西藏错那洞穹窿同构造矽卡岩特征及相关铍钨锡稀有金属矿化的成矿时代

错那洞穹窿位于北喜马拉雅片麻岩穹窿带（NHGD）的东段，是近年来新发现的穹窿构造。穹窿由内向外依次由核部、滑脱系和盖层三部分组成，错那洞铍钨锡稀有金属矿化主要赋存在穹窿滑脱系的矽卡岩和矽卡岩化大理岩中，矿体产在含石榴子石十字石云母片岩中，与强烈变形的淡色花岗岩或伟晶岩密切相关，部分矽卡岩矿物呈定向排列，具强烈的剪切特征；淡色花岗岩与矽卡岩的接触关系部分呈渐变接触，部分呈突变关系，表明矽卡岩与该期岩浆关系密切，矽卡岩与淡色花岗岩属于同构造的产物。本次研究获得错那洞穹窿滑脱系含石榴子石十字石云母片岩中黑云母Ar-Ar坪年龄为（16.6±0.3）Ma，反等时线年龄为（16.7±0.3）Ma，该年龄代表第二期由南向北伸展构造变形时间，即藏南拆离系（STDS）在错那洞穹窿的活动时间；含白云母的矽卡岩化大理岩中白云母Ar-Ar坪年龄为（16.9±0.2）Ma，与含石榴子石十字石云母片岩中黑云母Ar-Ar年龄一致，代表同构造矽卡岩的形成时间，也是错那洞铍钨锡稀有金属矿床的成矿时间。错那洞铍钨锡稀有金属矿床形成于由藏南拆离系强烈活动引起的伸展减薄构造背景，减压熔融形成的岩浆沿着构造通道上涌侵位，并与围岩交代反应形成同构造矽卡岩及其中的富铍钨锡矽卡岩型矿体。

Syntectonic Skarn Characteristics and Mineralization Age of Associated Be-W-Sn Rare Metal Deposit in Cuonadong Dome,Southern Tibet,China

The newly discovered Cuonadong dome is located in the eastern part of the northern Himalayan gneiss domes (NHGD), which consists of three lithologic-tectonic units, i.e., core, detachment system,and cover rocks. Cuonadong super-large Be-W-Sn rare metals deposit is hosted by skarn and skarn marble in the middle of the dome. The skarn and/or skarnization marble are located in garnet-staurolite-bearing mica schist, and are closely related to the intensively deformed leucogranite and pegmatite, and some skarn minerals are in directional arrangement with strong shear characteristics (i.e. garnet, epidote and amphibole). The boundary between leucogranite and skarn is gradual or sharp, which suggests that both the skarn and the deformed leucogranite were resulted from the syntectonic magmatism.The Ar-Ar dating of biotite from the ore-hosting schist yields Ar-Ar plateau age of (16.6±0.3) Ma and inverse isochronal age of (16.7±0.3) Ma, which represent the age of D₂ top-to north extension deformation, and also represent the activity time of the southern Tibetan detachment system (STDS) of Cuonadong dome. The Ar-Ar dating of muscovite from skarn in Cuonadong dome yields Ar-Ar plateau age of (16.9±0.2) Ma, which is consistent with the Ar-Ar plateau age of (16.6±0.3) Ma in schist, and represent the formation age of the syntectonic skarns, which is interpreted as the mineralization age of Cuonadong Be-W-Sn rare metals deposit. Therefore, we suggest that Cuonadong Be-W-Sn rare metals deposit was resulted from the activity of the STDS, and the syntectonic magma intruded in the host rocks along the structural passage, further replaced the marble, which, in turn, resulted in the formation of the Be-W-Sn-bearing skarn ore bodies.