RT Journal Article
SR Electronic
T1 Deformation-driven emplacement-differentiation in the Closepet pluton, Dharwar Craton, South India: an alternate view
JF Geological Society, London, Special Publications
JO Geological Society, London, Special Publications
FD Geological Society of London
SP SP489-2019-315
DO 10.1144/SP489-2019-315
VO 489
A1 Bhattacharya, Abhijit
YR 2019
UL http://sp.lyellcollection.org/content/early/2019/02/21/SP489-2019-315.abstract
AB In the Late Archean north-trending Closepet pluton, trains of euhedral K-feldspar phenocrysts and matrix-supported idiomorphic K-feldspar crystals in the central part of the pluton define oblique-to-pluton margin steep-dipping east/ENE-trending magmatic fabrics. The magmatic fabric is defined by phenocryst-rich and phenocryst-poor layers, with the euhedral porphyries continuous across the layers. The fabrics are near-orthogonal to the gently-dipping gneissic layers in the host gneisses. The fabrics curve adjacent to locally-developed north/NNE-trending melt-hosted dislocations parallel to the axial planes of horizontal/gently-plunging north-trending upright folds in the host gneisses. In the pluton interior, both fabrics in the intrusives formed at supra-solidus conditions, although the volume fraction of melts diminished drastically due to cooling/melt expulsion. At the pluton margin, the north-trending fabric is penetrative and post-dates magma solidification. Within the pluton, the major element oxides, rare earth elements, anorthite contents in plagioclase, and (Mg/Fe + Mg) ratios in biotite decrease with increasing SiO2 from phenocryst-rich (up to 75% by volume) granodiorite to phenocryst-poor (<15 vol%) granite that broadly correspond to minimum melt composition. The chemical-mineralogical variations in the pluton is attributed to deformation-driven ascent of magma with heterogeneous crystal content, ascending at variable velocities (highest in crystal-poor magma) along oblique-to-pluton margin east/ENE-trending extensional fractures induced by dextral shearing.Supplementary Material: Locations of field photographs (*) and samples used for whole-rock geochemistry;mean size (length of >35 phenocrysts in each outcrop) of K-feldspar phenocrysts (>1 cm long: see Appendix A) in the A, D-type intrusives in the Closepet pluton (Fig. 1); whole-rock chemical analyses of Closepet granite-granodiorite suite and the host gneisses (oxides in wt%, trace and rare earth elements in ppm); and histograms showing variations of XFe in biotite and mol% An in plagioclase in each of the 11 samples analysed available at https://doi.org/10.6084/m9.figshare.c.4356893.