Petrology and Geochemistry of the Grubergebirge Anorthosite and Marginal Rocks, Central Dronning Maud Land: Further Characterization of the Late Neoproterozoic Magmatic Event in East Antarctica

Abstract

The Grubergebirge anorthosite, a Late Neoproterozoic massif-type anorthosite, was emplaced into Late Mesoproterozoic-aged metamorphosed orthogneisses and supracrustal rocks in the Wohlthat Mountains. Mineralogically and chemically, the marginal rocks to the anorthosite massif classify as ferromonzodiorite and ferromonzonite. Variations in trace and rare earth element abundances and normalized patterns between the anorthosite and associated marginal ferromonzodiorite (and minor ferromonzonite) and distinct differences between the ferromonzodiorite and ferromonzonite have been observed. Whereas the magmas from which the anorthosite crystallized have been slightly contaminated by incorporating crustal material (now occurring as enclaves), the marginal ferromonzodiorite represent rocks that originated due to mixing (hybridization) of injected primitive ferrodiorite magma(s) with preexisting crustal material, resulting in the hybrid ferromonzodiorite.These events at the margin of the massif anorthosite represent a widespread Late Neoproterozoic magmatic event with accompanying crustal mixing; all these rocks were thereafter metamorphosed under amphibolite-to granulitefacies conditions during the Early Cambrian Period. In contrast, unmetamorphosed dykes with a ferrodiorite mineralogy, of Late Cambro-Ordovician age, have been found that probably represent a part of the late magmatic suites of the south Petermannketten (Zwiesel).

Advances in Antarctic geoscience studies: Indian contributions

“…The nature and petrography of the Anorthosite Massif exposed in the Gruber Mountains as intrusives into Late Mesoproterozoic orthogneisses and other supracrustal rocks, and its magmatic history have been described by Mukerji et al (1988) and Ravikant et al (2011). Mukerji et al (1988) point out the alkali enrichment and silicarich nature of these anorthosites while drawing a similarity of these anorthosite to those of Adirondack (USA) and Perinthatta (India)'.…”

“…Mukerji et al (1988) point out the alkali enrichment and silicarich nature of these anorthosites while drawing a similarity of these anorthosite to those of Adirondack (USA) and Perinthatta (India)'. Ravikant et al (2011) have classified the rocks marginal to the anorthosite massif as ferro-monzodiorite and ferro-monzonite. They postulate that the magma from which the anorthosite crystallized has been contaminated by crustal material that now occurs as enclaves within it.…”

Recent Contribution to the Antarctic Gelology

“…The studies which began as localized geological descriptions have assumed significance lately for two reasons-first recognition of cDML terrain as possible extension of the East African Orogen (EAO) in Antarctica and the significance of sub-ice geology in the context of understanding and predicting East Antarctic Ice Sheet (EAIS) behaviour, the largest single mass of fresh 270 Naresh C Pant et al nature of this magmatism which ranged from ultrabasic to acidic in composition besides establishing presence of a distinct charnockitic magma in the region (Kaul et al, 1991, Joshi et al, 1991, Joshi and Pant, 1995, Ravindra and Pandit, 2000. Ravikant (1998) presented a thermal model for one of the largest Proterozoic anorthosite massif located at the Gruber Mountains in cDML which was followed by petrological and geochemical studies of this Neoproterozoic magmatic intrusive (Ravikant et al, 2011). The inter-relationship between various magmatic bodies is debatable and requires further investigation.…”

“…Ravikant (1998) presented a thermal model for one of the largest Proterozoic anorthosite massif located at the Gruber Mountains in cDML which was followed by petrological and geochemical studies of this Neoproterozoic magmatic intrusive (Ravikant et al, 2011 The shear zones of the Schirmacher oasis were studied in detail (Sengupta 1993, Roy et al, 2015a. The dominant shear zones have a NE-SW trend with a variable southerly dip.…”

“…Central Dronning Maud Land, East Antarctica is a high grade polymetamorphosed and polydeformed terrain (Ravikant 2008(Ravikant , 2009Ravikant et al, 2011). In several papers the Neoproterozoicage of metamorphism in the Schirmacher Oasis was demonstrated including the nature of the oceanic crust Indian Contributions to Antarctic Geology 271 which allowed the authors to conclude that the proposed extension of EAO is likely to be within the Schirmacher Oasis (Ravikant et al, 2004(Ravikant et al, , 2005(Ravikant et al, , 2007Ravikant 2005Ravikant , 2006Ravikant , 2008.…”