Postorogenic Dike Complexes and Implications for Metallogenesis

Large scale granitic magmatism is commonly followed by emplacement of postorogenic dike swarms. These dikes swarms are characterized by a wide compositional spectrum and are volumetrically minor with respect to the associated granitic intrusions. Observations in the Taihangshan, Yanshan, Eastern Kunlun and Tianshan orogenic belts, show that dikes can be divided into five groups: lamprophyric, basaltic, dioritic (andesitic), granodioritic (dacitic) and granitic (rhyolitic). Most researchers have paid attention only on the basaltic or lamprophyric dikes and often confused them with the dike swarms related to the continental breakup. Combined with recent works on studies of magmatic processes, it can be inferred that these dikes are the products of primary or near-primary magmas. Based on the analysis of thermal regimes and regional lithospheric petrological structures, the authors suggest that conditions for the production of these magmas require lithospheric delamination of an orogen with a thickened mafic lower crust. Therefore, the dikes should be formed at the stage of transition of the regional structural stress field from compression to extension and can be used to mark the ending of an orogenic cycle. In this case, the dike swarm can be considered as postorogenic dike complexes. Furthermore, we suggest that such dike complexes are widespread worldwide. Thus, there are three types of dike swarms: (1) dikes related to continental breakup, (2) dikes related to batholiths, and (3) dikes associated with large igneous provinces. The emplacement of a postorogenic dike complex should be also accompanied by the large scale hydrothermal activity, when the rate of the heat transfer is considered. As the concentration of the ore-forming elements in the deep fluids depends on pressure, a new petrogenetic model implies that metallogenesis accompanies the postorogenic dike swarm. Field examinations suggest that the observations of outcrops can be used to recognize the paths of the ore-forming fluids and the locations where the ore-forming elements accumulate. Therefore, we conclude that a postorogenic dike complex not only indicates the ending of an orogenic process, but is also an effective vector for mineralization allowing a degree of predictability that can assist in exploration targeting.