Neubauer Franz, Chang Ruihong, Dong Yunpeng, Genser Johann, Liu Yongjiang
Department of Environment and Biodiversity, Paris-Lodron University of Salzburg, Salzburg, Austria.
Department of Earth Sciences, The University of Hong Kong, Hong Kong, Hong Kong.
Isotopes Environ Health Stud. 2025 Mar;61(1):114-132. doi: 10.1080/10256016.2024.2367099. Epub 2024 Jul 24.
Radiogenic isotopes of igneous and detrital minerals from various clastic rocks of mountain belts are used to reveal tectonic and sedimentary processes, which are otherwise difficult to detect. Here, we discuss the results of U-Pb and Lu-Hf zircon systems, and Ar/Ar on detrital white mica in Eastern Alps. Zircon and white mica are chemically and mechanically stable and occur in magmatic, metamorphic and sedimentary rocks. During subsequent metamorphism, zircon is resistant against high temperature, >650 °C (U-Pb) and 900 °C (Lu-Hf). The Lu-Hf zircon system is used as a tracer of initial magma separation from the mantle, and the U-Pb zircon system records magmatic crystallization. The Ar/Ar white mica system is stable up to 400-450 °C dating either formation or cooling after high-grade metamorphism. Detrital U-Pb zircon ages on two major rivers draining the Eastern Alps do not record any sign of Alpine orogeny or metamorphism. Consequently, U-Pb zircon studies can entirely miss the record of collisional orogeny in cool, magma-poor collision orogens. In contrast, Ar/Ar white mica ages record Early and Late Alpine metamorphism but are limited to revealing the pre-orogenic history. U-Pb zircon and Ar/Ar white mica yield different information in provenance studies. In the Eastern Alps, U-Pb zircon dating of magmatic and clastic rocks indicates intense formation of magmatic rocks between 630 and 230 Ma. Felsic rocks dominate the older age groups, and increasingly young mafic rocks were dated, specifically between 265 and 230 Ma. Hf isotopes record increasing juvenile input since ∼630 Ma. Two different groups with respect to Mesoproterozoic depleted mantle ages are shown: (1) one group with a Mesoproterozoic age gap typical for Gondwana-derived units, and (2) a rare group with Mesoproterozoic ages recording a new tectonic element in the Austroalpine basement in Alps.
来自山区各种碎屑岩中岩浆矿物和碎屑矿物的放射性同位素被用于揭示构造和沉积过程，否则这些过程很难被探测到。在此，我们讨论东阿尔卑斯山碎屑白云母的U-Pb和Lu-Hf锆石体系以及Ar/Ar的研究结果。锆石和白云母在化学和机械方面都很稳定，存在于岩浆岩、变质岩和沉积岩中。在随后的变质作用中，锆石能抵抗高温，>650 °C（U-Pb）和900 °C（Lu-Hf）。Lu-Hf锆石体系被用作初始岩浆从地幔分离的示踪剂，而U-Pb锆石体系记录岩浆结晶过程。Ar/Ar白云母体系在高达400 - 450 °C时稳定，可测定高级变质作用后的形成或冷却时间。流经东阿尔卑斯山的两条主要河流的碎屑U-Pb锆石年龄并未记录到阿尔卑斯造山运动或变质作用的任何迹象。因此，U-Pb锆石研究可能会完全遗漏冷的、岩浆匮乏的碰撞造山带中碰撞造山作用的记录。相比之下，Ar/Ar白云母年龄记录了早阿尔卑斯和晚阿尔卑斯变质作用，但仅限于揭示造山运动前的历史。U-Pb锆石和Ar/Ar白云母在物源研究中提供了不同的信息。在东阿尔卑斯山，岩浆岩和碎屑岩的U-Pb锆石测年表明在630至230 Ma之间岩浆岩强烈形成。长英质岩石在较老年龄组中占主导，且测定的镁铁质岩石年龄越来越年轻，特别是在265至230 Ma之间。Hf同位素记录了自约630 Ma以来新生地壳物质的增加。关于中元古代亏损地幔年龄显示出两个不同的组：（1）一组具有典型的冈瓦纳衍生单元的中元古代年龄间隔，（2）一个罕见的组，其中元古代年龄记录了阿尔卑斯澳阿尔卑斯基底中的一个新构造元素。
