Structural Imprints of Andaman Accretionary Prism and Its Tectonic Relation with Ophiolite Belt of Indo-Burma Ranges

Petrological, mineral chemical and geochemical characteristics are reported for the basalts of South Andaman ophiolite suite (India) of Cretaceous age to infer its petrogenesis, magma source characteristics and tectonic setting. In the field, both massive basalts and basalts with wellpreserved pillow morphology are present. The basalts consist of plagioclase, clinopyroxene, Fe-Ti oxide and Cr-spinel. They are tholeiitic in composition with low concentrations of Na 2 O + K 2 O (3 -5 wt.%). The representative samples of these basalts have a nearly flat chondrite-normalized REE pattern [(La/Yb) N = 0.29 -2.27)] with minor Eu anomaly (Eu/Eu* = 0.90 -1). Our findings suggest that the arc-like massive basalts were generated before the back-arc rifting initiated in an earlier stage of back-arc extension as a result of eastward subduction of the Neotethyan oceanic slab. The MORB-like pillow basalts were erupted due to further back-arc spreading in response to the roll-back of the Neotethyan oceanic lithospheric slab. The pillow and massive basalts assemblage in the South Andaman ophiolite records the evolution of a back-arc basin from initial rifting to subsequent spreading, documenting how basaltic magmatism evolves during the formation of the back-arc basin in a suprasubduction zone setting.

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“…The lavas of the ophiolite suite of South Andaman Island are largely accreted fragments of oceanic crust (Ghosh et al, 2017;Pal, 2020).…”

Section: Tectono-magmatic Significance and Geodynamic Implicationsmentioning

confidence: 99%

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

et al. 2022

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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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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

Lithos

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Structural Imprints of Andaman Accretionary Prism and Its Tectonic Relation with Ophiolite Belt of Indo-Burma Ranges

Cited by 5 publications

References 55 publications

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

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

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