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Chromite chemistry as an indicator of petrogenesis and tectonic setting of the Ranomena ultramafic complex in north-eastern Madagascar

Ishwar-Kumar, C and Rajesh, VJ and Windley, BF and Razakamanana, T and Itaya, T and Babu, EVSSK and Sajeev, K (2018) Chromite chemistry as an indicator of petrogenesis and tectonic setting of the Ranomena ultramafic complex in north-eastern Madagascar. In: GEOLOGICAL MAGAZINE, 155 (1). pp. 109-118.

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Official URL: http://dx.doi.org/10.1017/S0016756816000972

Abstract

The Ranomena ultramafic complex in NE Madagascar consists of layered gabbro, harzburgite, orthopyroxenite, clinopyroxenite, garnet websterite and chromitite-layered peridotite. This study of the Ranomena chromite chemistry aims to better understand the petrogenesis and palaeotectonic environment of the complex. The chromite from the Ranomena chromitite is unzoned/weakly zoned and has a Cr# (Cr/(Cr + Al)) of 0.59-0.69, a Mg# (Mg/(Fe + Mg)) of 0.37-0.44, and low Al2O3 (15-23 wt %) suggesting derivation from a supra-subduction zone arc setting. Calculation of parental melt composition suggests that the parental magma composition of the Ranomena chromitite was similar to that of a primitive tholeiitic basalt formed at a high degree of mantle melting, suggesting the parental melt composition was equivalent to that of an island-arc tholeiite (IAT). The parental magma of the Ranomena chromite had a FeO/MgO ratio of 0.9 to 1.8, suggesting arc derivation. The parental magma was Al- and Fe-rich, similar to a tholeiitic basaltic magma. The composition of orthopyroxene from the chromitite indicates a crystallization temperature range of 1250-1300 degrees C at 1.0 GPa. The chemistry of the chromite in the Ranomena chromitite further suggests that the complex formed in a supra-subduction zone arc tectonic setting.

Item Type: Journal Article
Additional Information: Copy right for this article belongs to the CAMBRIDGE UNIV PRESS, 32 AVENUE OF THE AMERICAS, NEW YORK, NY 10013-2473 USA
Department/Centre: Division of Mechanical Sciences > Centre for Earth Sciences
Depositing User: review EPrints Reviewer
Date Deposited: 12 Jan 2018 09:25
Last Modified: 12 Jan 2018 09:25
URI: http://eprints.iisc.ac.in/id/eprint/58665

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