| 阿尔金山北东东向构造带内枕状玄武岩的发现及其大地构造意义 |
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| 关键词:pillow basalts geochemistry N-MORB back-arc basin NEE-trending Altun Mountains Belt |
| 基金项目:国家专项“深部探测技术与实验研究”(编号: SinoProbe-08-04-1); 国家自然科学基金项目(编号: 41072071); 中国地质调查局地质调查项目(编号: 1212011220936; 12120114032401; 12120113095800) |
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| The Discovery of Pillow Basalts in the NEE-trending Altun Mountains Belt and Its Tectonic Implications |
| The Altun Mountains belt on the northern margin of the Tibetan Plateau plays a key role in the tectonic evolution and geomorphic formation of the Tibetan Plateau and western China. Pillow basalts were firstly recognized in the central segment of the NEE-trending Altun Mountains belt, which can furnish important clues to the interpretation of the structural evolution of the Altun Mountains belt and even the northern Tibetan Plateau. Pillow basalts are characterized by low SiO2, A12O3, P2O5 and (Na2O+K2O) values which suggest a transitional type between sub-alkaline basalt and andestie/basalt. There are two samples with relatively lower silicon and enriched iron and titanium (TFeO>12%, TiO2>2%, and TFeO/MgO＞1.75), which can be classified as Fe-Ti basalts. The chondrite-normalized REE patterns, trace element ratios and Ti/100-Zr-Y×3, Ti/100-Zr-Sr/2 and Zr/4-2×Nb-Y diagrams show N-MORB affinity. The Th/Nb-Ce/Nb diagram along with a slight enrichment of the Large Iron Lithosphile Elements and depletion of HFS elements Zr, Hf and Ti indicates a tectonic setting of back-arc basin. The coexistence of mafic-ultramafic rocks in surrounding areas implies that pillow basalts were derived from the N-MORB-like depleted mantle source in a spreading ridge of trench-distal back-arc basin. Further geochemical comparison shows that these basalts are significantly different from the basalts developed in the EW-trending Hongliugou-Lapeiquan belt in Northern Altun Mountains, indicating a different tectonic setting; nevertheless, these basalts are similar to basalts from the Early Paleozoic ophiolite belt in the North Qaidam Basin, suggesting that they were probably developed in similar Early Paleozoic back-arc basins. These newly-recognized pillow basalts in the central segment of the NEE-trending Altun Mountains belt are considered to be remnant parts of the ophiolite belt assembly in the North Qaidam Basin, resulting from the drag and destruction of the Altun Mountains strike-slip fault. |
| WU Yu,CHEN Zheng-le,CHEN Bai-lin,WANG Yong,SUN Yue,ZHANG Hao,MENG Ling-tong.2015.The Discovery of Pillow Basalts in the NEE-trending Altun Mountains Belt and Its Tectonic Implications[J].Acta Geoscientica Sinica,36(3):293-302. |
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