南岭与中生代花岗岩类有关的成矿作用及其大地构造背景

Metallogeneses and Their Geodynamic Settings Related to Mesozoic Granitoids in the Nanling Range

由于受到来自印支半岛的挤压,在华南内部发生了以碰撞-挤压-推覆-隆升为主的印支造山运动.南岭地区印支期花岗岩(240～205 Ma)主要形成于碰撞及'后碰撞'(post-collision)的动力学环境,但没有造成大规模的金属成矿作用.南岭地区从燕山期进入后造山(post-orogeny)地球动力学环境.从花岗岩类的成矿学特征及其大陆动力学背景出发,尝试把燕山期划分为早、中、晚三期.南岭地区燕山早期(185～170 Ma)出现了玄武质岩浆活动、双峰式岩浆活动、A型花岗岩及板内高钾钙碱性岩浆活动,反映了岩石圈的局部'伸展-裂解'和地幔物质的上涌,伴随Pb,Zn,Cu,Au成矿作用.燕山中期南岭地区岩石圈全面拉张-减薄,地幔上涌-玄武质岩浆底侵引发大规模的地壳熔融,导致大范围陆壳重熔型花岗岩的生成.该期的第一阶段(170～150 Ma)以大规模花岗岩类侵位为主,第二阶段(150～140 Ma)花岗岩类活动很少,却发生了W,Sn及其他稀有金属的大规模成矿作用.燕山晚期虽然是华南地区岩石圈全面发生裂解的时期,但由于受太平洋构造体系的影响,在南岭东端至东南沿海广大地区,燕山晚期(140～65 Ma)出现了先挤压、后拉张的动力学背景,在100 Ma前形成的钙碱性和橄榄安粗两个系列的岩浆活动,伴随Au,Ag,Pb-Zn,Cu,(Mo,Sn)等成矿作用.而在南岭地区,该时期花岗质火山-侵入杂岩及基性岩脉等广泛发育,有关的成矿作用以火山岩型U矿、斑岩型Sn矿,以及印支期花岗岩中的铀活化成矿作用为特征.

Affected by the compressive stress from the Indo-China Peninsula, the Indosinian Orogenesis, characterized by collision, thrust and uplifting, took place inside the South China plate the Indosinian granitoids in the Nanling Range and vicinity areas are mostly of during 250 -230 Ma. The ages of 240 -205 Ma, indicating that they were emplaced in both syn-collision and post-collision geodynamic settings. No important granite-related metallogeneses occurred in this duration. A post-orogeny setting started from the beginning of the Yanshanian Period, which controlled the large-scale granitic magmatism and related metallogeneses. This paper makes the first attempt to divide the Yanshanian Period into three sub-periods, i.e. the Early, Middle and Late Yanshanian Periods, based on the metallogenic features of granitoids and their geodynamic backgrounds. The magmatic association of the Early Yanshanian Period （about 185 - 170 Ma）comprises four categories of magmafism, i. e. basalt, bimodal volcanics, A-type granite, and the intra-plate high-K calc-alkaline, which indicates the beginning of extensionthinning of lithosphere and upwelling of mantle material in a relative small and local extent. Pb-Zn, Cu, and Au mineralization associated with high-K calc-alkaline magmatism represents the metallogeny of this period. During the Middle Yanshanian Period, lithospheric extending-thinning developed more widely and intensively, and hence the mantle upwelling and basaltic magma underplating, which caused the formation of great amount of crust re-melting granitoids. This period can further be divided into two stages. The first stage （ 170 - 150 Ma） is represented by large-scale emplacement of crust re-melting granites with some tungsten mineralization at the end. The second stage （ 150 - 140 Ma） is the most important time of large-scale mineralizations of non-ferrous and rare metals, e.g. W, Sn, Nb-Ta, Bi, Mo, Be, in the Nanling Range area, although much less granitoid developed. The Late Yanshanian Period （140 -65 Ma） was generally characterized by full extension and breakup of the lithosphere of South China. However, owing to the influence of Pacific plate movement, the eastern part of South China was predominated by subduction-related compression, which resulted in magmatism of calc-alkaline and shoshonite series and related metallogeneses of Au, Ag, Pb-Zn, Cu, （Mo, Sn） , followed by extension in late stage. In the Nanling Range area, Late Yanshanian magmatism was represented by emplacement of granitic volcanic-intrusive complexes which were genetically related to volcanic-type uranium and porphyry type tin deposits, as well as mafic dykes which caused the mobilization, transportation and mineralization of uranium in pre-existing Indosinian granites.