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Chlorine‐rich amphibole and biotite in the A ‐type granites, R ajasthan, NW I ndia: P otential indicators of subsolidus fluid–rock interaction and metallogeny
Author(s) -
Kaur Parampreet,
Chaudhri Naveen,
Eliyas Nusrat
Publication year - 2018
Publication title -
geological journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.721
H-Index - 54
eISSN - 1099-1034
pISSN - 0072-1050
DOI - 10.1002/gj.3211
Subject(s) - amphibole , geology , biotite , hydrothermal circulation , geochemistry , epidote , mineralogy , quartz , chlorite , paleontology , seismology
The A‐type granites in the northern Delhi fold belt, Rajasthan, India, comprise Cl‐enriched amphibole and biotite. These hydrous phases, in general, show significant variation in the Cl and F contents on the scale of individual intrusions and also at times on thin‐section scale. This variation of the hydrous phases that equilibrated with the fluid is principally controlled by the variation in the fluid activity ratios of a Cl ‐/a OH ‐ and a F ‐/a OH ‐. The activity gradients in the fluid developed due to the interaction between the granites and an externally derived Cl‐bearing fluid coupled with limited integrated fluid flux. The fraction of the fluid that reached the least albitised granite was highly Cl‐rich as a consequence of preferential extraction of water from the grain‐boundary fluid for the formation of hydrous phases like epidote and sericite. The occurrence of Cl‐rich amphibole and biotite coupled with the variation in their halogen contents in the A‐type granites can act as potential indicators of hydrothermal fluid activity and the subsequent mineralisation in a region.