Zircon U-Pb ages and element geochemistry characteristics of magmatic rocks in Nanling-Xuancheng area of Anhui, China
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| Authors: | Xu Xiaochun, An Yuhua; Xu Xinyue, Fu Zhongyang |
| Year: | 2020 |
| Journal: | Journal of Earth and Environment 42(1): 15-35 Article Link (DOI) |
| Title: | Zircon U-Pb ages and element geochemistry characteristics of magmatic rocks in Nanling-Xuancheng area of Anhui, China |
| Abstract: | The Nanling-Xuancheng area of Anhui, which is a Meso-Cenozoic volcanic-sedimentary basin, is located in the southeastern limb of the northeastern part of middle-lower Yangtze river valley tectonic-magmatic-metallogenic belt. Zircon U-Pb dating, and major, trace and rare earth elements of the magmatic rocks in Nanling-Xuancheng area were focused, and compared with those of the magmatic rocks in other areas of middle-lower Yangtze river valley tectonic-magmatic-metallogenic belt, for determining the age, and discussing the petrogenesis of the magmatic rocks and the relationship between the magmatism and mineralization. In Nanling-Xuancheng area, a part of the magmatic rocks intruded into the basement of the basin or erupted as the cover rocks of the basin, and the other part of the magmatic rocks occurred in the nappe above the basin. The intrusive rocks are mainly granite, granodiorite, quartz diorite and pyroxene diorite, and the volcanic rocks are dacitic pyroclastic rocks and lavas. The results show that the zircon U-Pb ages of the intrusive rocks are between 138 Ma and 135 Ma, and the ages of the volcanic rocks are all less than 134 Ma, suggesting that the magmatism occurred in Early Cretaceous of Late Mesozoic(Late Yanshanian). The characteristics of major elements show that the magmatic rocks are high for Si and K, belonging to sub-alkaline and high-K calc-alkaline series; the characteristics of trace elements show that the magmatic rocks are rich in Rb, Th, U and K, and poor in Ti, Nb and Ta, the volcanic rocks are more deficient from intrusive rocks in Sr and P; the chondrite-normalized REE patterns show that the magmatic rocks are rich in LREE and have weak negative Eu anomalies. The element geochemical characteristics indicate that the magmatic rocks have the characteristics of crust-mantle mixed and mainly mantle-derived. Zircon U-Pb dating, and geological and geochemical characteristics of the magmatic rocks in Nanling-Xuancheng area indicate that the Late Mesozoic magmatism in the area has the dual characteristics of those in upwelling areas and depression areas of the middle-lower Yangtze river valley tectonic-magmatic-metallogenic belt, that is, the study area not only develops intrusive rocks in the upwelling area(such as Tongling area), but also develops volcanic rocks in the depression area(such as Luzong and Ningwu basins). The duality of magmatism may imply the duality of mineralization, that is, the study area may develop hydrothermal porphyry-type, skarn-type and vein-type Cu-Au and other polymetallic deposits related to intrusive magmatism, also porphyry-type Fe(S)deposits associated with volcanic-subvolcanic rocks. References: |
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