Journal of Geology & Geophysics
Open Access

1.4-0.6 Ga Precambrian alkaline magmatism along continental margin setting of southern India

5^th International Conference on Geological and Environmental Sustainability

August 13-14, 2018 Bali, Indonesia

Jandhyala Ratnakar

Osmania University, India

Posters & Accepted Abstracts: J Geol Geophys

Abstract :

Alkaline magmatism along the eastern margin of Indian subcontinent during the Precambrian, precisely during 1.4 Ga to 0.6 Ga (mesoproterozoic to neoproterozoic) has resulted into emplacement of alkaline igneous rock complexes. These complexes consist of rocks with modal nepheline�?�alkali pyriboles and normative nepheline (ne)�?�acmite (ac). They are emplaced along the boundary between granulite terrains and the Dharwar and Bastar cratons at Rairakhol, Khariar, Koraput, Kunavaram, Elchuru, Purimetla, Uppapadu and Sivamalai that together cover an area of ~250 sq km. The alkaline rocks vary from ultramafic through mafic to felsic and from melanocratic through mesocratic to leucocratic. Under the microscope alkaline rocks exhibit equigranular hypidiomorphic, inequigranular porphyritic, allitriomorphic and panidiomorphic textures. Most of these silica-undersaturated plutons consist of silica-oversaturated rock member. The nepheline syenites are generally miaskitic and rarely agpaitic wherein the ratio (Na2O+K2O)/Al2O3 (mol. prop.) is <1 or >1 respectively. These alkaline rocks generally show LREE-enriched and HREEdepleted patterns with negative Eu anomalies. The differentiation of alkali basalt magmas is by Fractional Crystallization (FC); however, Assimilation Fractional Crystallization (AFC) and liquid immiscibility are also involved to produce Si-oversaturated rocks. The liquid lines of descent have followed a general sequence, that is, [shonkinite/melteigite]�??[malignite/alkali syenite]�??nepheline syenite�??[quartz syenite/alkali granite]�??lamprophyre[camptonite/sannaite]. The alkaline rock complexes have different ages with similar initial 87Sr/86Sr ratios or have similar ages but have different initial ratios implying existence of mantle heterogeneity below the cratonic regions in southern India during the precambrian.

Biography :

E-mail: jrtnkr@yahoo.com