Ultramafic to mafic granulites from the Larsemann Hills, East Antarctica: Geochemistry and tectonic implications
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 ult...
Published in: | Journal of Asian Earth Sciences |
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Main Authors: | , , , , , |
Format: | Report |
Language: | English |
Published: |
PERGAMON-ELSEVIER SCIENCE LTD
2017
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Subjects: | |
Online Access: | http://ir.gig.ac.cn/handle/344008/45379 https://doi.org/10.1016/j.jseaes.2017.06.012 |
Summary: | 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. |
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