Abstract
The Andaman Ophiolite, India, is located at the southeastern end of the Tethyan ophiolites. We examine petrology and mineralogy of two lherzolites and a completely serpentinized dunite associated with lherzolite from the middle Andaman Island. Major and trace element compositions of minerals in the lherzolites suggest their residual origin after low-degree of partial melting with less flux infiltration, and are similar to those of abyssal peridotites recovered from mid-ocean ridges. The dunite with spinels having low-Cr/(Cr + Al) ratio was formed by interaction between peridotite and mid-ocean ridge basalt-like melt. The 87Sr/86Sr and 143Nd/144Nd isotopic systematics of clinopyroxenes of the two lherzolites are consistent with MORB-type mantle source. Petrology and light rare earth element (LREE)-depleted patterns of clinopyroxene from the studied lhezolites are the same as those from some of the western Tethyan ophiolites. The age-corrected initial εNd values of the Tethyan lherzolite clinopyroxenes with LREE-depleted patterns are likely to be consistent with the depleted mantle evolution line.
Highlights
The Mesozoic peri-Gondwanan ophiolites are distributed in the Alpine-Himalayan orogenic belt, the Indo-Myanmar (Burma) Range and the Sunda subduction zone [1,2,3,4]
The Rutland Island peridotites are mainly composed of harzburgite and high-Cr chromitite indicating their formation in supra-subduction zone environments, whereas lherzolite-dominated outcrops are well observed in the middle/north Andaman Island [4,8,9,12]
To avoid mineralogical and geochemical modifications caused by serpentinization, deformation and infiltration of late melts related to the formation of pyroxenite/gabbro veins, we selected two least serpentinized, less deformed and vein-free spinel lherzolites for further mineralogical and geochemical investigations: one from a massive outcrop of a quarry where no visible variations in terms of modal abundances of pyroxene were observed on the weathered surface (M21), and the other is one of the least altered/deformed clinopyroxene-rich lherzolite boulders (M31) recovered from the strand line (Figures 2 and 3)
Summary
The Mesozoic peri-Gondwanan ophiolites are distributed in the Alpine-Himalayan orogenic belt, the Indo-Myanmar (Burma) Range and the Sunda subduction zone [1,2,3,4]. These ophiolites were formed by the closing of the Tethyan oceans with different ages, such as the Paleo-Tethys (Devonian–Triassic), Meso-Tethys (late Early Permian–Late Cretaceous) and Neo-Tethys (Late Triassic–Late Cretaceous) [2]. The Rutland Island peridotites are mainly composed of harzburgite and high-Cr chromitite indicating their formation in supra-subduction zone environments, whereas lherzolite-dominated outcrops are well observed in the middle/north Andaman Island [4,8,9,12].
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