GRANITOIDS OF NORTHERN VICTORIA LAND, ANTARCTICA (TECTONICS, NEODYMIUM-ISOTOPES, GEOCHEMISTRY, PETROLOGY, STRONTIUM-ISOTOPES).

摘要

The pre-Permian metamorphic rocks of north Victoria Land (NVL), Antarctica, are divided into three terranes separated by NNW-trending, high-angle faults. From west to east, these are the Wilson (WT), Bowers (BT), and Robertson Bay (RBT) Terranes. Granites are widespread and most are grouped as Granite Harbour (GHI) or Admiralty (AI) Intrusives. These groups are spatially and temporally distinct and each exhibits well-defined but differently-directed compositional polarity.;The Devonian AI occur only in the BT and RBT and consist of I-type plutons ranging from tonalite to monzogranite. Compositional polarity exhibited by major and trace components and initial (epsilon)(,Nd) and (epsilon)(,Sr) indicates increasing contribution of old crustal material to the AI from south to north in the BT+RBT, and does not support a model of AI emplacement in an orogenic belt marginal to East Antarctica. Rather, the data indicate that the AI were emplaced on the margin of a crustal block which lay to the NNE, relative to the present configuration of terranes. Thus, an allochthanous origin for the BT+RBT is inferred. These data for the AI and GHI indicate that a major lower crustal discontinuity coincides with the geologic boundary between the WT and BT+RBT. This is interpreted as a plate boundary, perhaps a transform fault, along which the BT+RBT was juxtaposed to the WT. Details of juxtapositioning are unclear, but it must have occurred after the Devonian and before opening of the ocean between NVL and Australia at about 60 Ma.;Apart from the AI and GHI are two other groups of granites. The Carboniferous Salamander Granite Complex may have been related to volcanism in the WT, but it was not co-magmatic with the coeval Gallipoli Rhyolites. Two syenogranites identified in the Cenozoic Hallett Volcanic Province provide the first evidence of such extreme fractionation in this alkaline province.;The Cambro-Ordovician GHI are confined to the WT and comprise a variety of lithologies of both I- and S-type. Compositional polarity derived from major and trace components and initial (epsilon)(,Nd) and (epsilon)(,Sr) values indicates increasing involvement of old continental crustal material in production of GHI from east to west in the WT. These data support a model of GHI emplacement as a plutonic belt within the Ross Orogen on the margin of the East Antarctic Craton. Also, the isotopic data indicate that the GHI and WT are the continental "inboard" side of the plutonic belt.