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

Abstract

The Central India Tectonic Zone (CITZ) marks the trace of a major suture zone along which the south Indian and the north Indian continental blocks were assembled through subduction-accretioncollision tectonics in the Mesoproterozoic. The CITZ also witnessed the major, plume-related, late Cretaceous Deccan volcanic activity, covering substantial parts of the region with continental flood basalts and associated magmatic provinces. A number of major fault zones dissect the region, some of which are seismically active. Here we present results from gravity modeling along five regional profiles in the CITZ, and combine these results with magnetotelluric (MT) modeling results to explain the crustal architecture. The models show a resistive (more than 2000 U$m) and a normal density (2.70 g/cm 3 ) upper crust suggesting dominant tonaliteetrondhjemiteegranodiorite (TTG) composition. There is a marked correlation between both high-density (2.95 g/cm 3 ) and low-density (2.65 g/cm 3 ) regions with high conductive zones (<80 U$m) in the deep crust. We infer the presence of an interconnected grain boundary network of fluids or fluid-hosted structures, where the conductors are associated with gravity lows. Based on the conductive nature, we propose that the lower crustal rocks are fluid reservoirs, where the fluids occur as trapped phase within minerals, fluid-filled porosity, or as fluid-rich structural conduits. We envisage that substantial volume of fluids were transferred from mantle into the lower crust through the younger plume-related Deccan volcanism, as well as the reactivation, fracturing and expulsion of fluids transported to depth

New seismic images of the Central Indian Suture Zone and their tectonic implications

“…The lower crust beneath the CITZ may contain fluids generated by plume‐related mantle‐derived magmas associated with the Deccan volcanic activity during 66 Ma in the region. It could also be due to the reactivation, fracturing, and expulsion of fluid from metamorphic orogens extending into the middle and lower crust, which were generated during the Mesoproterozoic subduction and collision tectonics [ Naganjaneyulu and Santosh , ]. The presence of fluids may cause a reflective lower crust [ Frost and Bucher , ; Rudnick and Fountain , ].…”

The Magmatic Architecture of Continental Flood Basalts I: Observations From the Deccan Traps

“…This is further reflected in the vertical magmatic features associated with fault zones (Chowdari et al., 2017). These magma bodies may have acted as conduits for upward transportation of magmatic material to other intrusive bodies (Naganjaneyulu & Santosh, 2011; Patro & Sarma, 2016).…”

Interplay of Cretaceous transpressional deformation and continental arc magmatism in a long-lived crustal boundary, central Fiordland, New Zealand

“…Field-based and modeling studies investigating structural reactivation show that the process can range in scale from small individual fault surfaces to crustal-scale structures formed by terrane accretion, deformation, and magmatism (e.g., Bitencourt and Nardi, 2000;Scott et al, 2011;Miller and Becker, 2014;Klepeis et al, 2019aKlepeis et al, , 2019bNabavi et al, 2020). Inherited structures have both the ability to localize deformation and to act as conduits for the transport of melt and fluids (e.g., Naganjaneyulu and Santosh, 2011;Lu et al, 2012;Klepeis et al, 2019a). This latter process is of particular interest because transport of melt and fluids through the crust has the potential to influence geothermal gradients at mid-and lower-crustal levels (Depine et al, 2008;Schwartz et al, 2016).…”