Low-degree melting of a metasomatized lithospheric mantle for the origin of Cenozoic Yulong monzogranite-porphyry,east Tibet: Geochemical and Sr–Nd–Pb–Hf isotopic constraints |
| |
| Institution: | 1. State Key Laboratory of Isotope Geochemistry, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou 510640, China;2. CAS Center for Excellence in Tibetan Plateau Earth Sciences, Beijing 100101, China;3. University of Chinese Academy of Sciences, Beijing 100049, China;4. Chengdu Institute of Geology and Mineral Resources, Chengdu 610081, China;5. The University of Queensland, Brisbane QLD 4072, Australia;1. State Key Laboratory of Earthquake Dynamics, Institute of Geology, China Earthquake Administration, Beijing 100029, China;2. Key Laboratory of Deep-Earth Dynamics of Ministry of Natural Resources, Institute of Geology, Chinese Academy of Geological Sciences, Beijing 100037, China;3. Institute of Mineral Resources, Chinese Academy of Geological Sciences, Beijing, 100037, China;1. Institute of Geology, Chinese Academy of Geological Sciences, Beijing 100037, China;2. China University of Geosciences, Beijing 100083, China;3. State Key Laboratory of Continental Dynamics, Department of Geology, Northwest University, Xi''an 710069, China;4. Institute of Mineral Resources, Chinese Academy of Geological Sciences, Beijing 100037, China;1. State Key Laboratory of Isotope Geochemistry, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou 510640, China;2. College of Earth and Planetary Sciences, University of Chinese Academy of Sciences, Beijing 100049, China;3. CAS Center for Excellence in Tibetan Plateau Earth Sciences, Beijing 100101, China;4. Department of Geosciences, Fort Hays State University, Hays, KS 67601-4099, USA;5. Institute of Geology and Geophysics, Chinese Academy of Science, Beijing 100029, China;1. School of Earth Science and Mineral Resources, China University of Geosciences, Beijing 10083, China;2. Institute of Geology, Chinese Academy of Geological Sciences, Beijing 100037, China;3. State Key Laboratory of Geological Processes and Mineral Resources, China University of Geosciences, Beijing 100083, China |
| |
| Abstract: | SHRIMP zircon U–Pb dating, mineral chemical, element geochemical and Sr–Nd–Pb–Hf isotopic data have been determined for the Yulong monzogranite-porphyry in the eastern Tibet, China. The Yulong porphyry was emplaced into Triassic strata at about 39 Ma. The rocks are weakly peraluminous and show shoshonitic affinity, i.e., alkalis-rich, high K2O contents with high K2O / Na2O ratios, enrichment in LREE and LILE. They also show some affinities with the adakite, e.g., high SiO2 and Al2O3, and low MgO contents, depleted in Y and Yb, and enrichment in Sr with high Sr / Y and La / Yb ratios, and no Eu anomalies. The Yulong porphyry has radiogenic 87Sr / 86Sr (0.7063–0.7070) and unradiogenic 143Nd / 144Nd (εNd = ? 2.0 to ? 3.0) ratios. The Pb isotopic compositions of feldspar phenocrysts separated from the Yulong porphyry show a narrow range of 206Pb / 204Pb ratios (18.71–18.82) and unusually radiogenic 207Pb / 204Pb (15.65–15.67) and 208Pb / 204Pb (38.87–39.00) ratios. In situ Hf isotopic composition of zircons that have been SHRIMP U–Pb dated is characterized by clearly positive initial εHf values, ranging from + 3.1 to + 5.9, most between + 4 and + 5. Phenocryst clinopyroxene geothermometry of the Yulong porphyry indicates that the primary magmas had anomalously high temperature (> 1200 °C). The source depth for the Yulong porphyry is at least 100 km inferred by the metasomatic volatile phase (phlogopite–carbonate) relations. Detailed geochemical and Sr–Nd–Pb–Hf isotopic compositions not only rule out fractional crystallization or assimilation-fractional crystallization processes, but also deny the possibility of partial melting of subducted oceanic crust or basaltic lower crust. Instead, low degree (1–5%) partial melting of a metasomatized lithosphere (phlogopite–garnet clinopyroxenite) is compatible with the data. This example gives a case study that granite can be derived directly by partial melting of an enriched lithospheric mantle, which is important to understand the source and origin of diverse granites. |
| |
| Keywords: | |
| 本文献已被 ScienceDirect 等数据库收录！ |
|
