Deccan Basalts in and around Koyna — Warna Region, Maharashtra: Some Reflections

Abstract

In this paper, an attempt is made to review the current status of chemo-and magnetostratigraphy of the Deccan Traps, particularly in the Western Province, and to interpret geomorphological and borehole data in relation to the earlier known structural data in the whole region, to that of the Koyna-Warna region, covering Deccan Traps and part the Archean basement. Koyna and Warna region comprises of chemically defined younger Formations of Wai Subgroup and Lonawala Subgroup displaying over-stepping arrangement from older Formations further north in the Nasik area and younger Formations down south. This is further corroborated by a single polarity change from reversed to normal, all the way to Belgaum. This is considered as a time marker around 65Ma (Chron C29r/C29n) matching with the K-T boundary. The Deccan Trap contact with the Archean basement in the 7 boreholes shows a plateau around 200m in the western section but a variation ranging up to 500m in the eastern side of the Warna region. These variations may be due to faulting or upwrap in this region. It is to be noted that the Koyna –Warna volcanic pile is similar to the thick sequences of the Mahabaleswar Ghat section further north in terms of their chemistry and magnetostratigraphy. A combination of surface and sub-surface data of the Koyna-Warna region may not show the presence of older volcanic formations such as Kalsubai Subgroup nor ages older than 65Ma. A few points are raised in this paper which may necessitate a detailed field, chemical, magnetic and geochronological study of both surface and drill cores in tandem with the available huge data base of the Deccan Traps, which may reveal surprises and perhaps provide clues to the origin of seismicity in this region and provide possible clues to a better understanding of the study area.

Thermal and Physical Properties of Deccan Basalt and Neoarchean Basement Cores From a Deep Scientific Borehole in the Koyna−Warna Seismogenic Region, Deccan Volcanic Province, Western India: Implications on Thermal Modeling and Seismogenesis

“…Reportedly, these formations can be differentiated on the basis of their trace elements (Sr, Rb, Ba, TiO 2 ) and isotopic ratios ( 87 Sr/ 86 Sr) (Cox & Hawkesworth, 1985; Peng et al., 1994). Based on surface geology, chemo‐ and magneto‐stratigraphy, and the boreholes studies, out of the total 12 Deccan volcanic formations, five formations (Desur, Mahabaleshwar, Poladpur, Bushe, and Khandala), belonging to two sub‐groups, Lonavala and Wai, are present in the Koyna−Warna region (Subbarao & Courtillot, 2017). According to the present study, differences in radioelements and heat production within the two basaltic layers and their five sub‐layers can be explained by the variations in the composition and the radioactive elements (Th, U).…”

“…Reportedly, these formations can be differentiated on the basis of their trace elements (Sr, Rb, Ba, TiO 2 ) and isotopic ratios ( 87 Sr/ 86 Sr) (Cox & Hawkesworth, 1985;Peng et al, 1994). Based on surface geology, chemo-and magneto-stratigraphy, and the boreholes studies, out of the total 12 Deccan volcanic formations, five formations (Desur, Mahabaleshwar, Poladpur, Bushe, and Khandala), belonging to two sub-groups, Lonavala and Wai, are present in the Koyna−Warna region (Subbarao & Courtillot, 2017).…”

“…Deep drilling confirms that the flood basalt cover (usually referred to as the Deccan traps), is underlain by the granitoid rocks (TTG) below this seismic region (Bhaskar Rao et al., 2017; Misra et al., 2017). Uneven basement topography, as revealed by the borehole studies, may either be due to its original uneven nature or due to the fault systems that ought to have developed later (Subbarao & Courtillot, 2017).…”

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

“…Sarkar and Saein (2017) highlight the need for doing new seismic studies to constrain faults in the Koyna region better. Subbarao and Courtillot (2017) question the tectonic significance of the triangular fracture set in the Warna region. Kumar and Dixit (2017), based on local earthquake tomography document a ~ 5 km wide and 3-7 km deep seismic cluster south of the Warna region.…”

New 40 Ar/ 39 Ar dating of the Antrim Plateau Volcanics, Australia: clarifying an age for the eruptive phase of the Kalkarindji continental flood basalt province

“…6). This is still a very small dataset when compared with more wellknown CFB provinces such as the Deccan (Pande et al, 2017;Subbarao and Courtillot, 2017), which shows the work still to be done to improve upon the accuracy of the age of Kalkarindji to better understand the nuances and complexities of the geodynamics of this CFBP. The dates of this study do give us a slight peek into the possible evolution and impact of this eruption.…”