The crustal electrical structure beneath the western segment of Narmada-Son lineament zone in Central India has been imaged using MT data set of 153 stations distributed over a grid (∼7–8 km site spacing). Three dimensional modeling of this data set brought out several major crustal conductors with different geometries at different depth levels in the crustal column interpreted to be maﬁc-ultramaﬁc bodies derived from mantle. We infer that these bodies represent the intrusive component of the Large Igneous Province (LIP) of the Deccan volcanic episode triggered by the passage of the Indian continent over the Reunion hot spot during the Late Cretaceous. The disposition and the geometry of the subsurface magmatic bodies, which must have served as magma chambers for outpouring of the Deccan lavas, suggest that they are closely related to the plumbing geometry of the LIP of the Deccan volcanic episode.
Regional scale deep 3D electrical resistivity variations in north-western part of the Indian subcontinent covering Rajasthan and its adjoining regions revealed a high conductive (< 10 Ohm-m) zone confined to an ~100 km corridor in NW-SE direction at the base of the lithosphere, starting from Jaisalmer in the NW to Ujjain in the SE, which can be attributed to the pre-outburst trace of the Reunion mantle plume. It is also interesting to note that the volume of the high conductive zone increases towards SE and raises to shallow level which might be acted as a feeder to conductive magma chambers ultimately resulted in the outpouring of the Deccan traps at ~65 Ma.
The occurrence of lower crustal earthquakes in the Central Indian Tectonic Zone (CITZ) was investigated using crustal resistivity sections derived from magnetotelluric (MT) data along multiple profiles across the CITZ and subsurface constraints obtained from other geophysical and geological data. MT models inferred small volume (<1 vol. %) of aqueous fluids in most part of the lower crust, which in conjunction with xenoliths and other geophysical data support a predominant brittle/semi-brittle lower crustal rheology. The resistivity models, particularly a new resistivity model across the 1938 Satpura lower crustal earthquake epicenter, also showed localized deep crustal zones with higher fluid content (2.2 - 6.5 vol. %), which imply high pore pressure conditions. The above observations and the significant strain rate evidenced for the region provide favorable conditions (strong/moderate rock strength, moderate temperature, high pore pressure and high strain rate) for brittle failure to occur in the lower crust. The fluid-rich pockets in the mid-lower crust seems to catalyze earthquake generation either as the source of local stress (fluid pressure), which together with the regional stress produce critical seismogenic stress conditions, or reduce the shear strength of the rocks to favour tectonic stress concentration at the low resistive (weak) zones, which is being transferred to seismogenic faults to cause earthquake.
A technique to evaluate effect of evaluation frequency separation on magnetotelluric resolution is developed. Aiming at the resolution enhancement of the subsurface objects, an evaluation (target) frequency separation criterion is proposed for MT method.
|Dr. Patro B. P. K||Senior Principal Scientist|
|Dr. Abdul Azeez K. K||Principal Scientist|
|Dr. Naganjaneyulu K||Senior Scientist|
|Mr. Chinna Reddy K||Senior Technical Officer(1)|
|Mr. Narendra Babu||Technical Officer|
|Mr. Arvind Kumar Gupta||Technical Officer|
|Mr. Appala Raju P||Technical Officer|
|Mr. Mothukuri Shiva Krishna||Technical Assistant|
|Mr. Balakrishna C||Multi Tasking Staff|
Page Last Updated On : 26-06-2020