Influence of Deccan volcanism/synrift magmatism on the crust–mantle structure and its implications for the seismogenesis of earthquakes occurring in the Kachchh rift zone
Prantik Mandal, 2017. "Influence of Deccan volcanism/synrift magmatism on the crust–mantle structure and its implications for the seismogenesis of earthquakes occurring in the Kachchh rift zone", Tectonics of the Deccan Large Igneous Province, S. Mukherjee, A. A. Misra, G. Calvès, M. Nemčok
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The present study focuses on the delineation of the crust–mantle structure underlying the Kachchh rift zone (KRZ), by modelling P-wave receiver functions (P-RFs) and P-wave teleseismic tomography. Our RF study delineates marked crustal and lithospheric thinning below the central KRZ relative to the unrifted surrounding regions. This thinning model receives further support from crust-corrected normalized P-residuals, which suggest dominant negative residuals associated with the central KRZ. Teleseismic tomography using these P-residuals reveals low velocity to a depth of 170 km below the central KRZ, while there are positive residuals associated with the surrounding unrifted zones. Such a complex heterogeneous crust–mantle structure, which could be related to K/T boundary Deccan mantle plume activity and rift-related magmatism, might play a crucial role in seismogenesis of lower crustal earthquakes that have occurred in the KRZ since 2001. Inverted crust–mantle models obtained from P-RFs suggest a low shear velocity zone extending from 70–110 to 170–220 km depth beneath the central KRZ. This receives further support from the presence of low P-wave velocity down to 170 km modelled using teleseismic tomography. This low V p and V s zone in the upper mantle could be explained by the presence of trapped melts related to Deccan volcanism at 65 Ma or older rift-related magmatism.
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Understanding the Deccan Trap Large Igneous Province in western India is important for deciphering the India–Seychelles rifting mechanism. This book presents 13 studies that address the development of this province from diverse perspectives including field structural geology, geochemistry, analytical modelling, geomorphology and geophysics (e.g., palaeomagnetism, gravity and magnetic anomalies, and seismic imaging). Together, these papers indicate that the tectonics of Deccan is much more complicated than previously thought. Key findings include: the Deccan province can be divided into several blocks; the existence of a rift-induced palaeo-slope; constraints on the eruption period; rift–drift transition mechanisms determined for magma-rich systems; the tectonic role of the Deccan or Réunion plumes; sub-surface structures reported from boreholes; the delineation of the crust–mantle structure; the documentation of sub-surface tectonic boundaries; post-Deccan-Trap basin inversion; deformed dykes around Mumbai, and also from the eastern part of the Deccan Traps, documented in the field.