Geochemistry and geochronology of high-grade rocks from the Grove Mountains, East Antarctica: Evidence for an Early Neoproterozoic basement metamorphosed during a single Late Neoproterozoic/Cambrian tectonic cycle

Abstract

The Grove Mountains of East Antarctica are an inland continuation of the Prydz Belt. The high-grade metamorphic complex in this area is composed of felsic orthogneisses and mafic granulites, with minor paragneisses and calc-silicate rocks. U-Pb zircon analyses using SHRIMP and LA-ICP-MS techniques reveal that the protoliths of mafic granulites and felsic orthogneisses were emplaced during a short time interval of ca. 920-910 Ma. Mafic granulites can be divided into low- and high-Ti groups. They have initial εNd values [εNd(T)] ranging from +0.8 to -1.9. TiO2 is positively correlated with FeOt/MgO and La/Nb ratios, whereas it shows a negative correlation with εNd(T) values, indicating that the petrogenesis of their protoliths involved partial melting of a weakly enriched subcontinental lithospheric mantle and fractional crystallization of the magma accompanied by minor crustal contamination. Felsic orthogneisses have an affinity of A2-type granites, characterized by enrichment in REE, Y, Zr, Th and Ga and high Ga/Al and Y/Nb ratios. Most of them have εNd(T) values of -0.7 to -3.5 and Nd depleted mantle model ages (TDM) of 1.76-1.65 Ga, and a few have low εNd(T) values of -10.4 to -10.6 and old TDM of 2.46-2.27 Ga, reflecting a heterogeneity in their source region. Their protoliths were probably produced by high-temperature partial melting of tonalitic-granodioritic rocks triggered by the underplating of mantle-derived mafic magma during post-orogenic extension. U-Pb analyses also reveal a metamorphic age of ca. 2050 Ma from detrital zircons in a paragneiss, suggesting that the sedimentary materials of the paragneiss may have come from an as yet undiscovered Early Paleoproterozoic orogen of unknown provenance. Voluminous mafic-felsic intrusives and a small amount of sedimentary rocks constitute an Early Neoproterozoic basement of the Grove Mountains. Subsequently, this basement experienced only a single Late Neoproterozoic/Cambrian metamorphic cycle at ca. 550-535 Ma. The available data indicate that the Prydz Belt is a collage of multiple basement terranes and each of them has a distinct tectonic evolution. This supports the suggestion that the Prydz Belt may represent a Late Neoproterozoic/Cambrian collisional orogen that resulted in the final phase of the Gondwana assembly. © 2007 Elsevier B.V. All rights reserved.