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

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 degrees C. The retrograde amphibolite facies assemblage suggests conditions of 10-12 kbar and 460-600 degrees 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. (c) 2006 Elsevier B.V. All rights reserved.