Geochronology, structural geology and petrology of the northwestern Lagrange Nunataks, Shackleton Range, Antarctica

Brommer, A.; Millar, I. L.; Zeh, A.. 1999 Geochronology, structural geology and petrology of the northwestern Lagrange Nunataks, Shackleton Range, Antarctica. Terra Antartica, 6 (3). 269-278.

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The metamorphic rocks of the La Grange Nunataks, northwestern Shackleton Range, have a complex structural and metamorphic history, involving Mid-Proterozoic and Ross- (Cambro-Ordovician) aged events. The protolith of the Stratton Group Mathys Gneiss was emplaced at 2328 ± 47 Ma (U-Pb zircon), and underwent migmatization at 1715 ± 6 Ma. Migmatization took place at P-T conditions of > 640 ºC / > 4-6 kbar and was accompanied by the formation of multiple generations of ductile structures (D1) and the development of local shear zones (D2). Three distinct deformation events (D3 – D5) took place during the Ross Orogeny, affecting the supracrustal Schimper Group, and to a lesser extent, the Mathys Gneiss. The Ross events, which disturbed the U-Pb systems of zircons in the Proterozoic gneisses, are dated by an Sm-Nd garnet age of 535 ± 22 Ma for Schimper Group kyanite-staurolite-garnet-gneiss. The penetrative event D3, which is characterized by west-directed shearing, took place under Barrovian-type peak P-T conditions of 645 ºC / 7.05 kbar, reflecting crustal thickening during the Ross Orogeny. Subsequent polyphase folding (D4) formed the dominant E-W trending fold axes, and can be correlated with a NW-SE to N-S crustal shortening during initial exhumation. The final deformation episode (D5) is characterized by sinistral strike-slip displacement related to a final transpressional overprint. The D5 event took place under low grade metamorphic conditions, in the stability field of chlorite.

Item Type: Publication - Article
Programmes: BAS Programmes > Pre 2000 programme
ISSN: 1122-8628
Additional Keywords: geochronology, geology, petrology, La Grange, nunataks, petrographics, Shackleton Range, Schimper
NORA Subject Terms: Earth Sciences
Date made live: 28 Aug 2013 13:13 +0 (UTC)

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