Late Triassic ultrahigh-temperature mafic granulite from the North Dabie terrane, Central China

Abstract

Ultrahigh-temperature (UHT) granulites, essential components of collisional orogens, preserve key records of orogenic geodynamics. This investigation provides a systematic examination of mafic granulites from the Dabie orogenic belt through integrated petrological and geochronological analyses. Petrographic observations and phase equilibria modeling reveal clockwise pressure-temperature (P–T) paths, involving an inferred middle-pressure (MP) high amphibolite–granulite-facies (M₁; 10.7–11.7 kbar and 745–810 °C) followed by decompressional heating, UHT granulite-facies metamorphism (M₂; 6.5–6.8 kbar and 938–950 °C) and subsequent cooling, amphibolite-facies stage (M₃; 3.6–4.5 kbar and 636–660 °C). In-situ zircon dating show that the granulite has a protolith age of ∼1805 Ma and underwent HP and UHT metamorphism during the Late Triassic (∼215–197 Ma; M₁–M₂), followed by amphibolite-facies retrograde metamorphism from 193 to 172 Ma (M₃). Meanwhile, zircons within the granulites document anatexis at ∼120 Ma, corresponding to orogenic collapse of the Dabie orogenic belt. We propose a metamorphic process of the mafic granulite as follows: the ∼1.8 Ga mafic rock was buried to the MP amphibolite-granulite-facies level during the Triassic continental collision orogenesis, and was heated by the upwelling asthenosphere during exhumation, leading to UHT metamorphism; and subsequently, it was chilled and retrograded to amphibolite-facies level. This study establishes critical constraints on syn-collisional thermal-tectonic coupling in continental collision zones, with deep thermal processes recorded by mafic granulites enhancing our understanding of the spatiotemporal evolution of orogenic events in both ancient and active mountain belts globally.