Back-arc basin origin for the basalts of the South Andaman Island Ophiolite (India)

Akhtar, Salim; Saikia, Ashima; Negi, Priyanka; Kalita, Bikas Jyoti

doi:10.18814/epiiugs/2021/021001

Cited by 4 publications

(1 citation statement)

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“…However, this region has been less explored due to its remoteness and inaccessibility. Most studies are on either the mantle rocks or the basic volcanics of the Andaman Ophiolite (Akhtar, Saikia, Negi, & Kalita, 2021;Bandyopadhyay et al, 2020). In this contribution, we investigate the geochemical makeup of the intermediate (basaltic-trachyandesites, trachyandesites) to acidic (dacite and rhyodacites) rocks of the Andaman Ophiolite, which is considered an extension of the Phanerozoic Indonesian-Myanmar orogenic belt (Figure 1a).…”

Section: Dismembered Occurrences Of Ophiolitic Rocks In the Andamanmentioning

confidence: 99%

Role of fractional crystallization and partial melting in the generation of intermediate and acidic magmas of the Andaman Island Ophiolite suite of India

2021

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The Mesozoic-age Andaman Island Ophiolite located in the southeastern fringe of the Indian plate margin is one of the well-preserved supra-subduction-zone oceanic lithospheric slices. It is tectonically associated with the Indonesian arc system and is an extension of the Phanerozoic Indonesian-Myanmar orogenic belt. Thus, it offers a unique opportunity to study oceanic crust formation and specify magma evolution processes in the Tethyan subduction system. The volcanics of the Andaman Islands ophiolite display a wide compositional variation. Rock types vary from basic (basalts) to intermediate (basaltic-trachyandesites, basaltic andesites) to acidic differentiates like dacites and rhyolites. This contribution presents the petrochemistry of the intermediate rock types-basaltic-trachyandesites, trachyandesites and acidic-dacites and rhyodacites of Andaman Island Ophiolite (India). This study examines the role of fractional crystallization and partial melting in the generation of intermediate and acidic magmas of the Andaman Ophiolite suite. Plagioclases and pyroxenes are the major mineral constituents of these rocks on petrographic observation. Plagioclases of the intermediate rocks are of albite composition Ab 98-99. The acidic rocks show compositional variation from albite to oligoclase (Ab 83-99 ). Analysed pyroxenes of intermediate and acidic rocks are augite (Wo 46-49 En 34-41 Fs 13-17 ) . The studied calcalkaline rocks show variable abundance of Large-Ion Lithophile Elements and display strong positive Pb and negative Ti anomalies. The chondrite-normalized Rare Earth Elements display an enriched pattern with varying degrees of enrichment. Clinopyroxene thermobarometry reveals that the intermediate magma and acidic magma becomes saturated with clinopyroxene at 1,062-1,133 C and 1,016-1,079 C, respectively, at 2 kbar and H 2 O = 2 wt%. Petrochemical findings and model calculations using PELE are consistent with a derivation of intermediate rocks from the basaltic melt by fractional crystallization. In contrast, acidic rocks are the product of partial melting of hydrothermally altered oceanic crust. The association of basaltic and intermediate rocks suggests a relatively stable magma chamber to generate differentiated intermediate magmas by fractional crystallization.

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Section: Dismembered Occurrences Of Ophiolitic Rocks In the Andamanmentioning

confidence: 99%

Role of fractional crystallization and partial melting in the generation of intermediate and acidic magmas of the Andaman Island Ophiolite suite of India

2021

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Geochemistry and zircon U-Pb geochronology of diabase, gabbros, anorthosites and ultramafic rocks from the South Andaman Island ophiolite suite on the South-Eastern margin of the Indian plate

Akhtar,

Santosh,

Gao

et al. 2024

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Cumulate gabbros in the South Andaman Island ophiolite suite (India): their bearing on the tectonic setting

2021

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The Andaman Ophiolite of south-eastern India is located on the outer arc of the Andaman-Java subduction zone. It is represented by thrust slices formed in the Mesozoic Neo-Tethyan Ocean. Lithologically, it consists of dismembered mafic and ultramafic rocks and associated oceanic pelagic sediments. The present study focuses on the mafic cumulate rocks of the Andaman Ophiolite preserved in the Kodiaghat and the Mundapahar area of the South Andaman Island. The mafic cumulates are represented by olivine-bearing and olivine-free gabbros. The sequence of crystallisation in the gabbros is olivines (Fo~80) ± chromian spinels (Cr# 59 - 57), plagioclases (An95−61), clinopyroxenes (Mg# = 89 - 82) and amphiboles (Mg-hornblende, edenite and pargasite). Major oxide and trace element whole rock geochemistry and mineral compositions are consistent with a hybrid signature of Island Arc Tholeiite (IAT) - Mid Oceanic Ridge Basalt (MORB). Geochemical modelling shows that trapped melt fractions of 0 – 20 % can produce the observed trace element signatures of these gabbros. Our findings suggest that the gabbroic cumulates of the Andaman ophiolite were formed in an oceanic back-arc and oceanic arc setting developed in the Neo-Tethyan oceanic domain between the Indian and the Burmese plates during Late Cretaceous age.

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Back-arc basin origin for the basalts of the South Andaman Island Ophiolite (India)

Cited by 4 publications

References 113 publications

Role of fractional crystallization and partial melting in the generation of intermediate and acidic magmas of the Andaman Island Ophiolite suite of India

Role of fractional crystallization and partial melting in the generation of intermediate and acidic magmas of the Andaman Island Ophiolite suite of India

Geochemistry and zircon U-Pb geochronology of diabase, gabbros, anorthosites and ultramafic rocks from the South Andaman Island ophiolite suite on the South-Eastern margin of the Indian plate

Cumulate gabbros in the South Andaman Island ophiolite suite (India): their bearing on the tectonic setting

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