Characteristics and Petrogenesis of Late Mesozoic Granitic Volcanic-Intrusive Complexes in Southeastern China

During the late Mesozoic, magmatic activities in southeastern China were very intensive. In the products of magmatism, the granites rhyolites are predominant, and the andesitic basaltic rocks are less important. The statistical data on the isochron ages for over 200 granite and volcanics samples show that the early Cretaceous ages make up about 60% of age population; and the late Jurassic, 20%; the late Cretaceous, 10%; the middle Jurassic, 10%. The ages of Mesozoic volcanics and related granites in southeastern China have a tendency of getting younger from the inland toward the coast. In some cases, granites and associated acidic and intermediate volcanic rocks are comagmatic. Under the condition of uniformity in time, space and source materials, the granities can be considered as the “roots” of the central type volcanic apparatuses composed of rhyolites and dacites, forming so called granitic volcanic intrusive complexes. The granitic volcanic intrusive complexes in southeastern China may be divided into three types, i.e., syntexis type, continental crust remelting type and A type. Their petrogenesis is controlled by different tectonic settings, rock forming mechanisms and source materials. The syntexis type is dominantly distributed in the coastal area, whereas the continental crust remelting type is mainly located in the inner land. This spatial pettern is constrained by two factors: the composition of basement rocks and the intensity of crust mantle interactions. Underplating of basaltic magma took place more intensively in the coastal area of Zhejiang and Fujian provinces during the late Mesozoic. Therefore, the crust mantle interaction was also more intensive in the coastal area than in the inner land. In the west of Wuyishan Mts., the continental crust usually possesses higher maturity. The meta igneous materials, such as amphibolites, are rare or absent in the basement rocks of the area. The combining constraints of these two factors led to a regular spatial distribution of above mentioned two types of granitic volcanic intrusive complexes in southeastern China. The distribution of A type granitic volcanic intrusive complexes is mainly controlled by Changle Nanao fault zone in the coastal area of Zhejiang and Fujian provinces. The thickness of both lithosphere and continental crust is obviously thinned and the asthenosphere is upwelled in this region. It is evident that A type granitic volcanic intrusive complexes were formed in a extensional tectonic setting and display the post orogenic features. Since then, the Yanshanian magmatic activities were toward the end. In this paper, the authors show the uniformity in emplacement time, space and source materials for granitic volcanic intrusive complexes, taking both Tonglu and Xiangshan complexes as examples. Some regularities summarized may be very important for understanding the genesis of granitic volcanic intrusive complexes in southeastern China.