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Structure and origin of the 85 degrees E ridge

DRS at CSIR-National Institute of Oceanography

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Title Structure and origin of the 85 degrees E ridge
 
Creator 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.
 
Subject ridges
anomalies
geophysical data
hot spots
mantle plumes
plate tectonics
 
Description The submerged 85 degrees E Ridge in the Bay of Bengal trends approximately N-S between 19 degrees N and 6 degrees N latitudes. Off the southeast coast of Sri Lanka it takes an arcuate shape and seems to terminate with the northweard extension of the Afanasy Nikitin seamounts situated around 2 degrees S latitude. The ridge is characterized by positive magnetic (100-400 nT) and negative free-air gravity (less than -60 mGal) anomalies with variable widths of 100-180 km. Magnetic model studies revealed that the rocks of the 85 degrees E Ridge are magnetized with revesed polarity. The well-defined geophysical anomalies and and lack of magnetic polarity reversals together with the deep burial nature of the ridge may not favor a hotspot origin. Two alternative processes for the ridge emplacement have been suggested. Ridge emplacement may be (1) due to shearing of the lithosphere caused by stretching and compressional forces associated at the time of major plate reorganization immediately after the evolution of the early Cretaceous crust in the Bay of Bengal, more precisely at MO isochron or during the middle Albian reversals within the Cretaceous long normal polarity (K-T superchron) epoch when the Earth's magnetic polarity changed from normal to reversed polarity, and/or (2) due to sagging followed by deformation produced by the buckling instability of the oceanic plate caused by horizontal compressional forces on the passive continental margin. However, more marine geophysical data are required to support the postulated coincidence of the ridge with a reversed polarity magnetic anomaly and their associated model. Further, the Rajmahal traps (normally polarized) and the 85 degrees E Ridge (reversely polarized) appear to be associated with two different episodes of eruptional that might have been triggered by the Kerguelen mantle plume. The 85 degrees E Ridge seems to extend into the onshore West Bengal Basin as a subsurface ridge and merges with the reported NNE-SSW trending zone of strong geophysical anomalies east of Rajmahal traps up to 25 degrees N latitude
 
Date 2009-01-12T09:14:41Z
2009-01-12T09:14:41Z
1997
 
Type Journal Article
 
Identifier Journal of Geophysical Research (B: Solid Earth), Vol.102; 17995-18012p.
http://drs.nio.org/drs/handle/2264/2041
 
Language en
 
Rights Copyright [1997]. All efforts have been made to respect the copyright to the best of our knowledge. Inadvertent omissions, if brought to our notice, stand for correction and withdrawal of document from this repository.
 
Publisher American Geophysical Union