Structure and tectonics of the continental margins of India and the adjacent deep ocean basins: current status of knowledge and some unresolved problems

Abstract

March 2020 586 The Indian Ocean and the bordering continental margins are characterized by a number of tectonic features consisting of deep ocean basins, aseismic ridges/ submarine plateaus and seamounts. Marine geophysical studies carried out over these regions for the past four decades have led to an increased understanding of the formation and evolution of these features. The present paper synthesizes an up-to-date compilation of the results of the salient inferences of those studies to describe the structure and tectonic evolution of these features as well as the Indian Ocean in general. A review of the existing knowledge on the structure and tectonics of the continental margins of India and the adjacent ocean basins reveal the existence of several unresolved problems, primarily due to the inherent tectonic complexities or the paucity of adequate data. Some of the major problems that need to be addressed/examined are: the existence and extent of the Prathap and Kori-Comorin ridges; the locations of the continent-ocean boundaries around the continental margins of India; the timing of formation of the deep offshore regions adjacent to the Indian continental margins; the deeper crustal structure and trend of the 85°E Ridge; the crustal configuration as well as the extent of the postulated micro-continental slivers; and the cause of intense seismicity over the Chagos Bank segment of the Laccadive-Chagos Ridge. In addition to addressing these questions, the present paper suggests ways to go forward by acquiring high-resolution and deep penetration multichannel seismic reflection data, seismic refraction data using Ocean Bottom Seismometers (OBS) and closely spaced sea-surface and deep-tow magnetic profiles along with high-resolution seafloor mapping.

Geochemistry of Deccan Tholeiite Flows and Dykes of Elephanta Island: Insights into the Stratigraphy and Structure of the Panvel Flexure Zone, Western Indian Rifted Margin

“…The data suggest instead that E-W extensional strain was already active at 66-65 Ma along this future (62.5 Ma) rifted continental margin. The Powai ankaramite flow in the 62.5 Ma Mumbai sequence, 20 km to the northwest, may have been fed by the young (~62 Ma) Elephanta ankaramite dyke which, along with 62.5 Ma, strongly N-S-oriented tholeiitic dykes [23,39] and rhyolitic lava flows in Mumbai [42], represents continental breakup between India-Laxmi Ridge and the Seychelles [23,24].…”

“…Several lava flow sequences located in the central, northern, and northeastern parts of the Deccan province broadly correlate with the WG sequence [20][21][22], implying that large-volume lava flows of the WG region may have travelled hundreds of kilometers to these distant areas. The Deccan CFB eruptions were followed by the India-Laxmi Ridge-Seychelles breakup at 62.5 Ma [23,24], with significant Deccan magmatism occurring syn-breakup and continuing post-breakup up to~61 Ma in Mumbai and the Seychelles [23,25]. Notes: * The Desur is considered by some workers as a "Unit" of the Panhala Formation.…”

The Amirante Ridge and Trench System in the Indian Ocean: the southern termination of the NW Indian subduction

“…The opening of the NW Indian Ocean results from the fragmentation of Gondwana since the Late Jurassic [McKenzie and Sclater, 1971, Norton and Sclater, 1979, Schlich, 1982, Besse and Courtillot, 1988, in response to complex interactions between subduction zones and mantle plumes [Coltice et al, 2009, Gaina et al, 2013, Matthews et al, 2012, which led to the separation of the India-Seychelles-Madagascar block from Africa and Australia [Gibbons et al, 2013]. The initiation of the Southern Neotethys Subduction documented around 110-105 Ma from metamorphic soles of the related ophiolites [Guilmette et al, 2018, Pourteau et al, 2018 drove the India's drift toward Eurasia, while the Marion and Deccan plumes acted as rheological facilitators over the breakup of the Madagascar-Seychelles-India continent [Torsvik et al, 2000, van Hinsbergen et al, 2011, which occurred in three major steps (see paleogeographic reconstructions of McKenzie and Sclater, 1971, Norton and Sclater, 1979, Schlich, 1982, Calv ès et al, 2011, Gaina et al, 2015, Yatheesh et al, 2019, Yatheesh, 2020.…”

“…The age of basalts dredged at the Amirante Ridge spans the Late Cretaceous-Early Paleocene period [Fisher et al, 1968, Johnson et al, 1982, a period marked by drastic changes in the configuration of the Indian Ocean's plate boundaries (i.e. curvature of fracture zones at the SW Indian Ridge, Cande and Patriat, 2015; migration of the India-Africa transform boundary; Rodriguez et al, 2016Rodriguez et al, , 2020; extinction of the Mascarene and East Somali Basin spreading centers and rifting between Seychelles and India; Gaina et al, 2015, Yatheesh, 2020.…”

“…The objective of this paper is to determine how the Amirante Ridge and Trench System fits in the complex framework of the Indian Ocean's fabric during the Late Cretaceous-Early Paleocene interval in order to unravel its tectonic origin. I provide a comprehensive paleogeographic reconstruction of the NW Indian Ocean from the Late Cretaceous to the Early Paleocene ( Figure 2), based on magnetic anomalies recorded in the oceanic basins [Dyment, 1993, 1998, Bernard and Munschy, 2000, Yatheesh, 2020 and the distribution of ophiolites surrounding the Arabian Sea [Gnos et al, 1998, Mahoney et al, 2002, Khan et al, 007b,a, Kakar et al, 2012, Siddiqui and Ma, 2017. I show that prior to the eruption of the Deccan Traps and India-Seychelles breakup circa 65 Ma [Yatheesh et al, 2009, Calv ès et al, 2011, the Amirante Ridge and Trench System was in line with a ∼1500-km-long subduction zone running along NW India, nowadays preserved in the ophiolites running from Bela to Waziristan in Pakistan (Figure 1).…”