Sm-Nd ages of two meta-anorthosite complexes around Holenarsipur: Constraints on the antiquity of Archean supracrustal rocks of the Dharwar craton |
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| Authors: | Y J Bhaskar Rao Anil Kumar A B Vrevsky R Srinivasan G V Anantha Iyer |
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| Institution: | (1) National Geophysical Research Institute, 500 007 Hyderabad, India;(2) Institute of Precambrian Geology and Geochronology, St. Petersburg, Russia;(3) Department of Inorganic and Physical Chemistry, Indian Institute of Sciences, 560 012 Bangalore, India |
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| Abstract: | Whole-rock Sm-Nd isochron ages are reported for two stratiform meta-anorthosite complexes emplaced into the Archean supracrustal-gneiss
association in the amphibolite facies terrain around Holenarsipur, in the Dharwar craton, South India. While these metaperidotite-pyroxenite-gabbro-anorthosite
complexes are petrologically and geochemically similar, they differ in the intensity of tectonic fabric developed during the
late Archean (c. 2.5 Ga) deformation. They also differ in their whole-rock Sm-Nd isochron ages and initial Nd isotopic compositions:
3.285 ± 0.17 Ga,ɛNd0.82 ± 0.78 for the Honnavalli metaanorthosite complex from a supracrustal enclave in the low-strain zone, and 2.495 ± 0.033
Ga, ɛNd = -2.2 ± 0.3 for the Dodkadnur meta-anorthosites from the high-strain southern arm of the Holenarsipur Supracrustal
Belt (HSB). We interpret these results as indicating that the magmatic protoliths of both meta-anorthosite complexes were
derived from a marginally depleted mantle at c. 3.29 Ga but only the Dodkadnur rocks were isotopically reequilibrated on a
cm-scale about 800 Ma later presumably due to the development of strong penetrative fabrics in them during Late Archean thermotectonic
event around 2.5 Ga. Our results set a younger age limit at c. 3.29 Ga for the supracrustal rocks of the HSB in the Dharwar
craton. |
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| Keywords: | Archean anorthosite Dharwar craton Sm-Nd Geochronology |
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