Geochemistry of the Desur lavas, Deccan traps: Case study from the vicinity of Belgaum, Karnataka and their petrogenetic inferences.

Geochemical characteristics of Desur-type basalt flows in the southern and southwestern part of Belgaum in Karnataka, India have been investigated to understand their petrogenesis. The basalts are compact, hard, massive, and show characteristic microporphyritic textures with abundant well-twinned and un-twinned plagioclase phenocrysts and minor clinopyroxene set in a fine-grained groundmass consisting of plagioclase, clinopyroxene, glass and Fe-Ti oxides. Thin sections show sub-ophitic, intergranular and intersertal textures. The basalts are Fe-rich tholeiites (13.4-13.8 wt %), characterized by high TiO (3.64 to 3.94 wt %); moderate MgO contents (4.79 to 5.41 wt %), low KO contents (<0.58 wt %) and low Mg# (42.4-45.9). They are enriched in large ion lithophile elements, moderately enriched in the light rare earths (chondrite-normalized La/Yb 3.37-4.24), and exhibit nearly flat heavy rare-earth patterns that lack significant Eu anomalies (Eu/Eu* 0.86-1.10). Primitive-mantle-normalized element patterns for these rocks show characteristic troughs at K and Sr, absence of a Nb anomaly, and a low Zr/Nb ratio (<15), which suggest insignificant contamination by many types of continental crust, whereas, enrichments in the large ion lithophiles, La, P and Th could suggest enriched source characteristics. Based on the geochemical characteristics of the basalts, it is inferred that the Desur basalts representing the youngest flows of the Deccan Basalt Group are derived by partial melting of a peridotite source, and subsequent fractionation gave rise to the compositions of the basalts that are found in the Belgaum region. [ABSTRACT FROM AUTHOR]