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首页> 外文期刊>Brazilian Journal of Geology >Geochronological systematics of the Huayna Potosí, Zongo and Taquesi plutons, Cordillera Real of Bolivia, by the K/Ar, Rb/Sr and U/Pb methods
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Geochronological systematics of the Huayna Potosí, Zongo and Taquesi plutons, Cordillera Real of Bolivia, by the K/Ar, Rb/Sr and U/Pb methods

机译：通过K / Ar，Rb / Sr和U / Pb方法对玻利维亚皇家山脉的HuaynaPotosí，Zongo和Taquesi岩体的年代学系统

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The Huayna Potosi, Zongo and Taquesi are Triassic plutons located at the core of the Real Cordillera of Bolivia. In this paper, several Rb-Sr and K-Ar ages obtained in the past at the S?o Paulo Geochronology Laboratory, yet unpublished, will be presented, along with newer U-Pb Sensitive High-Resolution Ion Microprobe (SHRIMP) determinations made in the same laboratory, allowing us to redefine the geologic history of this part of the Central Andes. Rb/Sr analyses of some low grade metapelitic country rocks of the early Paleozoic (Amutara and Canca?iri Formations) yielded a Rb-Sr isochron age of 344 ± 38 Ma, indicating the action of an early Gondwanide regional event. A five-point Rb-Sr isochron from a granite outcrop of the Huayna Potosi pluton yielded an age of 224 ± 28 Ma. In addition, an important Ar loss in micas was detected in the Zongo granitoids and their country rocks, recording a thermal event that opened this isotopic system in the Oligocene. Newer U-Pb SHRIMP zircon ages of ca. 221 Ma were obtained in two other granitic outcrops of the Huayna Potosi granite. They confirmed its Triassic crystallization age, and a similar U-Pb SHRIMP age of 221.9 ± 1.5 Ma was obtained for one sample of the Taquesi pluton. For the Zongo pluton, many of the zircon grains obtained from one sample of its Kuticucho facies yielded extremely high uranium content, which produced reverse discordant apparent ages. However, due to the fair alignment of the analytical points in the Concordia diagram, possibly corresponding to a linear correlation, we made a regression calculation and the interception of the Concordia curve resulted in a rather imprecise age of 220 ± 20 Ma. Our conclusion was that the final magmatic crystallization and the intrusion of plutons in the central part of the Cordillera Real of Bolivia have occurred close to 221.5 ± 2.0 Ma, in late Triassic times. Finally, the U-Pb SHRIMP ages obtained in inherited zircon xenocrysts from the four available granitic rocks yielded very different ages, and many of them are related to previous magmatic episodes of the Andean Tectonic System. A few other age measurements indicated sources related to much older Proterozoic magmatic events associated with rocks from the Andean basement.
机译：Huayna Potosi，Zongo和Taquesi是位于玻利维亚真正山脉中心的三叠纪小行星。在本文中，将介绍过去在圣保罗地质学实验室获得的，尚未发布的几种Rb-Sr和K-Ar年龄，以及新的U-Pb敏感型高分辨离子微探针（SHRIMP）测定方法。在同一实验室中，使我们能够重新定义安第斯中部这部分的地质历史。对早期古生界（阿穆塔拉和Canca？iri组）的一些低品位变质岩体进行Rb / Sr分析，得出Rb-Sr等时年龄为344±38 Ma，表明了刚德万德早期区域性事件的作用。来自Huayna Potosi岩体的花岗岩露头的五点Rb-Sr等时线的年龄为224±28 Ma。此外，在Zongo花岗岩和它们的乡村岩石中发现了云母中重要的Ar损失，记录了一个热事件，该事件在渐新世中打开了该同位素系统。较新的U-Pb SHRIMP锆石年龄约。在Huayna Potosi花岗岩的另外两个花岗岩露头中获得了221 Ma。他们证实了它的三叠纪结晶年龄，并且为一个Taquesi岩体样品获得了类似的U-Pb SHRIMP年龄221.9±1.5 Ma。对于Zongo岩体，从一个Kuticucho相样品中获得的许多锆石晶粒都具有极高的铀含量，从而产生了不一致的表观年龄。但是，由于Concordia图中分析点的合理对齐（可能对应于线性相关性），我们进行了回归计算，并且Concordia曲线的截距导致了220±20 Ma的不精确年龄。我们的结论是，在三叠纪晚期，最后的岩浆结晶和p侵入玻利维亚皇家山脉的中央部分接近221.5±2.0 Ma。最后，从四个可用的花岗岩岩石中继承的锆石异晶中获得的U-Pb SHRIMP年龄产生了截然不同的年龄，其中许多与安第斯构造系统的岩浆事件有关。其他一些年龄测量表明，与安第斯地下室岩石相关的远古元古代岩浆事件有关。

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