斑岩铜矿的源岩或源区探讨

Approach on source rock or source region of porphyry copper deposits.

世界斑岩铜矿主要产于中亚-蒙古带,环太平洋带和特提斯带。上述三个地带分别为古生代、中新生代和新生代聚合板块最活跃的地区。还有少数斑岩铜矿产于前寒武纪造山带,推测类似的板块聚合的地质环境可能从前寒武纪就开始了。作者结合斑岩铜矿产出的地质环境分析,利用大量锶初始值、εNd(t),εSr(t)和REE等资料,说明成矿斑岩的源岩或源区与大洋玄武岩(或亏损上地幔)比较接近。由此推测成矿斑岩主要是洋壳或上地幔部分熔融的产物,但也有部分下地壳混合的证据。斑岩铜矿带在空间上与活动大陆边缘相吻合,与板块缝合带相伴生(产于板块缝合带的上盘);在时间上从洋壳俯冲(subduction)到陆陆碰撞造山过程(Continent-continent collision orogeny)都有斑岩铜矿产生,因此,它们贯穿活动大陆边缘增生到岩石圈折沉整个过程。

Most of porphyry copper deposits are confined to Central Asian-Mongolian belt, circum-Pacific belt and Tethyan belt where Paleozoic, Meso-Cenozoic and Cenozoic convergent plates lies respectively. A small amount of porphyry copper deposits are confined to Precambrian orogenic zones. It is inferred that geological setting characteristic of convergent plate existed as early as in the Precambrian. A great amount of initial Sr isotopic ratios, epsilon(Nd) (t), epsilon(Sr), (t) and REE data in combination with the geological setting indicate that the source rock or source region of ore-bearing porphyry might be ocean basalt (depleted upper mantle). It is inferred from ore-bearing porphyry was derived from partial melting of oceanic crust or upper mantle, however, there is evidence for contamination with lower crust. The porphyry copper belts, spatially, are coincident with active continental margins and associated with plate suture zones (confined to the hanging wall of the suture zone), and, temporally, with interval from subduction of oceanic crust to continent-continent collision orogeny. Thus, porphyry copper ore-formation occurs through whole pcocess from active continent margin accretion to lithosphere delamination.