Kumar N.,GX Technology |
Danforth A.,GX Technology |
Nuttall P.,GX Technology |
Helwig J.,GX Technology |
And 2 more authors.
Geological Society Special Publication | Year: 2013
The first comprehensive geological and geophysical surveys of the Brazilian continental margin during the 1970s recognized the crust in the SE Brazilian basins as 'anomalous' but models for the opening of the South Atlantic proposed at that time invoked a very narrow continent- ocean transition. Nevertheless, such studies established the presence of a thick sedimentary prism, including an extensive salt layer under the São Paulo Plateau. The earliest reconstructions for the South Atlantic invoked a seaward shift of the spreading axis to account for the asymmetric widths of the salt layer between the Brazilian margin and its conjugate in offshore Africa. Although our understanding of continent-ocean transition has progressed since then, direct seismic imaging at crustal scale has only been possible recently through long offset (10 km), deep recording (18 s), pre-stack depth migrated (PSDM) to 40 km, seismic-reflection data. These data allow us to generally image the Moho from under thick continental crust (> 30 km) to thin oceanic crust (c. 5 km). Although the nature of the transitional crust is still contested, these seismic data allow for constraints on various models for continent-ocean transition. Future integrated studies utilizing PSDM and refraction-seismic data will further refine these models. © The Geological Society of London 2013.
Choudhuri M.,Reliance Industries Ltd. |
Nemeok M.,University of Utah |
Stuart C.,University of Utah |
Welker C.,University of Utah |
And 2 more authors.
Journal of the Geological Society of India | Year: 2014
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. © 2014, Geological Society of India.