Southern region of Bundelkhand Craton 

The Bundelkhand craton (BnC), surrounded on its eastern, western, and southern sides by the Vindhyan Supergroup, is bounded by the Son-Narmada fault in the south, while the north of the Bundelkhand Tectonic Zone (BTZ) is covered by the Indo-Gangetic alluvium plain. Outcrops of Deccan traps line parts of the southwestern margin of the BnC, while the southeastern edge shows exposures of the Bijawar group of rocks, largely consisting of volcanogenic metasediments with major basic/ultrabasic intrusives supposedly formed in an extensional environment over rifted platforms of the Bundelkhand craton. These rocks, with the Bundelkhand craton form the basement of the Vindhyan sediments of Paleo-Neoproterozoic age. The Vindhyan supergroup comprises of the Semri (Lower Vindhyan), Kaimur, Rewa and Bhander (together form the Upper Vindhyan) series, showing sequences of sandstones, limestones, and shales, etc. The BnC lithology consists Archean TTG gneisses, volcano-sedimentary rocks, meta-supracrustals (amphibolites, komatiitic basalts) the Madawara Ultramafic complex, Bundelkhand granitoids, along with quartz veins and dyke swarms of mafic composition.

The study area lies to the south of the BnC, located between 78°40’0’’ E-79°00’0’’ E and 24°10’0’’ N-24°30’0’’ N. Most of the study area is covered by the Archean gneissic complex. The E-W trending lenses of ultrabasic-mafic rocks of the Madawara Igneous Complex (MIC) occur near the southern margin of the BnC, enclosed between the Madwara- Karitoran and Sonrai- Girar shear zones in the north and south, respectively. This complex comprises of high Mg ultrabasic/basic rocks and undeformed ultramafic as well as mafic rocks, with their ages ranging from 3.2-2.57 Ga. The study area also comprises of NW-SE trending mafic dyke swarms (2.1-2.0 Ga) and NE-SW (2.4-2.0 Ga) trending quartz reefs. The Sonrai basin consists of NE-SW trending series of shear zones, occupied by quartz reefs while the NW-SE trending swarms of mafic dykes of Paleoproterozoic period. 

• Gravity survey data

The land gravity data were acquired at 734 stations covering an area of about 1120 km2 in and around the area of Madawara and Sonrai Basin with stations spacing varying between 200 m to 500 m depending on accessibility, using Scintrex CG-6 gravimeter (with resolution 0.001 mGal). The associated gravity corrections like Free-air, Bouguer, were applied and the Bouguer anomaly map was generated. Regional-residual separation was applied to the complete Bouguer anomaly map by to decipher the anomalies generated by the deeper (regional anomaly, upward continued up to 10 km) and shallow (residual anomaly) sources. 

• Regional global gravity grid data

We have also utilized regional scale Free-air anomaly data for the study (between 23.50N- 250N and 780E-800E), provided by an improved high-resolution gravity grid from the website of the Scripps Institution of Oceanography, https://topex.ucsd.edu/cgi-bin/get_data.cgi. Topographic corrections using the topographic data, also acquired from the same site, are applied on the acquired free-air anomaly to get the Bouguer anomaly data. This anomaly map was again separated into the regional and residual anomaly maps. The regional anomaly, generated by upward continuing up to 30 km is being used for developing 2D models at present. 

The Bouguer gravity anomaly from the global gravity grid data is inverted following the algorithm developed by Gomez-Oritz & Agarwal (2005) and the modified version by Gao & Sun (2019), based on Parker-Oldenburg iterative inverse method, to obtain the Moho topography below the study area. An inverted Moho topography map is generated giving insights on the crustal variation below the study area.

The results of this study is being used in a manuscript which is in the submission stage.

The same 734 gravity observation points were used for magnetic measurements using GSM 19T Proton Magnetometer with resolution 0.01 nT. Diurnal and International Geomagnetic Reference Field (IGRF-2017) corrections were applied on the acquired data to get the total field magnetic anomaly values. The total magnetic anomaly is then plotted as a contour map using minimum curvature gridding technique in Geosoft software. Reduced to Equator (RTE) transformation is applied to the total magnetic anomaly to correct the asymmetric nature and lateral shift of the observed magnetic anomalies, using the MAGMAP 1-step filtering feature in the Geosoft, where parameters like the average inclination and declination (37.50 and 0.450, respectively), calculated after the IGRF correction is applied to the magnetic observations. The RTE anomaly map is then used for the regional- residual separation by upward continuation up to 15km.

The results of this study is being used in a manuscript which is in the submission stage.