Sm-Nd, Pb-Pb and Rb-Sr geochronology and petrogenesis of the mafic dyke swarm of Mahbubnagar, South India; implications for Paleoproterozoic crustal evolution of the Eastern Dharwar Craton

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doi: 10.1016/S0301-9268(97)00027-2
Authors:Pandey, B. K.; Gupta, J. N.; Sarma, K. J.; Sastry, C. A.
Author Affiliations:Primary:
Atomic Minerals Division, Hyderabad, India
Other:
Geological Survey of India, Southern Region, Hyderabad, India
Volume Title:Precambrian Research
Source:Precambrian Research, 84(3-4), p.181-196. Publisher: Elsevier, Amsterdam, International. ISSN: 0301-9268
Publication Date:1997
Note:In English. Includes one appendix. 47 refs.; illus., incl. 4 tables, geol. sketch maps
Summary:The Sm-Nd, Rb-Sr and Pb-Pb isotopic systematics of whole rock and separated mineral fractions from four tholeiitic mafic dykes of the Mahbubnagar swarm have been investigated. This dyke swarm intrudes the granitic basement of the Cuddapah basin in the Eastern Dharwar Craton (EDC). The Sm-Nd data on whole rock samples of four gabbros and one dolerite and 15 mineral fractions yielded a linear array with an isochron age of 2173±64 Ma and an initial εNd value of 0.4±0.3. The Sm-Nd data of a metapyroxenite and its three mineral fractions plot parallel to this array yielding an isochron age of 2189±123 Ma with a negative initial εNd value of -1.8±1.4. Rb-Sr and Pb-Pb internal isochron ages of three gabbros and a Pb-Pb internal isochron age of a metapyroxenite dyke range between 2031 and 2284 Ma and, within the limits of experimental error, broadly conform to the Sm-Nd isochron age. By contrast, Rb-Sr internal isochron ages of three other samples range between 1474 and 1952 Ma, and one sample yields a Pb-Pb internal isochron age of 3446 Ma, showing the effects of partial isotopic resetting, possibly due to hydrothermal alteration. These data suggest that mafic dykes of the Mahbubnagar swarm were emplaced at c. 2170 Ma, marking an episode of the crustal extension and fracturing which ultimately resulted in the formation of the Cuddapah basin. Different petrological and geochemical variants of mafic dykes seen in the area most probably represent generation and/or crystallization of the progressively evolved batches of magma during a relatively short time interval. The initial εNd values calculated at 2170 Ma range from 0.6 to -2.0 and can be explained as reflecting contamination of depleted mantle derived magma by crustal rocks of EDC. The initial 87Sr/86Sr ratios (0.7027-0.7064) and model µ1 values (8.3-8.5) of apparently undisturbed samples are also consistent with this suggestion. Abstract Copyright (1997) Elsevier, B.V.
Sections:Age determination
Subjects:Absolute age; Crust; Dates; Diabase; Dike swarms; Emplacement; Gabbros; Genesis; Igneous rocks; Isochrons; Mafic composition; Mass spectra; Metaigneous rocks; Metals; Metamorphic rocks; Metapyroxenite; Paleoproterozoic; Pb/Pb; Plutonic rocks; Precambrian; Proterozoic; Rare earths; Rb/Sr; Sample preparation; Sm/Nd; Spectra; Upper Precambrian; Whole rock; Andhra Pradesh India; Asia; Cuddapah Basin; India; Indian Peninsula; Eastern Dharwar Craton; Mahbubnagar India; Southern India
Coordinates:N163400 N170000 E0780000 E0773000
Abstract Numbers:99M/1175
Record ID:1998002284
Copyright Information:GeoRef, Copyright 2019 American Geosciences Institute. Reference includes data from CAPCAS, Elsevier Scientific Publishers, Amsterdam, Netherlands
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