Geochronology, Geochemistry And Petrogenesis Of Thegranites Of Fuzhou Double-pluton

There are a large number of Mesozoic granites in the south China. The igneous rocks in this area have been intensive studied by geologists, but the complex double-rock during the period of the region is not a lot, its petrogenesis and tectonic setting are still uncertain and controversial. This paper reports the results of petrology, zircon U-Pb isotope chronology, Hf and whole rock major, trace geochemistry study of Fuzhou double-granite in the coastal areas of Fu jian, trying to provide new information of petro genesis of the period for further research.Fuzhou double-granite is divided into two categories: calc-alkaline and alkaline, collected respectively from Fuzhou pluton, Danyang pluton and Kuiqi pluton. Rocks types are mainly as follows: biotite potassium granites, monzonitic granites and alkaline granites. LA-ICP-MS zircon U-Pb dating results show that the ages of granites formed in Danyang pluton and Fuzhou pluton are about: 106 Ma and 111 Ma and 101 Ma. These plutons are the products of magma activity in the early Cretaceous period times; the ages of Kuiqi granites : 93 Ma and 95 Ma, which are the products of the late cretaceous magmatic activity. Differences of zircon trace elements can be concluded that the early cretaceous calc-alkaline granites are I-type granites but late cretaceous alkaline granites are A-type granites. They constitute the I-A type rocks series.Samples in the study have Eu negative anomaly, characterized by LREE enrichment and HREE loss, and they are all relatively enriched in Rb, Th, U, K, Pb and other LILE, depleted in Ba, Sr and high field strength elements Nb, Ta, P, Ti. light-heavy RE fractionation of I-type granites is more obvious than A-type granites and the LREE/HREE ratio of I-type granites is larger. However, compared with I-type granites, the negative Eu anomaly of A-type granites is more obvious. At the same time, these support above speculation of I-A rocks series. The results of Zircon Hf isotope show that the ε Hf(t) of I type granites values from negative to positive, and the crustal model ages indicate that the source rocks of granitic magma derived from the remelting of Neoproterozoic ancient crust, with a small amount of mantle components. Compared with I-type granites, A-type granites ε Hf(t) value is positive, the crust model ages suggest granitic magma derived from the remelting of Neoproterozoic ancient crust, and mixed with A large number of mantle components.I-A granites in Fuzhou doule-pluton have the same source area, but the difference of the formation is the results of comprehensive shaping of many factors mainly including changes of tectonic environment, the addition of mantle-derived magma and magmatic evolution.