Geochemistry,zircon UPb geochronology and LuHf isotopic composition of eclogites and their host gneisses in the Dulan area,North Qaidam UHP terrane: New evidence for deep continental subduction |
| |
Authors: | Shengyao Yu Jianxin Zhang Huaikun Li Kejun Hou CG Mattinson Jianghua Gong |
| |
Institution: | 1. Institute of Geology, Chinese Academy of Geological Sciences, 26 Baiwanzhuang, Beijing 100037, PR China;2. Tianjin Institute of Geology and Mineral Resources, CGS, 8th Road, Dazhigu, 300170 Tianjin, China;3. Institute of Mineral Resources, Chinese Academy of Geological Sciences, 26 Baiwanzhuang, Beijing 100037, China;4. Department of Geological Sciences, Central Washington University, 400 E. University Way, Ellensburg, WA 98926, USA |
| |
Abstract: | In this study, we link zircon U Pb SHRIMP and LA-ICP-MS geochronology and the Lu Hf isotopic composition of eclogites and their host gneisses/schists with whole-rock geochemistry of eclogites in the Dulan area to constrain their protoliths and metamorphic relationships. U Pb dating suggests that the protolith of one of the eclogites was a Neoproterozoic mafic intrusive rock (828 ± 58 Ma) and the protolith of enclosing orthogneiss was an early-Neoproterozoic granitoid (923 ± 12 Ma). Detrital zircons from Grt-bearing mica-schists yield ages of 0.9–2.5 Ga, with a dominant range of 1.0–1.8 Ga, indicating sedimentary sources from Neoproterozoic to Neoarchean crust and a depositional age ≤ 0.9 Ga. The matching metamorphic ages of eclogites (438 ± 5 Ma, 436 ± 4 Ma) and their country rocks (Grt-bearing mica-schists: 438 ± 4 Ma, 439 ± 8 Ma; orthogneiss: 427 ± 8 Ma) indicate that all studied samples experienced coeval Early Paleozoic HP/UHP metamorphism. The U Pb ages and Hf isotopic compositions of the inherited magmatic zircon cores of an eclogite sample (εHf (800) = 2.6–9.2, TDM1 = 1.0–1.3 Ga, TDM2 = 1.1–1.4 Ga) suggest that the protolith may be derived from Neoproterozoic depleted mantle with variable proportions of an older crustal component. The magmatic zircon cores of the orthogneiss (εHf (900) = ? 7.3 to ? 0.2; TDM2 = 1.8–2.1 Ga) suggest that the parental magma was derived from a Paleoproterozoic crustal source. Hf isotopic compositions of the detrital zircons from the metasediments (εHf(t) = ? 19.4 to + 10.6) suggest three crust formation and reworking events: (1) Archean (TDM2 = 2.7–2.9 Ga) juvenile crust reworked at ~ 2.5 Ga; (2) early Paleoproterozoic (TDM2 = 2.3–2.5 Ga) juvenile crust reworked at ~ 1.8 Ga; and (3) late Paleoproterozoic (TDM2 = 1.5–1.9 Ga) juvenile crust reworked in the Neoproterozoic.Whole-rock geochemical data suggest that the protoliths of the Dulan eclogites were probably derived from a continental rift or an incipient oceanic basin rather than a large, long-lived ocean basin. Thus, combined with field relationships, petrology, geochemistry, zircon U Pb dating and the Lu Hf isotopic analysis presented in this paper and reported from previous studies, we suggest that the Dulan eclogites and their country rocks experienced a common UHP metamorphism during Late Ordovician deep continental subduction. |
| |
Keywords: | |
本文献已被 ScienceDirect 等数据库收录! |
|