic uplift is likely to have<br />

enhanced relief to <strong>the</strong> west and northwest <strong>of</strong> <strong>the</strong> <strong>Oslo</strong><br />

Graben system (Rohrman et al. 1995, Gabrielsen et al.<br />

2010). By <strong>the</strong> early Triassic, sediments <strong>of</strong> Caledonian orig<strong>in</strong><br />

were transported southwards to become deposited<br />

<strong>in</strong> <strong>the</strong> Central European Bas<strong>in</strong> (Paul et al. 2009). Unfortunately,<br />

no Hf isotope data are available from Caledonian<br />

<strong>in</strong>trusions. The considerable range <strong>of</strong> ε (+ 1.4<br />

Hf<br />

to -11) observed suggests, however, that <strong>the</strong>se zircons<br />

ei<strong>the</strong>r crystallized from magmas with variable amounts<br />

<strong>of</strong> a TIB-like crustal component, or that <strong>the</strong>y are zircons<br />

from Sveconorwegian protoliths that have lost lead <strong>in</strong><br />

Caledonian metamorphism.<br />

With<strong>in</strong>-rift sources. Permian gra<strong>in</strong>s make up ca. 10 % <strong>of</strong><br />

<strong>the</strong> analysed detrital zircon population (Fig. 5). Rocks<br />

from <strong>the</strong> Larvik pluton have been dated to 292-298 Ma<br />

by U-Pb on zircon and baddeleyite (Dahlgren et al. 1998,<br />

Dahlgren 2010). This event was, however, followed by<br />

<strong>the</strong> emplacement <strong>of</strong> syenitic to granitic plutons around<br />

280 Ma (Pedersen et al. 1995, Haug 2007). Magmatic<br />

zircon from larvikite, nordmarkite and biotite granite<br />

<strong>in</strong> <strong>the</strong> ca. 280 Ma Sande and Drammen plutons have<br />

ε Hf <strong>in</strong> <strong>the</strong> range - 4 to +6, whereas zircons from pegmatites<br />

<strong>in</strong> <strong>the</strong> Larvik pluton are slightly more radiogenic<br />

at ε Hf = +8 ± 2 (Andersen et al. 2009b); no evidence has<br />

so far been found <strong>of</strong> hafnium derived from a late Paleozoic<br />

depleted mantle reservoir (ε Hf ≈ + 15) <strong>in</strong> any <strong>of</strong> <strong>the</strong>se<br />

rocks. The 176 Hf/ 177 Hf at 280 Ma <strong>of</strong> <strong>the</strong> late Paleozoic<br />

zircons falls with<strong>in</strong> <strong>the</strong> age and Hf isotope range <strong>of</strong> zircon<br />

<strong>in</strong> <strong>the</strong> younger group <strong>of</strong> <strong>in</strong>termediate to felsic <strong>in</strong>trusions<br />

<strong>in</strong> <strong>the</strong> rift. Two dist<strong>in</strong>ct types <strong>of</strong> REE patterns have<br />

been observed, with “deep” and “shallow” Eu anomalies,<br />

respectively (Fig. 9). The first group has REE pattern<br />

geometry similar to that <strong>of</strong> zircon from larvikite reported<br />

by Belousova et al. (2002), and <strong>the</strong>refore most likely orig<strong>in</strong>ates<br />

from <strong>in</strong>termediate <strong>in</strong>trusive rocks. The o<strong>the</strong>r type<br />

must orig<strong>in</strong>ate from o<strong>the</strong>r syenitic or (alkali) granitic<br />

plutonic rocks, which cannot be identified.<br />

Recycl<strong>in</strong>g <strong>of</strong> sedimentary rocks<br />

Most <strong>of</strong> <strong>the</strong> ma<strong>in</strong> documented crust-form<strong>in</strong>g events <strong>in</strong><br />

Fennoscandia are represented <strong>in</strong> <strong>the</strong> detrital zircon population<br />

<strong>of</strong> <strong>the</strong> <strong>Brumunddal</strong> <strong>sandstone</strong>, <strong>in</strong>clud<strong>in</strong>g accessory<br />

late Archaean and Paleoproterozoic zircons that<br />

must have orig<strong>in</strong>ated <strong>in</strong> protosources east <strong>of</strong> <strong>the</strong> Transscand<strong>in</strong>avian<br />

Igneous Belt. It is highly unlikely that zircon<br />

from such a wide range <strong>of</strong> sources could have been<br />

brought <strong>in</strong>to <strong>the</strong> rift <strong>in</strong> a s<strong>in</strong>gle event <strong>of</strong> one-way transport<br />

from protosource to depositional bas<strong>in</strong>. Ra<strong>the</strong>r, zircon<br />

must have been recycled through deposition <strong>in</strong> <strong>in</strong>termediate,<br />

sedimentary reservoirs followed by erosion and


14 T. Andersen et al. NORWEGIAN JOURNAL OF GEOLOGY<br />

new transport. This has eventually caused a relatively<br />

well mixed sample <strong>of</strong> <strong>the</strong> entire Fennoscandian surface to<br />

be brought <strong>in</strong>to <strong>the</strong> <strong>Oslo</strong> Rift, <strong>in</strong>clud<strong>in</strong>g far-transported<br />

material from eastern Fennoscandia.<br />

The close similarity <strong>in</strong> age and <strong>in</strong>itial 176 Hf/ 177 Hf distribution<br />

<strong>of</strong> detrital zircon <strong>in</strong> <strong>the</strong> <strong>Brumunddal</strong> and Orsa <strong>sandstone</strong>s<br />

<strong>in</strong>dicates that Silurian <strong>sandstone</strong> is a very likely<br />

immediate precursor. Silurian, cont<strong>in</strong>ental deposits may<br />

have had a wide distribution <strong>in</strong> western and central Fennoscandia<br />

<strong>in</strong> post-Caledonian time; outside <strong>of</strong> <strong>the</strong> <strong>Oslo</strong><br />

Rift <strong>the</strong>y are now preserved only as small erosional remnants.<br />

Like <strong>the</strong> Orsa <strong>sandstone</strong>, <strong>the</strong> late Silurian R<strong>in</strong>gerrike<br />

Group with<strong>in</strong> <strong>the</strong> <strong>Oslo</strong> Rift itself (Davies et al. 2005<br />

and references <strong>the</strong>re<strong>in</strong>) conta<strong>in</strong>s material derived from<br />

both Fennoscandian and Caledonian sources (Turner &<br />

Whitaker 1976, Dahlgren & Corfu 2001).<br />

The Silurian cont<strong>in</strong>ental sediments make up <strong>the</strong> youngest<br />

<strong>of</strong> several cover sequences <strong>in</strong> Fennoscandia, rang<strong>in</strong>g<br />

<strong>in</strong> age from Paleoproterozoic (e.g. Claesson et al. 1993,<br />

Lundqvist & Persson 1999, Laht<strong>in</strong>en et al. 2002, Bergman<br />

et al. 2008), through Mesoproterozoic (e.g. B<strong>in</strong>gen et al.<br />

2001, 2003, 2005b, Kuhonen & Rämö 2005, Andersen et<br />

al. 2004, Lamm<strong>in</strong>en & Köykkä 2010) and Neoproterozoic<br />

(e.g. Nystuen et al. 2008, B<strong>in</strong>gen et al. 2005a, Lamm<strong>in</strong>en<br />

et al. 2008, 2009) to Phanerozoic (e.g. Thorslund<br />

1960, Bjørlykke 1974a, Turner & Whitaker 1978, Davies<br />

et al. 2005). Each <strong>of</strong> <strong>the</strong> successive cover sequences must<br />

have conta<strong>in</strong>ed clastic material recycled from older<br />

deposits, as well as detritus derived directely from crystall<strong>in</strong>e<br />

protosource rocks.<br />

Bas<strong>in</strong>s such as <strong>the</strong> late Vendian – Cambrian Peri-Thornquist,<br />

and <strong>the</strong> Pre-Baltic sub-bas<strong>in</strong>s (Sliaupa et al. 1997,<br />

Poprawa et al. 1999), <strong>the</strong> southwestern part <strong>of</strong> <strong>the</strong> Baltic<br />

Bas<strong>in</strong> (Lazauskiene et al. 2002), as well as <strong>the</strong> Scand<strong>in</strong>avian<br />

(Bjørlykke 1974b, Worsley et al. 1983) and German-Polish<br />

Caledonian foreland bas<strong>in</strong>s (Lazuskiene et<br />

al. 2002) may have acted as <strong>in</strong>termediate repositories for<br />

far-transported detritus, <strong>in</strong>clud<strong>in</strong>g Paleoproterozoic and<br />

Archaean detrital zircons <strong>of</strong> east Fennoscandian orig<strong>in</strong>.<br />

The Caledonian forebulge may have promoted uplift and<br />

erosion <strong>of</strong> <strong>the</strong>se bas<strong>in</strong>s, thus releas<strong>in</strong>g zircons <strong>of</strong> an easterly<br />

orig<strong>in</strong>.<br />

The most zircon-fertile rocks with<strong>in</strong> each <strong>of</strong> <strong>the</strong> protosource-terranes<br />

are granitic. Never<strong>the</strong>less, <strong>the</strong> trace element<br />

patterns are more <strong>in</strong> l<strong>in</strong>e with mafic to <strong>in</strong>termediate<br />

source rocks than with granite. Zircons with a relatively<br />

less steep LREE pattern are also likely to be more heavily<br />

enriched <strong>in</strong> uranium and thorium (Fig. 7; Belousova<br />

et al. 2002), and would <strong>the</strong>refore more easily become<br />

metamict due to <strong>in</strong>ternal radiation damage than less U<br />

and Th enriched (and hence also more strongly LREE<br />

depleted) ones. Metamict zircon is brittle and much<br />

more likely to be destroyed by abrasion dur<strong>in</strong>g transport<br />

than gra<strong>in</strong>s with an <strong>in</strong>tact crystal structure. A scarcity <strong>of</strong><br />

typical “granitoid” zircon is <strong>the</strong>refore to be expected <strong>in</strong><br />

sediments with a long and complex transport history.<br />

The significance <strong>of</strong> Neoproterozoic detrital zircon ages <strong>in</strong><br />

southwestern Fennoscandia.<br />

The Neoproterozoic was a quiet period <strong>in</strong> Fennoscandia,<br />

with little or no production <strong>of</strong> zircon-fertile igneous<br />

rocks. Never<strong>the</strong>less, Neoproterozoic detrital zircon ages<br />

have been reported from both <strong>the</strong> Neoproterozoic Hedmark<br />

bas<strong>in</strong> (B<strong>in</strong>gen et al. 2005a) and from <strong>the</strong> Carboniferous<br />

Asker Group with<strong>in</strong> <strong>the</strong> <strong>Oslo</strong> Rift (Dahlgren &<br />

Corfu 2001). In <strong>the</strong> <strong>Brumunddal</strong> <strong>sandstone</strong>, such zircons<br />

are conspicuously absent. A non-Fennoscandian source<br />

for Neoproterozoic zircon has been suggested (Dahlgren<br />

& Corfu 2001), but <strong>the</strong> range <strong>of</strong> 176 Hf/ 177 Hf <strong>in</strong> Neoproterozoic<br />

zircons <strong>in</strong> <strong>the</strong> Hedmark Bas<strong>in</strong> with <strong>the</strong> observed<br />

U/Pb ages is fully compatible with Neoproterozoic loss <strong>of</strong><br />

radiogenic lead <strong>in</strong> zircon from Sveconorwegian granitoids<br />

(Fig. 6). This could be caused by surface wea<strong>the</strong>r<strong>in</strong>g<br />

prior to deposition, or by <strong>in</strong>teraction with diagenetic<br />

fluids with<strong>in</strong> <strong>the</strong> Hedmark Bas<strong>in</strong>.<br />

Time <strong>of</strong> deposition and tectonostratigraphic status <strong>of</strong> <strong>the</strong><br />

<strong>Brumunddal</strong> <strong>sandstone</strong><br />

The weighted average U/Pb age <strong>of</strong> 283±4 Ma (Fig. 3b)<br />

confirms <strong>the</strong> previous estimate <strong>of</strong> <strong>the</strong> maximum age limit<br />

for sedimentation based on Rb-Sr ages <strong>of</strong> <strong>the</strong> underly<strong>in</strong>g<br />

rhomb porphyry lavas (Sundvoll et al. 1990, Larsen et<br />

al. 2008). By <strong>the</strong> time <strong>of</strong> deposition <strong>of</strong> <strong>the</strong> <strong>Brumunddal</strong><br />

<strong>sandstone</strong>, rocks belong<strong>in</strong>g to <strong>the</strong> ca. 280 Ma “batholith<br />

stage” <strong>of</strong> rift evolution must have been exposed to erosion<br />

at <strong>the</strong> surface, which suggests that deposition took<br />

place dur<strong>in</strong>g <strong>the</strong> f<strong>in</strong>al stages <strong>of</strong> rift evolution (stage 6 <strong>in</strong><br />

<strong>the</strong> chronology <strong>of</strong> Larsen et al. 2008), ra<strong>the</strong>r than dur<strong>in</strong>g<br />

or immediately after rhomb porphyry volcanism (i.e. <strong>in</strong><br />

stage 3), which preceded emplacement <strong>of</strong> <strong>the</strong> younger,<br />

batholitic bodies. Plausible sources <strong>of</strong> Permian zircon are<br />

only exposed to <strong>the</strong> south <strong>of</strong> <strong>the</strong> site <strong>of</strong> deposition, <strong>in</strong> <strong>the</strong><br />

<strong>in</strong>trusive complexes <strong>of</strong> <strong>the</strong> Akershus and Vestfold graben<br />

segments. These zircon gra<strong>in</strong>s must <strong>the</strong>refore have been<br />

transported from south to north along <strong>the</strong> rift axis. The<br />

observation that some <strong>of</strong> <strong>the</strong>se zircons are quite severely<br />

rounded due to abrasion dur<strong>in</strong>g transport <strong>in</strong>dicates significant<br />

transport for some, but not for all <strong>of</strong> <strong>the</strong> young<br />

zircons observed.<br />

The present data suggest that sediment transport took<br />

place from south to north along <strong>the</strong> graben axis, perhaps<br />

suggest<strong>in</strong>g a topographic gradient <strong>in</strong> this direction. It is<br />

<strong>of</strong> particular <strong>in</strong>terest to note that one <strong>of</strong> <strong>the</strong> REE-patterns<br />

shows <strong>the</strong> presence <strong>of</strong> a deep (plutonic) source, suggest<strong>in</strong>g<br />

that plutons became exposed and eroded <strong>in</strong> <strong>the</strong><br />

sou<strong>the</strong>rn part <strong>of</strong> <strong>the</strong> graben simultaneously with ongo<strong>in</strong>g<br />

volcanism <strong>in</strong> <strong>the</strong> <strong>Brumunddal</strong> area. This situation is not<br />

unique and is paralleled <strong>in</strong> <strong>the</strong> present East African rift<br />

system (Barberi et al. 1970, 1972).


NORWEGIAN JOURNAL OF GEOLOGY <strong>Provenance</strong> <strong>characteristics</strong> <strong>of</strong> <strong>the</strong> <strong>Brumunddal</strong> <strong>sandstone</strong> <strong>in</strong> <strong>the</strong> <strong>Oslo</strong> Rift<br />

Why are Permian zircons only found <strong>in</strong> <strong>the</strong> magnetic<br />

fraction?<br />

Permian zircons were only found <strong>in</strong> <strong>the</strong> magnetic<br />

fraction at 1.5 A. With ca. 10% <strong>of</strong> <strong>the</strong> total number<br />

<strong>of</strong> analyzed zircons, this fraction is relatively large.<br />

However , if each <strong>of</strong> <strong>the</strong> two fractions from <strong>the</strong> magnetic<br />

separator are considered <strong>in</strong>dividually, <strong>the</strong>ir sizes are not<br />

sufficient to guarantee detection <strong>of</strong> even relatively large<br />

age fractions <strong>in</strong> each (Andersen 2005). However, it is still<br />

fully possible that <strong>the</strong> absence <strong>of</strong> syn-rift zircons from <strong>the</strong><br />

non- magnetic fraction reflects a real physical property <strong>of</strong><br />

<strong>the</strong>se zircons. If so, relatively standard use <strong>of</strong> magnetic<br />

separation has efficiently removed <strong>the</strong>m from <strong>the</strong> least<br />

magnetic fraction. The tendency <strong>of</strong> magnetic m<strong>in</strong>eral<br />

separation to <strong>in</strong>troduce undesirable bias <strong>in</strong> detrital zircon<br />

populations was po<strong>in</strong>ted out by Sircombe and Stern<br />

(2002), and <strong>the</strong> present results could imply that such<br />

effects can be due to even a moderate use <strong>of</strong> <strong>the</strong> magnetic<br />

separator.<br />

Conclusions<br />

The <strong>Brumunddal</strong> <strong>sandstone</strong> was deposited dur<strong>in</strong>g<br />

<strong>the</strong> f<strong>in</strong>al stages <strong>of</strong> evolution <strong>of</strong> <strong>the</strong> <strong>Oslo</strong> Rift, at a time<br />

when plutonic rocks formed dur<strong>in</strong>g <strong>the</strong> ca. 280 “batholith”<br />

stage were exposed to erosion. The <strong>sandstone</strong> conta<strong>in</strong>s<br />

detrital zircon rang<strong>in</strong>g <strong>in</strong> age from late Archaean to<br />

Permian. Comb<strong>in</strong>ed U-Pb and Lu-Hf data suggest that<br />

detrital zircons from most <strong>of</strong> <strong>the</strong> region-wide petrogenetic<br />

events <strong>in</strong> Fennoscandia are represented <strong>in</strong> this s<strong>in</strong>gle<br />

sediment, <strong>in</strong>clud<strong>in</strong>g zircons formed <strong>in</strong> events not represented<br />

by rocks with<strong>in</strong> reasonable distance from <strong>the</strong><br />

site <strong>of</strong> deposition. The likely explanation for this broad<br />

distribution <strong>of</strong> detrital zircon is recycl<strong>in</strong>g <strong>of</strong> material<br />

from Phanerozoic sedimentary cover on Fennoscandian<br />

basement, which may <strong>in</strong> turn conta<strong>in</strong> material recycled<br />

from still older sedimentary rocks. Repeated transport<br />

and deposition has effectively mixed detrital zircon from<br />

a wide range <strong>of</strong> protosources, and depleted <strong>the</strong> detritus <strong>in</strong><br />

metamict, high U zircons with typical “granitoid” trace<br />

element distribution patterns, leav<strong>in</strong>g a population with<br />

a large proportion <strong>of</strong> zircons hav<strong>in</strong>g trace element distributions<br />

more characteristic <strong>of</strong> “mafic” source rocks.<br />

Acknowledgments. - The research reproted her could be carried out<br />

thanks to economic support from <strong>the</strong> University <strong>of</strong> <strong>Oslo</strong> and Macquarie<br />

University. Thanks are due to Tr<strong>in</strong>e-Lise Knudsen for assistance <strong>in</strong><br />

<strong>the</strong> field, Gunborg Bye-Fjeld for technical assistance with m<strong>in</strong>eral separation,<br />

Just<strong>in</strong> Payne for help with <strong>the</strong> LAM-ICPMS, to Elena Belousova<br />

and Norman Pearson for many helpful discussions, and to Bernard<br />

B<strong>in</strong>gen and an anonymous reviewer for helpful comments. T.A. wants<br />

to thank GEMOC and its directors S.Y. O’Reilly and W.L. Griff<strong>in</strong><br />

for repeated <strong>in</strong>vitations to spend fruitful research time <strong>in</strong> Australia .<br />

This is publication no. 17 from <strong>the</strong> Isotope Geology Laboratory at <strong>the</strong><br />

Department <strong>of</strong> Geosciences, University <strong>of</strong> <strong>Oslo</strong> and contribution 696<br />

from <strong>the</strong> Australian Research Council National Key Centre for <strong>the</strong><br />

Geochemical Evolution and Metallogeny <strong>of</strong> Cont<strong>in</strong>ents (http://www.<br />

gemoc.mq.edu.au).<br />

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