Geological mapping and new structural observations during the 1994/95 EUROSHACK Expedition lead us to propose a new lithological subdivision of the Proterozoic Read Group, which is exposed in a tectonic window framed by the Ross-age low-grade Mount Wegener Nappe in the southern Shackleton Range. The oldest rock-units of the Read Group comprise several varieties of high-grade gneisses, ranging in composition from pelitic to quartzo-feldspathic and mafic, interlayered with minor amphibolites, Ca-silicate rocks, quartzites, marbles and serpentinites. On the basis of the petrological evidence provided by the mafic gneisses, the metamorphic evolution of these rock units includes at least three main metamorphic stages: a medium-P granulite facies stage (8 kbar, ca. 800°C) (M1), a low-P upper amphibolite to granulite facies stage (5 kbar, ca. 700 °C) (M2), and a low-P lower-amphibolite to greenschist facies stage (M3). Several distinct plutonic suites were distinguished and mapped. They range from syn-metamorphic metaluminous to peraluminous granitoids to post-tectonic swarms of peraluminous granitic dykes. The plutonic suites were emplaced mainly after M1 and throughout M2. The overall tectono-metamorphic evolution from M1 to M3 is interpreted as a continuous record of the exhumation of a thickened crust, controlled mainly by extension and triggered by voluminous magmatism in middle-Proterozoic time. Younger, Ross-age deformation and greenschist facies metamorphism occur mainly close to the contact zone with the Mount Wegener Nappe and provide evidence for reactivation of the Proterozoic Read Group associated with its incorporation, under a prevailing transpressional regime, within the Ross-age thrust-fold system of the Shackleton Range.
|Titolo:||Geology and tectono-metamorphic evolution of the Read Group, Shackleton Range: a part of the East Antarctic Craton|
|Appare nelle tipologie:||1.1 Articolo in rivista|