Trace element geochemistry of parts of the Closepet granite, Mysore State, India

Abstract

SummaryTrace elements in twenty samples of the Closepet granite (grey and pink varieties) and the related rocks have been determined by neutron activation analysis (Th, Rb, and Cs), fluorometry (U), flame-photometry (K), and emission spectroscopy (Pb, Sr). The trace element contents of the grey and pink varieties are generally similar. An analysis of the magnitudes of the trace element and other ratios (K/Rb, 235; Th/U, 6·4; U/K (× 104), 0·7; K/Cs (× 10−4), 3·6; Th/K (× 104), 5·3; Fe2O3/(FeO+Fe2O3), 0·27) as well as 87Sr/86Sr initial ratio (0·705; Crawford, 1969) of the Closepet granite indicate two possible modes of genesis: Either the granite magma was not highly differentiated and the vapour phase was relatively insignificant; the crystallization of the magma took place under essentially non-oxidizing conditions; the pink variety, which followed the grey variety, crystallized under essentially the same conditions as the grey variety. Or the Closepet granite had a two-stage history—palingenesis (starting from the Peninsular gneiss) and metasomatism involving the enrichment in K, Rb, Pb, and Th and depletion of Sr and Cs, among others.

High-temperature Metamorphism and Crustal Anatexis

“…The Closepet Granite is thus a feature of the middle and upper crust which grades downwards into migmatitic roots in the lower crust, similar in aspect to Hutchison's (1970) =,..,...,..,------,45' Rogers & Greenberg (1981). Petrographie evidence of K-metasomatismexists in the form of marginal K-feldspar replacement of plagioclase and biotite re placement of amphibole (Divakara Rao et al 1972). Near the town of Ramnagaram (formerly Closepet) the granite consists of several phases, including migmatitic gneiss, grey clinopyroxene-bearing granite with abundant pink megacrysts, and pink leucogranite in discrete vein networks.…”

“…Theories of the origin of Closepet Granite include purely igneous intrusion and differentiation , in situ anatexis (Friend 1984), and combined metasomatic infiltration and partial melting (Radhakrishna 1956, Divakara Rao et al 1972. Various uncertainties attend all of these proposals.…”

Late Archaean crust-mantle interactions: geochemistry of LREE-enriched mantle derived magmas. Example of the Closepet batholith, southern India

“…Several theories have been proposed for the origin of the Closepet batholith, including metasomatism of gneisses and schists (Radhakrishna 1956;Suryanarayana 1960;Divakara Rao et al 1972, 1990, in situ partial melting of Peninsular Gneisses (Friend 1983;Jayananda 1988;Newton 1990a;Jayananda and Mahabaleswar 1991a) or batch melting of gneisses followed by fractional crystallisation (Allen et al 1986). Although most of these models can account for anatectic granite genesis, they appear inappropriate for intrusive monzogranites.…”

“…1); it forms the latest Archaean event in this area (Newton 1990a). Because of its exceptional fresh exposures and its close association with different tectono-metamorphic domains, the Closepet batholith has been investigated in many studies (Radhakrishna 1956;Suryanarayana 1960;Divakara Rao et al 1972, 1990Friend 1983Friend , 1985Allen et al 1986;Jayananda 1988;Newton 1990b;Jayananda et al 1992). However, most of these studies concentrate on field and petrological descriptions, whereas detailed gcochemical and isotopic studies arc generally lacking.…”

Studies on radon concentration in aqueous samples at Mysore city, India

“…[6,16,17] The study area contains metabasalt-amygdaloidal, pillowed and meta-ultramafites means Dharwar super group granites and pink granite of Chamundi hill, which have an average uranium content of 3.0 ppm. [12,18] These granites are rich in radium and potassium radioactive elements. The bore wells dug up to a depth of about 30-92 m bgl, [19] the contact between water and the rocks in the drilled wells are responsible for the highest radon concentration.…”