云南中甸刺来斑岩体地球化学特征及成岩构造环境
Geochemical Characteristics and Diagenetic Tectonic Environment of the Cilai Porphyry in the Zhongdian Area,Yunnan Province
滇西北中甸地区位于三江特提斯成矿域,该区新发现的刺来复式斑岩体具有重要成矿意义。刺来岩体石英闪长玢岩具高硅[w(SiO₂)=64.94%~67.31%]、富碱[w(K₂O+Na₂O)=7.27%~8.84%]特征,属于高钾钙碱性系列岩石。地球化学组分揭示其富集轻稀土[(La/Yb)N=33.11~39.41]和大离子亲石元素(Rb、Ba、Th、U),显著亏损高场强元素(P、Ti、Zr),呈现高Sr(692×10⁻⁶~1 180×10⁻⁶)、低Y(11.7×10⁻⁶~13.1×10⁻⁶)、高Sr/Y比值(56.7~100)和La/Yb比值(48.7~58.0),符合埃达克(质)岩的地球化学特征。刺来岩体整体Th/U比值偏高(0.56~1.24),MgO(1.11%~2.69%)、Cr(12.2×10⁻⁶~18.6×10⁻⁶)和Ni(4.3×10⁻⁶~5.8×10⁻⁶)含量较低,Th/La比值(0.15~0.20)和Nb/Ta比值(13.6~15.2)介于地幔与地壳端元间,揭示其岩浆源区存在俯冲洋壳熔体与地幔熔体的混合作用。MgO-Fe₂O₃-Al₂O₃图解及构造判别图解显示,该岩体形成于岛弧环境;锆石U-Pb定年显示其结晶年龄为(217.0±1.8)~(216.9±1.4)Ma,属晚三叠世岩浆活动的产物。刺来岩体与中甸斑岩成矿带内春都、雪鸡坪等大型斑岩矿床同属晚三叠世甘孜—理塘洋壳西向俯冲背景下的产物。
The Zhongdian region is divided into eastern and western porphyry metallogenic belts. The Cilai copper deposit, located within the western belt, represents a newly identified porphyry copper system in this area. To determine the petrogenetic age, tectonic setting, and magmatic source of the Cilai porphyry body, we performed zircon U-Pb dating and comprehensive whole-rock major and trace element analyses on the Cilai quartz diorite porphyry. The zircon U-Pb dating results reveal that the formation age of the Cilai quartz diorite porphyry ranges from(217.5±1.8)Ma to (216.9±1.4)Ma, situating its origin in the Late Triassic period. This porphyry is characterized by high SiO2 content(64.94%~67.31%) and elevated alkali levels (K2O+Na2O=7.27%~8.84%), classifying it as part of the high-K calc-alkaline series. The rock exhibits enrichment in light rare earth elements (LREEs), significant LREE-HREE fractionation , and a weak negative Eu anomaly(δEu=0.81~0.98). It is enriched in large-ion lithophile elements (LILEs) such as Rb, Ba, Th, and U, while it is depleted in high field strength elements (HFSEs) like P, Ti and Zr. The rock exhibits elevated strontium (Sr) concentrations(692×10-6~1 180×10-6), reduced yttrium (Y) levels (11.7×10-6~13.1×10-6), and increased Sr/Y(56.7~100.0) and La/Yb (48.7~58.0) ratios, which are characteristic of adakitic magma. The Cilai quartz diorite porphyry is characterized by high thorium/uranium (Th/U) ratios and low, concentrations of magnesium oxide (MgO), chromium (Cr), and nickel (Ni). The Th/La, Nb/Ta, Rb/Sr, and Ba/La ratios are intermediate between those of the upper mantle and crust, with certain values aligning more closely with average mantle values. This suggests that the melt from subducted oceanic crust ascends and interacts with the mantle wedge, producing adakitic magma, which subsequently interacts with the crust to form the current thorn rock mass. The geochemical properties and zircon U-Pb dating of the Cilai quartz diorite porphyry, combined with the positioning of sample points on the MgO-Fe2O3-Al2O3 diagram and tectonic environment discrimination diagrams within island arc and active continental margin regions, suggest that the Cilai deposit, along with other significant copper deposits, such as the Chundu deposit, originated from the same magmatic event within the western porphyry metallogenic belt. These deposits are the result of the westward subduction of the Ganzi-Litang oceanic crust during the Late Indosinian period.
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第二次青藏高原综合科学考察研究方向三之专题一“青藏高原东南缘构造—沉积—岩浆作用与Cu-Pb-Zn成矿”(2021QZKK0301)
国家自然科学基金项目“斑岩型矿床”(42022021)
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