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Cr-spinel records metasomatism not petrogenesis of mantle rocks.

ABSTRACT: Mantle melts provide a window on processes related to global plate tectonics. The composition of chromian spinel (Cr-spinel) from mafic-ultramafic rocks has been widely used for tracing the geotectonic environments, the degree of mantle melting and the rate of mid-ocean ridge spreading. The assumption is that Cr-spinel's core composition (Cr# = Cr/(Cr + Al)) is homogenous, insensitive to post-formation modification and therefore a robust petrogenetic indicator. However, we demonstrate that the composition of Cr-spinel can be modified by fluid/melt-rock interactions in both sub-arc and sub-mid oceanic mantle. Metasomatism can produce Al-Cr heterogeneity in Cr-spinel that lowers the Cr/Al ratio, and therefore modifies the Cr#, making Cr# ineffective as a geotectonic and mantle melting indicator. Our analysis also demonstrates that Cr-spinel is a potential sink for fluid-mobile elements, especially in subduction zone environments. The heterogeneity of Cr# in Cr-spinel can, therefore, be used as an excellent tracer for metasomatic processes.

SUBMITTER: Gamal El Dien H

PROVIDER: S-EPMC6841941 | biostudies-literature | 2019 Nov

REPOSITORIES: biostudies-literature

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Cr-spinel records metasomatism not petrogenesis of mantle rocks.

Gamal El Dien Hamed H Arai Shoji S Doucet Luc-Serge LS Li Zheng-Xiang ZX Kil Youngwoo Y Fougerouse Denis D Reddy Steven M SM Saxey David W DW Hamdy Mohamed M

Nature communications 20191108 1

Mantle melts provide a window on processes related to global plate tectonics. The composition of chromian spinel (Cr-spinel) from mafic-ultramafic rocks has been widely used for tracing the geotectonic environments, the degree of mantle melting and the rate of mid-ocean ridge spreading. The assumption is that Cr-spinel's core composition (Cr# = Cr/(Cr + Al)) is homogenous, insensitive to post-formation modification and therefore a robust petrogenetic indicator. However, we demonstrate that the c ...[more]

PMID: 31704918

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Cr-spinel records metasomatism not petrogenesis of mantle rocks.

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Cr-spinel records metasomatism not petrogenesis of mantle rocks.

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