| 甘孜—理塘蛇绿混杂岩带中三叠世洋岛型岩石组合的识别及其构造意义——来自岩石学、地球化学和年代学证据 |
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| 关键词:ocean island rock association geochemistry geochronology Garze–Litang ophiolite mélange belt ‘Three-River’ orogenic belt in Southwest China |
| 基金项目:中国地质调查局地质矿产评价项目(编号: 12120115041701) |
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| Identification of the Middle Triassic Ocean Island Rock Association in the Garze–Litang Ophiolite Mélange Zone and Its Tectonic Significance:Constraints from Petrology, Geochemistry and Geochronology |
| The Garze–Litang ophiolite mélange zone is an important part of the ‘Three-River’ archipelagic arc basin system in Southwest China, and is also an important boundary between the regional Yidun island arc belt and Yangtze plate. The oceanic island rock assemblage in the study area is mainly composed of crystal ignimbrite and micrite, with a small amount of siliceous rocks and basalt in the local part, and the terminal elements are in contact with each other. Detailed rock geochemical studies of the basic volcanic rocks show that SiO2 content is 47.16%~54.30%, TiO2 content is 2.76%~5.66%, MgO content is 5.29%~6.65%, K2O content is 0.82%~3.66% and Na2O content is 2.52%~3.66%, suggesting alkaline basalt series. Geochemical analysis reveals that the features of basalt in the REE patterns and spider diagrams are similar to features of typical OIB, with REE values being (195.21×10–6~341.81×10–6) and REE being [(La/Yb)N=11.75~13.62], no obvious europium anomaly, and significant enrichment of large-ion lithophile elements (Rb, Ba, Th and K) as well as high strength field elements (Nb, Ta, Zr and Hf). The identification of trace elements in basic volcanic rocks indicates that they were formed in the oceanic island tectonic environment, and studies of the genesis of the rocks show that they originated from the mantle source region and did not suffer obvious contamination of continental crust materials. The zircon U-Pb age of the crystal ignimbrite is (245.1±1.5) Ma, indicating that the formation of the oceanic island basic volcanic rock took place in the early middle Triassic. The discovery of the ocean island rock association in the study area has enriched the research content of the Garze–Litang ophiolite mélange belt and provided direct material evidence for the tectonic evolution of the Garze–Litang mid-Triassic period. |
| YAN Song-tao,DUAN Yang-hai,TAN Chang-hai,WEN Lang.2019.Identification of the Middle Triassic Ocean Island Rock Association in the Garze–Litang Ophiolite Mélange Zone and Its Tectonic Significance:Constraints from Petrology, Geochemistry and Geochronology[J].Acta Geoscientica Sinica,40(6):816-826. |
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