Significant, but volumetrically smaller, unmetamorphosed and largely undeformed alkaline magmatic suites have been reported from the Southern Granulite Terrain in southern India. These Neoproterozoic alkaline magmatic rocks occur as lenses, dykes and plugs that are mostly within, or proximal to, major shear zones or transcrustal faults. In this contribution, Beld, petrographic and whole-rock geochemical data of Sullya syenites and associated maBc granulites from the Mercara Shear Zone (MSZ), which separates low-grade (greenschist to upper amphibolite facies) Dharwar Craton and high-grade (granulite facies) Southern Granulite Terrain is presented. The isolated body of the Sullya syenite, similar to other alkaline plutons of the Southern Granulite Terrain, shows an intrusive relationship with the host hornblende-biotite gneisses and maBc granulites. The Sullya syenites lack macroscopic foliations and unlike, other plutons, they are not associated with carbonatites and ultrapotassic granites. Potash feldspar and plagioclase dominates the felsic phases in the Sullya syenite and there is negligible quartz. The studied syenites show evidence of melt supported deformation, but show no evidence of recrystallization. Geochemically, they most resemble the Angadimogar syenites (situated 3 km west of the Sullya syenites) with similar major oxide and trace element concentrations. The petrogenetic studies of the Sullya syenite have indicated that they were generated by mixing of two different sources derived from the partial melting of metasomatized continental mantle lithosphere and lower crustal maBc granulites. This melt source could have been emplaced in a rift-related tectonic setting. The emplacement is considered to be controlled by shears.
The Late Archaean Shimoga schist belt in the Western Dharwar Craton, with its huge dimensions and varied lithological associations of different age groups, is an ideal terrane to study Archean crustal evolution. The rock types in this belt are divided into Bababudhan Group and Chitradurga Group. The Bababudhan Group is dominated by mafic volcanic rocks followed by shallow marine sedimentary rocks while the Chitradurga Group is dominated by greywackes, pillowed basalts and deep marine sedimentary rocks with occasional felsic volcanics. The Nb/Th and Nb/La ratios of the studied metabasalts of the Bababudhan Group indicate crustal contamination. They were extruded onto the vast Peninsular Gneisses through the rifting of the basement gneiss.The Nb/Yb ratios of high magnesium basalts and tholeiitic basalts of Chitradurga Group suggest the enrichment of their source magma. Based on the flat primitive mantle normalized multi element plot with negative Nb anomalies and Th/Ta-La/Yb ratios, the high magnesium basalts and tholeiitic basalts are considered to have erupted in an oceanic-plateau setting with minor crustal contamination. The high magnesium basalts and tholeiitic basalts formed two different pulses of same magma type, in which first pulse of magma gave rise to high magnesium basalts which were derived from deep mantle sources and underwent minor crustal contamination enroute to the surface. While the second pulse of magma which gave rise to tholeiitic basalts formed at similar depths to that of high magnesium basalts and escaped crustal contamination. The associated lithological units found with the studied metavolcanic rock types of Bababudan and Chitradurga Group of Dharwar Supergroup of rocks in Shimoga schist belt of Western Dharwar Craton confirms the mixed-mode basin development with a transition from shallow marine to deep marine settings.
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