Eclogites from central Qiangtang, northern Tibet (China) and tectonic implications

Abstract

Eclogites in central Qiangtang, northern Tibet (China) are characterized by the garnet+omphacite+rutile+phengite+quartz assemblage. Hornblende, plagioclase, and sphene occur as retrograde amphibolite facies phases in the eclogites. Pressure–temperature estimates for the primary eclogite assemblage are consistent with minimum pressures of 20–25 kbar at 482 to 625 °C. The retrograde amphibolite facies assemblage suggests conditions of 10–12 kbar and 460–600 °C. Consequently, the eclogites from central Qiangtang have undergone unambiguous ultrahigh- pressure (UHP) metamorphism. The presence of UHP metamorphic rocks implies a likely deep-seated continental subduction along the Shuanghu suture within the Qiangtang terrain. The denudation of these UHP metamorphic rocks correlates well with the main interval that the Songpan–Ganzi turbidites accumulated and could have provided a significant source for these sedimentary rocks.