GEOLOGY AND GEOCHEMISTRY OF AMPHIBOLITES FROM CHATASER AREA, MAHENDRAGARH DISTRICT, HARYANA

摘要

Rocks of Ghataser area, Mahendragarh District, Haryana belong to Mid-Proterozoic Alwar Group of Delhi Supergroup and include thinly bedded feldspathic and micaceous quartzite with bauds of mica schist. Within this sedimentary assemblage there are bands of amphibolite and associated anthophyllite-cordierite schists structurally conformable to the fabric of the enclosing metasediments. Amphibolites are dominantly hornblende-rich rocks with subordinate plagioclase, quartz and minor mafic minerals. Anthophyllite schist occurs as lensoid bodies and pockets within amphibolites and has anthophyllite and cordierite as major minerals. The K-Mg plot suggests igneous trend for amphibolites, while only a few samples of anthophyllite schist plot in the igneous field. Modified Niggli 'c' vs. (al-alk) plot also suggests an igneous affinity for the amphibolite that is also confirmed by Niggli 'c' vs. 'nig' plots of Leake (1963) and Niggli 100 mg-c- (al-alk) triangular plot, K_2O vs. SiO, and Na_2O + K_2O vs. SiO_2 plots reveal that the amphibolites are basaltic to andesitic in composition and are of tholeiitic affinity. Chemical classification and nomenclature of rocks using the total alkali versus silica (TAS) diagram (Le Bas et al., 1986) indicate that the rocks of Ghataser area have been derived from basalt to basaltic-andesite parent rocks. Anthophyllite schist is high in MgO. total iron and alkalis and low in silica and calcium as compared to amphibolite. Alumina content is same in both the rock types. The high MgO content may be ascribed to variable amounts of MgO introduced during metasomatism. The anthophyllite schists represent preexisting igneous suite of rocks with mafic-rich segregations. Selective metasomatism and introduction of magnesium into this suite has converted the mafic-rich portions into pockets of anthophyllite-bearing assemblages.