Age and P–T evolution of the Neoproterozoic Turkel Anorthosite Complex, Eastern Ghats Province, India

Abstract

Massif-type anorthosite complexes constitute a distinct component of the Proterozoic Eastern Ghats Province in India. They intruded the poly-deformed and poly-metamorphic granulite facies terrane near its western and northern tectonic contacts with the Archaean Bastar and Singhbhum cratons, respectively. Following their emplacement, the complexes were variously affected by high-grade metamorphism and deformation. The Turkel Anorthosite Complex comprises an anorthosite–leuconorite diapir encircled by voluminous crust-derived quartz–monzonite intrusions hosted within an expansive batholithic complex of megacrystic K-feldspar granite and remnants of an older gneissic unit. This contribution evaluates the pressure-temperature history of the anorthosite complex based on textural relations, paragenetic characteristics, and mineral chemistry, and provides for the first time, constraints on the timing of emplacement and subsequent metamorphism of the rocks through in situ U–Pb dating of zircon from several members of the suite.Emplacement of the Turkel Anorthosite Complex occurred after the fabric-defining late Mesoproterozoic deformation (D1–D3) and high-grade metamorphism of the country rocks and was shortly preceded by the surrounding expansive intrusion of the megacrystic K-feldspar granite. The leuconorite-anorthosite suite crystallized at 980±8Ma while the other components including the monzonite, quartz–monzonite, and ferrodiorite were emplaced later between 956±6 and 945±5Ma. The post-intrusion evolution of the complex is characterized by partial re-equilibration of the igneous parageneses and textures during an initial episode of cooling and decompression from the magmatic crystallization stage (1100–950°C, 12–7kbar) towards the ambient thermobaric regime, and following prolonged slow cooling by an episode of renewed compressional deformation (late-D3; ca. 750°C, 6.5–7.0kbar) that caused the thorough high-grade recrystallization of the rocks and produced the monophase planar fabric of the complex. U–Pb spot ages from metamorphic domains of zircon grains constrain the age of this metamorphism to 901–879Ma. The complex was moderately affected by the late Neoproterozoic to early Palaeozoic Pan-African tectonothermal event which led to internal tectonic segmentation and westward thrusting of the Khariar and Rampur domains of the northern Eastern Ghats Province onto the Bastar craton.