3D upper crustal density structure of the Deccan Syneclise, Central India

Abstract

A constrained 3D density model of the upper crust along a part of the Deccan Syneclise is carried out based on the complete Bouguer anomaly data. Spectral analysis of the complete Bouguer gravity anomaly map of the study region suggests two major sources: short wavelength anomalies (<100 km) caused primarily due to the density inhomogeneities at shallow crustal level and long wavelength anomalies (>100 km) produced due to the sources deeper than the upper crust. A residual map of the short wavelength anomalies is prepared from the complete Bouguer anomaly using Butterworth high‐pass filter (100 km cut‐off wavelength). Utilizing the constraints from deep resistivity sounding, magnetotellurics and deep seismic sounding studies, 2.5D density models have been generated along 39 profiles of this region. The mismatch between the calculated response of the a priori 2.5D model with the residual (short wavelength) gravity anomalies is minimized by introducing high‐density intrusive bodies (≥2.81 g/cm3) in the basement. With these 2.5D density models, the initial geometry of our 3D density model, which includes alluvium, Deccan trap, Mesozoic sediment and high‐density intrusive bodies in the basement up to a depth of 7 km (upper crust), is generated. In the final 3D model, Deccan trap extends from 200 m to nearly 1700 m below the 90–150 m thick Quaternary sediment. Further down, the sub‐trappean Mesozoic sediment is present at a depth range of 600–3000 m followed by the basement. The derived 3D density model also indicates six intrusive bodies of density 2.83 g/cm3 in the basement at an average depth of about 4–7 km that best fits the residual gravity anomaly of the study area.

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

“…Analogously, Patro and Sarma (2016); Prasad et al. (2018) find that using higher‐resolution datasets, the magma bodies in Narmada‐Tapi Rift Zone are smaller and connected (if at all) thorough narrow zones instead of a larger, thicker, single magma body proposed originally by Bhattacharji et al. (2004).…”

“…However, Rao et al (2018) used gravity datasets in combination with constraints from seismic observations, as well as magnetic datasets, and found that the observation can be better explained with much smaller crustal magma bodies along with a Moho depth underplate. Analogously, Patro and Sarma (2016); Prasad et al (2018) find that using higher-resolution datasets, the magma bodies in Narmada-Tapi Rift Zone are smaller and connected (if at all) thorough narrow zones instead of a larger, thicker, single magma body proposed originally by Bhattacharji et al (2004). 1).…”

“…If the large magma reservoir model were to be correct, especially with multiple large magma reservoirs, we would expect to see some geophysical evidence for this. Instead, the individual magma bodies, when detected, are typically small (5–15 km across and a few km thick, e.g., Patro & Sarma, 2016; Prasad et al., 2018), are prismatic in shape, and are distributed in complex patterns depending on the pre‐existing crustal structure. Since smaller magma bodies of this size are close to the resolution limit for many studies, our estimated Intrusive/Extrusive ratio may be biased to smaller values.…”

Systematic and Temporal Geochemical Changes in the Upper Deccan Lavas: Implications for the Magma Plumbing System of Flood Basalt Provinces

“…However, these long lifespans are only valid for upper‐crustal and felsic magmatic systems (e.g., Cooper, 2019; Mutch et al., 2019) in contrast to the tholeiitic basaltic composition of the Poladpur to Mahabaleshwar lavas. In addition, there is no geophysical evidence for large continuous upper crustal intrusive bodies below India, which could represent former magma reservoirs with corresponding dimensions (Mittal et al., 2021; Prasad et al., 2018). The detected intrusions are prismatic in shape and have a diameter between 5 and 15 km as well as a thickness of few km (e.g., Prasad et al., 2018), which is contrary to a single large upper crustal magma reservoir with volumes between 10 5 and 10 6 km 3 (Mittal & Richards, 2021; Mittal et al., 2021).…”

Cryptic Magma Chamber in the Deccan Traps imaged using receiver function

“…Numerous geophysical experiments have been performed over the DVP to investigate its crustal structure. None of them, however, show evidence of an upper-crustal magma chamber beneath it (e.g., Bhattacharji et al, 2004;Chopra et al, 2014;Kaila et al, 1981;Krishna et al, 1991;Mohan & Kumar, 2004;Patro & Sarma, 2016;Patro et al, 2018;Prasad et al, 2018;Tiwari et al, 2001). Some of these studies do indicate the presence of magma underplating, albeit with poorly quantified thickness, location, velocity, and density.…”