Document Type


Date of Degree Completion

Winter 2015

Degree Name

Master of Science (MS)


Geological Sciences

Committee Chair

Chris Mattinson

Second Committee Member

Audrey Huerta

Third Committee Member

Wendy Bohrson


Ultrahigh-pressure rocks of a Paleozoic continental suture zone are exposed in the southeastern North Qaidam terrane (Dulan region). Garnetite sample D119 contains minor Czo+Qtz+Chl+Ttn; rutile inclusions in titanite suggest that titanite replaced rutile during decompression. Pressure-temperature estimates of sample D119 are 16.1-18.4 kbar and 485-520 °C. Sample D130B is a mafic band in calc-silicate gneiss, with garnet porphyroblasts in a fine-grained Hbl-Cpx-Pl-Qtz symplectite that is interpreted as former omphacite. D130B symplectite pressure-temperature estimates are 7.7-9.4 kbar and 623-708 °C. Titanite U-Pb ages of 419.7±3.1 Ma and 415.9±4.2 Ma are interpreted to date retrogression of D119 and D130B, respectively. Average exhumation and cooling rates from ultrahigh-pressure to retrograde conditions are 6.4±6.0 mm/yr and 30±27 °C/Ma (D119) and 7.9±6.1 mm/yr and 3.9±8.0 °C/Ma (D130B). These data are compatible with early, rapid exhumation of a coherent block large enough to experience nearly-isothermal decompression in its insulated interior (D130B), while colder crust conductively refrigerates the block's margins (D119).