Arun Kumar Ojha
@ngri.res.in/researcher
Scientist
CSIR-National Geophysical Research Institute
RESEARCH INTERESTS
Structural Geology, Tectonics, Fluid inclusions
Scopus Publications
Scholar Citations
Scholar h-index
Scholar i10-index
Scopus Publications
Swastik Suman Behera, Sonal Tiwari, Ambrish Kumar Pandey, Amar Agarwal, and Arun Kumar Ojha
Springer Science and Business Media LLC
AbstractThe most widely used method of determining impact direction employs asymmetric ejecta distribution around the crater. However, the active terrestrial landscape seldom preserves the pristine ejecta blanket, making it challenging for this analysis to be carried out. The deeply eroded Dhala impact structure, formed during the Proterozoic, is devoid of an ejecta blanket. We, therefore, utilize the variation in the full width at half maxima (FWHM) of the quartz (100) peak in X-ray diffraction (XRD) spectra and the P10 microfracture intensity in the monomict breccia to estimate the probable downrange direction of the Dhala impact structure. The monomict breccia rocks of the Dhala impact structure have experienced low shock pressures (< 10 GPa) and are highly fractured, making them the ideal target lithology for our study. Previous studies have used XRD extensively for strain analysis in synthetic materials and rocks. Microfracture intensity acts as an indicator for the degree of fracturing or brittle damage in the rocks, with the maximum shock-induced damage being concentrated in the downrange direction. The results from the XRD are consistent with the microfracture intensity analyses and indicate that the probable direction of impact was from southwest to northeast, with northeast being the downrange direction. Furthermore, we suggest that the degree of fracturing and X-ray diffractometry can be used to identify the downrange direction of an impact crater. Graphical Abstract
Arun Kumar Ojha, Deepak Srivastava, Marnie Forster, and Gordon Lister
Elsevier BV
Arun K. Ojha, D.P. Monika Saini, Amar Agarwal, and Ambrish K. Pandey
Elsevier BV
Imlirenla Jamir, Vipin Kumar, Arun Kumar Ojha, Vikram Gupta, Tapas Ranjan Martha, and D. V. Griffiths
Springer Science and Business Media LLC
Gaurav Joshi, Amar Agarwal, Thomas Kenkmann, and Arun Kumar Ojha
Elsevier BV
Gaurav Joshi, Pradyut Phukon, Amar Agarwal, and Arun Kumar Ojha
American Geophysical Union (AGU)
We investigate the magnetic fabrics and magnetic mineralogy of the impact melt rock at the Dhala impact structure to understand its emplacement mechanism. Pseudo‐single domains of Ti‐poor magnetite and Ti‐hematite are the prime magnetic carriers in the impact melt rock. The magnetic foliations show a range of dip amounts. The overall trend of the magnetic foliation of the impact melt rock draws a resemblance with the flood basalts or lava flows. A well‐developed magnetic lineation (K1) indicates the strong alignment of Ti‐poor magnetite grains. Therefore, the magnetic carriers may have crystallized and aligned themselves along the flow direction before the emplacement. It may be possible that after the crystallization of the magnetic carriers, the impact melt moved in a semi‐molten state similar to lava flows with temperatures below c. 1,500°C, which is the melting point of Ti‐magnetite and was emplaced as crater‐fill deposits. Among the three principal magnetic susceptibility axes, K1 aligns best with the mesoscopic flow indicators. K1 of individual specimens' trends between NW and SW, while the mean K1 at all the sites trends westward. Thus, at the studied sites, the impact melt flow was dominantly eastward. In the sites located to the NW and W, the eastward flow could be due to gravity‐driven crater inward flow toward the center. At site IM2, which is located to E, the eastward flow of the impact melt is possibly due to crater outward excavation flow.
Ajit Kumar Sahoo, Rajagopal Krishnamurthi, Gautam Kumar Dinkar, N. V. Chalapathi Rao, Arun Kumar Ojha, Sneha Raghuvanshi, and Sudipa Bhunia
Springer Science and Business Media LLC
Rudra Mohan Pradhan, Anand Singh, Arun Kumar Ojha, and Tapas Kumar Biswal
Springer Science and Business Media LLC
AbstractCrystalline basement rock aquifers underlie more than 20% of the earth’s surface. However, owing to an inadequate understanding of geological structures, it is challenging to locate the groundwater resources in crystalline hard rock terranes. In these terranes, faults, fractures, and shear zones play an important role in bedrock weathering and ultimately groundwater storage. This study integrates important geological structures with 2D high-resolution subsurface resistivity images in understanding the factors that influenced bedrock weathering and groundwater. The results reveal the variability of weathered zone depth in different structural zones (Zone-I to Zone-IV). This is due to the presence of foliations, fractures, and faults. A thicker weathered zone develops when a fracture/fault overprints a pre-existing planar pervasive structure like foliations (Zone-II) as compared to zones only with faults/fractures (Zone-III). Further, the transmissivity of boreholes also shows relatively higher in Zone-II than Zone-III, which implies a good pact between different structural features and possible groundwater storage. The study also demonstrates the role of paleostress and different tectonic structures influencing the depth of the “Critical Zone”. While the geology may vary for different structural terranes, the approach presented in this paper can be readily adopted in mapping bedrock weathering and groundwater resources in crystalline basement terranes globally.
Shashi Ranjan Rai, Himanshu K. Sachan, Christopher J. Spencer, Aditya Kharya, Saurabh Singhal, Arun Kumar Ojha, Pallavi Chattopadhaya, and Pitambar Pati
Cambridge University Press (CUP)
AbstractU–Pb geochronology, Hf isotopes and trace-element chemistry of zircon grains from migmatite of the upper Sutlej valley (Leo Pargil), Northwest Himalaya, reveal a protracted geological evolution and constrain anatexis and tectonothermal processes in response to Himalayan orogenesis. U–Pb geochronology and ϵHf record separate clusters of ages on the concordia plots in the migmatite (1050–950 Ma, 850–790 Ma and 650–500 Ma). The 1050–950 Ma zircon population supports a provenance from magmatic units related to the assembly of Rodinia. A minor amount of Palaeoproterozoic grains were likely derived from the Indian craton. The potential source rock of the 930–800 Ma detrital zircons may be granitoid present in Greater Himalayan rocks themselves and the Aravalli Range, which has 870–800 Ma granitic rocks. The arc-type basement within the Himalayan–Tibet orogen recorded (900–600 Ma) igneous activity, which may depict a northeasterly extension of juvenile terranes in the Arabian–Nubian Shield. The granitoid of 800 Ma may be a potential source for 790 Ma detrital zircons owing to scatter in 206/238 dates. The 650–500 Ma zircon population suggests their derivation from the East African Orogen and Ross–Delamerian Orogen of Gondwana. The Cambrian–Ordovician magmatism during the Bhimphedian Orogeny and observed late Neoproterozoic to Ordovician detrital zircons have been derived to some extent from Greater Himalayan magmatic sources. We found no detrital zircon grains that cannot be explained as coming from local sources. One sample yielded a discordia lower intercept age of 15.6 ± 2.2 Ma, the age of melt crystallization.
Arun K. Ojha, D. Srivastava and Rajesh Sharma
Arun K. Ojha, Rajesh Sharma, D. Srivastava and G. Lister
Arun Kumar Ojha and Deepak C Srivastava
Springer Science and Business Media LLC
Rajan Kumar, Deepak C. Srivastava, and Arun K. Ojha
Elsevier BV