Untitled

Lower Palaeozoic carbonates. East of the
marginal thrust belt, thrust inclinations
steepen, and by implication the remaining part
of the Caledonian orogen extending eastwards
to the present Atlantic Ocean coast is allochthonous
and thick-skinned. The contrast between
the restricted Neoproterozoic-Lower
Palaeozoic foreland succession and the very
thick and almost continuous sedimentation of
the allochthonsus Neoprotetozoic Eleonore
Bay Supergroup-Tillite Group-Cambro-
Ordovician sequence of the fjord zone of East
Greenland confirms the presence of distinct
N-S trending facies belts on the northwestern
passive margin of Iapetus. Comparisons with
the Caledonides of Northwest Scotland, which
may originally have lain as little as 500 km
south of the East Greenland Caledonides, provide
further clues to the understanding of
Neoproterozoic-Early Palaeozaic basin geometry
on this sector of the developing Iapetus
margin. The areas of the Laurentian margin
represented in the foreland windows of
East Greenland were inboard of Neoproterozoic
rifting but, with respect to the Torridonian
basins of Northwest Scotland, the Eleonore
Bag. Supergroup succession must have
been laid down further outboard. Similarly the
Lower Palaeozoic developments of the foreland
of Northwest Scotland are thicker than
the equivalent foreland sequences of East
Greenland, but much thinner than the allochthonous
East Greenland Cambro-Ordovician
succession.
2010040519
西 福 克 兰 岛 中 元 古 代 Cape Meredith 混 合
岩 体 的 地 球 化 学 和 同 位 素 演 化 = Geochemistry
and isotopic evolution of the Mesoproterozoic
Cape Meredith Complex, West Falkland.
( 英 文 ). Thomas R J; Jacobs J; Eglington
B M. Geological Magazine, 2000, 137(5):
537-553
Whole-rock major and trace element geochemical
and Rb-Sr/Sm-Nd isotopic data are
presented for the Mesoproterozoic (similar
to1.0 Ga) metamorphic and igneous rocks of
the Cape Meredith Complex, West Falkland.
The data indicate that the oldest rocks, the
similar to1.1 Ga supracrustal gneisses of the
Big Cape Formation, which form three petrographic
and geochemical groups (mafic amphibolite,
quartz-plagioclase-biotitehornblende
intermediate gneiss and acid
gneiss), probably represent a juvenile calcalkaline,
basalt-andesite-rhyolite volcanic sequence,
with epsilon (epsilon NdT) values and
T-Nd(DM) ages of similar to +3 to +6 and
similar to 1100 to 1400 Ma respectively. It is
argued on geochemical grounds that these
metavolcanics were extruded in an island-are
at around 1120 Ma. The Big Cape Formation
was intruded by granitoids during and after a
collisional orogenic event at around 1090 Ma.
The oldest, foliated, (G1) granodiorite was
emplaced as thin sheets at approximately 1090
to 1070 Ma and is characterized by epsilon Nd
Values of similar to +1.5 to 4 (T-DM = similar
to 1200 to 1400 Ma), showing its juvenile nature.
The similar to 1070 Ma (G2) syntectonic
granitoid gneisses and similar to 1000 Ma G3
post-tectonic granites also exhibit juvenile
characteristics (epsilon (Nd) = similar toO to
+5 and T-DM = 2200 to 1200 Ma, respectively).
The granitoids show a timecomposition
evolution from Na-rich (G1)
granodiorite to potassic, high-High Field
Strength Element granites (G3). The geochemical
and isotopic characteristics and geological
evolution of the Cape Meredith Complex
is comparable with that of the adjacent
Gondwana crustal blocks in Natal (SE Africa)
and Dronning Maud Land (East Antarctica),
supporting models that demonstrate these areas
evolved in a contiguous, juvenile are environment
prior to, and during, a major orogenic
event at similar to1.1 Ga. These events were
associated with the birth of the Rodinian supercontinent.
The three areas remained juxtaposed
during Rodinia break-up and were subsequently
incorporated into Gondwana in the
same relative positions.
2010040520
伽 马 射 线 光 谱 学 在 构 造 对 比 中 的 应 用 : 以
多 内 加 尔 ( 爱 尔 兰 西 北 部 ) 新 元 古 代 达 雷
德 期 序 列 为 例 = Gamma-ray spectroscopy in
structural correlations: an example from the
Neoproterozoic Dalradian succession of
Donegal (NW Ireland). ( 英 文 ). Hadley M J;
Ruffell A; Leslie A G. Geological Magazine,
2000, 137(3): 319-333
The Caledonian Horn Head Slide is a spectacular
ductile shear zone transecting Neoproterozoic
Appin Group Dalradian metasediments
in Donegal (NW Ireland). Two conflicting
stratigraphic interpretations exist for the
inverted succession exposed in the hanging
wall of the structure. These are based on correlation
with two quite separate exposed pelite
formations elsewhere. The two formations are
lithologically indistinct and unfossiliferous.
Here we document the novel use of assayed
and logged spectral gamma-ray measurements
151