Abstract:
The Panjal volcanics are tholeitic to mildly alkalic rocks. The basaltic lava flows of these rocks show continuous compositional change from low temperature sea water chemical exchange to the development of rocks with spilitic characters. The rocks were further altered and metamorphosed during Himalayan orogeny. The Panjal volcanics are altered to lower greenschist facies. Major minerals assemblage are chlorite, epidote, albite and actinolite. Based on the mineralogy these rocks may be divided into chlorite rich and epidote rich mineral assemblages. Both the chlorite and epidote rock assemblage show chemical changes in composition compared with their assumed basaltic precursors. The change involves addition of K, Na, Si and loss of Ca. Severe alteration leads to spilitization rocks with release of Ca from calcic plagioclase and inversion of plagioclase to albite. The lithology and geochemistry of the Panjal volcanic rocks suggest that they were thoroughly altered by hydrothermal and metamorphic processes. Chemically, the Panjal volcanics are greatly enriched in Na and K. The elements Na, K, Ca, Sr and Ba demonstrate large variations in the Panjal volcanics. Na2O varies from 0.05 to 4.57 wt.%, K2O from 0.11 to 2.78 wt.%, CaO varies from 4.82 to 10.35 wt.%, Ba from 24 to 1847 ppm, Sr from 42 to 423 ppm and Rb upto 224 ppm. The geochemical data mainly suggest an increase in Na, K, Si and a decrease in Ca. The alteration of the Panjal volcanic rocks resemble with that observed in recent submarine volcanics. The mineralogy of these rocks was mainly controlled by water/rock ratio during alteration. Subsequent Himalayan regional metamorphism had only a minor effect on the geochemistry of the rocks and had only readjusted the mineralogy of the rocks to the conditions of lower greenschist facies.
Page(s):
23-34
DOI:
DOI not available
Published:
Journal: Geological Bulletin of the Punjab University, Volume: 38, Issue: 1, Year: 2003