The Dulan ultrahigh-pressure (UHP) rocks of the North Qaidam terrane in Western China represent continental crust that has been subducted ~100 km. High-pressure (HP) granulites, representing rocks buried ~50 km, are found adjacent to these UHP rocks. The two units are presumed to be in fault contact, however, the contact has yet to be mapped.

A Ky-bearing mafic granulite sample yields a U-Pb zircon mean age of 449 ± 3 Ma. A Grt-Cpx thermometer and GASP and GADS barometers yield 750-850 ˚C, 13-16 kbar. Average P-T calculations using the program Thermocalc yield ~770 ˚C, ~16 kbar. Ti-in-zircon analysis indicates temperatures 670-760 ˚C for zircon cores and rims. Zircon REE patterns show a weak negative Eu anomaly, indicating growth in the presence of plagioclase. There is no apparent HREE depletion despite the ~30% modal abundance of Grt in the sample.

A Ky-bearing intermediate granulite sample yields a U-Pb zircon mean age of 418 ± 2 Ma. A Grt-Cpx thermometer and GASP and GADS barometers yield 800-875 ˚C, 14-16 kbar. Average P-T calculations using the program Thermocalc yield ~750 ˚C, 15 kbar. Ti-in-zircon analysis indicates temperatures 760-820 ˚C for zircon cores, with an increase in temperature to 870-940 ˚C for zircon rims. Despite this apparent increase in temperature, both cores and rims have identical REE patterns and indistinguishable ages. Zircon REE patterns show depleted HREE trends, indicating growth in the presence of garnet. There is no apparent Eu anomaly despite the 5-10 % modal abundance of Pl in the sample.

The ages for these two granulites indicate HP-granulite conditions occurred at the same time as UHP conditions: 459 – 422 Ma (UHP), 450 – 418 Ma (HP-granulite). This overlap indicates the HP-granulites are a separate unit and do not represent overprinted UHP rocks. Trace element patterns and Ti-in-zircon thermometry indicate the increase in temperature at 418 Ma occurred within the HP granulite facies, meaning juxtaposition with the UHP rocks had not yet occurred by this point. An amphibolite overprint seen in both the HP-granulites and UHP rocks suggests the two units came together at lower crustal levels after ~418 Ma.