Tectonic restoration of the Precambrian crystalline rocks along the west coast of India: Correlation with eastern Madagascar in East Gondwana

Abstract

New structural–mineralogical data and U–Th-total Pb monazite chemical ages in 27 samples in a 430km long corridor along the west coast of India are combined with existing data to reconstruct the tectonic set up of the Meso/Neoarchean crystalline rocks in the Western Dharwar Craton (WDC). The data helps to delineate two NW-trending Paleoproterozoic ductile shear zones that limit the southern and the northern margins of the WDC. The southern shear zone (metamorphic age: 2.3–2.4Ga) separates the greenschist facies supracrustal belts (2.5 and 3.3Ga), foliated granitoids (2.5 and 2.9Ga) and amphibolite facies anatectic gneisses (>3.0Ga) of the WDC from the >2.9Ga granulite facies ortho/para-gneisses of the Coorg Block. This shear zone is correlated with the ∼2.4Ga Betsimisaraka suture zone in east-central Madagascar that demarcates the accretion zone between the Antongil Block (≈WDC) and the granulite facies lithologies of the Antananarivo domain (≈Coorg Block). The northern shear zone system (metamorphic age: 2.2–1.8Ga) extending NW into Madagascar possibly exists as a hitherto undiscovered tectonic zone forming the basement of the Mesoproterozoic Sahantaha Formation underlying the Neoproterozoic Bemarivo Belt supracrustals in NE Madagascar.Within the WDC, the Meso/Neoproterozoic ages retrieved from poorly-defined margins in monazite are uncommon, dispersed within the craton, and do not define localized zones within the craton. The chemical ages of metamorphic monazites formed at greenschist/amphibolite facies conditions preclude metamorphism–deformation associated with accretion of crustal blocks within the WDC during the Rodinia assembly.