East Indian margin evolution and crustal architecture: integration of deep reflection seismic interpretation and gravity modelling

Abstract

The segmented East Indian continental margin developed after the Early Cretaceous break-up from Antarctica. Its continental crust terminates abruptly without considerable thinning along the Coromondal strike-slip segment and thins considerably before it terminates in the orthogonal rifting segments. The segments have an exhumed continental mantle corridor oceanwards of them. This, proto-oceanic crust, corridor varies in width from segment to segment, indicating a relationship with varying break-up-controlling tectonics of the adjacent margin segments.The top of the proto-oceanic crust is imaged by a higher reflectivity zone, while its base does not have any distinct signature. A contorted system of reflectors represents its internal structure. Its gravity signature is a longer-wavelength anomaly with peak values up to 30 mGal less negative than surrounding values. Its magnetic signature is represented by a positive anomaly with peak values of 0–56 nT. Wide proto-oceanic segments are adjacent to margin segments that are preceded by the orthogonally rifting Cauvery, Krishna–Godavari and Mahanadi rift zones. A narrow proto-oceanic segment is adjacent to the margin segment initiated by the dextral Coromondal transfer zone. A combination of seismic interpretation and gravity/magnetic forward modelling indicates that proto-oceanic crust is most probably composed of lower crust slivers and unroofed hydrated upper mantle, being formed between the late rifting and the organized sea-floor spreading.

Transform margins: development, controls and petroleum systems – an introduction

“…The breakup trajectory in the brittle upper crust usually follows the Andersonian geometry of the normal and strike-slip faults with respect to the stress field that resulted in the breakup, unless their geometry is affected by pre-existing anisotropy. Examples of zig-zag trajectories with normal, oblique-slip or strike-slip faulting-dominated control come from the offshore Gabon (Nemčok et al 2012a), offshore East India (Nemčok et al 2012c) and both sides of the Equatorial Atlantic (Nemčok et al 2012b). Subsequently, the initial spreading centres have to clear their contact with the continental -oceanic transform changing into transform margin segments.…”

“…In this example, the distance between the two rift zones was probably too large for them to be fully linked by the transfer zone. This can be interpreted from the observation that, while the faults of the northern horse-tail structure of the transform are fully linked with syn-rift faults of the Krishna-Godavari rift zone, the faults of the southern horse-tail structure first crosscut the syn-rift faults of the Cauvery rift zone and only subsequently both structures became kinematically linked (Nemčok et al 2012c;Sinha et al 2015). The southern transform linkage could have been developed by the east -west Indian Ocean propagation through the evolving rift system.…”

Recognizing remnants of magma-poor rifted margins in high-pressure orogenic belts: The Alpine case study

“…In this area serpentinized mantle is locally overlain by slivers of continentderived blocks, referred to as 'extensional allochthons', often consisting of upper crustal rocks and/or pre-tectonic sediments, originated from the stretched and fragmented hanging wall. This kind of margin architecture is being increasingly recognized in present-day magma-poor rifted margins, including the eastern Indian margin (Nemčok et al, 2012), the South Atlantic (Unternehr et al, 2010), the southern Australian margin (Espurt et al, 2012) and the late Jurassic to lower Cretaceous Møre and Vøring margins, in the North Atlantic (Osmundsen and Ebbing, 2008). Fossil hyper-extended crust and lithosphere characterized by extensional allochthons related to Jurassic rifting have also been extensively detected in sections of Alpine mountain belts that were only marginally affected by orogeny-related deformation and metamorphism (e.g.…”

85°E Ridge, India – Constraints on its Development and Architecture

“…The breakup of India from Antarctica took place during Valanginian to Hauterivian age (Reeves and Wit, 2000;Nemèok et al, 2007;Nemèok et al, 2012) of the Early Cretaceous epoch (e.g., Powel et. al., 1988;Storey, 1995;Acharyya, 1998;Subramanyanm and Chand, 2006;Gaina et.…”