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Spherulites and thundereggs from pitchstones of the Deccan Traps: geology, petrochemistry, and emplacement environments

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Title Spherulites and thundereggs from pitchstones of the Deccan Traps: geology, petrochemistry, and emplacement environments
 
Creator KSHIRSAGAR, PV
SHETH, HC
SEAMAN, SJ
SHAIKH, B
MOHITE, P
GURAV, T
CHANDRASEKHARAM, D
 
Subject Spherulites
Lithophysae
Thundereggs
Rhyolite
Pitchstone
Deccan Traps
Volcanism
INFRARED-SPECTROSCOPY
RHYOLITIC GLASSES
BASALTIC GLASSES
VOLCANIC GLASSES
MELT INCLUSIONS
CHEMICAL CLASSIFICATION
MOLAR ABSORPTIVITIES
WATER CONCENTRATION
ANDESITIC GLASSES
SILICATE-GLASSES
 
Description Spherulites and thundereggs are rounded, typically spherical, polycrystalline objects found in glassy silicic rocks. Spherulites are dominantly made up of radiating microscopic fibers of alkali feldspar and a silica mineral (commonly quartz). They form due to heterogeneous nucleation in highly supercooled rhyolitic melts or by devitrification of glass. Associated features are lithophysae ("stone bubbles"), which have an exterior (sometimes concentric shells) of fine quartz and feldspar, and internal cavities left by escaping gas; when filled by secondary silica, these are termed thundereggs. Here, we describe four distinct occurrences of spherulites and thundereggs, in pitchstones (mostly rhyolitic, some trachytic) of the Deccan Traps, India. The thundereggs at one locality were previously misidentified as rhyolitic lava bombs and products of pyroclastic extrusive activity. We have characterized the thundereggs petrographically and geochemically and have determined low contents of magmatic water (0.21-0.38 wt.%) in them using Fourier transform infrared spectroscopy. We consider that the spherulite-bearing outcrops at one of the localities are of lava flows, but the other three represent subvolcanic intrusions. Based on the structural disposition of the Deccan sheet intrusions studied here and considerations of regional geology, we suggest that they are cone sheets emplaced from a plutonic center now submerged beneath the Arabian Sea.
 
Publisher SPRINGER
 
Date 2014-10-16T05:59:08Z
2014-10-16T05:59:08Z
2012
 
Type Article
 
Identifier BULLETIN OF VOLCANOLOGY, 74(2)559-577
http://dx.doi.org/10.1007/s00445-011-0543-3
http://dspace.library.iitb.ac.in/jspui/handle/100/15398
 
Language en