Metamorphism of the host and associated rocks at the Rajpura–Dariba massive sulfide deposit, Northwestern India

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• 作者：Biswajit Mishra ; Dewashish Upadhyay and Heinz-Juergen Bernhardt
• 关键词：Rajpura– ; Dariba ; Metamorphism ; Thermobarometry ; Raman spectroscopy ; Graphite crystallinity
• 刊名：Journal of Asian Earth Sciences
• 出版年：2006
• 出版时间：January 2006
• 年：2006
• 卷：26
• 期：1
• 页码：21-37
• 全文大小：1054 K

文摘

Field and detailed petrographic studies of rocks exposed around the Rajpura–Dariba massive sulfide deposit led to the identification of three distinct, broad SUITS of rocks, namely calc-silicate rocks, calc-pelite schist and pelites. Although the pelites constitute various litho units, they are broadly classified into two types, i.e. garnet-bearing (kyanite-absent) and garnet-absent (kyanite-bearing) sub-units. The calc-silicate rocks show the formation of amphibole as the peak metamorphic mineral while the calc-pelite schist contains garnets at the highest grade. The pelites, on the other hand, extend up to kyanite grade. The garnets in pelites are prograde garnets as manifested by strong growth zoning with a typical bell shaped X_Mn profile. Using several calibrations, the garnet–biotite Fe–Mg exchange thermometer furnished temperatures in the range of 530–555 °C for pelites and 500–625 °C for the calc-biotite schist. Thus these rocks have been metamorphosed to mid-amphibolite facies, attaining peak metamorphic conditions within the temperature range 580–600 °C and corresponding pressure 5.5–6.1 kbar, inside the kyanite stability field. The fluid composition was constrained within a narrow range of X_H2O≈0.85–1.0 during peak metamorphism. Considering relevant univariant equilibria in the assemblage garnet+staurolite+muscovite+biotite+chlorite in pelites and constraints from fluid inclusion studies, a clockwise P–T–t path is proposed by the intersection of relevant reactions. The proposed path corroborates the results of earlier fluid inclusion studies and accounts for the metamorphic evolution of the Rajpura–Dariba sulfide deposit.

Laser Raman micro-spectroscopic studies on graphite flakes in pyrite-bearing graphite–mica schist indicate the presence of graphites from chlorite–biotite to staurolite–kyanite grades. Although such a wide variation implies graphite formation both in the prograde and retrograde sequences, consideration of some pertinent spectral parameters such as the average O-peak width and the asymmetric nature of the S-peaks indicates preservation of higher grade graphite crystallinity.