Detrital zircon U‐Pb ages and Hf isotopic constraints on the terrigenous sediments of the Western Alps and their paleogeographic implications
Detrital zircon U‐Pb ages and Hf isotopic constraints on the terrigenous sediments of the Western Alps and their paleogeographic implications
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DOI：
10.1002/2016tc004276
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发表时间：
2016-11
期刊：
影响因子：
4.2
通讯作者：
Y. Chu;Wei Lin;M. Faure;Qingchen Wang
中科院分区：
文献类型：
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作者：
Y. Chu;Wei Lin;M. Faure;Qingchen Wang
来自西阿尔卑斯山白垩纪云母片岩、始新世晚期-渐新世早期砂岩和渐新世早期粉砂岩的碎屑锆石分为三个主要的可分离年龄组，分别为610-540 Ma、490-430 Ma和340-280 Ma，对应于广泛分布于西欧和中欧的Cadomian（新元古代）、Ordovician和Variscan（石炭纪）事件。Hf同位素结果表明，这三个岩浆和构造幕并没有引起显着的生产的青年地壳。在渐新世早期的“Alcantes à Blocs”地层和Briançonnais“Flysch Noir”地层中发现了一组三叠纪锆石，年龄约为250-200 Ma，被认为来自南阿尔卑斯山。相反，始新世晚期至渐新世早期砂岩中不存在这一年龄组。与沉积学研究一致，我们的研究结果表明，始新世砂岩的主要源区可能位于欧洲大陆。内带碎屑的到达发生在渐新世早期，与外来单元传播过程中由西北向西的构造旋转同步。根据以前的研究和我们的新数据，我们认为，Briançonnais区可能是一个古浮雕，因为始新世中期，缺乏碎屑从亚得里亚海单位。当时的沉积物堆积在亚得里亚海板块的前渊。从渐新世开始，在区域性隆升之后，堵塞被切断，因此，内部带开始向西部挠曲盆地提供碎屑。
Detrital zircons from Cretaceous micaschist, late Eocene‐earliest Oligocene sandstone and early Oligocene siltstone of the Western Alps fall into three main separable age clusters at 610–540 Ma, 490–430 Ma, and 340–280 Ma that correspond to the Cadomian (Neoproterozoic), Ordovician, and Variscan (Carboniferous) events widespread in western and central Europe. Hf isotopic results indicate that these three magmatic and tectonic episodes did not give rise to significant production of juvenile crust. A distinguishable group of Triassic zircons, around 250–200 Ma which is considered to derive from the Southern Alps, has been detected in the early Oligocene “Schistes à Blocs” formation and the Briançonnais “Flysch Noir”. In contrast, this age group is absent in late Eocene to earliest Oligocene sandstones. In agreement with sedimentological studies, our results show that the main source areas of the Eocene sandstone were probably located in the European continent. The arrival of detritus from the Internal Zone occurred in early Oligocene, coeval with the tectonic rotation from northwestward to westward in the propagation of allochthonous units. Based on previous studies and our new data, we argue that the Briançonnais Zone was likely a paleorelief since the middle Eocene that accounts for the lack of detritus from the Adriatic units. Contemporary sediments were accumulated in the foredeep of the Adriatic plate. From Oligocene time onward, the blockage was cut through after a regional uplifting, and thus, the Internal Zone started to provide detritus into the western flexural basins.