Petrogenesis And Tectonic Geological Setting Of Caledonian Granitoids In Northeast Guangxi

Northeastern Guangxi is located between the Yangtze and Cathaysian blocks.Northeastern Guangxi mainly distributed Caledonian, Indosinian and Yanshanian granites, Previous research more focused on the Yanshanian granites instead of studing the Caledonian and Indosinian granites.This study focused on the Haiyangshan pluton, Guiling pluton and the MMEs（mafic microgranular enclaves） in them, based on many analyses of petrology, geochemistry, geochronology and isotope geochemistry, this study obtained some results of the geneses and the regional tectonic evolution of this igneous rocks as follow.1. Haiyangshan pluton mianly consist of biotite monzogranite. The biotite monzogranite is characterized by high K, enrich alkaline, It belongs to strongly peraluminous-peraluminous S-type granite. On average, the REE content is231.2×10-6, and the LREE and HREE fractionation is not obvious, relatively low Eu/Eu* ratios, with enrichment of large ion lithophile element（Rb、Th、K、U） and strong negative high field strength elements（Nb、Ba、Ti、Zr）. The SHRIMP zircon U-Pb dating suggests that the crystallization age of Haiyangshan pluton is432.2±6.3Ma. The MMEs’ crystallization age is 413.0±8.1Ma, slightly later than the host granite. The haiyangshan pluton was form at 432⁴13Ma. both results have coherence in the scope of errors.2. The MMEs in Haiyangshan pluton are schlierens which formed during the magma crystallization process. It has rich mica with fine grain granite structure, and low SiO₂ content, while the elements such as Mg、Al、Rb、Ba and REE are relatively slightly than host granite, and have relative slightly fractionated REE patterns, with the slightly lower Eu negative anomaly than the host rocks.3. Guiling pluton was mainly composed of the fine grain porphyritic（hornblende）biotite monzogranite. It exhibits weakly peraluminous and high-K calc-alkaline series.The average REE content is 158.51×10-6, with enrichment of LREE and depletion of HREE, and relatively negative Eu-anomalies. The biotite monzogranites haveenrichment of LILE（Rb、Th、U） and depletion of Ba、Sr、Nb、P、Ti.4. The ISr of Guiling biotite monzogranite and MMEs in it is 0.7049⁰.7206 and0.7058⁰.7084, respectively, with εNd（t） values of-13.5^-5.0 and 3.4³.6. The Nd model ages are 1.4-2.1Ga and 0.8-0.9 Ga, respectively, indicating that the large distinct source between MMEs and host granite.5. This article suggests that Caledonian pluton in the studied area mainly formed in the compression setting. The Haiyangshan pluton is mainly a product of anatexis of the ancient crust, and the Guiling pluton are product of anatexis both of the mafic rocks which emplaced early and the ancient crust.