Geochemical and geochronological record of the Andaman Ophiolite, SE Asia: From back-arc to forearc during subduction polarity reversal?

Abstract

Ophiolites are widely studied to unravel how new subduction zones form. They may contain crustal and mantle rocks that formed during juvenile stages of intra-oceanic subduction, modifying the pre-existing oceanic lithosphere within which subduction started, and in which a magmatic arc formed upon subduction maturation. Previous geochemical work on the Cretaceous Andaman Ophiolite and its metamorphic sole, located in the forearc of the Sunda subduction zone of south-east Asia, has revealed geochemical signatures that are difficult to reconcile in a single tectonic setting but may rather record different stages in a longer evolution. A recent kinematic reconstruction proposed that the Andaman Ophiolite may have formed during subduction initiation in a former back-arc basin, when the former (Woyla) arc collided with the Sundaland continent. Here, we evaluate whether such a scenario may provide a feasible context to explain the enigmatic geochemical signatures preserved in the Andaman Ophiolite. To this end, we provide new, and review existing geochemical as well as geochronological constraints on the formation of its crustal rocks, as well as the evolution of its mantle portion. We identify mafic magmatic rocks and cogenetic plagiogranites that are consistent with formation in a magmatic arc, whereas other magmatic rocks, as well as metamorphic sole protoliths, have characteristics indicative of a back-arc origin. Three new, and two previous zircon U/Pb ages of arc magmatic rocks give a 99-93 Ma age range, but we also identify an inherited ~105 Ma age. This latter age coincides with Ar/Ar cooling ages of the Andaman metamorphic sole, and with a plagioclase xenocryst age from recent Barren Island volcanics east of Andaman. The geochemical and geochronological constraints of the Andaman ophiolites are straightforwardly explained in the context of the regional kinematic history: (1) The original lithosphere formed in the back-arc basin of the Woyla intra-oceanic arc; (2) Subduction initiation and SSZ ophiolite formation within this basin occurred around or slightly before 105 Ma; (3) This was followed by arc magmatism between 99 and 93 Ma upon subduction maturation.

The forearc ophiolites of California (USA) formed during trench-parallel spreading: kinematic reconstruction of the western USA Cordillera since the Jurassic

“…Our analysis favors such a scenario. This would be comparable to the reconstruction of a subduction polarity reversal that followed upon the collision of the Woyla intraoceanic arc with Sundaland, on Sumatra, in the Cretaceous, and the coeval initiation of the Sunda subduction zone and the associated Andaman Ophiolites in the original back-arc basin (Advokaat et al, 2018;Bandyopadhyay et al, 2021;Plunder et al, 2020). In the Sumatra-Andaman system, the time span between the onset of the new and arrest of the old subduction zone is on the order of 10…”

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

“…The bulk rock geochemical analysis of 18 samples of the Andaman Ophiolite from the South Andaman is presented in Table 1. Sea region of previous studies Bandyopadhyay et al, 2020;Bhattacharya et al, 2013;Ghosh et al, 2014;Jafri et al, 1990;Jafri et al, 2010;Jafri & Sheikh, 2013;Pal, 2011;Pal et al, 2007;Pedersen et al, 2010;Ray et al, 1988;Sachin et al, 2017;Saha et al, 2020;Srivastava et al, 2004) = 57-63 wt% may be either due to the data gap or what is known as the Daly Gap (Daly, 1925). It can be a subject of investigation in future studies.…”

“…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).…”

“…They suggested at least 5 Ma of magmatism with a diverse geochemical signature offering an arc setting for parts of the Andaman Ophiolites. Bandyopadhyay et al (2020) have also carried zircon U/Pb dating yielding a 99-93 Ma age range of magmatic arc rocks (gabbro and plagiogranite) in the Andaman Islands. This study also identifies an inherited 105 Ma age for the gabbros.…”

“…Some suggested settings include N-MORB, island-arc, and back-arc tectonic settings (e.g., Ghosh et al, 2017;Jafri, Sarma, & Sheikh, 2010;Jafri & Sheikh, 2013;Pal, 2011;Srivastava, Chandra, & Shastry, 2004). Bandyopadhyay et al (2020) has proposed a threestage regional kinematic history based on the available geochemical and new geochronological inputs. The findings of their study argue for an SSZ origin for the Andaman Ophiolite.…”