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Magnetotelluric Investigations in Tuwa-Godhra Region, Gujarat (India)

Authors:
Kapil Mohan at Ministry of Earth Sciences
Kapil Mohan
Peush Chaudhary at Institute of Seismological Research
Peush Chaudhary
Pavankumar Gayatri at National Geophysical Research Institute
Pavankumar Gayatri
Girish Ch. Kothyari at University of Petroleum & Energy Studies
Girish Ch. Kothyari
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Magnetotelluric (MT) data have been acquired at 40 locations in Tuwa and its surrounding region (200 km east of Ahmedabad and 15 km north–northwest of Godhra) in the Mainland Gujarat with an average station spacing of 1.5 km. MT impedance tensors have been estimated in the period range of 0.001–100 s. The data have been modeled using non-linear conjugate gradient scheme taking both apparent resistivity and phase into account. From the 2D models of the MT data, the weathered granite with Quaternary sediments (with resistivity of < 700 Ω m) have been inferred up to a depth of 500 m followed by Godhra granite (having resistivity up to 105 Ω m) with a thickness 6.5 km. The Aravalli supergroup has been inferred below Godhra granite. The Lunavada group of rocks have been inferred in the eastern part of the study area (having resistivity value ranging from 103 to 104 Ω m) separated from the Godhra granite by a contact zone. The comparatively very low-resistivity rocks (< 400 Ω m) of Udaipur formation followed by Paleoproterozoic carbonate rocks with fluid have been inferred below 8–10 km depth. The percolation of water from the surface through the contact zone of Lunavada and Champaner groups has been suggested. The presence of hot water springs in 10 km SW from the center of the study area (at the contact zone of Godhra granite and basalt) might be due to the western trending lithostratigraphic slope, hydrostatic pressure generated due to heat produced from interaction of water with the carbonate rocks at deeper depth and high subsurface temperature due to high geothermal gradient. The segmented nature of Himmatnagar Fault (HnF) is identified in the central portion of the study area.
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Magnetotelluric Investigations in Tuwa-Godhra Region, Gujarat (India)
KAPIL MOHAN,
1
PEUSH CHAUDHARY,
1
G. PAVAN KUMAR,
1
GIRISH CH.KOTHYARI,
1
VIRENDER CHOUDHARY,
1
MEHUL NAGAR,
1
PRUTHUL PATEL,
1
DRASTI GANDHI,
1
DILIP KUSHWAHA,
1
and B. K. RASTOGI
1
Abstract—Magnetotelluric (MT) data have been acquired at 40
locations in Tuwa and its surrounding region (200 km east of
Ahmedabad and 15 km north–northwest of Godhra) in the Main-
land Gujarat with an average station spacing of 1.5 km. MT
impedance tensors have been estimated in the period range of
0.001–100 s. The data have been modeled using non-linear con-
jugate gradient scheme taking both apparent resistivity and phase
into account. From the 2D models of the MT data, the weathered
granite with Quaternary sediments (with resistivity of \700 Xm)
have been inferred up to a depth of 500 m followed by Godhra
granite (having resistivity up to 10
5
Xm) with a thickness 6.5 km.
The Aravalli supergroup has been inferred below Godhra granite.
The Lunavada group of rocks have been inferred in the eastern part
of the study area (having resistivity value ranging from 10
3
to
10
4
Xm) separated from the Godhra granite by a contact zone. The
comparatively very low-resistivity rocks (\400 Xm) of Udaipur
formation followed by Paleoproterozoic carbonate rocks with fluid
have been inferred below 8–10 km depth. The percolation of water
from the surface through the contact zone of Lunavada and
Champaner groups has been suggested. The presence of hot water
springs in 10 km SW from the center of the study area (at the
contact zone of Godhra granite and basalt) might be due to the
western trending lithostratigraphic slope, hydrostatic pressure
generated due to heat produced from interaction of water with the
carbonate rocks at deeper depth and high subsurface temperature
due to high geothermal gradient. The segmented nature of Him-
matnagar Fault (HnF) is identified in the central portion of the
study area.
Key words: Magnetotellurics, Himmatnagar Fault, Godhra
granite, geothermal spring.
1. Introduction
The Godhra region is located in the eastern part of
Gujarat state, in western India (Fig. 1). The Godhra
region is covered with the Precambrian Godhra
granite (of 955 ±20 Ma) occurred in parts of central
Gujarat which overlies the metasediments of Luna-
vada and Champaner groups (Gopalan et al. 1979).
The Godhra area was well investigated for geological
and geochemical aspects. However, the subsurface
structures of Godhra and surrounding region were not
mapped using geophysical surveys. Naganjaneyulu
(2010) has acquired one MT profile from Chinchpada
to Godhra with very high station spacing near Godhra
(only two stations up to 20 km were acquired in the
vicinity of Godhra) inferred the upper high resistive
crustal rocks in the north of Narmada river as granite
and the lower conductive crust as composed of mafic
granulites with only a small fluid content. Chopra
et al. (2014) through teleseismic receiver functions
from the data of 32 broadband stations from all over
the Gujarat region estimated the shear wave velocity
structure and suggested the basement depth of *4
km in at a macroscale. Most of the geophysical
studies (Verma and Banerjee 1992; Singh and
Meissner 1995; Kaila et al. 1985,1989; Tewari and
Kumar 2003; Gokarn et al. 2001; Rao et al. 2004;
Patro et al. 2005) were conducted *100 km south
of Godhra region, near and in the Son Narmada
region. These studies suggested the crustal thickness
from 32 to 45 km with several deep faults reaching
Moho in the Son Narmada region. The geophysical
surveys in Son Narmada region also indicated both
high-density mafic/ultramafic and low-density felsic
intrusions in the deep crust with
detectable thicknesses.
The Godhra area is characterized by the presence
of two prominent NNW–SSE and ENE–WSW Pre-
cambrian tectonic trends. These tectonic trends have
been represented by the presence of several faults and
lineaments (Chandra and Chowdhary 1969; Wani and
Electronic supplementary material The online version of this
article (https://doi.org/10.1007/s00024-018-1883-0) contains sup-
plementary material, which is available to authorized users.
1
Institute of Seismological Research, Gandhinagar, Gujarat
382007, India. E-mail: kapil_geo@yahoo.co.in
Pure Appl. Geophys. 175 (2018), 3569–3589
Ó2018 Springer International Publishing AG, part of Springer Nature
https://doi.org/10.1007/s00024-018-1883-0 Pure and Applied Geophysics
Content courtesy of Springer Nature, terms of use apply. Rights reserved.
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