Abstract U-series data are combined with major and trace element constraints to construct a detailed view of the magmatic system feeding the San Pedro-Linzor volcanic chain, aiding the understanding of how stratovolcanoes in extremely thick arc crust evolve. Lavas from the Quaternary San Pedro-Linzor volcanic chain (Central Andes) have (238U/230Th) ranging from 1.015 to 1.072, with 238U excess even in the less evolved (~57 wt% SiO2) analyzed lavas. Contrary to well-established trends between fluid mobile elements and 238U excess, (238U/230Th)0 shows no systematic correlation with ratios indicative of fluid-driven melting (e.g. Ba/Hf and K/La). Moreover, the inverse correlation between (238U/232Th) with the amount of slab-derived fluid and the oxidation state of the mantle below Central Andes, which decreases eastwards, suggests that the main control of the 238U excess is not associated with hydration of the mantle wedge. Changes in (238U/232Th) and (230Th/232Th)0 are observed with variations in SiO2 and CaO + Al2O3 contents, and 87Sr/86Sr and Dy/Dy* ratios of the lavas. These changes correspond to increasing (238U/232Th) with decreasing Dy/Dy* and CaO + Al2O3 ratios, which is attributed to changes in crystallization of mineralogical phases within magmatic chambers during differentiation. Also, 230Th in-growth is produced during stagnation within magmatic chambers located below the San Pedro-Linzor volcanic chain. Finally, a positive correlation between (230Th/232Th)0 and 87Sr/86Sr indicates an important role of crustal contamination, and of new mafic inputs during evolution of the volcanic chain with time. Our observations suggest that better constraints of all magmatic processes are needed to fully understand the U-series disequilibria recognized for the different volcanic structures developed within subduction-related tectonic environments.

中文翻译：

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上地壳分异过程及其在圣佩德罗-林佐火山链（安第斯中部）238U-230Th不平衡中的作用

摘要 U系列数据结合主量元素和微量元素约束，构建了供给圣佩德罗-林佐火山链的岩浆系统的详细视图，有助于理解极厚弧形地壳中的层状火山如何演化。来自第四纪圣佩德罗-林佐尔火山链（安第斯山脉中部）的熔岩的 (238U/230Th) 范围从 1.015 到 1.072，即使在分析较少的熔岩中（~57 wt% SiO2）也有 238U 过量。与流体移动元素和 238U 过量之间的公认趋势相反，(238U/230Th)0 与指示流体驱动熔化的比率（例如 Ba/Hf 和 K/La）没有系统相关性。此外，(238U/232Th)与板片衍生流体的量与安第斯山脉中部下方地幔的氧化态呈负相关，向东降低，表明 238U 过剩的主要控制与地幔楔的水合无关。观察到 (238U/232Th) 和 (230Th/232Th)0 的变化随 SiO2 和 CaO + Al2O3 含量的变化以及熔岩的 87Sr/86Sr 和 Dy/Dy* 比率的变化而变化。这些变化对应于 (238U/232Th) 随着 Dy/Dy* 和 CaO + Al2O3 比率的降低而增加，这归因于分异过程中岩浆房内矿物相结晶的变化。此外，在位于圣佩德罗-林佐火山链下方的岩浆房内停滞期间会产生 230Th 向内生长。最后，(230Th/232Th)0 和 87Sr/86Sr 之间的正相关表明地壳污染和新的镁铁质输入在火山链随时间演化过程中的重要作用。