Document Type
Thesis
Date of Degree Completion
Winter 2015
Degree Name
Master of Science (MS)
Department
Geological Sciences
Committee Chair
Chris Mattinson
Second Committee Member
Audrey Huerta
Third Committee Member
Wendy Bohrson
Abstract
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).
Recommended Citation
Fagin, Brittany Kristine, "Pressure-temperature-time constraints for exhumation of ultrahigh-pressure metamorphic rocks, North Qaidam terrane, Western China" (2015). All Master's Theses. 1803.
https://digitalcommons.cwu.edu/etd/1803