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.
The study focuses on Equatorial Atlantic margins, and draws from seismic, well, gravimetric and magnetic data combined with thermo-mechanical numerical modelling.Our data and numerical modelling indicates that early drift along strike-slip-originated margins is frequently characterized by up to 10°–20° spreading vector adjustments. In combination with the warm, thinned crust of the continental margin, these adjustments control localized transpression.Our observations indicate that early-drift margin slopes are too steep to hold sedimentary cover, which results in their inability to develop a moderately steep slope undergoing cycles of gravitational instability resulting in cyclic gravity gliding. These slopes either never develop such conditions or gain them at later development stages.Our modelling suggests that the continental margin undergoing strike-slip-controlled break-up experiences warming due to thinning along pull-apart basin systems. Pull-apart basins eventually develop sea-floor spreading ridges. Margins bounded by strike-slip faults located among pull-apart basins with these ridges first undergo cooling. However, spreading ridges leaving the break-up trace along its strike eventually pass by these cooling margins, warming them again before the final cooling proceeds. As a result, the structural highs surrounded by several source rock kitchens witness a sequential expulsion onset in different kitchens along the trajectory of spreading ridges.Supplementary material:Discussion of the methods used, chronostratigraphic results and strike-slip margin characteristics are available at http://www.geolsoc.org.uk/SUP18518
Continental break-up mechanisms vary systematically between slow- and fast-extension systems. Slow-extension break-up has been established from studies of the Central Atlantic, European and Adria margins. This study focuses on the intermediate and fast cases from Gabon and East India, and draws from the interpretation of reflection seismic, gravimetric and magnetic data.Interpretation indicates continental break-up via continental mantle unroofing in all systems, with modifications produced by magmatism in faster-extension systems. Break-up of the intermediate-extension Gabon system involves partial upper continental crustal decoupling from continental mantle; whereas, in the fast East Coast India system, decoupled and lower-crustal regimes underwent upwarping in ‘soggy’ zones in the footwalls of major normal faults. Usually, upper-crustal break-up is affected by pre-existing anisotropies, which form systems of constraining ‘rails’ for extending continental crust. This modifies the local stress regimes. They regain a regional character as the function of constraining rails vanishes during progressive unroofing of the upper mantle. Different regions attain different amounts of upper-crustal stretching prior to the break-up. The break-up location is then controlled by the upper-crustal energy balance principle of ‘wound linkage’, by which the minimum physical work is performed for linking upper-crustal ‘wounds’, leading to successful upper-crustal break-up.Supplementary material:Supplementary information and figures on the modelling of the mechanisms and architecture is available at http://www.geolsoc.org.uk/SUP18525.
The 85°E Ridge is a buried aseismic ridge running parallel to the 85°E meridian in the Bay of Bengal, India. Its origin has been a subject of debate, with opinions ranging from an abandoned spreading centre to a hotspot track. The present study follows the hotspot hypothesis and incorporates gravity, magnetic and seismic data to identify the nature and interpret the origin of the 85°E Ridge. It differs from earlier studies in the integration of deep seismic lines and gravity inversion to identify crustal architecture below the 85°E Ridge. Seismic interpretation along with gravity inversion has been used to determine the crustal structure below the ridge, while sediment thickness maps have been used to infer the uplift during the ridge emplacement. Seismic interpretations together with isostatic residual gravity anomaly map have been used to associate large negative anomalies with hotspot related magmatism. The negative anomaly increases with increasing volcanic load, indicating the presence of a crustal root and magmatic underplating. Typical flexural moat and arch, indicative of hotspot volcanism, is also observed in the seismic profiles. Gravity inversion modeling indicates an "onion-shell" like structure within the volcanic load, inferring the presence of less dense outer layers with a heavier core within the complex. Sediment thickness maps show the presence of dynamic uplift of more than 2000 milliseconds from early Cretaceous onwards. The study concludes that the 85°E Ridge is a result of hotspot volcanism, and proposes a plausible model for the origin of the structure.
Compared segments of East and West Indian passive margins have different evolution and crustal architecture. The East Indian margin is less magmatic. It results from a crust first/mantle second breakup scenario of a continent experiencing two rift events. The West Indian margin is more magmatic. It results from a mantle first/crust second breakup scenario of a continent experiencing four rift events. The architecture across both margins can be divided into stretching, thinning and hyperextension zones. The East Indian margin is characterized by oceanward-dipping listric normal faults accommodating thinning in the thinning and hyperextension zones and a zone of the exhumed mantle separating continental and oceanic crusts. The West Indian margin in contrast is characterized by landward-dipping listric faults accommodating magma-assisted thinning in the thinning and hyperextension zones and no exhumed mantle. The final breakup affects the lithospheric mantle layer in the East Indian case and the crustal layer in the West Indian case. Although the temperature-dependent rheologies of these two last unbroken layers are rather different, seismic interpretation suggests that they are both broken by upward-convex normal faults, which succeed the development of listric faults. They appear to be the first spontaneously formed faults in the breakup-delivering process, although their nucleation may be magma-assisted. The main difference between controlling factors of the aforementioned breakup scenarios affecting similar lithospheres at similar extension rates is the cumulative time length of pre-breakup rift events, being 62 and 115 Ma at East and West Indian margins.Supplementary material at https://doi.org/10.6084/m9.figshare.c.5912978
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.