摘要
四川盐源西范坪斑岩铜矿处于扬子地块西缘,靠近盐源-丽江坳陷带与甘孜-理塘缝合带的结合部位,该矿区侵入岩体主要为石英二长斑岩组成。西范坪铜矿石英二长斑岩LA-ICP-MS锆石U-Pb年龄为(100.8±0.7)Ma(MSWD=0.2),表明了斑岩侵位时代为早白垩世。石英二长斑岩富集大离子亲石元素(Rb、Ba、K),亏损高场强元素(Nb、Ta、Ti、P),LREE富集、HREE亏损,为高钾准铝质花岗岩。w(Si O2)为64.06%~65.24%,具有高w(Al_2O3)(15.58%~16.55%)、w(Sr)(719×10~(-6)~1221×10~(-6))及Sr/Y比值(49.2~82.5),低w(MgO)(1.30%~1.63%)、w(Yb)(1.08×10~(-6)~1.55×10~(-6))及w(Y)(13.7×10~(-6)~14.8×10~(-6)),Eu异常(0.83~0.90)不明显,轻重稀土分异明显((La/Yb)N=29.94~52.14),具有埃达克岩特征。西范坪埃达克岩富钾贫钠(K_2O/Na_2O=0.78~2.44),低Cr、Ni,高Th、Th/U以及相对低的Sr/Y等特征,表明其为加厚下地壳部分熔融形成。西范坪早白垩世(100.8Ma)地壳增厚作用可能受控于甘孜-理塘洋闭合后的造山运动,该斑岩体为印支期褶皱造山后(200 Ma),喜马拉雅期碰撞造山之前(65 Ma),陆内由挤压向伸展转换期岩浆作用的产物。
Xifanping porphyry-copper deposit in Yanyuan County of Sichuan Province, China is located at the west margin of the Yangtze Platform and near the connection between Yanyuan-Lijiang depression zone and Ganzi-Litang suture zone. The rock masses in the mining area are mainly quartz monzonite porphyry(QMP). Laser ablation-inductively coupled plasma-mass spectrometry(LA-ICP-MS) shows that the zircon U-Pb age of QMP is(100.8±0.7) Ma(MSWD=0.2), indicating the emplacement age of QMP being the Early Cretaceous. The QMP is enriched with large-ion lithophile elements(Rb, Ba, and K) and light rare earth elements(LREEs), but deficient in high-field-strength elements(Nb, Ta, Ti, and P) and heavy rare earth elements(HREEs), indicating the nature of high-K quasi-aluminous granite. The porphyry also contains 64.06%-65.24% w(Si O2), high w(Al_2O3)(15.58%-16.55%), high w(Sr)(719 ×10~(-6)-1221 ×10~(-6)) with high Sr/Y ratio(49.2-82.5), low w(MgO)(1.30%-1.63%), low w(Yb)(1.08 ×10~(-6)-1.55 ×10~(-6)), low w(Y)(13.7×10~(-6)-14.8×10~(-6)), unobvious Eu anomaly(0.83-0.90), and significant LREE-HREE differentiation, with(La/Yb)N=29.94-52.14, indicating the properties of adakites. The adakites in Xifanping is characterized with high K and low Na(K_2O/Na_2O=0.78-2.44); low Cr and Ni; high Th, Th/U, and relatively low Sr/Y, indicating the adakites originated from the partial melting of the thickened lower crust. The crust thickening effect at Early Cretaceous(100.8 Ma) in Xifanping Deposit might be controlled by the orogeny after the Ganzi-Litang ocean closure. The porphyritic masses resulted from the magmatism during the intracontinental extrusion-to-extension transitional period, which appeared after the Indo-Chinese folding orogeny(200 Ma) and before the Himalayan collisional orogeny(65 Ma).
引文
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