Geoid and gravity anomaly data of conjugate regions of Bay of Bengal and Enderby Basin: New constraints on breakup and early spreading history between India and Antarctica

Abstract

[1] Timing of breakup of the Indian continent from eastern Gondwanaland and evolution of the lithosphere in the Bay of Bengal still remain as ambiguous issues. Geoid and free-air gravity data of Bay of Bengal and Enderby Basin are integrated with shipborne geophysical data to investigate the early evolution of the eastern Indian Ocean. Geoid and gravity data of the Bay of Bengal reveal five N36°W fracture zones (FZs) and five isolated NE-SW structural rises between the Eastern Continental Margin of India (ECMI) and the 85°E Ridge/86°E FZ. The FZs meet the 86°E FZ at an angle of $39°. The rises are associated with low-gravity and geoid anomalies and are oriented nearly orthogonal to the FZs trend. The geoid and gravity data of the western Enderby Basin reveal a major Kerguelen FZ and five N4°E FZs. The FZs discretely converge to the Kerguelen FZ at an angle of $37°. We interpret the FZs identified in Bay of Bengal and western Enderby Basin as conjugate FZs that trace the early Cretaceous rifting of south ECMI from Enderby Land. Structural rises between the FZs of Bay of Bengal may either represent fossil ridge segments, possibly have extinct during the early evolution of the Bay of Bengal lithosphere or may have formed later by the volcanic activity accreted the 85°E Ridge. Two different gravity signatures (short-wavelength high-amplitude negative gravity anomaly and relatively broader low-amplitude negative gravity anomaly) are observed on south and north segments of the ECMI, respectively. The location of continent-ocean boundary (COB) is at relatively far distance (100-200 km) from the coastline on north ECMI than that (50-100 km) on the south segment. On the basis of geoid, gravity, and seismic character and orientation of conjugate FZs in Bay of Bengal and western Enderby Basin, we believe that transform motion occurred between south ECMI and Enderby Land at the time of breakup, which might have facilitated the rifting process in the north between combined north ECMI-Elan Bank and MacRobertson Land and in the south between southwest Sri Lanka and Gunnerus Ridge region of East Antarctica. Approximately during the period between the anomalies M1 and M0 and soon after detachment of the Elan Bank from north ECMI, the rifting process possibly had reorganized in order to establish the process along the entire eastern margins of India and Sri Lanka.

A seismotectonic study of the 21 May 2014 Bay of Bengal intraplate earthquake: evidence of onshore-offshore tectonic linkage and fracture zone reactivation in the northern Bay of Bengal

“…Furthermore, due to the requirement of accommodating the Elan Bank microcontinent in the breakup scenario, Gaina et al (2003) proposed a two-stage breakup history for the Eastern Continental Margin of India (ECMI): first, the India-Antarctica separation during M9o-M2o; second, the separation of Elan Bank from the present-day ECMI at M2. Recent geophysical studies along the ECMI are in agreement with the above doublebreakup scenario (Krishna et al 2009;Radhakrishna et al 2012). Based on the basement trends in the multichannel seismic reflection data, Radhakrishna et al (2012) identified several NW-SE-oriented fracture zones in the BOB, and these are in accordance with the earliest seafloor spreading direction.…”

“…1). The oceanic lithosphere in the BOB region evolved during the breakup of India and Antarctica in the Early Cretaceous period (Powell et al 1988) followed by three major phases of seafloor spreading: the initial NW-SE spreading up to the Mid-Cretaceous period, the N-S spreading until the early Tertiary and the present NE-SW spreading (Curray et al 1982;Krishna et al 2009). Royer and Sandwell (1989) observed that most of the BOB oceanic crust was formed during the above first two phases.…”

Development of the negative gravity anomaly of the 85°E Ridge, northeastern Indian Ocean – A process oriented modelling approach

“…The first breakup occurred with separation of Greater India from Australia and East Antarctica during the Early Cretaceous Royer and Coffin 1992;Gopala Rao et al 1997;Müller et al 2000). In the second stage the Elan Bank, a submerged microcontinent lies presently on the western margin of the Kerguelen Plateau in the southern Indian Ocean, broke up from the present-day eastern margin of India at about 120 Ma (Gaina et al 2003(Gaina et al , 2007Borissova et al 2003;Krishna et al 2009). The breakup sequences and their timings suggest that most part of the oceanic crust in the Bay of Bengal was evolved during the Cretaceous Magnetic Quiet Period (120-83 Ma).…”

Lithosphere structure and upper mantle characteristics below the Bay of Bengal

“…1); the presence of thick sediments and lack of identifiable magnetic anomalies in the northern part of BOB prevents the recognition of NW-SE spreading regime identified elsewhere (e.g. Krishna et al, 2009). Recently, based on basement trends observed from large number of multi-channel reflection profiles, Radhakrishna et al (2012) have mapped several NW-SE trending fracture zones in the northern part of the BOB.…”