Geochronology And Geochemistry Of The Late Mesozoic Igneous Rocks In The Southeastern Coastle Area Of Quanzhou, Fujian Province

Fujian Province is located in the southeastern part of China, and on the intersection point between Eurasian and Pacific plate. The geographical location of this area is to the southeastern margin of South China Block(SCB) in which great amount of magmatic rock intruded since Caledonian especially the granitoids intruded in Mesozoic. This area has a special structural environment and a complex geodynamic history. The researches on petrogenesis, structural-magmatic evolutional history will mean a lot to reveal the structural-magmatic evolution history of the whole part of SCB.Quanzhou area is located in the southeastern coastal side of Fujian Province, where magmatic rocks are mainly granitoids which intruded in Triassic, Jurassic, Neozoic and Quaternary strata in forms of batholith and stock. In the area closed to the coastline, there are mafic dikes which intruded in the granitic batholith through the cleavage and weak parts. Zircon U-Pb geochronology test shows that there are three stages of magmatism in this area: Late Jurassic-Early Cretaceous Epoch(162~141Ma), Early Cretaceous-Late Cretaceous Epoch(132~96Ma) and Late Cretaceous Epoch(96~90Ma). Magmatic rocks in the first Epoch grow in the farthest area from the coastline and are mainly high-K calc-alkaline, metaluminous granitoids; Magmatic rocks in the second Epoch grow in a closer area away from the coastline and are mainly high-K calc-alkaline, metaluminous granitoids; Magmatic rocks in the third Epoch in this area are mainly medium to high-K calc-alkaline mafic dikes with a small amount of granitoid. Granitoids in Quanzhou area are all I-type granitoids and some of which have a feature of high-grade differentiation. Nearly all of samples are rich of LILE and lack of HFSE, which shows some island arc characters. Zircon Hf and whole rock Sr, Nd isotopic feature showes that there were mantle source infusions during the formation process of the granitoids at different levels. From inland to the coastal part, the degree of infusions increases obviously, and the multi-peak TDM C age indicates an extensive mantle-crustal interaction. Mafic dikes have an arc-related REE feature, and have continental margin characters as well. Source region of the mafic dikes shows a characteristic of a combination between EMI, EMII and DMM. Geochronology result shows that the intrusion time of the dikes is coinstantaneous with the regional 100~110, 85~95Ma stretching affairs.Take other researchers’ achievements in this area into consideration, the Quanzhou area of Fujian province might have experienced transformation from Tethys tectonic domain to Palo Pacific tectonic domain in Late Jurassic-Early Cretaceous Epoch; Large-scale stretching affairs, mantle magma intrusion, slab roll-back and slab break off caused by the subduction of Palo Pacific ocean plate during Early Cretaceous-Late Cretaceous Epoch; Transition phase from subduction domain to extension domain in Late Cretaceous Epoch. And the research in this thesis can provide some new evidence to reveal the structural-magmatic evolution history of the coastal area of Fujian Province.