Ultramafic to mafic granulites from the Larsemann Hills, East Antarctica: Geochemistry and tectonic implications

• Published in: Journal of Asian Earth Sciences
• Main Authors: Tong, Laixi, Jahn, Bor-ming, Liu, Xiaohan, Liang, Xirong, Xu, Yi-gang, Ionov, Dmitri
• Format: Report
• Language: English
• Published: PERGAMON-ELSEVIER SCIENCE LTD 2017
• Subjects: Geology; Ultramafic to mafic granulites; Geochemistry; Rayner orogeny (990-900 Ma); Larsemann Hills; East Antarctica; Geosciences; Multidisciplinary; PRINCE-CHARLES MOUNTAINS; AMERY ICE SHELF; PRYDZ BAY AREA; FACIES METAMORPHISM; RAUER GROUP; BRATTSTRAND BLUFFS; CRUSTAL EVOLUTION; CONTINENTAL-CRUST; VESTFOLD BLOCK; 500 MA; Amery; Amery Ice Shelf; Brattstrand Bluffs; Prince Charles Mountains; Prydz Bay; Rauer Group; Rayner; Vestfold; Antarc*; Antarctica; Ice Shelf
• Online Access: http://ir.gig.ac.cn/handle/344008/45379; https://doi.org/10.1016/j.jseaes.2017.06.012

The Larsemann Hills area is part of a reworked early Neoproterozoic metamorphic terrain in southwestern Prydz Bay, East Antarctica. Ultramafic and mafic granulites, whose origins remain controversial, occur as lenses, boudins or layered bodies within the para- and ortho-gneiss in the region. The ultramafic and mafic granulites show spinel-olivine-bearing and two-pyroxene-bearing mineral assemblages recrystallized at 860-900 degrees C. Their bulk rock analyses indicate an origin as igneous cumulates, with high Mg-# (molar MgO/(MgO + FeO)) from 0.73 to 0.84 for ultramafic granulite and from 0.46 to 0.78 for mostly mafic granulite as well as high Cr and Ni contents ([Cr] and [Ni] up to 1826 ppm and 1400 ppm respectively for ultramafic granulite and [Cr] of 1460 ppm for mafic granulite). Trace element patterns show pronounced negative Nb anomalies, suggesting a subduction-related tectonic setting for their precursors, consistent with derivation from arc basalts, also suggested by low TiO2 and K-enrichment in mafic granulites. The ultramafic to mafic granulites may have been formed in a subduction-related continental back-arc basin environment simultaneously with peak metamorphism associated with arc-continent collision during the early Neoproterozoic (990-900 Ma) Rayner orogeny.