Structure and origin of the 85°E ridge

Ramana, M.V.; Subrahmanyam, V.; Chaubey, A.K.; Ramprasad, T.; Sarma, K.V.L.N.S.; Krishna, K. S.; Desa, M.; Murty, G.P.S.; Subrahmanyam, C.

doi:10.1029/97jb00624

Cited by 59 publications

(26 citation statements)

References 51 publications

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“…The crustal model also suggests that the 85 • E Ridge and sedimentary load over the ridge are compensated by the regional flexure of the Moho boundary (figure 4). This observation is not in agreement with the earlier interpretations of the ridge structure (Liu et al 1982;Mukhopadhyay and Krishna 1991;Ramana et al 1997;Subrahmanyam et al 1999;Anand et al 2009), wherein they favoured the Airy model of isostatic compensation for the 85 • E Ridge. Subrahmanyam et al (1999) have considered underplated magmatic material within the deep crust beneath the ridge in order to explain the negative gravity field satisfactorily; this led to believe that the 85 • E Ridge was formed by a hotspot on young oceanic crust similar to the cases of emplacement of the Ninetyeast and Chagos-Laccadive ridges.…”

Section: Structure and Tectonics Of The 85 • E Ridgecontrasting

confidence: 76%

“…Though many subsequent researchers favoured the hotspot activity for the emplacement of the ridge (Müller et al 1993;Gopala Rao et al 1997;Subrahmanyam et al 1999;Krishna 2003;Bastia et al 2010;Radhakrishna et al 2010;Michael and Krishna 2011), the source of the hotspot volcanism remains speculative. Alternatively, formation of the ridge due to shearing or sagging of crust by horizontal stretching/compressional forces has been proposed by others (Ramana et al 1997;Anand et al 2009). Following the analogy of the negative gravity signature of the Laxmi Ridge in the Arabian Sea and its continental sliver interpretation (Naini and Talwani 1983;Talwani and Reif 1998;Krishna et al 2006), one can also think in the direction of continental origin to the 85 • E Ridge.…”

Section: Introductionmentioning

confidence: 94%

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

et al. 2011

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The 85 • E Ridge extends from the Mahanadi Basin, off northeastern margin of India to the Afanasy Nikitin Seamount in the Central Indian Basin. The ridge is associated with two contrasting gravity anomalies: negative anomaly over the north part (up to 5 • N latitude), where the ridge structure is buried under thick Bengal Fan sediments and positive anomaly over the south part, where the structure is intermittently exposed above the seafloor. Ship-borne gravity and seismic reflection data are modelled using process oriented method and this suggest that the 85 • E Ridge was emplaced on approximately 10-15 km thick elastic plate (Te) and in an off-ridge tectonic setting. We simulated gravity anomalies for different crust-sediment structural configurations of the ridge that were existing at three geological ages, such as Late Cretaceous, Early Miocene and Present. The study shows that the gravity anomaly of the ridge in the north has changed through time from its inception to present. During the Late Cretaceous the ridge was associated with a significant positive anomaly with a compensation generated by a broad flexure of the Moho boundary. By Early Miocene the ridge was approximately covered by the postcollision sediments and led to alteration of the initial gravity anomaly to a small positive anomaly. At present, the ridge is buried by approximately 3 km thick Bengal Fan sediments on its crestal region and about 8 km thick pre-and post-collision sediments on the flanks. This geological setting had changed physical properties of the sediments and led to alter the minor positive gravity anomaly of Early Miocene to the distinct negative gravity anomaly.

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Section: Structure and Tectonics Of The 85 • E Ridgecontrasting

confidence: 76%

Section: Introductionmentioning

confidence: 94%

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

et al. 2011

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“…Subrahmanyam et al (2001) modeled the strong gravity low associated with the submerged 85 • E Ridge and convincingly attributed it to a depression-like structure in the Moho, created by the volcanic load of the ridge which has as much density as that of the oceanic crust. The proposition of Subrahmanyam et al (2001) differed from the other interpretations which attributed the strong gravity low of the 85 • E Ridge to several anomaly sources, viz., thickening of the crust beneath the ridge on account of the isostatic compensation (Liu et al 1982;Gopala Rao et al 1997;Subrahmanyam et al 1999), an up-warped model of the ridge with a low-density crust and a shallow root (Ramana et al 1997) and combined sources of meta-sediments having high densities against the volcanic material, and flexure at Moho boundary due to volcanic load of the ridge (Krishna 2003). Subrahmanyam et al (2001) have also opined that each gravity low in the Bay of Bengal should be associated with a structural high like feature as in the case of 85 • E Ridge, and need to be explained by a corresponding flexure in the mantle.…”

Section: Introductionmentioning

confidence: 99%

Magnetic anomalies of offshore Krishna-Godavari basin, eastern continental margin of India

et al. 2009

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The marine magnetic data acquired from offshore Krishna-Godavari (K-G) basin, eastern continental margin of India (ECMI), brought out a prominent NE-SW trending feature, which could be explained by a buried structural high formed by volcanic activity. The magnetic anomaly feature is also associated with a distinct negative gravity anomaly similar to the one associated with 85 • E Ridge. The gravity low could be attributed to a flexure at the Moho boundary, which could in turn be filled with the volcanic material. Inversion of the magnetic and gravity anomalies was also carried out to establish the similarity of anomalies of the two geological features (structural high on the margin and the 85 • E Ridge) and their interpretations. In both cases, the magnetic anomalies were caused dominantly by the magnetization contrast between the volcanic material and the surrounding oceanic crust, whereas the low gravity anomalies are by the flexures of the order of 3-4 km at Moho boundary beneath them. The analysis suggests that both structural high present in offshore Krishna-Godavari basin and the 85 • E Ridge have been emplaced on relatively older oceanic crust by a common volcanic process, but at discrete times, and that several of the gravity lows in the Bay of Bengal can be attributed to flexures on the Moho, each created due to the load of volcanic material.

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“…• E Ridge running parallel to the Ninetyeast Ridge and almost buried under the sediments of Bengal fan, evolved due to the interaction of the Indian plate with the Crozet hotspot (Curray and Munashinghe, 1991;Ramana et al, 1997;Subrahmanyam et al, 1999). The extended chain of submarine volcanic islands, ChagosLacadive ridge system, in the western margin and stretching to the proximity of central Indian Ocean, define the track of the Reunion hotspot.…”

Section: Geology and Tectonicsmentioning

confidence: 99%

Integrated modeling of EM response functions from Peninsular India and Bay of Bengal

Arora

Rao

2014

Earth Planet Sp

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Existing sets of magnetovariational data from the large numbers of sites distributed across the peninsular India and those in the Bay of Bengal are reanalysed to obtain inter-site vertical and horizontal field transfer functions. Maps of induction arrows relocate the earlier reported conductive zones beneath the Palk-Strait and a regional scale anomaly in the offshore region, immediately southwest of the southern tip of Indian Peninsula, named South India Offshore Conductivity Anomaly (SIOCA). Period dependence of the induction arrows suggests that with increasing period SIOCA tends to control the induction pattern over the entire peninsula. Presentation of the horizontal transfer functions in the form of ellipses of anomalous currents helps to characterize the period and spatial behaviour of horizontal fields at seafloor sites. Integrated thin sheet modeling of the on-land and seafloor induction features suggest that the greater part of the anomalous behaviour of the horizontal fields at seafloor sites can be attributed to the shielding effects due to seawater. The weak anisotropic behaviour of the horizontal fields at selected sites can be explained in terms of the concentration of the induced currents in the sediment filled troughs on either side of the 85• E Ridge. Several lines of geophysical evidence favour the hypothesis that SIOCA, low velocity zone, low magnetization anomaly, all centered near the southern tip of the India, are the relics of the interaction of Marion Plume outburst with Indian lithosphere.

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Structure and origin of the 85°E ridge

Cited by 59 publications

References 51 publications

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

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

Magnetic anomalies of offshore Krishna-Godavari basin, eastern continental margin of India

Integrated modeling of EM response functions from Peninsular India and Bay of Bengal

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