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首页> 外文期刊>Contributions to Mineralogy and Petrology >U-series evidence for crustal involvement and magma residence times in the petrogenesis of Parinacota volcano, Chile
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U-series evidence for crustal involvement and magma residence times in the petrogenesis of Parinacota volcano, Chile

机译：智利帕里纳科塔火山成岩作用中地壳参与和岩浆停留时间的U系列证据

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In this study, we present Th-U disequilibria as well as radiogenic and trace element data for recent volcanic rocks from the Nevados de Payachata volcano which erupted through ~70 km of continental crust in the Central Volcanic Zone of the Andes (18C5, 690W). Both lavas and mineral separates were analyzed by mass spectrometry for ~(238)U~(230)Th disequilibria. The lavas are characterized either by ~(230)Th enrichment or depletion relative to its parent nuclide ~(238)U. Mineral separates are used to derive U-Th isochron ages and these ages compare favorably with inferred stratigraphic ages or K-Ar ages, although in one case the U-Th age is significantly older than the stratigraphic age. Despite relatively constant Sr, Nd, and Pb isotope ratios, the lavas display inverse trends in U~(230)/~(238) versus Ce/Yb or Ba/Hf diagrams. These trends cannot be interpreted by simple two-component mixing. Rather, there must be three (and perhaps four components) involved in the genesis of the Parinacota lavas. A mantle wedge, a slab fluid, and a lower crustal component can be identified. A sediment component is more difficult to detect as it is difficult to decipher its signature because of the strong crustal influence. The existence of binary arrays can be explained by variable amounts of crustal material. The process of crust-mantle interaction must have been short enough to preserve U-Th disequilibrium (<300 ka).
机译：在这项研究中，我们提供了Th-U失衡以及内华达斯·德·帕亚查塔火山最近火山喷发的放射性和痕量元素数据，这些火山岩通过安第斯山脉中部火山区〜70 km的大陆壳喷发（18C5，690W） 。熔岩和矿物分离物均通过质谱分析了〜（238）U〜（230）Th不平衡。相对于其母体核素〜（238）U，熔岩的特征是〜（230）Th富集或耗尽。矿物分离可用于推导出U-Th等时年龄，并且这些年龄与推断的地层年龄或K-Ar年龄相比具有优势，尽管在一种情况下，U-Th年龄显着大于地层年龄。尽管Sr，Nd和Pb同位素比率相对恒定，但熔岩在U〜（230）/〜（238）与Ce / Yb或Ba / Hf图中却显示出相反的趋势。这些趋势不能通过简单的两组分混合来解释。相反，Parinacota熔岩的成因必须涉及三个（也许四个组成部分）。可以识别出地幔楔，板状流体和下部地壳成分。由于强烈的地壳影响，沉积物成分更难检测，因为难以解读其特征。二元阵列的存在可以通过不同数量的地壳物质来解释。地幔相互作用的过程必须足够短，以保持U-Th不平衡（<300 ka）。

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