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Ar-40/Ar-39 geochronology and geochemistry of the Central Saurashtra mafic dyke swarm: insights into magmatic evolution, magma transport, and dyke-flow relationships in the northwestern Deccan Traps

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Title Ar-40/Ar-39 geochronology and geochemistry of the Central Saurashtra mafic dyke swarm: insights into magmatic evolution, magma transport, and dyke-flow relationships in the northwestern Deccan Traps
 
Creator CUCCINIELLO, C
DEMONTEROVA, EI
SHETH, H
PANDE, K
VIJAYAN, A
 
Subject EXTRACTION CHROMATOGRAPHY
PICRITE BASALTS
VOLCANIC-ROCKS
MANTLE SOURCES
WESTERN INDIA
PETROGENESIS
LAVAS
CLASSIFICATION
STRATIGRAPHY
PROVINCE
Volcanism
Deccan Traps
Flood basalt
Dyke swarms
India
Saurashtra
 
Description The Central Saurashtra mafic dyke swarm in the northwestern Deccan Traps contains a few picrites, several subalkalic basalts and basaltic andesites, and an andesite. We have obtained precise Ar-40/Ar-39 ages of 65.6 +/- 0.2 Ma, 66.6 +/- 0.3, and 62.4 +/- 0.3 Ma (2 sigma errors) for three of the dykes, indicating the emplacement of the swarm over several million years. Mineral chemical and whole-rock major and trace element and Sr-Nd isotopic data show that fractional crystallization and crystal accumulation were important processes. Except for two dykes (with epsilon(Nd)t values of -8.2 and -12.3), the magmas were only moderately contaminated by continental crust. The late-emplaced (62.4 Ma) basalt dyke has compositional characteristics (low La/Sm and Th/Nb, high eNdt of +4.3) suggesting little or no crustal contamination. Most dykes are low-Ti and a few high-Ti, and these contrasting Ti types cannot be produced by fractional crystallization processes but require distinct parental magmas. Some dykes are compositionally homogeneous over tens of kilometers, whereas others are heterogeneous, partly because they were formed by multiple magma injections. The combined field and geochemical data establish the Sardhar dyke as >= 62 km long and the longest in Saurashtra, but this and the other Central Saurasthra dykes cannot have fed any of the hitherto studied lava-flow sequences in Saurashtra, given their very distinct Sr-Nd isotopic compositions. As observed previously, high-Ti lavas and dykes only outcrop eastnortheast of a line joining Rajkot and Palitana, probably because of underlying enriched mantle at similar to 65 Ma.
 
Publisher SPRINGER
 
Date 2016-01-14T10:59:09Z
2016-01-14T10:59:09Z
2015
 
Type Article
 
Identifier BULLETIN OF VOLCANOLOGY, 77(5)
0258-8900
1432-0819
http://dx.doi.org/10.1007/s00445-015-0932-0
http://dspace.library.iitb.ac.in/jspui/handle/100/17419
 
Language en