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Geological and Ar-40/Ar-39 age constraints on late-stage Deccan rhyolitic volcanism, inter-volcanic sedimentation, and the Panvel flexure from the Dongri area, Mumbai

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Title Geological and Ar-40/Ar-39 age constraints on late-stage Deccan rhyolitic volcanism, inter-volcanic sedimentation, and the Panvel flexure from the Dongri area, Mumbai
 
Creator SHETH, HC
PANDE, K
 
Subject Flood volcanism
Deccan Traps
Panvel flexure
Mumbai
Rhyolite
K-T BOUNDARY
CONTINENTAL-MARGIN
INTERTRAPPEAN BEDS
SPECTRUM TECHNIQUE
BOMBAY TRACHYTES
EXCESS ARGON
INDIA
TRAPS
ROCKS
BASALTS
 
Description Post-K-Pg Boundary Deccan magmatism is well known from the Mumbai area in the Panvel flexure zone. Represented by the Salsette Subgroup, it shows characters atypical of much of the Deccan Traps, including rhyolite lavas and tuffs, mafic tuffs and breccias, spilitic pillow basalts, and "intertrappean" sedimentary or volcanosedimentary deposits, with mafic intrusions as well as trachyte intrusions containing basaltic enclaves. The intertrappean deposits have been interpreted as formed in shallow marine or lagoonal environments in small fault-bounded basins due to syn-volcanic subsidence. We report a previously unknown sedimentary deposit underlying the Dongri rhyolite flow from the upper part of the Salsette Subgroup, with a westerly tectonic dip due to the Panvel flexure. We have obtained concordant Ar-40/Ar-39 ages of 62.6 +/- 0.6 Ma (2 sigma) and 62.9 +/- 0.2 Ma (2 sigma) for samples taken from two separate outcrops of this rhyolite. The results are significant in showing that (i) Danian inter-volcanic sedimentary deposits formed throughout Mumbai, (ii) the rock units are consistent with the stratigraphy postulated earlier for Mumbai, (iii) shale fragments known in some Dongri tuffs were likely derived from the sedimentary deposit under the Dongri rhyolite, (iv) the total duration of extrusive and intrusive Deccan magmatism was at least 8-9 million years, and (v) Panvel flexure formed, or continued to form, after 63 Ma, possibly even 62 Ma, and could not have formed by 65-64 Ma as concluded in a recent study. (C) 2013 Elsevier Ltd. All rights reserved.
 
Publisher PERGAMON-ELSEVIER SCIENCE LTD
 
Date 2014-12-28T17:30:52Z
2014-12-28T17:30:52Z
2014
 
Type Article
 
Identifier JOURNAL OF ASIAN EARTH SCIENCES, 84167-175
1367-9120
1878-5786
http://dx.doi.org/10.1016/j.jseaes.2013.08.003
http://dspace.library.iitb.ac.in/jspui/handle/100/16994
 
Language English