论文部分内容阅读
A systematic study combining U-Pb zircon dat-ing,lithogeochemical and Sr-Nd isotopic analyses was carried out upon the Xinping granodiorite porphyry in the Dayaoshan metallogenic belt to understand its petrogenesis and tectonic significance.LA-ICP-MS U-Pb zircon dating yielded a 442.7 ± 5.8 Ma age,indicating that the gran-odiorite porphyry was emplaced during the Llandovery Silurian of the Early Paleozoic.The granodiorite porphyry shares the same geochemical characteristics such as Eu negative anomaly as other syn-tectonic granite plutons in the region,including the granodiorite porphyry in Dawangding and granite porphyries in the Dali Cu-Mo deposit and Longtoushang old deposit,indicating a similar magma evolution process.The Xinping granodiorite por-phyry has high contents of Si02(67.871.8％)and K2O(1.78-3.42％)and is metaluminous-peraluminous with A/CNK ratios ranging from 0.97 to 1.06,indicative of high-potassium calc-alkaline to calc-alkaline affinity.It is a I-type granite enriched in large ion lithophile elements Rb,Sr,while depleted in Ba and high field-strength element Nb.Tectonically,a collision between the Yunkai Block from the south and the Guangxi Yunnan-North Vietnam Block from the north during the Early Paleozoic was fol-lowed by uplifting of the Dayaoshan terrane.The Xinping granodiorite porphyry was likely emplaced during the collision.Sr-Nd isotopic analyses show that the granodi-orite porphyry has initial 87Sr/86Sr ratios(Isr)of 0.7080-0.7104,εNd(t)range from-0.08 to-4.09,and t2DM between 1.19 and 1.51 Ga,well within the north-east low-value zone of the Cathaysia block,indicating a Pale-oproterozoic Cathaysia basement source and an involve-ment of under plating mantle magma.Field observations,geochronological data,and 3D spatial distribution all lead to the conclusion that the Early Paleozoic Xinping gran-odiorite porphyry does not have any metallogenic and temporal relationships with the Xinping gold deposit(which has a Jurassic-Early Cretaceous age based on pre-vious studies)but a close metallogenic relation to W-Mo mineralization.