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引用本文:侯增谦1 钟大赉2 邓万明2. 青藏高原东缘斑岩铜钼金成矿带的构造模式[J]. 中国地质, 2004, 31(1): 1-14.
HOU Zeng-qian1, ZHONG Da-lai2, DENG Wan-ming2. A tectonic model for porphyry copper-molybdenum-gold metallogenic belts on the eastern margin of the Qinghai-Tibet Plateau[J]. Geology in China, 2004, 31(1): 1-14(in Chinese with English abstract).
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青藏高原东缘斑岩铜钼金成矿带的构造模式
侯增谦1 钟大赉2 邓万明21,2
1.中国地质科学院矿产资源研究所, 北京 100037;2.中国科学院地质与地球物理研究所,北京 100029
摘要:
提要:在印度—亚洲大陆碰撞形成的青藏高原东缘, 伴随着高钾富碱斑岩的浅成侵位, 发育 “成对”出现的、受大规模走滑断裂控制的新生代陆内斑岩铜钼金成矿带, 其中西带为江达—芒康—祥云铜钼金成矿带, 东带为中甸—盐源—姚安斑岩铜金铅银成矿带。含矿斑岩岩石类型为花岗斑岩、二长花岗斑岩、二长斑岩和少量正长斑岩, 以较高的SiO2(>63%)和较低的Y(<20×10-6)区别于非含矿斑岩, 并具有似埃达克岩(adakite-like)岩浆亲合性。富碱斑岩相对富集LILE (K、Rb、Ba) 、亏损HFSE (Nb、Ta、Ti、P), Nb/Y比值具有较大的变化范围, REE分馏强烈但不出现明显的负Eu异常, 反映岩浆源区曾经历过古俯冲洋壳板片流体的交代富集作用和软流圈小股熔融体的注入。含矿的似埃达克斑岩可能源于玄武质下地壳, 后者经历高压(>40 km)下角闪岩-榴辉岩相变质和板片流体交代, 并作为下地壳角闪岩包体在富碱斑岩中出现;不含矿的正长斑岩可能起源于含水的金云母橄榄岩富集地幔。微量元素和Sr-Nd-Pb同位素系统反映, 该源区遭受了更强烈的板片流体交代和软流圈物质混染。深部地球物理探测资料表明, 50 Ma以来的扬子大陆板片向西俯冲, 并与印度大陆俯冲板片对挤, 诱发了软流圈上涌热蚀及其熔融体的底侵注入, 引起了壳幔过渡带的部分熔融。似埃达克斑岩岩浆以相对富水、富S和高氧逸度(fo2)特征, 成为成矿金属和硫的重要载体, 并在浅位封闭系统形成斑岩铜钼金矿床。
关键词:  斑岩矿床  铜钼金成矿带  构造模式  青藏高原东缘
DOI:
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基金项目:国家重点基础研究发展规划“973”项目(2002CB412600)资助。
A tectonic model for porphyry copper-molybdenum-gold metallogenic belts on the eastern margin of the Qinghai-Tibet Plateau
HOU Zeng-qian1, ZHONG Da-lai2, DENG Wan-ming21,2
1. Institute of Mineral Resources,Chinese Academy of Geological Sciences, Beijing 100037, China;2. Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029, China
Abstract:
Abstract:Accompanied by hypabyssal emplacement of high-potassic alkali-rich porphyries, “paired” Cenozoic intracontinental porphyry copper-molybdenum-gold belts, controlled by large strike-slip faults, occurred on the eastern margin of the Qinghai-Tibet Plateau formed by India-Asia collision. Of the two metallogenic belts, the west belt is the Jomda-Markam-Xiangyun copper-molybdenum belt and the east belt is the Zhongdian-Yanyuan-Yao'an porphyry copper-gold-lead-silver belt. The rock types of ore-bearing porphyry include granite porphyry, monzogranite porphyry and monzonite porphyry with small amount of syenite porphyry. They are distinguished from barren porphyry by their higher SiO2 (>63%) and lower Y (<20×10-6) and their adakitic magma affinity. Alkali-rich porphyry is relatively enriched in large-ion lithophile elements (K, Rb and Ba) and depleted in high-field strength elements (Nb, Ta, Ti and P) with a wider range of Nb/Y ratios and shows strong REE fractionation but no pronounced negative Eu anomaly—all these suggest that the magma source region underwent metasomatism and concentration of ancient subducted oceanic slab fluids and was injected by small streams of melts from the asthenosphere. Ore-bearing adakite-like porphyry might originate from the basaltic lower crust. The latter underwent high-pressure (>40 km) low amphibolite-eclogite facies metamorphism and slab fluid metasomatism and occurs as lower-crustal amphibolite xenoliths in alkali-rich porphyry. Barren syenite porphyry might originate from the hydrated phologopite peridotite-enriched mantle. Its trace element and Su-Nd-Pb isotope systematics indicate that their source region was subjected to much stronger slab fluid metasomatism and mixing of asthenospheric material. Available data of deep geophysical exploration suggest that since 50 Ma BP the Yangtze continental slab was subducted westwards and collided with the subducted Indian continental slab, thus inducing upwelling, thermal erosion and underplating of asthenospheric melts and giving rise to partial melting of the crust-mantle transition zone. The magma of adakite-like porphyry is characterized by the presence of relatively rich water, rich sulfur and higher oxygen fugacity (fo2). It was an important metal and sulfur carrier and formed porphyry copper-gold-lead-silver deposits in a shallow-level closed system.
Key words:  porphyry deposit  Cu-Mo-Au metallogenic belt  tectonic model  eastern margin of the Qinghai-Tibet Plateau