The Subsurface Megascopic Characteristics of Basalt and Basement Rocks from Koyna-Warna Area of Maharashtra, India

Abstract

Vertical deep boreholes of depth up to 1522.50m have been drilled in Koyna-Warna area of Maharashtra State within the Deccan Volcanic Province to study the most outstanding example of Reservoir Triggered Seismicity (RTS). The drilling of 9 bore-holes in the area has provided a window to earth scientists to peep into geological details available below Deccan Trap. The 932.50m thick pile of Deccan basalt, consisting of 30 flows at Rasati, near Koyna, which has been physically seen through cores, present a marvellous geological repository for observations. The megascopic characteristics of various flows and variation in composition have been presented in this paper. The microscopic and geochemical characteristics have been kept out of this communication, as the relevant studies are not completed to draw any conclusion. This study records the presence of granite wash (≈1m thick) over basement and below basalt representing Late Archaean to Cretaceous period hiatus. The basement rocks, presumably of Late Archaean age have been described mega-scopically. A fair picture of sub-surface pre-Deccan topography is shown with the help of borehole data, which confirm the nearly flat topography of pre-Deccan surface especially in this part of the area occupied by 30 flows of Deccan basalt. Correlation of 30 flows with the established stratigraphy has also been attempted for subsurface existence of Ambenali (Upper) and Poladpur Formations of Wai Subgroup in Koyna-Warna area.

Thickness Characteristics of Pāhoehoe Lavas in the Deccan Province, Western Ghats, India, and in Continental Flood Basalt Provinces Elsewhere

“…For the Deccan and Karoo, the logs are exemplified by those in Figure 3A (Supplementary Figure S1, see also Figure 4 in Jay et al, 2009 andJay et al, 2018). Data also exist from drill-hole cores in the Koyna region of the Western Ghats, part of the Deccan where scientific drill-holes were made (Mishra et al, 2017;Sinha et al, 2017), as well as the Killari Scientific Drill Hole (Gupta et al, 2003;Kumar et al, 2010). In order to extend the spatial coverage to other Deccan subprovinces besides the Western Ghats, we also include previously published sections from the north-western Deccan (Peng and Mahoney, 1995), Narmada-Tapi Rift Zone region (Mahoney et al, 2000;Tejankar, 2002;Doke, 2014), Malwa Lobe (Kasiviswanandham, 2003), and Mandla Lobe (Sengupta and Ray, 2006;Pathak et al, 2017).…”

“…An independent Deccan data set comes from lobe thickness measurements on drill core obtained from the Koyna area in the Western Ghats (Sinha et al, 2017;Mishra et al, 2017), near to our Khumbarli Ghat traverse. Although the cored lava formations are not named in these papers, the local geology suggests they are Wai Sub-group (Duraiswami et al, 2017).…”

“…Thus, analysis of lava flow morphology can help examine the spatial and temporal variations in the emplacement rate of a CFB province. These spatiotemporal eruptive rate variations are critical for understanding the magmatic plumbing systems of CFBs (Sheth and Cañón-Tapia, 2015;Ernst et al, 2019) as well as the environmental impacts (e.g., Schmidt et al, 2016;Clapham and Renne 2019;Hull et al, 2020;Landwehrs et al, 2020).…”

Cooling history and emplacement dynamics within rubbly lava flows, southern Deccan Traps: insights from textural variations and crystal size distributions

“…The thickness data for the surface lava flows were taken from Duraiswami et al (2017). For the subsurface drill cores, thickness data from the KBH-1 borehole was taken from Sinha et al (2017) and for the KBH-7 borehole, from Mishra et al (2017).…”

Tectonics of the Deccan Trap: Focus on Indian geoscientists’ contribution in last four years

“…High-velocity seismic anomalies reaching up to the Moho in the Saurashtra region probably indicates the intrusives related to the Deccan Traps (Prajapati et al 2016). Mishra et al (2017) and Sinha et al (2017) detail the structural geology (fractures, faults, conjugate joints, gouge, and breccia) to some extent from the basement rocks located at the Koyna deep drilling site.…”