Article ID Journal Published Year Pages File Type
4730871 Journal of Asian Earth Sciences 2014 18 Pages PDF
Abstract
Understanding postmineralization tectonic movements in porphyry deposits, is critical to interpreting the complete thermal-tectonic history. This study reports new zircon U-Pb ages, hydrothermal biotite 39Ar/40Ar age, and zircon and apatite (U-Th)/He ages from the Baogutu porphyry copper deposit, which, in conjunction with pre-existing geochronology and thermochronology and inverse modeling simulations, constrain the thermal-tectonic history of the deposit. Zircon LA-ICP-MS U-Pb concordia ages indicate a Late Carboniferous age of 320.1 ± 2.2 Ma for the diorite complex and 309.8 ± 2.2 Ma for the mineralized granodiorite porphyry. Hydrothermal biotite selected from a quartz-biotite-chalcopyrite vein yields a plateau age of 311.0 ± 1.8 Ma which agrees with the age of the granodiorite porphyry and a previously reported molybdenite Re-Os age, and suggests that hydrothermal fluid circulated about 310 m.y. ago. Diorite and granodiorite porphyry yield weighted mean zircon (U-Th)/He ages of 200.6 ± 5.7 Ma and 241.1 ± 8.1 Ma, respectively, with ages ranging from 221.0 Ma to 174.3 Ma and 225.9 to 261.6 Ma. Weighted mean diorite and granodiorite porphyry apatite (U-Th)/He ages of 87.4 ± 2.3 Ma and 120.0 ± 4.2 Ma were obtained with ages ranging from 68.9 Ma to 100.8 Ma, and from 91.0 Ma to 152.0 Ma, respectively. The wide range of zircon (U-Th)/He ages may be due to the combined effects of U and Th zonation and radiation damage, and radiation damage effect may also account for the wide range of apatite (U-Th)/He ages. The combined effects of depth and cooling due to meteoric water circulation contribute to an older (U-Th)/He age for the granodiorite porphyry, relative to the diorite. A five-episode cooling rate history for the diorite can be deduced by inverse model simulation: fast cooling-moderate fast cooling-relatively slow cooling-fast cooling again-very slow cooling. The thermal and tectonic history of the wall rock indicates that it suffered significant far-field effects from the Qiangtang-Eurasia and Lhasa-Qiangtang collision, however, no visible thermal effect from the India-Asia collision is observed.
Related Topics
Physical Sciences and Engineering Earth and Planetary Sciences Geology
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