Geology of the Kaikoura Area - GNS Science

TECTONIC HISTORYEarly to mid-PaleozoicGreenland Group rocks of the Buller terrane were depositedon the Australo-Antarctic margin of Gondwanaland in theEarly Ordovician (Cooper & Tulloch 1992). In the Silurianthe group was tightly folded and metamorphosed to lowergreenschist facies (Adams & others 1975). The HaupiriGroup of the Takaka terrane formed in a volcanic island arcand back-arc setting at a convergent plate boundary(Münker & Cooper 1999). The carbonate-rich Mt ArthurGroup rocks were deposited on a passive continentalmargin, east of the volcanic arc, after cessation ofsubduction; they were subsequently thrust over thevolcanic rocks of the Haupiri Group and folded (Cooper &Tulloch 1992). Accretion of the Takaka terrane onto theBuller terrane occurred in the mid-Devonian, in part bymovement along the Anatoki Fault. The tectonic suturingwas followed shortly afterwards by the intrusion ofvoluminous granitic rocks of the Karamea Batholithbetween 370 and 328 Ma (Cooper & Tulloch 1992).Late Paleozoic to Early CretaceousThe emplacement of the Median Batholith, dominated inthe Kaikoura map area by Triassic to Early Cretaceousintrusions, occurred along the margin of Gondwanalandand sutured the Western Province to the western part ofthe Eastern Province (Bradshaw 1993; Mortimer & others1999). Subsequently much of the eastern part of thebatholith has been excised by the Delaware-SpeargrassFault Zone (Johnston & others 1987; Johnston 1990). TheEastern Province contains six terranes within the map areaand all record convergent margin tectonism and volcanosedimentaryprocesses (Coombs & others 1976; Bradshaw1989; Mortimer 2004). The westernmost is the volcanogenicBrook Street terrane, consisting of a tectonicallydismembered remnant of a calc-alkaline island arc. Anintrusive contact between the Brook Street terrane and theMedian Batholith in Southland constrains accretion of theterrane to Gondwanaland to between 230 and 245 Ma(Middle to Late Triassic; Mortimer & others 1999). In eastNelson the contact between the Brook Street and Murihikuterranes is faulted. However the Brook Street terrane mayhave originally been overlain by the volcaniclasticMurihuku terrane in a Triassic-Jurassic back-arc basin.Farther east, a “slab” of Permian oceanic ridge or back-arcbasin crust, the Dun Mountain Ophiolite Belt, wasobducted onto Murihiku and Brook Street terranes duringEarly to mid-Permian subduction (Coombs & others 1976;Sano & others 1997). Overlying Late Permian to TriassicMaitai Group accumulated in a trench forearc settingadjacent to a convergent margin. Although faulted, andfolded into the Roding Syncline, the group has largelyretained internal stratigraphic coherence.The Patuki Mélange separates the Dun Mountain-Maitaiterrane rocks from the Caples terrane; the latteraccumulated as an accretionary wedge in a Late Permianto Triassic trench or trench slope. The original suturebetween the Caples and Rakaia terranes (not seen in theKaikoura map area) is within a zone of greenschist toamphibolite facies schist with multiple generations ofrecumbent folds and penetrative foliations (Mortimer1993a,b; Johnston 1994; Begg & Johnston 2000). In theKaikoura map area the Caples-derived schist was laterjuxtaposed by Cenozoic movement of the Alpine Faultagainst non-schistose Rakaia terrane rocks. Greenschistfacies (garnet zone) schist is present in the western part ofthe Rakaia terrane (Turnbull & Forsyth 1986), includingthe Aspiring lithological association, but farther eastweakly metamorphosed, lithologically monotonous,quartzofeldspathic sedimentary rocks predominate. Theserocks accumulated in a Late Triassic to Early Jurassicsubduction setting and were progressively imbricated anddeformed in an accretionary wedge (MacKinnon 1983;Bradshaw 1989). The Esk Head belt, comprising mélangeand generally more deformed rock, including theSilverstream Fault Zone in Branch River, is the tectonicsuture between the Rakaia terrane and the Pahau terraneto the east. Rocks of the Pahau terrane were deposited in asubduction setting and deformed in an accretionary wedgein the Late Jurassic to Early Cretaceous. The Caples, Rakaiaand Pahau terranes were amalgamated during convergenttectonism along the Gondwanaland margin between theMiddle Jurassic and the late Early Cretaceous, whensubduction ceased (Coombs & others 1976; Bradshaw1989). Major igneous intrusion occurred in and beyondthe west of the Kaikoura map area in the Early Cretaceouswith the emplacement of the Separation Point suite andother granitoids (Tulloch 1983).Mid- to Late Cretaceous and PaleogeneFollowing cessation of subduction and amalgamation ofthe Eastern Province terranes, a prolonged period ofextensional tectonics resulted in the opening of the TasmanSea and, within the Kaikoura map area, widespread erosionand deposition into numerous mid-Cretaceous basins(Crampton & others 2003). Intrusion of the TapuaenukuIgneous Complex and associated dikes was accompaniedby extrusive basalt flows, which interfingered withterrestrial and shallow marine sedimentary rocks.In the Late Cretaceous, subsidence become more regionalin extent (Crampton & Laird 1997) as the tempo ofextensional tectonics waned and a passive margindeveloped. Relative quiescence from the end of theCretaceous resulted in regional subsidence and marinetransgression, followed by the slow accumulation ofwidespread, fine-grained clastic and carbonate rocks (Field,Browne & others 1989). This was punctuated by sporadicintraplate volcanism, particularly in the Canterbury Basin(Browne & Field 1985). In the northeast of the map areathis passive, basinal regime continued through into at leastthe Middle Eocene (Strong & others 1995; Crampton &others 2003). In northern Canterbury, deposition on a broad,relatively sheltered shallow shelf led to accumulation offine-grained clastic rocks and glauconitic sands. Thenorthern basins extended southwards during the Eoceneand Oligocene, resulting in the deposition of a blanket ofcarbonate rocks. The Early Oligocene period of erosion48