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

• Published in: Journal of Asian earth sciences Vol. 145; pp. 679 - 690
• Main Authors: Tong, Laixi, Jahn, Bor-ming, Liu, Xiaohan, Liang, Xirong, Xu, Yi-gang, Ionov, Dmitri
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 01.09.2017; Elsevier
• Subjects: Earth Sciences; East Antarctica; Geochemistry; Larsemann Hills; Rayner orogeny (990–900 Ma); Sciences of the Universe; Ultramafic to mafic granulites; Geochemistry; East Antarctica; Rayner orogeny (990–900Ma); Ultramafic to mafic granulites; Larsemann Hills; Rayner orogeny
• ISSN: 1367-9120; 0743-9547; 1878-5786
• DOI: 10.1016/j.jseaes.2017.06.012

[Display omitted] •Ultramafic to mafic granulites in the Larsemann Hills of East Antarctica show composition features of igneous cumulate.•Their peak granulite facies recrystallization condition is 860–900°C.•Their negative Nb and Ti anomalies suggest they were formed in a subduction zone related to arc-continent collision.•Peak granulite metamorphism and arc-continent collision occurred in the early Neoproterozoic (990–900Ma) Rayner orogeny. 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°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 1826ppm and 1400ppm respectively for ultramafic granulite and [Cr] of 1460ppm 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 (990–900Ma) Rayner orogeny.