REGIONAL GEOLOGICAL CHARACTERISTICS OF FUJIAN PROVINCE

Fujian Province is located in the southeastern coasts of China, on the continental margins of the Western Pacific, belonging to the South China fold system. In the province, there are a relatively full range of strata, frequent magmatic activity and rather complex geological structures, which create good conditions for the formation of abundant mineral resources. This paper briefly deals with the basic regional geological characteristics of Fujian Province by using the results of regional geological surveys and recent scientific achieve- ments on the basis of the monograph "Regional Geology of Fujian Province". Upper Proterozoic to Quaternary strata other than the Silurian, Middle and Lower Devonian and Lower Tertiary are all distributed in the province. Through a study of the stratigraphy and sedimentaion, it has been ascertained that in geological times the earth’s crust of Fujian received the pre-Sinian-Ordovician geosynclinal-type, Late Devonian-Middle Triassic platform-type and Late Triassic-Cretaceous volcanic island-arc sediments. Volcanic rocks are widespread in Fujian. Those of ultrabasic, basic, interme- diate, acid and slightly alkaline compositions are all present. Through a study of volcanic rocks and volcanisms, it have been demonstrated that there were three major volcanisms in geological times in Fujian. The first occurred in late Proterozoic time, along deep fractures. This volcanism generated three NE- trending belts of volcanic eruption. The rocks are represented by basic-acid volcanic rocks and partly calc-alkaline ones, and exhibit bimodal features. The second took place in Carboniferous time. The rocks include basalt, andesite and rhyolite, which all belong to the alkaline volcanic series and exhibit bimodal features. The third occurred in the Jurassic-Cretaceous. The rocks are repre- sented by intermediate-acid volcanic rocks, forming a series of NE-trending belts of volcanic eruption. The rocks all belong to the calc-alkaline volcanic series and exhibit unimodal features. These indicate that the earth’s crust in Fujian once underwent rifting in the late Proterozoic and Carboniferous and was strongly affected by plate motion in the Jurassic-Cretaceous. Studies of intrusive rocks and intrusion in Fujian show that there are Caledonian, Variscan-Indosinian, early Yanshanian, late Yanshanian and Hima- layan intrusive rocks. The rocks consist mainly of granites and subordinately of peridotites, gabbros and diorites. According to the mode of formation and material sources, metamorphic-metasomatic, anatectic, syntectic and differen- tiated granites may be distinguished. Their distribution exhibits a distinct feature of NE-trending zonal distribution and an eastward-younging trend. Metamorphic rocks are relatively widespread. Through a study of metamor- phic and metamorphism, it has been verified that there exist Caledonian, Indosinian and Yanshanian metamorphic rocks, distributed along deep fractures. They respectively form a Caledonian low-pressure, high-temperature metamorphic belt, an overlapped Caledonian and Indosinian medium-pressure, high-temper- ature metamorphic belt. Their formational ages become younger from the western part to the eastern coasts. Studies of the regional geological structures and the regularities of their evolution suggest that the development of the earth’s crust in Fujian has gone through the Proterozoic-early Paleozoic, Late Devonian-Middle Triassic, Late Triassic-Cretaceous and Cenozoic periods. During the four periods of development, the Caledonian, Indosinian, Yanshanian and Himalayan tectonic beds were formed, and accordingly there occurred the Yangtzeian-Caledonian, Variscan- Indosinian, Yanshanian and Himalayan tectonic cycles, involving the stages of formation of the geosyncline, paraplatform and circum-Pacific continental-margin mobile belt. Finally a present-day continental framework was formed. The regular distribution of a series of dominantly NE-trending deep fracture belts, volcanic belts, magmatic belts and metamorphic belts leads to the formation of the regional tectonic framework of Fujian Province.