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New 40Ar/39Ar ages are presented from the giant Sulu ultrahigh-pressure (UHP) terrane and surrounding areas. Combined with U-Pb ages, Sm-Nd ages, Rb-Sr ages, inclusion relationships, and geological relationships, they help define the orogenic events before, during and after the Triassic collision between the Sino–Korean and Yangtze Cratons. In the Qinling microcontinent, tectonism occurred between 2.0 and 1.4 Ga. The UHP metamorphism occurred in the Yangtze Craton between 240 and 222 Ma; its thermal effect on the Qinling microcontinent was limited to partial resetting of K-feldspar 40Ar/39Ar ages. Subsequent unroofing at rates of 5–25 km Myr−1 brought the UHP terrane to crustal levels where it underwent a relatively short amphibolite facies metamorphism. The end of that metamorphism is marked by 40Ar/39Ar ages in the 219–210 Ma range, implying cooling at crustal depths at rates of 50–200 °C Myr−1. Ages in the 210–170 Ma range may reflect protracted cooling or partial resetting by Jurassic or Cretaceous magmatism. Jurassic 166–149 Ma plutonism was followed by cooling at rates of c. 15 °C Myr−1, suggesting relatively deep crustal conditions, whereas Cretaceous 129–118 Ma plutonism was succeeded by cooling at rates of c. 50 C Myr−1, suggesting relatively shallow crustal depths. [ABSTRACT FROM AUTHOR]

The western Tianshan high-pressure/low-temperature orogenic belt in NW China contains eclogite-facies metavolcanic rocks and omphacite-bearing blueschists. Previous Sm-Nd (omphacite, garnet, glaucophane, whole rock) and 40Ar‘39’r (crossite) dating of eclogite-facies rocks has suggested an age of ca. 345 Ma as the best approximation for the timing of peak metamorphic conditions. The samples described here are blueschist-facies rocks that formed during or after the transition from the eclogite-facies to the epidote-blueschist-facies and subsequently experienced an incipient greenschist-facies overprint. By use of white mica geochronology (K-Ar, ‘40’r‘39’r, Rb-Sr), an attempt is made to date postpeak metamorphic stages of the complex PT path. Rb-Sr and 40Ar/39Ar ages range between 313 and 302 Ma and 323 and 312 Ma, respectively, but mostly cluster at ca. 310–311 Ma, indicating that the studied samples recrystallized at this time. However, the 40Ar/39Ar age spectra show complex release patterns that are interpreted to be influenced by excess argon to varying degrees. This conclusion is further corroborated by K-Ar dates ranging between 385 and 309 Ma. Younger dates of ca. 302 Ma (Rb-Sr) and ca. 296 Ma (K-Ar) indicate subsequent disturbances of these isotope systems in some rocks. The new ages are significantly younger than the time of eclogite-facies metamorphism (350–345 Ma), indicating resetting of the‘40’r‘39’r, K-Ar, and Rb-Sr systems during exhumation of the blueschist-facies rocks. Furthermore, this dataset suggests that high-pressure conditions were attained during the Carboniferous and not at Permian or Triassic time, as recently suggested by SHRIMP U-Pb zircon dating. [ABSTRACT FROM AUTHOR]