HP/UHP metamorphic time of eclogite in the Xitieshan terrane, North Qaidam UHPM belt, NW China.
柴北缘超高压带中锡铁山榴辉岩的变质时代

Xitieshan terrane is located in the middle part of the North Qaidam ultrahigh-pressure (UHP) metamorphic belt. It is one of the important terranes in the belt and consists of granitic and pelitic gneisses with lesser lensoid blocks of eclogite and serpentinized peridotite without garnet. Most eclogite blocks were retrograde to varying extent with symplectite and amphibolite overprinting. Although numbered zircon U-Pb geochronological data have been reported in recent years, time for HP-UHP eclogite-facies metamorphism remains debatable, and interpretations for the previous age data contradict against UHP metamorphic ages that have determined from the Yuka eclogite, Luliangshan garnet peridotite and coesite-bearing metapelite in Dulan. Using techniques of CL and SIMS analyses, combining studies on mineral inclusions in zircons, we obtained an eclogite-facies metamorphic age of 433±3Ma (weighted mean). This age is consistent with metamorphic ages of Yuka eclogites and should represent HP-UHP metamorphic time for continental subduction. This study plays important role in understanding metamorphic evolution and deep subduction of continental crust in the Xitieshan eclogite-bearing terrane.