INTRODUCTION

SUMMARY

Free air gravity anomaly profiles, which extend from 590E to 810 30’E longitude along the equator were used to model the deformed zones across the Central Indian Ridge (CIR), Chagos-Laccadive Ridge (CLR) and part of the abyssal plain of the Central Indian Ocean Basin (CIOB). The modeling reveals the nature of deformations, the possible block faulting, and intrusions. The CIR and CLR segments show crustal thickening whereas the CIOB segment shows normal crustal thickness. The CIR displays highly deformed crust-subcrust configuration while the CLR indicates a complex pattern of deformation. The abyssal plain segment of the CIOB has a subdued folded geometry. The modeling provides a transverse expression of the nature of buckling of this part of the oceanic lithosphere resulting from N-S compression and helps to ascertain whether the configurations of CIR, CLR & CIOB are in conjunction with the inferences drawn from earlier geophysical studies.

Contrary to the plate tectonic theory, intra-plate deformation of the Indian plate i.e. the Central Indian Ocean Basin (CIOB) has been reported and this interesting phenomenon has drawn attention of the scientific community to map the crustal features and to suggest the tectonic model to account them. Earlier studies based on seismicity, seismic profiling, heat flow and gravity have provided ample evidence on the intra-plate deformation of the Indian Ocean equatorial region. The intra-plate tectonics is clearly demonstrated by seismicity, especially with large earthquakes, which occur along and near the Ninetyeast and Chagos-Laccadive ridges and in the Wharton and Central Indian basins. Earthquakes within a few hundred kilometers east and west of the Ninetyeast ridge typically are strike-slip; earthquakes between 840E and 860E occur mainly on thrust faults with nearly east-west striking fault planes, suggesting north-south shortening (Stein and Okal, 1978; Bergman and Solomon, 1984). Normal faulting earthquakes characterize seismicity near Chagos Bank with tensional axes oriented approximately in the north-south direction. Seismic profiling (Eittreim and Ewing, 1972; Weissel at al., 1980) reveals wide spread tectonic deformation in the overlying sediments and basements in the Central Indian Ocean. Substantial heat flow anomalies found are suggestive of heat generation at shallow depths by some process possibly related to the deformation (Geller at al., 1983). Heat flow studies by Anderson et al., (1977), Weissel et al., (1980), Geller et al., (1980), Stein et al., (1988) show average values nearly 30 mW/m2 higher than expected from cooling models. The high heat flow values are not associated with earthquake epicentres, however they seem to be associated with broad region of deformation (Stein and Weissel, 1990). Sychev et al., (1987) suggest that the wide lateral propagation of magmatic intrusion in the lower and upper parts of the crust of the CIOB is the cause for anomalous heat flows. One of the possible sources of the additional heat may be thermal energy released during whole lithosphere folding caused by strong horizontal compression due to the collision in Oligocene- Miocene time (Weissel et al., 1980, Stein et al., 1988, Cochran et al, 1987, 1988).).

This content is only available via PDF.
You can access this article if you purchase or spend a download.