Plagiogranite from the Andaman ophiolite belt, Bay of Bengal, India

Abstract

Plagiogranites occur on the eastern margin of the southern part of South Andaman in the outer sedimentary arc of the Andaman-Nicobar islands, a part of the Sunda-Burmese double-chain arc system, in the Bay of Bengal. They intrude gabbros that are associated with pillow basalt, East Coast volcanic rocks (basalt, basaltic andesite to acid differentiates), radiolarian cherts, conglomerate and grit. The plagiogranite, characterized by the occurrence of interstitial vermicular and micrographic intergrowths of quartz and plagioclase, shows some geochemical similarities with ophiolitic plagiogranites, but Rb, Yb, Nb, Ta and Y abundances in the Andaman plagiogranite are characteristic of volcanic-arc granites rather than the ocean-ridge granites. It is suggested that the Andaman plagiogranite has been generated by low-pressure crystal fractionation of a low-K tholeiitic magma derived from a mantle source in a supra-subduction zone tectonic setting. Further, it is suggested that this plagiogranite intruded the gabbro of the Andaman ophiolite probably during Mid-Eocene times, as the Andaman ophiolitic rocks (Late Cretaceous to Early Eocene) are believed to have been obducted onto the leading edge of the Eurasian continent during the Mid-Eocene to Late Oligocene subduction event, prior to the currently active Andaman-Java subduction system, that was initiated during the Late Miocene.

Gabbro, plagiogranite and associated dykes in the supra-subduction zone Evros Ophiolites, NE Greece

“…Boninites and arc tholeiites known from the fore-arcs of modern arc/back-arc systems have been related to the early stages of arc systems evolution (Crawford, Falloon & Green, 1989;Pearce et al 1992;Stern & Bloomer, 1992;Bloomer et al 1995;Taylor, 1995), where they are associated with the plagiogranites (Jafri, Charan & Govil, 1995). The above magmatic assemblage is documented also in ancient arc systems and ophiolite suites (Coleman & Donato, 1979;Pearce, Harris & Tindle, 1984;Pedersen & Malpas, 1984;Floyd, Yaliniz & Göncüoglu, 1998;Luchitskaya, Morozov & Palandzhyan, 2005), including ophiolites in the Aegean region (Hatzipanagiotou & Tsikouras, 1999).…”

Isolation and characterization of nickel-resistant microflora from serpentine soils of Andaman

“…The occurrence of serpentine soils in Andaman Island (India) particularly in Saddle Hills, Chidyatapu and Rutland has been well documented (Halder 1984;Roy et al 1988;Vohra et al 1989;Jafri et al 2003;Pal et al 2003) but microbiological studies of these unique soil types have not been undertaken so far. The present study reports for the first time on the occurrence and characterization of nickel-resistant microorganisms from such naturally nickel-percolated serpentine ecosystems of Andaman, India.…”

The mafic–ultramafic complex of Aniyapuram, Cauvery Suture Zone, southern India: Petrological and geochemical constraints for Neoarchean suprasubduction zone tectonics

“…The plagiogranite intrusions within the AMUC are leucocratic and trondhjemitic in nature characterized by low potassium (<1 wt% K 2 O; (except one sample) and high sodium (4.9-7.1 wt% Na 2 O) contents. The very low potassium content is a diagnostic feature of oceanic and ophiolitic plagiogranites (Coleman and Peterman, 1975;Coleman and Donato, 1979;Aldiss, 1981;Pederson and Malpas, 1984;Kanaris-Sotiriou and Gibb, 1989;Jafari et al, 1995). The rare earth elements (REE) show relatively low absolute concentrations and flat chondrite normalized patterns (3-30 Â chondrite) with distinct, but variable, positive Eu anomalies (Fig.…”