The role of Indian and Tibetan lithosphere in spatial distribution of Cenozoic magmatism and porphyry Cu–Mo deposits in the Gangdese belt, southern Tibet
The role of Indian and Tibetan lithosphere in spatial distribution of Cenozoic magmatism and porphyry Cu–Mo deposits in the Gangdese belt, southern Tibet
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DOI：
10.1016/j.earscirev.2015.07.003
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发表时间：
2015-11
影响因子：
12.1
通讯作者：
Rui Wang;J. Richards;Zhou Limin;Z. Hou;R. Stern;R. Creaser;Jing-Jing Zhu-Jing
中科院分区：
文献类型：
--
作者：
Rui Wang;J. Richards;Zhou Limin;Z. Hou;R. Stern;R. Creaser;Jing-Jing Zhu-Jing
冈底斯岩浆岩带长1600 km，具有广泛的古新世-始新世I型侵入岩和同时代火山岩序列，丰富但局部化程度较高的渐新世-中新世钙碱性-碱性侵入岩和中新世钾质-超钾质火山岩。这些新生代火成岩记录了与55-50 Ma开始的印度-亚洲碰撞有关的地球动力学变化。新的和已发表的岩石地球化学和多种同位素对新生代岩浆岩的Os-Sr-Nd-O-Hf分析表明，古新世-始新世岩浆与大陆弧岩的成分相似，但中新世晚期岩浆在地球化学和同位素组成上具有明显的纵向差异，与斑岩型矿化的产出有关，中新世稀疏的高钾钙钛矿，冈底斯带东部碱性-钾玄质火山岩具有低-中等的（87 Sr/86 Sr）比值（0.7057-0.7121），ε Ndi值为中等负值（− 9.4至− 3.4），低（187 Os/188 Os）变形虫（0.154-0.210），高度可变的ε Hf值锆石δ 18 O值较低（+5.0-+6.7 ‰），反映了俯冲改造后的西藏次大陆岩石圈地幔（SCLM）部分熔融的产物。冈底斯带西部中新世高钾钙碱性-钾玄质火山岩具有较高的（87 Sr/86 Sr）比值（0.7069-0.7263），ε Ndi值更负（− 17.5至− 6.0）和ε Hf值（-15.2 ~+ 0.7），壳状锆石δ 18 O值（+ 6.2 ~+ 8.8‰），而幔状（187 Os/188 Os）i值（0.156-0.182），Ni、Cr含量高。这些特征表明，冈底斯带西部的钾质-超钾质岩浆也来自西藏SCLM的部分熔融，但有约3-25%的熔体±流体来自俯冲的印度板块（87 Sr/86 Sr = 0.74-0.76，εNd = − 18至− 10，δ 18 O = + 10 − + 14‰）。冈底斯带东部（东经189 °）与大型斑岩型铜钼矿床有关的渐新世-中新世钙碱性-高钾钙碱性花岗岩类，其地球化学特征与古新世-始新世早期岩石相似。它们被认为是俯冲改造的下地壳部分熔融与SCLM部分熔融的碱性熔体混合而成的，（87 Sr/86 Sr）比值（0.7047-0.7076），高ε Nd 2值ε Hf值（1.4-8.7），中等（187 Os/188 Os）比值（0.224-0.835），锆石δ 18 OVSMOW值（+ 5.5-+ 6.6‰）较低。这些岩浆还具有高含水量（Dy/Yb弱富集，具有角闪石分馏特征）和高氧化态（Δ FMQ0.8 -2.9），这说明它们与斑岩型铜钼成矿作用有独特的联系。冈底斯带西部中新世高钾钙碱性-钾玄质花岗岩类（东经189 °以西）与古新世-始新世早期岩浆活动在地球化学和同位素组成上存在差异，并以类壳锆石δ 18 O值为特征（+6.2-+8.8 ‰），高（87 Sr/86 Sr）i值（0.7147-0.7165），负ε Nd值（− 11.3-− 7.9），壳状（187 Os/188 Os）i值（0.550-1.035），低ε Hf值（− 13.0 - 3.9）。这些岩浆被解释为反映了来自俯冲印度板块的熔体±流体的参与以及侵位时的高度地壳污染。只有一个小型斑岩型铜钼存款与西部花岗岩类有关，我们认为这种差异反映了印度板块大陆岩石圈在青藏高原造山带的不同程度的下冲作用。
The 1600 km-long Gangdese magmatic belt features extensive Paleocene–Eocene I-type intrusive rocks and coeval volcanic successions, abundant but more localized Oligo-Miocene calc-alkaline to alkaline plutons, and Miocene potassic to ultrapotassic volcanic rocks. These Cenozoic igneous rocks record geodynamic changes related to the India–Asia collision which began at ~ 55–50 Ma. New and published lithogeochemical and multiple isotopic (Os–Sr–Nd–O–Hf) analyses of these Cenozoic igneous rocks reveal that the Paleocene–Eocene magmas have similar compositions to continental arc rocks throughout the belt, but later Miocene magmas show sharp longitudinal contrasts in geochemical and isotopic compositions, which are also correlated with the occurrence of porphyry-type mineralization.Sparse Miocene high-K calc-alkaline to shoshonitic volcanic rocks in the eastern Gangdese belt have low to moderate (87Sr/86Sr)iratios (0.7057–0.7121), moderately negative εNdivalues (− 9.4 to − 3.4), low (187Os/188Os)iratios (0.154–0.210), highly variable εHfivalues (− 5.9 to + 10.1), and low zircon δ18O values (+ 5.0–+ 6.7‰), which are interpreted to reflect derivation by partial melting of subduction-modified Tibetan sub-continental lithospheric mantle (SCLM). In contrast, Miocene high-K calc-alkaline to shoshonitic volcanic rocks in the western Gangdese belt have higher (87Sr/86Sr)iratios (0.7069–0.7263), more negative εNdivalues (− 17.5 to − 6.0) and εHfivalues (− 15.2 to + 0.7), and crust-like zircon δ18O values (+ 6.2–+ 8.8‰), but mantle-like (187Os/188Os)ivalues (0.156–0.182), and high Ni and Cr contents. These features suggest that potassic to ultrapotassic magmas in the western Gangdese belt were also derived from partial melting of Tibetan SCLM but with ~ 3–25% input of melts ± fluids from the underthrust Indian plate (87Sr/86Sr = 0.74–0.76, εNd = − 18 to − 10, δ18O = + 10 − + 14‰). In contrast, Miocene alkaline magmas to the east were unaffected by this source.Oligo-Miocene calc-alkaline to high-K calc-alkaline granitoids related to large porphyry Cu–Mo deposits in the eastern Gangdese belt (east of ∼ 89° E) are geochemically broadly similar to the early Paleocene–Eocene rocks. They are thought to be derived from partial melting of subduction-modified lower crust with mixing of alkaline melts from partial melting of SCLM, and have relatively low (87Sr/86Sr)iratios (0.7047–0.7076), high εNdivalues (− 6.1 to + 5.5) and εHfivalues (1.4–8.7), moderate (187Os/188Os)iratios (0.224–0.835), and low zircon δ18OVSMOWvalues (+ 5.5–+ 6.6‰). These magmas also had high water contents (weak Dy/Yb enrichment, characterized with amphibole fractionation) and oxidation states (ΔFMQ 0.8–2.9), which explain their unique association with porphyry Cu–Mo mineralization. In contrast, Miocene high-K calc-alkaline to shoshonitic granitoids in the western Gangdese belt (west of ∼ 89° E) show differences in geochemical and isotopic compositions to the earlier Paleocene–Eocene magmatism, and are characterized by crust-like zircon δ18O values (+ 6.2–+ 8.8‰), high (87Sr/86Sr)iratios (0.7147–0.7165), negative εNdivalues (− 11.3 to − 7.9), crust-like (187Os/188Os)ivalues (0.550–1.035), and low εHfivalues (− 13.0 to 3.9). These magmas are interpreted to reflect involvement of melts ± fluids from the underthrust Indian plate and high degrees of crustal contamination upon emplacement. Only one small porphyry Cu–Mo deposit is known to be associated with these western granitoids.We suggest that this difference reflects the variable extent of underthrusting of the Indian plate continental lithosphere beneath Tibet in the Oligo …