美国德克萨斯大学F.M. Rey及其研究团队使用巴塔哥尼亚安第斯山脉的案例，完善了后退增生造山带的碎屑同位素记录。该研究于2024年2月28日发表于国际一流学术期刊《地质学》杂志上。

研究结合弧后盆地的U-Pb锆石年龄、大块岩石εNd和新碎屑锆石εHf，探讨了巴塔哥尼亚—安第斯山脉中生代—新生代的构造演化，了解了边缘退进过程中伴生岩浆弧的演化。结果表明，在150和80Ma之间存在一个较长的同位素幼期岩浆活动阶段，该阶段始于弧后伸展期，并在边缘转为收缩期后持续了很长时间。

研究人员认为，延长的幼年同位素趋势主要始于弧后扩张期间(150-120Ma)，弧向海沟的迁移，并持续于弧后盆地闭合期间(120-80Ma)，未充分下沉的幼年衰减和洋壳的部分熔融。这一解释意味着构造应力本身并不能预测同位素的变化趋势，同化作用或俯冲地壳的组成等因素对岩浆同位素组成具有重要的控制作用，特别是在后退造山带和过渡造山带。

据悉，U-Pb锆石年代学和同位素记录对认识会聚边缘动力学具有重要意义。造山带旋回性模型将构造机制与推进造山带岩浆同位素特征联系起来，将挤压机制与演化特征联系起来，将伸展机制与幼期特征联系起来；然而，这种框架可能不适用于后退造山带，后者通常在弧后裂陷和海洋扩张期间产生大量的地壳非均质性。

附：英文原文

Title: Detrital isotopic record of a retreating accretionary orogen: An example from the Patagonian Andes

Author: F.M. Rey, M.A. Malkowski, J.C. Fosdick, S.C. Dobbs, M. Calderón, M.C. Ghiglione, S.A. Graham

Issue&Volume: 2024-02-28

Abstract: U-Pb zircon geochronology and isotopic records have played an influential role in our understanding of convergent margin dynamics. Orogenic cyclicity models link tectonic regimes with magmatic isotopic signatures in advancing orogens, relating compressional regimes with evolved signatures and extension with juvenile signatures; however, such frameworks may not apply for retreating orogens, which commonly produce substantial crustal heterogeneities during backarc rifting and ocean spreading. We explore the Mesozoic to Cenozoic Patagonian Andes tectonic evolution, combining U-Pb zircon ages, bulk rock εNd, and new detrital zircon εHf from the retroarc basin to understand the associated magmatic arc evolution during retreat and advance of the margin. Our results reveal a protracted phase of isotopically juvenile magmatism between 150 and 80 Ma, which began during backarc extension and persisted long after the margin switched to a contractional regime. We propose that the prolonged juvenile isotopic trend started mainly due to trenchward migration of the arc during backarc extension (150120 Ma) and persisted due to partial melting of underthrusted juvenile attenuated and oceanic crust during backarc basin closure (12080 Ma). This interpretation implies that tectonic stress alone does not predict isotopic trends, and factors like assimilation or the composition of underthrusted crust are important controls on magmatic isotopic composition, especially in retreating and transitional orogens.

DOI: 10.1130/G51918.1

Source: https://pubs.geoscienceworld.org/gsa/geology/article/doi/10.1130/G51918.1/635693/Detrital-isotopic-record-of-a-retreating