俯冲流体对中亚造山带镁铁-超镁铁质岩体的地幔源区性质和铜镍硫化物成矿作用的制约

Numerous Silurian to Triassic mafic-ultramafic intrusions occur along the central Asian orogenic belt and host Ni-Cu sulfide mineralization. All these intrusions are commonly depleted in PGE, Nb and Ta, and contain abundant hornblende and mica. Whether these petrologic and geochemical features are inherited from the mantle source matasomatized by subduction fluid or magma process in conduit is still under debate. The understanding of these features could be important to the genesis of these rocks and the mechanism of Ni-Cu sulfide mineralization. This study is going to carry on a comprehensive study of whole-rock B isotope, analysis of water content of clinopyroxene, and other geochemical analysis for representative sulfide-bearing and mafic-ultramafic intrusions in the central Asian orogenic belt, and is aimed to constrain the existence and source of subduction fluid the mantle source and calculate the water content of the parental magma. The results of this study may provide more constraints on the origin of the Ni-Cu minerallized mafic-ultramafic intrusions and find the connections between Ni-Cu sulfide mineralization with the mantle source and the water content of the parental magma. This study will discuss the influence of subduction fluid on the mantle source and metallogenic potential and will make contribution to the metallogenic theory of magmatic Ni-Cu sulfide deposits formed in in convergent margin.

中亚造山带分布着大量志留纪-三叠纪的镁铁-超镁铁质岩体并发育不同程度的铜镍硫化物矿化。这些岩体普遍富含角闪石和云母等含水矿物，并明显亏损PGE、Nb和Ta等元素。这些岩石学和元素地球化学特征是反映了俯冲板片流体对其地幔源区的交代？还是记录了岩浆的通道过程？这个问题的解决对于揭示相关岩石的成因和探究铜镍硫化物矿床的成矿机制均有重要启示。本项目拟对中亚造山带赋含铜镍硫化物矿化的代表性镁铁-超镁铁质岩体开展全岩硼同位素和单斜辉石水含量研究，利用全岩硼同位素组成限定含矿岩体地幔源区中俯冲流体的加入和来源，通过单斜辉石水含量的测定估算母岩浆的水含量，更进一步揭示俯冲流体对含矿岩体形成的制约，并探讨地幔源区俯冲流体的输入与母岩浆水含量和铜镍硫化物矿化之间的内在耦合关系。本项目研究的实施将阐述俯冲流体对镁铁-超镁铁质岩石源区性质及成矿潜力的制约，完善汇聚板块边缘铜镍硫化物矿床的成矿理论。

中亚造山带发育大量志留纪-三叠纪的镁铁-超镁铁质岩体，并赋存有不同程度的铜镍硫化物矿化。这些岩体具有Nb和Ta负异常，并发育角闪石和云母等含水矿物，普遍认为这些岩体的地幔存在交代作用，但交代物质的性质没有得到有效约束，也认为这些岩体的母岩浆富水，但缺乏测试和定量计算。.本项目开展了全岩主微量元素和Sr-Nd-B同位素分析，电子探针分析，LA-ICP-MS矿物原位微量元素分析，微区XRF扫面分析，锆石U-Pb定年和Hf-O同位素分析，尤其是建立了对岩石薄片开展激光微区傅里叶变换红外光谱（FTIR）分析的方法（抽真空模式），并取得以下关键进展：.1，查明了中亚造山带额尔齐斯构造带二叠纪镁铁质岩体地幔源区以沉积物熔体交代为主，而非前人研究经常提及的流体交代；2，提出了中亚造山带额尔齐斯构造带的同碰撞伸展作用控制了含矿岩体的侵位，这种短暂的同碰撞伸展也决定了成矿期的短暂；这对于整个中亚造山带岩浆铜镍硫化物矿床的成矿构造背景研究都具有借鉴意义；3，计算了菁布拉克岩体和红旗岭2号岩体的母岩浆水含量。虽然菁布拉克岩体形成于俯冲期，但其母岩浆水含量远低于岛弧玄武岩，推断菁布拉克岩体的母岩浆并非形成于岛弧环境，而是弧后裂谷环境；4，地幔中沉积物熔体交代也可以造成母岩浆中水含量相对于MORB较高，但结晶分异作用对母岩浆富水可能起到更加关键的作用。.在项目资助下，已有1篇论文被《Geological Society of America Bulletin》接收，1篇论文投至《Ore Geology Reviews》，收到中改意见，1篇投至《Journal of Asian Earth Sciences》，待审稿意见返回，并培养博士研究生2名，硕士研究生1名。