| 云南澜沧发展河花岗岩体成因研究——锆石U-Pb年龄、地球化学及Sr-Nd-Pb同位素制约 |
| 投稿时间：2025-08-15 修订日期：2025-11-16 |
| 关键词:Fazhanhe Zircon U-Pb Paleo-Tethys Geochemistry Post-collisional |
| 基金项目:本文由中国地质调查局项目(编号DD2016008005、DD20220987和DD20240207101)联合资助 |
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| Petrogenesis of the Fazhanhe Granitoids in Lancang, Yunnan, China: Constraints from Zircon U-Pb Dating, Geochemistry, and Whole-rock Sr-Nd-Pb Isotopes |
| During the subduction of the oceanic slab, collision between Baoshan Terrane and Simao Terrane, and post-collision extension of the Paleo-Tethys Ocean, a large number of Mesozoic magmatic activities developed in the Sanjiang area, southwest China. Based on the petrology, whole-rock geochemistry, zircon U-Pb geochronology, and whole-rock Sr-Nd-Pb isotopes analyses, we conducted systematic studies on the identified Fazhanhe granitoids in the Changning-Menglian suture zone to discuss their petrogenesis and magma sources. LA-ICP-MS zircon U-Pb analyses indicate a crystallization age of 237±2 Ma for the Fazhanhe biotite monzogranite, and the crystallization age of monzogranite are between 228±2 Ma and 224±5 Ma, belonging to the Middle-Late Triassic magmatic activity. Geochemical analyses reveal the granitic samples exhibit relatively high SiO2, aluminum, alkali concentrations, and metaluminous to peraluminous chemical compositions, belong to the high-K calc-alkaline series, which are enriched in Rb, Th, U, and light rare earth elements, and depleted inTi, P, Sr, Nb, with an insignificant negative Eu anomaly. The granites display high differentiation index (74.39~94.86), indicating predominant crystallization differentiation processes. Most samples exhibit S-type granite characteristics, while a small number of rocks belong to I-type granites. The granite samples have high initial ??Sr/??Sr ratios (0.70585~0.72036) and low εNd(t) value (-12.83~-11.70), with a two-stage Nd model age ranging from 1.96 to 2.23Ga, which are quite similar to the Proterozoic crustal basement in the region. Whole-rock Pb isotopic compositions (2??Pb/2??Pbi = 18.682~18.751, 2??Pb/2??Pbi = 15.769~15.780, 2??Pb/2??Pbi = 38.436~38.872) indicate that the sourced material came from the upper crust. Integrating regional tectonic evolution, we propose that the Fazhanhe granitoid are formed in the Middle-Late Triassic post-collision extension environment. These geochronology and geochemistry data provide Changning-Menglian Paleo-Tethys Ocean is closed prior to 224 Ma. |
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