The Andean margin of the South American continent has been magmatically and tectonically active for over 330 million years. It is the type location where “Cordilleran-type” magmatism and orogenesis are manifest. In Argentina and Chile, between the latitudes of 28° and 40° S, magmatism related to the Gondwanan “Cordilleran-type” orogeny is reflected in a series of Carboniferous to Triassic intrusions. A comprehensive model exists for the petrogenesis of such magmas in Chile, however there is relatively little understanding of the nature and timing of Permo-Triassic magmatism in the Frontal Cordillera and Precordillera in Argentina. To address this, we present a new dataset of in situ zircon U–Pb, O and Hf isotopes from 15 felsic intrusions from Argentina. Zircon geochronology shows that magmatism in this region commenced at ca. 285 Ma and continued until ca. 250 Ma. Zircon O and Hf isotopes suggest that the oldest Permian magmas were derived from young supracrustal sources, with elevated δ18O (~ 8.5 to 7.5‰) and negative εHf values (~ − 1 to − 3 εHf). The emplacement of these magmas was coeval with the formation of mantle-derived magmas characterised by mantle-like δ18O (~ 6.0 to 5.5‰) and moderately positive εHf values (~ 4 to 1 εHf). As magmatism continued, transitional isotope signatures became predominant as melts of these disparate sources interacted and hybridised. It is proposed that under a compressional regime, mantle-derived magmas were halted in the lower continental crust, where they exchanged heat and volatiles with an older fertile lithosphere to generate melts from supracrustal sources. A shift in the stress regime at ca. 285 Ma permitted both crustally derived and juvenile mantle-derived magmas to exploit newly formed conduits to rise into the upper crust. A regional compilation of zircon O and Hf isotopes from felsic igneous rocks reveals a coherent secular trend over ~ 100 million years, where the oldest magmatism exhibits a dominant supracrustal component and younger magmas progressively (over 50 Ma) transition towards juvenile mantle-like isotopic compositions. This new dataset from Argentina fills a significant gap in the previous regional models between 285 and 250 Ma and documents the isotopic response of magmas produced in back-arc regions to a transition between compression and extensional/neutral stress regimes. These results give insight into the generation of new, or recycling of, continental crust in a back-arc setting and how the transition from compression to extension is imperative for ore-forming magmas to reach the upper crust.

中文翻译：

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阿根廷 Frontal Cordillera 和 Precordillera 受锆石 O 和 Hf 同位素约束的弧后岩浆的岩石成因

南美大陆安第斯边缘的岩浆和构造活动已超过 3.3 亿年。是“科迪勒拉型”岩浆作用和造山作用明显的类型位置。在阿根廷和智利，在南纬 28°和 40°之间，与冈瓦纳“科迪勒拉式”造山运动相关的岩浆作用反映在一系列石炭纪至三叠纪侵入体中。智利此类岩浆的岩石成因存在综合模型，但对阿根廷前科迪勒拉和前科迪勒拉二叠纪-三叠纪岩浆作用的性质和时间的了解相对较少。为了解决这个问题，我们提供了来自阿根廷 15 个长英质侵入体的原位锆石 U-Pb、O 和 Hf 同位素的新数据集。锆石年代学表明，该地区的岩浆活动开始于约。285 Ma 并持续到大约 285 Ma。250 毫安。锆石 O 和 Hf 同位素表明，最古老的二叠纪岩浆来自年轻的地壳源，具有升高的 δ18O（~8.5 至 7.5‰）和负 εHf 值（~ - 1 至 - 3 εHf）。这些岩浆的侵位与地幔源岩浆的形成同时期，其特征是地幔样 δ18O（~6.0 至 5.5‰）和中等正的 εHf 值（~4 至 1 εHf）。随着岩浆活动的继续，过渡同位素特征变得占主导地位，因为这些不同来源的熔体相互作用和杂交。有人提出，在压缩机制下，地幔来源的岩浆在下大陆地壳中停止，在那里它们与较老的肥沃岩石圈交换热量和挥发物，从而从上地壳来源产生熔体。应力状态的变化约。285 Ma 允许地壳来源和年轻地幔来源的岩浆利用新形成的管道上升到上地壳。来自长英质火成岩的锆石 O 和 Hf 同位素的区域汇编揭示了约 1 亿年的连贯长期趋势，其中最古老的岩浆活动显示出占主导​​地位的地壳成分和较年轻的岩浆逐渐（超过 50 Ma）过渡到年轻地幔状同位素组成. 这个来自阿根廷的新数据集填补了之前 285 至 250 Ma 区域模型的重大空白，并记录了弧后区域产生的岩浆对压缩和拉伸/中性应力状态之间过渡的同位素响应。这些结果让我们深入了解新产品的产生或回收，