东昆仑祁漫塔格早中生代大陆地壳增生过程中的岩浆活动与成矿作用

Magmatism and mineralization during Early Mesozoic continental accretion process in Qimantag, East Kunlun Mountains

东昆仑祁漫塔格地区位于青藏高原北缘,为典型的大陆边缘增生造山带,经历了漫长的古生代—早中生代增生造山过程,其中以早中生代岩浆活动与成矿作用最为发育。文章系统总结了区内早中生代侵入岩分布及成因,对与其相关矿床地质、成矿流体特征及成矿物质来源进行分析,进一步探讨了祁漫塔格地区早中生代大陆地壳增生过程中的壳幔混合岩浆活动与成矿作用的关联。研究结果认为,中二叠世—早三叠世以俯冲阶段的侧向增生为主,中-晚三叠世以碰撞-后碰撞阶段的垂向增生为主,与成矿有关的岩浆岩主要为中-晚三叠世石英闪长岩、花岗闪长岩、二长花岗岩、正长花岗岩、花岗斑岩等,以I型、A型花岗岩为主,且多见暗色包体,Sr-Nd-Hf同位素组成表明其源于古陆壳物质的重熔,有地幔物质的参与,由地幔底侵古老陆壳,幔源基性岩浆与壳源花岗质岩浆发生不同程度混合作用而形成。与该时期岩浆活动关系密切的主要为斑岩型铜钼矿床、矽卡岩型铁多金属矿床、层控矽卡岩型铅锌矿床、与碱性花岗岩有关稀有金属矿化等。成矿时代集中于248~210 Ma,成矿流体主要来源于岩浆热液,成矿物质具有壳幔混合来源,区内中-晚三叠世大陆垂向增生过程中的壳-幔岩浆混合作用为区域大规模金属成矿提供大量热能、成矿流体及成矿物质。

The Qimantag area in East Kunlun Mountains, which is located on the northern margin of the Tibetan Plateau, is a typical continental accretion orogenic belt. During the Paleozoic to Early Mesozoic accretionary orogenic process, there were active magmatism and mineralization. Through the research about distribution and petrogenesis of Early Mesozoic intrusive magmatic rocks as well as geological characteristics, ore-forming fluids, ore-forming materials of deposits related to Early Mesozoic intrusive magmatism, the authors investigated the close relationship between magma mixing and mineralization during the Early Mesozoic vertical accretion process. The accretion was lateral accretion in the Middle Permian to Early Triassic subduction stage, and was vertical accretion in the middle to late Triassic collision and post-collision stage. The Middle-Late Triassic quartz diorite, granodiorite, monzogranite, syenogranite and granite porphyry formed with vertical accretion were related to the iron-copper-lead-zinc polymetallic mineralization, mainly I- and A-type granites. The dark enclave and Sr-Nd-Hf isotopic compositions indicate a significant involvement of mantle components in petrogenesis. It is suggested that the middle-late Triassic intrusive rocks in Qimantag might have been formed by underplating, remelting of ancient crust and magma mixing in the Late Paleozoic to Early Mesozoic collision and post-collision stage. Main deposits related to Early Mesozoic magmatism include porphyry Cu-Mo deposits, skarn Fe-Cu-Pb-Zn polymetallic deposits, layered skarn Pb-Zn deposits and rare metal deposits related to alkaline granite. The metallogenic ages are from 248 Ma to 210 Ma, the ore-forming fluids were derived from magmatic hydrothermal activity, and the ore-forming materials came from both of the crust and the mantle. The magma mixing in Middle-Late Triassic period during the vertical accretion process provided large quantities of thermal energy, ore-forming fluids and ore-forming materials for large-scale polymetallic mineralization.