India: A Co-genetic Origin during Neoproterozoic Alaskan-type Evolution

The Ti- rich gabbros are in association with serpentinized dunites and pyroxenites in the form of several intrusions at various locations of the Salem mafic and ultramafic complex (SMUC). The petrography of these gabbros shows sub-alkaline to alkaline in nature with mineralogy of two pyroxenes and plagioclases of calcic-sodic assemblages along with magnetite-titanomagnetite-ilmenite (Ti-spinels). The whole rock geochemistry indicates that they are tholeiitic in nature. The Ti- bearing oxides (ilmenites) of these gabbros are characterized by higher contents of TiO2 and FeO, similar to that of Ti-Fe rich Alaskan- type of mafic rocks. Tectonically, these gabbros reveal that they are derived from subduction related components of arc magmas of titanium rich, evolved through the process of high degree of crystal fractionation. From the two-pyroxene thermometry, the temperature of formation of these gabbros are determined as 893-1014°C and the clinopyroxene barometry results variable pressures of 8-13 kbars. The tectonic setting with the available age relationships from the complex suggest these intrusions are syntectonic and co-genetic of late emplacements along with the ultramafics during Neoproterozoic subduction events.



T. Yellappa, 2021, Journal Geological Society Of India, Vol.97, pp.21-34, https://DOI: 10.1007/s12594-021-1622-5