Zhao, Y (reprint author), CHINESE ACAD GEOL SCI,INST GEOL,BAIWANZHUANG RD,BEIJING 100037,PEOPLES R CHINA.
In this paper, we present Ar-40/Ar-39 hornblende, biotite, and K-feldspar and apatite fission track thermochronological data to constrain the cooling and exhumation of high-grade rocks of the Larsemann Hills, Antarctica, sychronous with and postdated regional intense orogenesis of the early Paleozoic. Combined with Pb-Pb, U-Pb, Sm-Nd and Ar-40/Ar-39 age data published, a Ar-40-Ar-39 plateau age of hornblende recorded cooling below c. 520 degrees C at 514 +/- 2 Ma at a rate of c. 40 degrees C/Ma. This rapid cooling can be attributed to the tectonically driven exhumation along the ductile shear zoons. By 514 Ma, c.10-15 km of exhumation kan achieved. Slowing of the cooling rate front c. 9 degrees C/Ma to c. 3 degrees C/Ma occurred during 500-490 Ma, when the geotherm dropped through the closure temperature for Ar-40/Ar-39 system iii biotite at c. 300 degrees C. Documented by an Ar-40/Ar-39 plateau age of K-feldspar. further drop of the geotherm below c. 160 degrees C took place around 455 Ma, by which erosionally controlled exhumation han become dominant, as suggested by the very slow cooling rate at c. 3-0. 3 degrees C/Ma. The final cooling through apatite partial annealing zone happened at c. 210 Ma and could correspond to an early per ion of aborted rifting in the Lambert Garben region.