Re-Os Isotope Systematics of Sulfides in Chromitites and Host Lherzolites of the Andaman Ophiolite, India

José González-Jiménez,Biswajit Ghosh,Suzanne O’Reilly,William Griffin,Sisir Mondal

doi:10.3390/min10080686

Abstract

Laser ablation MC-ICP-MS was used to measure the Os-isotope compositions of single sulfide grains, including laurite (RuS2) and pentlandite [(Fe,Ni)9S8], from two chromitite bodies and host lherzolites from ophiolites of North Andaman (Indo-Burma-Sumatra subduction zone). The results show isotopic heterogeneity in both laurite (n = 24) and pentlandite (n = 37), similar to that observed in other chromitites and peridotites from the mantle sections of ophiolites. Rhenium-depletion model ages (TRD) of laurite and pentlandite reveal episodes of mantle magmatism and/or metasomatism in the Andaman mantle predating the formation of the ophiolite (and the host chromitites), mainly at ≈0.5, 1.2, 1.8, 2.1 and 2.5 Ga. These ages match well with the main tectonothermal events that are documented in the continental crustal rocks of South India, suggesting that the Andaman mantle (or its protolith) had a volume of lithospheric mantle once underlaying this southern Indian continental crust. As observed in other oceanic lithospheres, blocks of ancient subcontinental lithospheric mantle (SCLM) could have contributed to the development of the subduction-related Andaman–Java volcanic arc. Major- and trace-element compositions of chromite indicate crystallization from melts akin to high-Mg IAT and boninites during the initial stages of development of this intra-oceanic subduction system.

Highlights

The association of chromitites with dunite diking harzburgite, and to a lesser extent lherzolite, of the mantle section of ophiolite complexes is well known [1,2,3]
The high degree of isotopic heterogeneity in the chromitite was interpreted as reflecting their formation from different pulses of melts that were extracted from mantle sources of isotopic heterogeneity in the was interpreted as reflecting their from different with a protracted history ofchromitite partial melting and metasomatism
The samples employed in this study were collected from two different chromitite pods known as Cr-6, Cr-7 and corresponding host lherzolite (N-3, N-4, N-5, N-6) North Andaman (Figure 1)

Summary

Introduction

The association of chromitites with dunite diking harzburgite, and to a lesser extent lherzolite, of the mantle section of ophiolite complexes is well known [1,2,3]. The in situ analyses of Re-Os isotopic composition of platinum-group minerals (PGM) and base-metal sulfides (BMS) using of LA-MC-ICP-MS have revealed significant isotopic heterogeneities in Os at all scales (km, hand-specimen, thin sections and within single grain) in both chromitites and host peridotites in the upper mantle [32,34,35,36,37,38,39,40,41,42]. LA-MC-ICP-MS have revealed significant isotopic heterogeneities in Os at all scales (km, hand-specimen, thin sections and within single grain) in both chromitites and host peridotites in the Minerals 2020, 10, 686 upper mantle [32,34,35,36,37,38,39,40,41,42]. Indonesian through Nagaland, Manipur and the western Burma (Myanmar) region and merges with modern subduction alongsystem the Andaman–Sumatra–Java (ASZ) trench where

Methods

Results

Conclusion