Metamorphic evolution of ultrahigh-temperature Fe- and Al-rich granulites in the south Yenisei Ridge and tectonic implications

Resumo

This study provides the first evidence for the occurrence of ultrahigh-temperature (UHT) granulite-facies metamorphism in the Yenisei Ridge (Angara–Kan block). UHT metamorphism is documented in Fe-Al-rich metapelites on the basis of the garnet–hypersthene–sillimanite–cordierite–plagioclase–biotite–spinel–quartz–K-feldspar assemblage. Microtextural relationships and compositional data for paragneisses of the Kan complex attest to three distinct metamorphic episodes: (M1) pre-peak prograde (820⎯900°C/5.5–7 kbar), (M2) peak UHT (920–1000°C/7–9 kbar), and (M3) post-peak retrograde (770⎯900°C/5.5–7.5 kbar). The observed counterclockwise P–T evolution at a high geothermal gradient (dT/dP = 100–200°C/kbar) suggests that UHT metamorphic assemblages were formed in an overall extensional tectonic setting accompanied by underplating of mantle-derived mafic magmas, which may be sourced from ~1750 Ma giant radiating dike swarms linked to the Vilyuy mantle plume as part of the Trans-Siberian LIP. The broad synchroneity of UHT metamorphism (1744 ± 26 Ma; monazite–zircon isochron age) and rift-related endogenic activity in the region can provide an additional line of evidence for the two-stage evolution of granulite-facies metamorphism in the Angara–Kan block. The Aldan–Stanovoy, Anabar, and Baikal basement inliers of high-grade metamorphic rocks within the Siberian craton record two Paleoproterozoic peaks (1.9 and 1.75 Ga) of granulite-facies metamorphism. The synchronous sequence of tectonothermal events at the periphery of the large Precambrian Laurentian, Baltica, and Siberian cratons provide convincing evidence for their spatial proximity over a wide time interval, which is consistent with the most recent paleomagnetic reconstructions of the Proterozoic supercontinent Nuna.