Abstract Views :186 |
PDF Views:1
Authors
Affiliations
1 Post Graduate Department of Geology, Govt College, Dharamsala, Himachal Pradesh - 176 215, IN
2 Isotope Geology Group, Mineralogical-Petrographical Institute, University of Bern, Erlachstr. 9A, CH-3012 Bern, CH
3 Department of Geology, Panjab University, Chandigarh - 160 014, IN
Source
Journal of Geological Society of India (Online archive from Vol 1 to Vol 78), Vol 48, No 2 (1996), Pagination: 151-160
Abstract
The Jalor and Siwana complexes belong to the Malani igneous suite, Rajasthan, India and are characterised by within - plate, A - type granites associated with coeval felsic and mafic volcanism. Sr, Pb and Nd isotopic compostions of the two complexes have been determined. Sr isotopic studies reveal an isochron age of 725±7 Ma for the felsic rocks of the Jalor Complex, with an initial 87Sr/86Sr ratio of 0.7062±0.0020. Three highly differentiated granites from Siwana plot on the same near-isochron, indicating that the complexes are coeval. The Pb and Nd isotopic ratios range between (206Pb/204Pb = 18.52-21.28, 207Pb208Pb = 15.58-15.98, 204Pb/204Pb/206Pb = 38.53-40.8) and (143Nd/144Nd = 0.5122-0.5127, 147Sm/144Nd = 1.1260-0.157) respectively. Pb and Nd isotopic compositions of the Siwana samples show that the magma is mantle derived; for the Jalor complex the combined Sr, Nd and Ph data indicate primary mantle derivation with a variable degree of crustal contamination. with the assimilated crust being most likely of Archaean age.The petrogenesis of the two complexes is interpreted as an effect of fractionation of a primary mantle derived magma, simultaneous with assimilation of rocks from the lower crust. The data further document the presence of Archaean crust in the area.
Keywords
Geochronology, Petrology, Malani Igneous Suite, Rajasthan.
