Crustal thickening under the palaeo-meso-Proterozoic Delhi Fold Belt in northwestern India: evidence from deep reflection profiling

Abstract

S U M M A R YThe results of deep reflection profiling studies carried out across thy palaeo-mesoProterozoic Delhi Fold Belt (DFB) and the Archaean Bhilwara Gneissic Complex (BGC) in the northwest Indian platform are discussed in this paper. This region is a zone of Proterozoic collision. The collision appears to be responsible for listric faults in the upper crust, which represent the boundaries of the Delhi exposures. In these blocks the lower crust appears to lie NW of the respective surface exposures and the reflectivity pattern does not correspond to the exposed blocks. A fairly reflective lower crust northwest of the DFB exposures appears to be the downward continuation of the DFB upper crust. The poorly reflective lower crust under the exposed DFB may be the westward extension of the BGC upper crust at depth. Thus, the lower crust in this region can be divided into the fairly reflective Marwar Basin (MB)-DFB crust and a poorly reflective BGC crust. Vertically oriented igneous intrusions may have disturbed the lamellar lower-crustal structure of the BGC, resulting in a dome-shaped poorly reflective lower crust whose base, not traceable in the reflection data, may have a maximum depth of about 50 km, as indicated by the gravity modelling.The DFB appears to be a zone of thick (45-50 km) crust where the lower crust has doubled in width. This has resulted in three Moho reflection bands, two of which are dipping SE from 12.5 to 15.0 s two-way time (TWT) and from 14.5 to 16.0 s TWT.Another band of subhorizontal Moho reflections, at = 12.5 s TWT, may have developed during the crustal perturbations related to a post-Delhi tectonic orogeny. The signatures of the Proterozoic collision, in the form of strong SE-dipping reflections in the lower crust and Moho, have been preserved in the DFB, indicating that the crust here has not undergone any significant ductile deformation since at least after the Delhi rifting event.

Development and Testing of a 3D Velocity Model for Improved Event Location: A Case Study for the India-Pakistan Region

“…This movement, along with plate margin geometry, gives rise to the unusual lobate shape of the Sulaiman Lobe and Range at this boundary (e.g., Haq and Davis, 1997;Bernard et al, 2000). In the north, bidirectional subduction of Indian and Eurasian continental lithosphere occurs where the plates meet beneath the 55Њ 60Њ 65Њ 70Њ 75Њ 80Њ 25Њ 30Њ 35Њ 40Њ Holt and Wallace, 1990Mellors et al, 1995Roecker et al, 1993Hearn and Ni, 1994Priestley, 1997Mangino & Priestley, 1998Byrne et al, 1992Davis and Lillie, 1994Gabriel and Kuo, 1966Banks and Warburton, 1986Lillie et al, 1987;Jadoon et al, 1996Jadoon et al, , 1994; Khurshid, 1991Tewari et al, 1997Kulagina et al, 1974Jadoon & Khurshid, 1996Lillie et al, 1987Searle & Tirrul, 1991Molnar, 1988Lyon-Caen & Molnar, 1984Mishra, 1982Yegorkin & Matushkin, 1970Ryaboy, 1969Singh et al, 1999Priestley, 1997 Krishna andRamesh, 2000;Krishna et al, 1999 Pamirs and Karakorum (e.g., Molnar, 1988;Fan et al, 1994). Subduction of the Arabian plate beneath southwestern Pakistan produced the Makran accretionary wedge evidenced in the east-west trending Makran Range.…”

Evidence for the Neoproterozoic Phulad Suture Zone and Genesis of Malani magmatism in the NW India from deep seismic images: Implications for assembly and breakup of the Rodinia

“…1b). Structure and tectonics along this transect were discussed in earlier papers (Tewari et al, 1997;Vijaya Rao et al, 2000), especially the broad structural features of both these fold belts. They essentially discussed the reflectivity characteristics to distinguish various tectonic domains in the region as well as the crustal thickness in each of them.…”

Geoelectric structure of northern Cambay rift basin from magnetotelluric data

“…The extensive deep seismic sounding (DSS) studies carried out over the Cambay basin for hydrocarbon exploration (Kaila et al 1990;Tewari et al 1991Tewari et al , 1997Dixit et al 2010) revealed major structural trends in the basin and supported the explanation of magmatic underplating beneath the Kutch and Cambay rift basins. The Cambay basin is complex in nature, containing horst structures and E-W directional faults that divide the basin into four sub-basins.…”