Synplutonic mafic injections into crystallizing granite pluton from gurgunta area, northern part of eastern dharwar craton: Implications for magma chamber processes


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Prabhakar, B.C. and Jayananda, M. and Shareef, M. and Kano, T. (2009) Synplutonic mafic injections into crystallizing granite pluton from gurgunta area, northern part of eastern dharwar craton: Implications for magma chamber processes. Journal of the Geological Society of India, 74 (2). pp. 171-188. ISSN 0974-6889

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In this paper we document widespread coeval felsic-mafic magma interaction and progressive hybridization near Gurgunta in the northern part of Eastern Dharwar Craton (EDC) where mafic magma pulses have injected into a 2.5 Ga granite pluton. The pluton contains voluminous pink porphyritic facies with minor equigranular grey facies. The mafic body shows compositional variation from diorite to meladiorite with hornblende as the chief mafic mineral with lesser clinopyroxene and biotite. The observed variation on binary diagrams suggests that granite was evolved by fractional crystallization. Chemical characteristics such as higher A12O3 and moderate to high CaO, Mg#, Ni, Cr, Co and V are interpreted by slab-melting. Mafic bodies show lower SiO2, Na2O and K20; but higher CaO, Mg#, FeO, Cr, Ni and V; higher LREE with moderate to higher HREE which suggest their derivation from mantle. A major active shear zone has played an important role at the time of synplutonic mafic injection and hybridization process. Field evidences suggest that the synplutonic mafic body has injected into the crystallizing felsic magma chamber in successive stages. The first stage injection has resulted in extensive mixing and hybridization due to the liquidus state of resident felsic magma to which hot mafic magma was injected. However, progressive mixing produced heterogeneity as the xenocrysts started mechanically dispersed into hybrid magma. The second stage injection, after a time gap, encountered colder and viscous hybrid magma in the magma chamber, which inhibited free injection. Asa consequence, the mafic magma spread into magma chamber as flows, producing massive mafic bodies. However, with the continued mafic pulses and the heat gradient, the viscosity contrasts of mafic magma and felsic magma were again lowered resulting in second stage mixing. This episode was followed by mingling when the granite was almost crystallized, but still viscous enough to accommodate lamellar and ribbon like mafic penetrations to produce mingling. The successive mixing and mingling processes account for the observed heterogeneity in the granite pluton. © geol. soc. india.

Item Type: Article
Additional Information: cited By 7
Uncontrolled Keywords: clinopyroxene; craton; crystallization; diorite; felsic rock; granite; mafic rock; magma; plutonic rock, Asia; Dharwar Craton; Eurasia; India; Karnataka; South Asia
Subjects: Faculty of Science > Earth Sciences > Geology
Divisions: Jnana Bharathi / Central College Campus > Department of Geology
Depositing User: Mr. Kirana Kumar D
Date Deposited: 15 Mar 2016 05:48
Last Modified: 15 Mar 2016 05:48

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