(1996). (2012) have mapped several NWSE trending fracture zones in the northern part of the BOB. The oceanic lithosphere in the Bay of Bengal (BOB) formed 80-120 Ma following the breakup of eastern Gondwanaland. Left- Cutaway showing continental and ocean crust, and upper mantle layers. In general, low GTR values (02 mkm1) indicate shallow level of compensation, whereas, the intermediate GTR values (26 mkm1) suggest that the compensation takes place at deeper level by lithosphere thinning (Crough 1978). 7(a). The lower mantle flows slowly, at a rate of a few centimeters per year. Several researchers have effectively used this approach (i) for evaluating isostatic response of the oceanic lithospheric using free-air gravity/geoid and bathymetry admittance function (e.g., McKenzie & Bowin 1976; Watts 1978; Black & McAdoo 1988); (ii) for estimation of flexural rigidity of continental lithosphere through Bouguer gravity and topography coherence function (Forsyth 1985; Lowry & Smith 1994; McKenzie & Fairhead 1997; Simons et al. The upper mantle is hot and variable. The density of the upper mantle varies between 2.9 g/cm3 and 3.3 g/cm3. 2011; Bhattacharya et al. Higher-pressure work has been completed on the effects of various species in the C-O-H system on the melt characteristics of mantle minerals (14, 15), but these results do not directly assess the stability of . Pressure increases with the increase of the depth. B) Oceanic Crust: thinnest layer. 1999, 2008; Grevemeyer et al. One idea is that it is minerals are undergoing another transition in this region because of pressure and temperature conditions, similar to the transition between the upper and lower mantle. Vertically, the Vs values present a high-low-high velocity (three layers) pattern within a depth range of 170 km.If the upper HVZ is interpreted as the mantle lithosphere or upper mantle cover, then the lower one belongs to a high velocity interlayer within the upper mantle asthenosphere. Rao G.S. Kopp C. Krishna K.S. After that,the mantle began the slow circulation it has had for the last four billion years. The study of the characteristics of this area is of the utmost importance, as it largely controls the mass transfer between the upper mantle and the underlying parts of the Earth and significantly affects the convective mantle processes. 2001; Sreejith & Krishna 2013). We further considered the division of post-collision sediment sequence into two layers; (i) upper layer with velocity 1.63.0 kms1 (ii) lower layer with velocity 3.04.4 kms1 (Michael & Krishna 2011). The sediment thickness estimated as over 22 km in offshore Bangladesh (Curray 1991), decreases towards the south with a significant decrease in sediments thickness between 8and 10N, with also relative thinning over the 85E and Ninetyeast ridges. Abraham H. The upper mantle extends to about 400 kms. Lower in the mantle, extreme pressures transform minerals and create rocks like eclogite (Figure 3.5), which contains garnets. The lithospheric structure was modelled along three regional transects AA to CC (two EW, one NS) in the BOB region (see Fig. The BOB is also characterized by the presence of one of the largest submarine fans of the world which extends from 20N to 740S over a length of 3000 km (Krishna et al. Minerals and rocks change under high pressure. What are 5 characteristics of the upper mantle? 2003). This difference in Te values is ascribed to subsequent modification of the ridge topography by subduction related forebulge effect of the Andaman-Sumatra arc system in this region. Majority of the GTR values computed for two bandpass filtered geoid and topography data sets (Figs5a and b) along the 85E and the Ninetyeast ridges range from 0 to 2 mkm1 at both wavelength scales, which indicate that these two ridges are compensated at shallow depths. Thick black line represents the LAB geometry from the PM_v2_2012 global shear wave velocity model of Priestley & McKenzie (2013). Twinkle D. Radhakrishna M. This procedure removes the contribution of the geoid of wavelengths>4000,>1334 and>800 km, respectively and give rise to different residual geoid anomalies. 7b) within the flexural waveband (0.01330 km). The modelling was iteratively carried out for a range of Te values, and the best-fitting Te was obtained based on the minimum RMS error between the observed and calculated by matching both amplitude and wavelength of anomalies. What risk did George Lucas take to break from Hollywood and begin truly building his empire?
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