Cryogenian transpression and granite intrusion along the western margin of Rodinia (Mt. Abu region): Magnetic fabric and geochemical inferences on Neoproterozoic geodynamics of the NW Indian block

Abstract

The Mt. Abu batholith in NW India comprises variably deformed porphyritic, granophyric to medium-grained granites and granite gneisses. They are intruded by rhyolitic and mafic dykes; the latter also mark the terminal magmatic phase in this batholith. Granitoids and rhyolitic dykes form a coherent group; petrographic and geochemical characteristics indicate high level intrusion of felsic magma generated from high temperature melting of a lower crustal source. Geochemical similarity, spatial contiguity and coeval emplacement (766 to 763Ma) of Mt. Abu granitoids with the Neoproterozoic (770 to 750Ma) Malani Igneous Suite (MIS) underline that both are related to the same thermal event with Mt. Abu batholith as southeastern continuity of the MIS.Anisotropy of magnetic susceptibility data shows parallel fabric orientation in all granitoid types (NE trend, steep SW dip) as well as in a prominent shear zone (Delwara Shear Zone) along the western margin of the batholith with continued deformation during and after the emplacement of granitic magma as inferred from deformation of late-stage mafic dykes. Including coeval shear zones and associated melting in the region NE of Mt. Abu shear-controlled magma generation and ascent along a >50km NE trending corridor (Mt. Abu–Sirohi fault zone) is inferred. Structural elements and microstructural criteria (steep foliations, vertical lineations, dextral displacement) indicate a transpressional setting for this Cryogenian event.In regional geodynamic context the Mt. Abu–MIS can be regarded as northeastern continuation of the Neoproterozoic (800–700Ma) magmatic belt extending from northern Madagascar, the Seychelles into NW India. This magmatic belt, located along the western margin of supercontinent Rodinia, was formed during eastward subduction of the Mozambique Ocean. Transpressional forces responsible for shaping the structural architecture in the Mt. Abu–Sirohi region were most likely induced during closure of the Mozambique Ocean and related translation of the Marwar craton.