Compositional and metamorphic controls on tectonic erosion along a continental subduction-collision zone: Implications from mafic granulites in the northern Sulu orogen

Subduction erosion has been reported recently in continental subduction-collision zones, and the response of the upper plate remains enigmatic. The Dabie-Sulu oro-gen is considered to have formed by deep northward subduction of the Yangtze block (lower plate) beneath the North China block (upper plate). However, within the north-ern Sulu ultrahigh-pressure (UHP) belt, the Haiyangsuo complex has intriguingly been accepted as Neoarchean-Paleoproterozoic metamorphic basement from the North China block, implying subduction-erosion could have occurred. Here, we examined new petrographic, mineral chemical, and published geochronological data from the Haiyangsuo mafic granulites to decipher their multiphase metamorphic evolution. Pressure-temperature (P-T) estimates from pseudosection modeling and geothermo-barometry show two major metamorphic events: a medium-pressure granulite-facies event (7.3-8.3 kbar and 830-895 degrees C) and a later high-pressure granulite-facies event (12.2-16.6 kbar and 800-875 degrees C). Geo-chronology and mineral geochemistry link these events to Paleoproterozoic and Trias-sic metamorphism, respectively. Peak Tri-assic high-pressure granulite-facies meta-morphism was followed by near-isothermal decompression and then near-isobaric cool-ing. These rocks derive from the upper plate and were metamorphosed at the same time as UHP eclogites, but maximum pressures were substantially lower, and P-T paths did not converge until late-stage exhumation. Evidently, metamorphic basement from the North China block was dragged to lower -crustal to upper-mantle depths (50-60 km) while that from the Yangtze block was sub -ducted deeply, and then they were tectoni-cally juxtaposed during exhumation. These data corroborate thermal-mechanical mod-els that predict tectonic erosion as a major process during continental subduction and collision.