Mesozoic anomalies in the Bay of Bengal

Ramana, M.V.; Nair, R.R.; Sarma, K.V.L.N.S.; Ramprasad, T.; Krishna, K. S.; Subrahmanyam, V.; D'Cruz, Maria; Subrahmanyam, C.; Paul, John F.; Subrahmanyam, Avanidhar; Sekhar, D.V. Chandra

doi:10.1016/0012-821x(94)90084-1

Cited by 110 publications

(52 citation statements)

References 23 publications

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“…In this paper, we use the most recent identification by Brown et al (2003) of anomalies M10y to M2o. Magnetic spreading anomalies have also been identified off the conjugate margin of east India, where Ramana et al (1994) interpreted anomalies back to M11, generated at a spreading rate of 3.5 cm a )1 . Banerjee et al (1995) proposed an alternative model for the Bay of Bengal in which they suggested that the Rajmahal hot spot powered the rifting of India from Antarctica from 117 Ma (Barremian) onwards.…”

Section: Seafloor Spreading Historymentioning

confidence: 95%

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Geology of the Continental Margin of Enderby and Mac. Robertson Lands, East Antarctica: Insights from a Regional Data Set

et al. 2004

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In 2001 and 2002, Australia acquired an integrated geophysical data set over the deep-water continental margin of East Antarctica from west of Enderby Land to offshore from Prydz Bay. The data include approximately 7700 km of high-quality, deep-seismic data with coincident gravity, magnetic and bathymetry data, and 37 non-reversed refraction stations using expendable sonobuoys. Integration of these data with similar quality data recorded by Japan in 1999 allows a new regional interpretation of this sector of the Antarctic margin. This part of the Antarctic continental margin formed during the breakup of the eastern margin of India and East Antarctica, which culminated with the onset of seafloor spreading in the Valanginian. The geology of the Antarctic margin and the adjacent oceanic crust can be divided into distinct east and west sectors by an interpreted crustal boundary at approximately 58°E. Across this boundary, the continent-ocean boundary (COB), defined as the inboard edge of unequivocal oceanic crust, steps outboard from west to east by about 100 km. Structure in the sector west of 58°E is largely controlled by the mixed rift-transform setting. The edge of the onshore ArchaeanProterozoic Napier Complex is downfaulted oceanwards near the shelf edge by at least 6 km and these rocks are interpreted to underlie a rift basin beneath the continental slope. The thickness of rift and pre-rift rocks cannot be accurately determined with the available data, but they appear to be relatively thin. The margin is overlain by a blanket of post-rift sedimentary rocks that are up to 6 km thick beneath the lower continental slope. The COB in this sector is interpreted from the seismic reflection data and potential field modelling to coincide with the base of a basement depression at 8.0-8.5 s two-way time, approximately 170 km oceanwards of the shelf-edge bounding fault system. Oceanic crust in this sector is highly variable in character, from rugged with a relief of more than 1 km over distances of 10-20 km, to rugose with low-amplitude relief set on a long-wavelength undulating basement. The crustal velocity profile appears unusual, with velocities of 7.6-7.95 km s )1 being recorded at several stations at a depth that gives a thickness of crust of only 4 km. If these velocities are from mantle, then the thin crust may be due to the presence of fracture zones. Alternatively, the velocities may be coming from a lower crust that has been heavily altered by the intrusion of mantle rocks. The sector east of 58°E has formed in a normal rifted margin setting, with complexities in the east from the underlying structure of the N-S trending Palaeozoic Lambert Graben. The Napier Complex is downfaulted to depths of 8-10 km beneath the upper continental slope, and the margin rift basin is more than 300 km wide. As in the western sector, the riftstage rocks are probably relatively thin. This part of the margin is blanketed by post-rift sediments that are up to about 8 km thick. The interpreted COB in the eastern sector is the...

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Section: Seafloor Spreading Historymentioning

confidence: 95%

“…At this time, a spreading ridge jump to the east Indian margin transferred the Elan Bank microcontinent to the Antarctic Plate. If this interpretation is correct, then the dating of magnetic anomalies older than M2 in the Bay of Bengal by Ramana et al (1994) is probably incorrect.…”

Section: Seafloor Spreading Historymentioning

confidence: 99%

Geology of the Continental Margin of Enderby and Mac. Robertson Lands, East Antarctica: Insights from a Regional Data Set

et al. 2004

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“…Royer and Sandwell (1989) observed that most of the BOB oceanic crust was formed during the above first two phases. However, the timing of the breakup between India and Antarctica is not clear, and based on magnetic anomaly identifications it ranges between 132 Ma (Ramana et al 1994) and *120 Ma (Gopala Rao et al 1997). 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.…”

Section: Regional Geotectonic History Of the Bobmentioning

confidence: 98%

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

2015

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The earthquake of 21 May 2014 (Mw 6.0) in the northern Bay of Bengal (BOB) highlights the importance of studies on intraplate earthquakes in the oceanic regime for understanding the stress state of the oceanic lithosphere. The epicenter of the earthquake is located at a water depth of 2.5 km where the sediment thickness is nearly 12 km, and it occurs at a depth of *50 km within the upper mantle. Its location on the seismotectonic map of the region shows that the epicenter is far from the seismically active zone of the Burmese Arc in the east and low-to-moderately active seismic region of the east coast of India in the west. The fault plane solution of this earthquake indicates that it was a strike-slip event with a right-lateral sense of motion on a NW-oriented nodal plane, and it occurred on one of the NW-SE-trending fracture zones previously mapped in the BOB. Based on a compilation of long-term (1900-2011) intraplate earthquakes along with available focal mechanisms in the BOB and the adjoining east coast of India, we conclude the following: (1) the Precambrian structural trends, basin-scale faults and minor lineaments on the east coast of India are favorably reactivated in their offshore extensions up to the shelf-slope areas of the margin; (2) earthquake occurrences in the BOB region can be correlated with the fracture zone trends in the central BOB and along the Ninetyeast ridge or at the intersections of fracture zones with the subsurface trace of the 85°E ridge. The 21 May 2014 earthquake is the result of reactivation of such a NW-SE-trending fracture zone lying in the lithosphere of [100 Ma in age. Further evaluation of this event in light of the global occurrence of oceanic intraplate earthquakes in the older lithosphere ([80 Ma) suggests that such reactivation is possible in the high ambient stress state.

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“…For instance, in the Bay of Bengal, Ramana et al [1994] and Gopala Rao et al [1997] identified magnetic anomalies as old as M11 and M0, respectively, whereas in the conjugate Enderby Basin, Ramana et al [2001] and Gaina et al [2003Gaina et al [ , 2007 identified anomalies as old as M11 or conjugate pairs of anomalies M9o-M2o, respectively. In view of this we have reexamined an up-to-date compilation of marine magnetic anomalies of the Bay of Bengal (Figure 7) and compared the data with a profile data of the central Enderby Basin (Figure 10).…”

Section: Breakup Of Eastern Gondwanaland and Evolution Of Fracture Zomentioning

confidence: 99%

“…On the basis of identification of M series magnetic anomalies (M11-M0) in Bay of Bengal and in offshore region of Sri Lanka, Ramana et al [1994] and Desa et al [2006] have inferred the occurrence of rifting between India and Antarctica at about 132 Ma. In another investigation, Gopala Rao et al [1997] found that the seafloor spreading in the Bay of Bengal was initiated mostly around the start of Cretaceous magnetic quiet epoch ($120 Ma).…”

Section: Introductionmentioning

confidence: 99%

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

et al. 2009

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[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.

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Mesozoic anomalies in the Bay of Bengal

Cited by 110 publications

References 23 publications

Geology of the Continental Margin of Enderby and Mac. Robertson Lands, East Antarctica: Insights from a Regional Data Set

Geology of the Continental Margin of Enderby and Mac. Robertson Lands, East Antarctica: Insights from a Regional Data Set

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

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

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