Stable isotope geochemistry of ultrahigh pressure metamorphic rocks from the Dabie–Sulu orogen in China: implications for geodynamics and fluid regime

Metamorphic chemical geodynamics in continental subduction zones

Zircon U-Pb and oxygen isotope evidence for a large-scale 18O depletion event in igneous rocks during the Neoproterozoic

The study of continental deep-subduction has been one of the forefront and core subjects to advance the plate tectonics theory in the twenty-first century. The Dabie-Sulu orogenic belt in China crops out the largest lithotectonic unit containing ultrahigh-pressure metamorphic rocks in the world. Much of our understanding of the world’s most enigmatic processes in continental deep-subduction zones has been deduced from various records in the Dabie-Sulu rocks. By taking these rocks as the natural laboratory, earth scientists have made seminal contributions to understanding of ultrahigh-pressure metamorphism and continental collision. This paper outlines twelve aspects of outstanding progress, including spatial distribution of the UHP metamorphic rocks, timing of the UHP metamorphism, timescale of the UHP metamorphism, the protolith nature of deeply subducted continental crust, subduction erosion and crustal detachment during continental collision, the possible depths of continental subduction, fluid activity in the continental deep-subduction zone, partial melting during continental collision, element mobility in continental deep-subduction zone, recycling of subducted continental crust, geodynamic mechanism of postcollisional magmatism, and lithospheric architecture of collision orogen. Some intriguing questions and directions are also proposed for future studies.

A perspective view on ultrahigh-pressure metamorphism and continental collision in the Dabie-Sulu orogenic belt

Tectonic implications from Re–Os dating of Mesozoic molybdenum deposits in the East Qinling–Dabie orogenic belt

The unusually low Ö180 values of -10.3 to -6.8%0 are found in mineral separates from an ec10gite pod (containing quartz-schist bands) in the Su-Lu terrane, East China. These are the lightest oxygen isotope compositions so far reported for metarnorphic rocks in the world. Oxygen isotope equilibrium has been approached among the minerals within both ec10gite and quartz-schist. This not only yields the concordant isotope temperatures of 655 to 765°C, but also indicates that the rocks have exchanged oxygen isotopes with a very 180-depleted fluid. A plausible interpretation for the anomalously low Ö180 values of the ec10gite pod is that it equilibrated isotopically with ancient meteoric water prior to ec1ogite-facies metamorphism and thus preserved the premetamorphic isotopic signature. The hydrothermally altered basaltic rocks kept this isotopic signature through all stages of progressive UHP metamorphism as weIl as subsequent exhumation and cooling. This provides insight into limited crust-mantle interactions under ultrahigh pressure metamorphic conditions in the suture zone of a continent-continent collision. Key-words: oxygen isotopes, water-rock interaction, isotope geothermometry, ec1ogite, UHP metamorphism, continental collision, Dabie Mountains.

Bing Gong

Papers

Extreme 18 O depletion in eclogite from the Su-Lu terrane in East China