| Summary: | 碩士 === 國立成功大學 === 地球科學系碩博士班 === 91 === The petrologic and geochronologic constraints of the basement rocks of Man Yuan basin, north Qilian suture belt, were studied with the EDS analyses and 40Ar /39 Ar thermochronology. The author took advantages of Molybdenum furnace (GD150) and continuous mode Laser probe (VG3600) on “pure’ minerals and found that the domain structure and diffusion parameters obtained from his biotite samples could be used to model a thermal history of back arc basin, Man Yuan basin. The basement rocks were collected from Pampo, Nanshihtougou, Daechingyen, and Dodatang in Man Yuan district. According to the geological map published by mainland China in 1965, these basement rocks Precambrian. Now we have argon isotopes ages of these basement rocks: Pampo area rock samples, there are two rock samples of bearing sillimanite-biotite gneiss: 399.0Ma and 398.0 Ma, were revealed by Laser probe and Ta furnace, respectively. Nanshihtou Gao area rock samples, there are two rock samples of bearing biotite-muscovite schist: 221.0Ma and 262.0 Ma, were revealed by Laser probe and Ta furnace, respectively. Daechingyen rock sample, there are two rock samples of bearing biotite-muscovite gneiss and one rock sample of bearing biotite-quartz schist: 410.0Ma, 409.0 Ma and 402.0 Ma, were revealed by Laser probe. Dodatang there is only one rock sample of bearing biotite-muscovite schist: 407.0 Ma, was revealed by Laser probe. There is a geochronologic implication about Man Yuan basin area, according to argon-argon dating method, that these basement rocks could be suffered at least once “continental reworking” in late Silurian to early Devonian and suffered another time “continental reworking” across P-T boundary. As well as a petrologic implication revealed that these basement rocks could be suffered at least once amphibolite facies of metamorphism of “continental reworking” in late Silurian to early Devonian and suffered another time green schist facies of metamorphism of “continental reworking” between Permian period and Triassic period. Finally, no region in the world offers such marvelous, amazing continental reactivation phenomenon as central Qilian deep fracture zone does.
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