Granitic and magmatic bodies in the deep crust of the Son Narmada Region, Central India: constraints from seismic, gravity and magnetotelluric methods

Abstract

Magnetotelluric (MT) data at 24 locations in the Son Narmada region, Central India, were collected across the Tapti North Fault and Son Narmada Fault along the Chinchpada-Godhra profile (220 km). MT impedance tensors were then estimated in the period range 0.001-1,000 s using robust processing codes. The N70• E geo-electric strike direction was obtained by multi-site, multi-frequency analysis. The data were modeled using non-linear conjugate gradient scheme taking both apparent resistivity and phase into account. The two-dimensional MT model obtained (after static shift correction) represents resistive bodies (1,000-3,000 ohm-m) and conductive bodies (<20 ohm-m) in the deep crust. The resistive bodies in the lower crust are interpreted to be granitic intrusive complexes. The conductor on the south of Son Narmada Fault is attributed to the presence of magmatic bodies due to underplating, and the conductor on the north as due to the presence of fluids. The highly resistive (>2,000 ohm-m) upper crust is interpreted to comprise felsic rocks of granitic composition, and the low-resistive (<100 ohm-m) deep crust as being composed of dense mafic granulites. The Domal upwarp structure near Son Narmada Fault, with a thick felsic crust sandwiched between the mafic and intermediate crust, can be explained by underplated sediments/felsic crust which jacked-up the lithounits above.

Geophysical signatures of fluids in a reactivated Precambrian collisional suture in central India

“…Recent magnetotelluric models (Azeez et al, 2010) along five profiles oriented approximately in NeS direction serve as cross sections of the CITZ and adds to the models proposed in earlier published results Patro et al, 2005;Naganjaneyulu et al, 2010;Naganjaneyulu, 2010). For example, several conductive zones are located near known faults.…”

“…However, in doing so, we also considered both the trend e increasing or decreasing e and also magnitude of the gravity anomalies in the vicinity. Near the Narmada River conductive zones were observed at the crustemantle boundary in previous magnetotelluric surveys ( Gokarn et al, 2001;Naganjaneyulu, 2010;Naganjaneyulu et al, 2010). This signature is modeled with a low-density feature where conductive zones are present near crustemantle boundary (C8) in the region beneath the Narmada River.…”

“…Several magnetotelluric studies carried out in the CITZ show high conductivity in the deep crust, possibly related to the presence of magmas and fluids at depth Patro et al, 2005;Naganjaneyulu et al, 2010;Naganjaneyulu, 2010), particularly around the major faults in the region. Here we show the results from two profiles which suggest that the deep crustal conductivity could possibly be linked to underplated magmas and fluids.…”

“…Various geophysical studies e magnetotellurics, seismic and gravity e undertaken in CITZ imaged these features. Magnetotelluric studies identified high-conductivity anomalies Patro et al, 2005;Naganjaneyulu et al, 2010;Naganjaneyulu, 2010) in the deep crust. Gravity studies identified high-density bodies in the southern part and low-density bodies in the northern part of the CITZ (Verma and Banerjee, 1992).…”

“…Two dimensional magnetotelluric models: (a) along ChinchpadaeGodhra profile (modified after Naganjaneyulu, 2010); and (b) MahaneKhajuria Kalan profile (modified after Naganjaneyulu et al, 2010). The models show a resistive upper crust (more than 2000 U$m) suggesting a dominant tonaliteetrondhjemiteegranodiorite (TTG) composition and correlation of high conductive zones (less than 30 U$m) in the deep crust with known faults in the region.…”