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越南西北部Pu Sam Cap高钾碱性杂岩位于哀牢山剪切带南段西侧,由粗面岩、煌斑岩、碱性正长岩与碱性花岗岩组成。其中粗面岩不整合于晚白垩世陆相沉积岩之上,碱性侵入岩侵入到三叠纪陆源沉积岩、侏罗纪流纹岩及40～35Ma含角闪石二长岩-花岗岩中。该杂岩的岩石具有低TiO2(<0.8%)、P2O5(<0.64%)和FeO*(<7.74%),高Na2O(1.41%～4.5%)和K2O(5.22%～9.4%)的地球化学属性,属于高钾碱性玄武质到高钾碱性长英质岩浆岩类型与钾质至超钾质岩浆系列。这套岩石富集大离子亲石元素LILE、轻稀土元素LREE和一组相容元素,具有明显的Ta、Nb和Ti异常,表明Pu Sam Cap高钾碱性杂岩形成于与俯冲带有关的大陆弧和后碰撞弧构造环境。锆石LA-ICPMS U-Pb年代学研究表明碱性正长岩与碱性花岗岩分别形成于32.70±0.24Ma、35.1±0.06Ma,上述年龄代表了Pu Sam Cap高钾碱性杂岩的侵入岩结晶年龄。两个样品中锆石的εHf(t)变化范围分别为-2.8～2.5和-4.9～0.1,在t-εHf(t)相关图上分析点落在下地壳和亏损地幔演化线之间,两阶段模式年龄变化范围为950～1286Ma和1107～1421Ma。该杂岩的εNd(t)变化范围-5.63～-3.26,具有低143Nd/144Nd比值(0.512336～0.512447)和高87Sr/86Sr比值(0.706254～0.707273),Sr-Nd同位素相关图上接近于EM2地幔端元趋势线,与大理地区新生代高钾岩浆岩十分相似,表明PuSamCap高钾碱性杂岩的岩浆是幔源岩浆和壳源岩浆的混合结果,同时可与大理地区新生代高钾岩浆岩对比,它们形成于哀牢山-红河左行走滑活动之前,墨江古特提斯洋盆的消减与印度-欧亚陆陆碰撞活动提供了宏观区域性构造背景。
Pu Sam Cap high-potassium alkaline complex in the northwestern part of Vietnam is located on the west side of the southern section of the Ailao Mountain shear zone and is composed of rough rock, lamprophyre, alkaline syenite and alkaline granite. The trachyte is not integrated with Late Cretaceous continental sedimentary rocks. The alkaline intrusive rocks intrude into the Triassic terrigenous sedimentary rocks, Jurassic rhyolite and 40 ~ 35Ma amphibole-granodiorite. The rocks of this complex have the geochemistry of low TiO2 (<0.8%), P2O5 (<0.64%) and FeO * (<7.74%), high Na2O (1.41% -4.5%) and K2O (5.22% -9.4% Belonging to the high-K alkaline basaltic to high-K alkaline alkaline magmatic rock type and the K-to-K-magmatic series. The rocks are enriched in LILE, LREE and a group of compatible elements, which have obvious anomalies of Ta, Nb and Ti, indicating that the Pu Sam Cap high-kurtite complex formed in the zone associated with the subduction zone Continental arc and post-collision arc tectonic setting. Zircon LA-ICPMS U-Pb chronology shows that alkaline syenite and alkaline granite are formed at 32.70 ± 0.24Ma and 35.1 ± 0.06Ma, respectively, and these ages represent intrusive rocks of the Pu-Kauk high-alkaline alkaline complex Crystallization age. The εHf (t) of zircons in the two samples range from -2.8 to 2.5 and -4.9 to 0.1, respectively. The analysis point on the t-εHf (t) correlation diagram falls between the lower crust and the depleted mantle evolution line. The two stages Modes of age range of 950 ~ 1286Ma and 1107 ~ 1421Ma. The εNd (t) of this complex varies from -5.63 to -3.26 with a low 143Nd / 144Nd ratio (0.512336 ~ 0.512447) and a high 87Sr / 86Sr ratio (0.706254 ~ 0.707273). The Sr-Nd isotope correlation diagram is close to the EM2 mantle The tectonic trend line is similar to the Cenozoic karstified magmatic rocks in the Dali area, indicating that the magmas of the PuSamCap high-kali-alkaline complex are the result of the mixing of the mantle-derived magmas and the crustal magmas and are compatible with the Cenozoic karstified magmatic rocks In contrast, they formed a macro-regional structural background before the Ailao-Red River strike-slip event, and the depletion of the Moutain Tidal Basin in the Mojiang River and the Indian-Eurasian continental collision.