投稿时间：2012-04-20
修订日期：2012-06-10
中文摘要:火山岩浆弧和大陆碰撞带是产出巨型斑岩矿床的两类重要环境。岩浆弧环境的斑岩铜矿成矿理论业已建立,而大陆碰撞环境的斑岩矿床则研究薄弱。在青藏高原,印度-亚洲大陆碰撞导致了大规模斑岩成矿作用,在主碰撞期(65~41 Ma)发育沙让式斑岩Mo矿和亚贵拉式斑岩-矽卡岩型Pb-Zn-Mo矿床,在晚碰撞期(40~26 Ma)形成明则式斑岩Mo矿和努日式斑岩-矽卡岩型Mo-W-Cu矿床,在后碰撞期(25~13 Ma)产生驱龙式斑岩Cu-Mo矿床。这些矿床构成了3条规模不等的成矿带,分别发育在冈底斯的北带(中拉萨地体)、南带(泽当弧地体)和中带(南拉萨地体)。冈底斯含矿斑岩系统通常为多期多相浅成侵入杂岩体。含矿斑岩以高K为特征,多为高K钙碱性岩和钾玄岩系列。含Cu斑岩以二长花岗斑岩为主,显示埃达克岩地球化学亲和性,含Mo斑岩以花岗斑岩为主,显示大陆壳成因特点。微量元素和Sr-Nd-Hf同位素地球化学研究表明,含Cu斑岩来自碰撞加厚的西藏镁铁质的新生下地壳(如角闪榴辉岩),早期卷入新生下地壳的幔源物质及硫化物的重熔为斑岩岩浆提供了部分金属Cu、Au和S;含Mo岩浆来自古老的西藏镁铁质下地壳(如角闪岩)的部分熔融,金属Mo主要来自古老地壳物质的贡献。冈底斯含矿斑岩均含有不同成分的微粒镁铁质包体(MME),并显示典型的长英质与镁铁质岩浆混合特征。以MME为代表的含Cu富H2O幔源岩浆,或底侵于冈底斯地壳底部,为下地壳熔融提供了热和H2O,或注入长英质岩浆房,为斑岩系统提供了部分金属Cu和S,并提升了岩浆氧逸度。冈底斯斑岩岩浆-热液-成矿系统受控于斑岩就位的地壳环境。在斑岩体侵位的花岗岩基环境,其良好的封闭性导致热液流体(岩浆出溶)以斑岩岩株为核心向外扩散,形成环状蚀变分带,并主要在钾硅酸盐化带发生Cu-Mo矿化;在碎屑岩-碳酸盐建造环境,碳酸盐建造发生矽卡岩化和金属淀积,不透水的细碎屑岩层阻挡热液流体扩散,热液矿化围绕斑岩体发育,形成斑岩型Mo-矽卡岩型Pb-Zn-Mo或Mo-W-Cu成矿系统;在层火山-沉积环境,良好的封闭盖层导致岩浆流体与天水强烈混合以及混合流体的长距离侧向流动,发育大面积蚀变岩盖,形成上部浅成低温热液Au-Cu和下部斑岩型Cu-Mo成矿系统。结合区域构造-岩浆分析,笔者认为,发育于冈底斯碰撞带3个不同碰撞期的幔源岩浆上侵-下地壳部分熔融-岩浆浅成侵位-斑岩成矿系统,受控于印度-亚洲大陆三阶段碰撞的不同深部过程,据此提出了大陆碰撞过程中斑岩型矿床的地球动力学模型。
Abstract:Giant porphyry deposits are generally found in magmatic arcs and continent collisional belt. Metallogenic theory of the porphyry copper deposit under the magmatic arc condition has been well established, while that in the continental collision setting has not been formed. A large number of porphyry deposits were formed in Tibetan plateau as the result of collision between the India and the Lhasa plates. Three different porphyry deposit belts have been found in the Lhasa terrene. The Sharang-type porphyry Mo deposit and the Yaguila-type porphyry-skarn Pb-Zn-Cu deposit distributed along the north margin of the Gangdese belt (the central Lhasa terrane) were formed in the main-collisional period (65~41 Ma). The Mingze-type porphyry Mo deposit and the Nuri-type porphyry-skarn Cu-Wu-Mo deposit in the central part of the Gangdese belt (southern Lhasa terrane) were formed in late-collisional period (40~26 Ma), whereas the Qulong-type porphyry Cu-Mo deposits developed in the Zedong arc belt was formed in the post-collisional period (25~13 Ma). The fertile Gangdese porphyry systems are generally composed of multistage hypergenic intrusive complexes. These complexes are generally characterized by high-K, and most of them are K calc-alkali and shoshonitic in composition. The Cu-bearing porphyries are dominated by monzogranite, and generally show geochemical affinity to adakites, while the Mo-bearing porphyry deposits are mainly associated with granite, which was most likely derived from continental crust. Whole-rock geochemistry and Sr-Nd-Hf isotopic data indicate that the Cu-bearing magmas were most probably derived from the thickened juvenile mafic lower-crust beneath south Tibet. The melting of sulfide-bearing phases in the juvenile mantle components of the Tibetan lower-crust probably provided parts of Cu, Au and S for the fertile magmas. However, the Mo-bearing magmas were likely derived from partial melting of the ancient Tibetan lower crust, while Mo was also mainly derived from the ancient crust. Large amounts of micro-mafic enclaves (MME) with varied components have been found in the porphyry magmas. These MMEs, which were derived from the enriched lithosphere mantle, probably represent the addition of the remnants of a mafic component to the host magma. These Cu and H2O-enriched mantle-derived magmas experienced underplating at the base of the Gangdese crust, supplied heat and H2O to inducing partial melting of the thickened lower-crust, and were partly injected into the lower-crust-derived felsic melts, probably providing heat and some fluids rich in H2O, metals and S and playing an important role in generating the hydrous, high f(O2), fertile porphyry magmas. The Gangdese porphyritic hydrothermal systems were commonly controlled by the settings of the crust where they intruded. In the granitoid batholiths setting, the impermeable wall rocks would result in the spreading of the hydrothermal fluid around the porphyry stocks core, which would form the concentric-circle alteration zones and generate Cu-Mo mineralization in the potassium-silicate alteration zone. In the clastic-limestone setting, carbonate was likely to be altered by skarn and then induced the precipitation of metals, while impermeable fine-grained clastic rocks would prohibit the penetration of the hydrothermal fluids, and thus porphyry Mo and skarn Pb-Zn-Mo or Mo-W-Cu ore-bodies were commonly developed around the porphyry bodies. In the bedding volcano-sediment setting, the impermeable overlying strata probably led to lateral migration of the hydrothermal fluids for a long distance and intense mixing with meteotic water. These processes could develop widespread hydrothermal alteration zones and finally resulted in the development of epithermal Au-Cu and porphyry Cu-Mo deposits at the shallow and deep level, respectively. Combined with the regional tectonic-magmatic evolution, the authors have concluded that the three stages of mantle-derived magamas underplating―partial melting of lower-crust―hypergenic emplacement of magama―porphyritic minerlization system might have been controlled by various deep processes in the three periods of India-Eurasia continental collision. Various geodynamic models have been established by the authors for the three types of porphyry deposits within the continental collision setting.
keywords:geology porphyry deposit wall-rocks formation deep lithospheric process metallogeny continental collisional orogeny Tibetan plateau
文章编号：
中图分类号：P611
文献标志码：
基金项目:本研究得到国家重点基础研究发展计划(973计划)项目(编号: 2011CB4031006);国家自然科学基金重点项目(编号: 238925,40425014)和地质调查项目(编号: 1212011121255)联合资助
引用文本：
侯增谦,郑远川,杨志明,杨竹森.2012.大陆碰撞成矿作用:I.冈底斯新生代斑岩成矿系统[J].矿床地质,31(4):647~670HOU ZengQian,ZHENG YuanChuan,YANG ZhiMing,YANG ZhuSen.2012.Metallogenesis of continental collision setting: Part Ⅰ. Gangdese Cenozoic porphyry Cu-Mo systems in Tibet[J].Mineral Deposits31(4):647~670
图/表
