Dike Swarms Related To Orogenic Belts And Their Geological Implication

Unlike large-scale features of magmatic activities, small-scale magmatic activities such as dikes should have non-linear, non-equilibrium physical and chemical magmatic processes. In this thesis, we select dike swarms to explore small-scale features of magmatic activities related to orogenic belts, different stages of an orogenic activity, and mineralization potentials of dike swarms.Based on their features, the orogenic dike swarms are simply divided into the initial stage (or pre-batholith), the peak stage (or syn-batholith) and the terminal stage (or post-batholith) types.As the initial stage type, Cenozoic basic dike swarms in Piqiang Basin, southwest Tienshan Mountains are subparallel and subvertical controlled with thicknesses between 0.2 m and 0.95 m, controlled by SN regional stress field. They are peridotite-bearing basalts, reflecting that these dikes had ascended rapidly and solidified quickly. Their parent magmas came from the level between 16.5 km and 37 km referring to the result of mineral geobarometer. Their ore-forming potentials are pessimistic since no mineralization about dikes have been found.Dike swarms, around Mapeng batholith, located in the north of Taihang Mountain, are considered as the peak stage type. Mapeng batholith and these dikes emplaced synchronously. These dikes are divided into three groups: the western, the southern and the southeastern groups.The western group is the regional dike swarm which can be divided into two subgroups. Dikes are generally subparallel, NW trend, which filled with diabase belong to the first subgroup. Whereas, dikes are generally subparallel, NE trend, which filled with intermediate and acid composition belong to the other. The second subgroup dikes are parallel to the long axis of Mapeng bathoith. The first subgroup dikes are older than the second one in view of their intercrossing relationship. It is suggested that the regional stress field had a clockwise rotation when Mapeng batholith emplaced. The southern group is controlled by both regional and local stresses with great various strikes, and thicknesses mostly less than 4 m.The southeastern group is mainly controlled by local stress field with similar thicknesses and strike as the southern group. The ore-forming potential of dike swarms around Mapeng batholith is optimistic when regional stress field met local stress field or when the local stress field dominated this area. For example, Tuling, Shihu and Qiupudong gold-silver deposits occur in these areas.Dike swarms, located in Wang’anzhen and Badaling batholiths, north of Taihang Mountains, are suggested to be the terminal stage type. This typical dike swarms have wide composition, small volume and contemporary emplacement features. Mafic dikes thicknesses are less than 1 m, whereas felsic dikes thicknesses vary from 4 m to 12 m. They are mainly controlled by local stress field with various direction. Mineralization is always observed and many ore deposits have been found in such dike swarm, such as Antuoling molybdenum minerals, Lianbaling lead-zinc minerals and Shangmingyu gold minerals.According to the metalogenic theory by transmagmatic fluid, cooling time and viscosity changed ratio of dikes have been modeled and the minimum critical thickness of the ore-bearing dike has been estimated by using the three typical dikes in Shihu gold mine. We obtained the minimum critical thickness of mineralization of three representative types of dikes as follows: 1.02 m for diabase, 8.22 m for quartz diorite and 33.45 m for granite porphyry. Furthermore, we estimate the minimum critical area according to the ratio of the length/ thickness, and the minimum critical volumes according to the depth of dikes emplaced.