Porphyry Cu (–Mo–Au) deposits related to melting of thickened mafic lower crust: Examples from the eastern Tethyan metallogenic domain
Porphyry Cu (–Mo–Au) deposits related to melting of thickened mafic lower crust: Examples from the eastern Tethyan metallogenic domain
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DOI：
10.1016/j.oregeorev.2010.09.002
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发表时间：
2011-02
影响因子：
3.3
通讯作者：
Z. Hou;Hongrui Zhang;Xiaofei Pan;Zhi-Ming Yang
中科院分区：
文献类型：
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作者：
Z. Hou;Hongrui Zhang;Xiaofei Pan;Zhi-Ming Yang
世界上大多数斑岩铜矿产于岩浆弧环境，与大洋岩石圈俯冲作用有关的钙碱性弧岩浆有关。本文综述了东特提斯成矿域中一些重要的斑岩铜矿。它们广泛出现在各种非弧环境中，从碰撞后（晚期）的压扭和伸展环境到与造山和非造山过程有关的陆内伸展环境。它们的时空定位受控于走滑断层、造山带-横断正断层、线性构造及其在这些非弧环境中的交点。这些矿床以斑岩型铜-钼矿床为主，也有少量斑岩型铜-Au和浅成低温热液型Au矿床，与岩浆弧型矿床具有广泛的相似性。伴生岩浆普遍为含水、相对高fO 2、高钾钙碱性和钾玄质岩浆，与埃达克岩具有地球化学亲和力。它们与弧岩浆和/或大洋板片衍生埃达克岩的区别在于，它们以孤立的杂岩形式出现，K2 O含量高（1.2-8.5%），εNd（t）值范围宽得多（−10至+3）和正εHf（t）值（+4.6至+6.9）。这些钾质岩浆很可能是由加厚的年轻镁铁质下地壳或脱层的下地壳部分熔融形成的，但也涉及不同数量的软流圈地幔成分。产生含水肥沃岩浆的关键因素很可能是在非弧环境中增厚的下地壳底部的地壳/地幔相互作用过程，而不是大洋板脱水（如弧环境）。在加厚的下地壳中角闪石的分解（例如，角闪岩榴辉岩和石榴角闪岩）在熔融过程中被认为释放流体到肥沃的岩浆中，导致了斑岩Cu-Mo-Au系统发展所必需的高氧化态和更高的H2O含量。含水岩浆中的铜和Au可能来自幔源组分和/或熔体，这些组分或在增厚的下地壳底部底侵，或通过熔体/地幔相互作用输入原始岩浆。而富氧岩浆中的Mo和（部分）S则可能在熔融和上升过程中由老地壳提供。
Most porphyry Cu deposits in the world occur in magmatic arc settings and are formed in association with calc-alkaline arc magmas related to subduction of oceanic lithosphere. This contribution reviews a number of significant porphyry Cu deposits in the eastern Tethyan metallogenic domain. They widely occur in a variety of non-arc settings, varying from post (late)-collisional transpressional and extensional environments to intracontinental extensional environments related to orogenic and anorogenic processes. Their spatial–temporal localization is controlled by strike–slip faults, orogen-transverse normal faults, lineaments and their intersections in these non-arc settings. These deposits are dominated by porphyry Cu–Mo deposits with minor porphyry Cu–Au and epithermal Au deposits, and exhibit a broad similarity with those in magmatic arcs. The associated magmas are generally hydrous, relatively high fO2, high-K calc-alkaline and shoshonitic, and show geochemical affinity with adakites. They are distinguished from arc magmas and/or oceanic-slab derived adakites, by their occurrence as isolated complexes, high K2O contents (1.2–8.5%), and much wider range of εNd(t)values(−10 to +3) and positive εHf(t)values (+4.6 to +6.9). These potassic magmas are most likely formed by partial melting of thickened juvenile mafic lower-crust or delaminated lower crust, but also involving various amounts of asthenospheric mantle components. Key factors that generate hydrous fertile magmas are most likely crust/mantle interaction processes at the base of thickened lower-crust in non-arc settings, rather than oceanic-slab dehydration (as in arc settings). Breakdown of amphibole in thickened lower crust (e.g., amphibole eclogite and garnet amphibolite) during melting is considered to release fluids into the fertile magmas, leading to an elevated oxidation state and higher H2O content necessary for development of porphyry Cu–Mo–Au systems. Copper and Au in hydrous magmas are likely derived from mantle-derived components and/or melts, which either previously underplated and infiltrated at the base of the thickened lower crust, or were input into the primitive magmas by melt/mantle interaction. In contrast, Mo and (part of the) S in the fertile magmas are probably supplied by old crust during melting and subsequent ascent.