US EPA

1758601 

Journal Article 

GEOLOGY AND GEOCHEMISTRY OF THE DEGANA PLUTON - A PROTEROZOIC RAPAKIVI GRANITE IN RAJASTHAN, INDIA 

Chattopadhyay, B; Chattopadhyay, S; Bapna, VS 

1994 

1 

Mineralogy and Petrology
ISSN: 0930-0708 

50 

1-3 

69-82 

WOS:A1994MR07300007 

The Degana pluton hosts one of the few known tungsten
deposits in India. It is an epizonal, moderately high silica pluton emplaced during the
Proterozoic in a post-tectonic setting. Though homogeneous in composition, it displays textural
heterogeneity from coarse-grained hypidiomorphic to fine-grained porphyritic to hypabyssal
granite porphyry. Genetically related rhyolites are also present. Coherency of geochemical and
mineralogical attributes in the Degana pluton can be explained by fractional crystallisation.
Complex variety of hydrothermal and pneumatolytic features is also present. At shallow depths,
emanation differentiation has led to progressive enrichment of Li, Rb, and W. Both the plutonic
and volcanic phases of the magma show development of rapakivi texture and other diagnostic
characteristics of the rapakivi granites. The Degana granite is a ''specialised granite'' and
classified as an A-type intraplate anorogenic granite of mantle plume origin. The mineralogy and
chemistry of the Degana pluton compares well with the various rapakivi granites of south-eastern
Fennoscandia. Chemical and textural characteristics of the Degana pluton provide a constraint on
the formation of the rapakivi texture when interpreted in terms of experimentally determined
phase equilibria. The mantling process is interpreted as a result of pressure fluctuations due to
escape and recharging of volatiles (e.g., H2O and F) accompanying the emplacement of the magma.