Early Mesoproterozoic (1.6–1.5 Ga) granulite facies events in the Ongole domain: geodynamic significance and global correlation

Abstract

AbstractThe late Palaeoproterozoic to early Mesoproterozoic Ongole domain of the Eastern Ghats Belt in southeastern India is composed of a suite of charnoenderbites with enclaves of metapelitic and mafic granulites. Geochemical data for all meta‐igneous rocks are typical for continental magmatic arc suites. The rocks preserve mineral assemblages and reaction textures indicating two separate metamorphic events: an initial counter‐clockwise medium‐pressure ultrahigh temperature (MP−UHT) event (>900 °C at 6.5–7.0 kbar), attributed to the magmatic accretion of the arc, which was followed by a clockwise HP‐MT event (~700 °C at 9 kbar), attributed to its tectonic crustal thickening. Zircon dating of charnoenderbites yield magmatic crystallization ages between 1.75 and 1.70 Ga and metamorphic ages between 1.62 and 1.60 Ga. Syn‐metamorphic enderbites yield magmatic and metamorphic zircon ages of c. 1.60 Ga, overlapping with all other metamorphic rim ages. In contrast, texturally controlled monazite dating of two chemically distinct monazite generations reveals two metamorphic events at c. 1.62 and c. 1.54 Ga. These data suggest that the Ongole domain was formed as a magmatic arc during the Palaeoproterozoic (c. 1.75–1.70 Ga), and subsequently experienced UHT metamorphism accompanied by syn‐metamorphic intrusions at c. 1.60 Ga, suggesting magmatic underplating as the metamorphic heat source. The subsequent crustal thickening at c. 1.54 Ga was due to the collision of the Ongole magmatic arc with the Indian craton. The UHT metamorphism and the related orogenic processes of the Ongole domain fall into the assumed late Palaeoproterozoic to late Mesoproterozoic ‘orogenic and UHT time gap’ (1.8–1.1 Ga) regarded by some studies as an orogenic quiescent period after the formation of the Palaeoproterozoic supercontinent known as Columbia or Nuna at c. 2.1–1.8 Ga. Coeval orogenic processes at c. 1.7–1.5 Ga occurring along accretionary margins in different fragments of Columbia (India, Australia, Antarctica and southwest Africa) indicate a protracted formation of this supercontinent.