The seismic structure of the Saurashtra crust in northwest India and its relationship with the Réunion Plume

Abstract

SUMMARY The Saurashtra Peninsula in northwest India, lying at the northern boundary of the Deccan Volcanic Province, is almost entirely covered by these volcanics. Analogue seismic refraction/wide‐angle reflection data along a 160 km long profile, from Navibandar to Amreli, were collected during 1977 to determine the crustal configuration. Reprocessing of these data, after digitization, has yielded a crustal model that is significantly different from the earlier model of Kaila et al. The model shows the upper crust down to a depth of 16 km in the west and 13 km in the east and underplating (velocity of 7.20 km s−1) of the lower crust. The Moho is at a depth of ∼36 km in the western part and at 32–33 km in the eastern part; the change of depth is quite sharp almost in the middle of the profile. Similar depth changes are seen in other crustal horizons indicating a deep fault that is in line with the extension of the Proterozoic Aravalli trend in to the Saurashtra Peninsula. The crustal structure in the eastern part is similar to that in the Cambay Basin and indicates that the crust to the east of the proposed fault is uplifted. The uplifted region extends as far as another arm of the Aravalli trend that turns eastwards. Crustal underplating in large parts of western India is confined to the corridors affected by the passage of India over the Réunion Plume in the Late Cretaceous. The shallower Moho appears to be confined to the areas close to the axis (trace of the plume) on Earth's surface of the plume.

Two-dimensional velocity model of the crust beneath the South Cambay Basin, India from refraction and wide-angle reflection data

“…South of Narmada River, the sediments decrease in thickness to about 0.25–0.30 km near SP 230. The underlying Deccan Traps volcanics vary in velocity between 4.75 and 5.2 km s −1 and are consistent with velocities Deccan Trap volcanics found elsewhere (Kaila et al 1990; Suryaprakash & Tewari 2005). Along our seismic profile, the Deccan Traps volcanics vary in thickness between 0.5 and 4.1 km, with the minimum thickness near SP 230 and the maximum thickness near SP 140.…”

“…Thickening of the crust to the south also indicates that only the shallower parts of the Cambay Basin extend on land south of the Cambay syncline. The high‐velocity lower crustal layer (7.2–7.5 km s −1 ) is present throughout the Cambay Basin, the Saurashtra Peninsula to its west and large parts of the Deccan Trap province to the east across the Narmada Zone (Kaila et al 1990; Tewari et al 2001; Sridhar & Tewari 2001; Suryaprakash & Tewari 2005). Singh & Messner (1995) have shown a high‐density layer at the base of crust in the same region.…”

Thermal regime of the northwest Indian rifted margin – Comparison with predictions

“…To the south the oldest known magnetic anomaly related to oceanic crust is An 28 (w63 Ma) and is located west of the Laxmi Ridge (Royer et al, 2002). The crustal thickness of the Indian Shield ranges from 32 to 45 km just south of the study area to a total lithospheric thickness of between 85 and 120 km estimated from deep seismic sounding and/or gravity modeling in the center of the shield (Todal and Eldholm, 1998;Walter et al, 2000;Surya Prakasa Rao and Tewari, 2005;Kumar et al, 2007). Along the distal portion of Murray Ridge (presumed to be a continental block, Edwards et al, 2008), the Moho discontinuity is estimated to be as deep as 18 km AE 1 from gravity modeling , and wide-angle seismic data allows a depth to Moho to be modeled to about 18e23 km on the SW portion of the ridge (Edwards et al, 2008).…”

Geophysical Identification and Characterization of Mafic-Ultramafic Intrusions in Plume Centre Regions

“…The Réunion plume is generally linked with the breakup of Madagascar from India during the Middle to Late Cretaceous, and the breakup of the Seychelles plateau from India during the late Cretaceous which was shortly followed by the eruption of the Deccan volcanic rocks (Figure 48b, c), (e.g., McKenzie and Sclater, 1971;Veeraswamy, 2003, 2000;Surya Prakasa Rao and Tewari, 2005). Following the arrival of the Réunion plume at 67 Ma, plate reconstruction models from paleomagnetic data indicate that the Indian subcontinent moved northward and rotated a total of 20⁰ counterclockwise (Figure 50), at rates of 20 cm/year and 1.0⁰/Myr from the Lake Cretaceous ( 67 Ma) to the Early Eocene ( 50 Ma), at which point it drastically slowed down to 5…”

“…Studies also indicate a thinned crust along the rift (32-33 km), (Surya Prakasa Rao and Tewari, 2005).…”