Petrography, chemistry and isotopic ages of Peninsular Gneiss, Dharwar acid volcanic rocks and the Chitradurga Granite with special reference to the late Archaean evolution of the Karnataka Craton, southern India

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doi: 10.1016/0301-9268(84)90050-0
Authors:Taylor, P. N.; Chadwick, B.; Moorbath, S.; Ramakrishnan, M.; Viswanatha, M. N.
Author Affiliations:Primary:
Oxford Univ., Dep. Geol. and Mineral., Oxford, United Kingdom
Univ., Exeter, Dep. Geol., United Kingdom
Geol. Surv. India, India
Volume Title:Precambrian Research
Source:Precambrian Research, 23(3-4), p.349-375. Publisher: Elsevier, Amsterdam, International. ISSN: 0301-9268
Publication Date:1984
Note:In English. 45 refs.; illus. incl. 7 tables, 3 plates, geol. sketch map
Summary:The Chikmagalur Granite (granodiorite), which with its host gneisses forms part of the basement (Peninsular Gneiss) to the Dharwar Supergroup in the Bababudan basin, yields Rb-Sr and Pb/Pb whole-rock isochron dates of 3080±110 Ma and 3175+45 Ma, respectively. Host tonalitic gneisses to the Chikmagalur Granite give an Rb-Sr whole-rock isochron date of 3190±100 Ma. A suite of granites and granodioritic-tonalitic gneisses (Chitradurga granitic rocks and gneisses) forming part of the Peninsular Gneiss basement to the Dharwar Supergroup west of the Chitradurga belt yields Rb-Sr and Pb/Pb whole-rock isochron dates of 2970±100 Ma and 3028+28 Ma. The suite of Dharwar acid volcanic rocks from north of Honnali defines a poorly fitted 207Pb/206Pb linear array (MSWD 15.8) which gives an apparent age of 2565±28 Ma. The poor fit of this "isochron" shows that a closed system was not maintained, a conclusion supported by high K abundances which are attributed to a syn- or post-magmatic ion exchange process. The Chitradurga Granite which intrudes the older rocks of the Dharwar Supergroup in the Chitradurga belt yields a well-fitted Pb/Pb whole-rock isochron date of 2605±18 Ma. [A.C.B.]
Subjects:Absolute age; Alkaline earth metals; Archean; Basement; Dates; Dharwar Supergroup; Geochemistry; Geochronology; Gneisses; Granites; Granitic composition; Granodiorites; Igneous rocks; Isotopes; Lead; Metals; Metamorphic rocks; Metamorphism; Metavolcanic rocks; Neoarchean; Pb/Pb; Peninsular Gneiss; Plutonic rocks; Precambrian; Rb/Sr; Sargur Group; Sr-87/Sr-86; Stable isotopes; Strontium; Trace elements; Asia; India; Indian Peninsula; Bababudan Basin; Chikmagalur Granite; Chitradurga Granite; Dharwar Rhyolites; Karnataka Craton; Ranibennur Formation; Southern India
Coordinates:N120000 N160000 E0783000 E0740000
Abstract Numbers:84M/3655
Record ID:1985013771
Copyright Information:GeoRef, Copyright 2019 American Geosciences Institute.
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