| Petrological, geochemical and chronological constraints for the tectonic setting of the Dongco ophiolite in Tibet |
| |
| 作者姓名： | BAO PeiSheng XIAO XuChang SU Li & WANG Jun Institute of Geology Chinese Academy of Geological Sciences Beijing China Experimental Center China University of Geology Beijing China |
| |
| 作者单位： | BAO PeiSheng1，XIAO XuChang1，SU Li2 & WANG Jun1 1 Institute of Geology，Chinese Academy of Geological Sciences，Beijing 100037，China; 2 Experimental Center，China University of Geology，Beijing 100029，China |
| |
| 基金项目： | Supported by China Geological Survey of Ministry of Land and Resources (Grant No. 200313000059)，Department of International-Cooperation of Ministry of Land and Resources (Grant No. 2001010205) |
| |
| 摘 要： | The Dongco ophiolite occurred in the middle-western segment of the Bangong-Nujiang suture zone. The thickness of the ophiolite suite is more than 5 km, which is composed, from bottom to top, of the mantle peridotite, mafic-ultramafic cumulates, basic sills (dykes) and basic lava and tectoni- cally emplaced in Jurassic strata (Mugagongru Group). The Dongco cumulates consist of dunite- troctolite-olivine-gabbro, being a part of DTG series of mafic-ultramafic cumulates. The basic lavas are characterized by being rich in alkali (Na2O K2O), TiO2, P2O5 and a LREE-rich type pattern dip- ping right with La/Yb]=6.94―16.6 as well as a trace elements spider-diagram with normal anomaly of Th, Nb, Ta, Hf. Therefore, the Dongco basic lavas belong to ocean-island basalt (OIB) and dis- tinctly differ from mid-ocean ridge basalt (MORB) and island-arc basalt (IAB) formed in the plate convergence margin. The basic lavas have higher 87Sr/86Sr (0.704363―0.705007), lower 143Nd/144Nd (0.512708―0.512887) and εNd(t ) from 2.7― 5.8, indicating that they derive from a two-components mixing mantle source of depleted mantle (DM) and enriched mantle (EMI). From above it is ready to see that the Dongco ophiolite forms in oceanic island (OIB) where the mantle source is replaced by a large amount of enriched material, therefore it distinctly differs from these ophiolites formed in island-arc and mid-oecan ridge. Newly obtained SHRIMP U-Pb dating for zircon of the cumulate troctolite is 132 ± 3 Ma and whole-rock dating of ~(39)Ar/~(40)Ar for the basalt is 173.4 ± 2.7 Ma and 140.9 ± 2.8 Ma, indicating that the Dongco ophiolite formed at Early Cretaceous and the middle-western segment of the Bangong-Nujiang oceanic basin was still in the developing and evolving period at Early Cretaceous.
|
| 收稿时间： | 19 September 2006 |
| 修稿时间： | 4 December 2006 |
Petrological,geochemical and chronological constraints for the tectonic setting of the Dongco ophiolite in Tibet |
| |
| BAO PeiSheng,XIAO XuChang,SU Li & WANG Jun Institute of Geology,Chinese Academy of Geological Sciences,Beijing ,China, Experimental Center,China University of Geology,Beijing ,China.Petrological, geochemical and chronological constraints for the tectonic setting of the Dongco ophiolite in Tibet[J].Science in China(Earth Sciences),2007,50(5):660-671. |
| |
| Authors: | Bao PeiSheng Xiao XuChang Su Li Wang Jun |
| |
| Institution: | 1. Institute of Geology, Chinese Academy of Geological Sciences, Beijing 100037, China
2. Experimental Center, China University of Geology, Beijing 100029, China |
| |
| Abstract: | The Dongco ophiolite occurred in the middle-western segment of the Bangong-Nujiang suture zone. The thickness of the ophiolite
suite is more than 5 km, which is composed, from bottom to top, of the mantle peridotite, mafic-ultramafic cumulates, basic
sills (dykes) and basic lava and tectonically emplaced in Jurassic strata (Mugagongru Group). The Dongco cumulates consist
of dunitetroctolite-olivine-gabbro, being a part of DTG series of mafic-ultramafic cumulates. The basic lavas are characterized
by being rich in alkali (Na2O+ K2O), TiO2, P2O5 and a LREE-rich type pattern dipping right with La/Yb]=6.94−16.6 as well as a trace elements spider-diagram with normal
anomaly of Th, Nb, Ta, Hf. Therefore, the Dongco basic lavas belong to ocean-island basalt (OIB) and distinctly differ from
mid-ocean ridge basalt (MORB) and island-arc basalt (IAB) formed in the plate convergence margin. The basic lavas have higher
87Sr/86Sr (0.704363–0.705007), lower 143Nd/144Nd (0.512708–0.512887) and ε
Nd(t) from +2.7−+5.8, indicating that they derive from a two-components mixing mantle source of depleted mantle (DM) and enriched
mantle (EMI). From above it is ready to see that the Dongco ophiolite forms in oceanic island (OIB) where the mantle source
is replaced by a large amount of enriched material, therefore it distinctly differs from these ophiolites formed in island-arc
and mid-oecan ridge. Newly obtained SHRIMP U-Pb dating for zircon of the cumulate troctolite is 132±3 Ma and whole-rock dating
of 39Ar/40Ar for the basalt is 173.4±2.7 Ma and 140.9±2.8 Ma, indicating that the Dongco ophiolite formed at Early Cretaceous and the
middle-western segment of the Bangong-Nujiang oceanic basin was still in the developing and evolving period at Early Cretaceous.
Supported by China Geological Survey of Ministry of Land and Resources (Grant No. 200313000059), Department of International-Cooperation
of Ministry of Land and Resources (Grant No. 2001010205) |
| |
| Keywords: | Dongco ophiolite geochemistry SHRIMP U-Pb dating for zircon whole-rock dating of 39Ar/40Ar Bangong-Nujiang suture zone |
| 本文献已被 CNKI 万方数据 SpringerLink 等数据库收录！ |
|
