Geochemical characterization, petrogenesis, and emplacement tectonics of Paleoproterozoic high‐Ti and low‐Ti mafic intrusive rocks from the western Arunachal Himalaya, northeastern India and their possible relation to the ~1.9 Ga LIP event of the Indian shield

Abstract

Paleoproterozoic mafic intrusive rocks from the western Arunachal Himalaya have been studied for understanding their petrogenesis and tectonic environment, in which they were emplaced, with the help of their bulk‐rock major, trace, and rare‐earth elements (REE) compositions. These mafic intrusive rocks, mostly small bodies of dykes, sills, and lenses, are exposed in the Higher as well as the Lesser Himalaya sequences. Geochemically, 2 suites of rocks are identified and grouped into high‐titanium and low‐titanium mafic intrusive rocks. High‐titanium mafic intrusive (HTMI) samples have comparatively low Mg number (Mg#) and high high‐field strength element contents in comparison to low‐titanium mafic intrusive (LTMI) rocks. Multielements and REE patterns for these two identified groups are distinct. The LTMI and HTMI were originally spatially separated at the time of their emplacement and believed that probably they have been juxtaposed during the Himalayan orogeny by crustal shortening through development of imbricated thrusts. It is perceived that the HTMI and LTMI have different petrogenetic histories and are derived from two different melts; however, they are postulated to be parts of the same igneous province. Geochemical characteristics do not support any serious effect of crustal contamination; however, interaction with metasomatized lithospheric mantle cannot be discounted. Trace element petrogenetic modelling suggests derivation of the LTMI samples from a parental magma generated in spinel stability field (thin lithosphere) through a ~20–25% melting of a lherzolite mantle source, whereas the HTMI samples were derived from ~5–10% melting of a similar mantle source but from garnet stability field (thick lithosphere). Widespread Paleoproterozoic mafic events in the Indian shield such as Bastanar dyke swarm in the Bastar and the Hampi dyke swarm (also includes Pulivendla sills in the Cuddapah Basin) in the eastern Dharwar Craton together with mafic intrusive and extrusive rocks in the Himalayan region suggest presence of a large igneous province at ~1.9 Ga.