Subduction, exhumation, and resubduction in the Scandinavian Caledonides: studying the deep levels of a Himalaya-type orogen

斯堪的纳维亚加里东山脉是一个碰撞造山带，与现在的喜马拉雅山脉相当，但自古生代形成以来就受到了严重的侵蚀。因此，可以直接在实地研究该山区的深层，并与现代山区的地表和地球物理信息相补充，形成喜马拉雅型碰撞造山作用的更完整的图像。Seve推覆复合体是一组来自Baltoscandian边缘外部的逆冲岩片，在约1000年与Laurentia碰撞期间向东侵位在波罗的海上空。400 Ma，并在约400 Ma的距离上出现。在瑞典和挪威的1000公里，最近被确定为超高压（UHP）变质火山岩的热压法和微金刚石夹杂物的发现。Seve的超高压变质作用可能发生在晚奥陶世（约1000年）。460至450 Ma），早于结构较深的西部片麻岩杂岩（约450 Ma）的超高压变质作用。420 ~ 400 Ma）。作为一个工作的假设，Seve超高压岩石形成于弧-陆碰撞，被挖出的提取弧前岩石圈块，部分resubducted与西部片麻岩复杂的波罗的海-劳伦提斯碰撞，并再次挖出提取的Iapetus大洋板。喜马拉雅山的类似过程将包括印度与科希斯坦-拉达克弧的碰撞和印度边缘岩石的超高压变质作用，通过提取上覆地幔楔而进行的折返，以及目前印度地壳向超高压深度的俯冲，无法直接观察。我们将使用以下方法来检验这一假设：结构和显微构造的工作，以建立的高压和超高压单位的Seve的变形历史;榴辉岩的Lu-Hf石榴石测年; U-Pb锆石测年的折返相关的熔体和前，同，和构造后的堤防;逐步逆变形的四个横截面跨越斯堪的纳维亚加里东山脉。

The Scandinavian Caledonides are a collisional orogen comparable to the present-day Himalaya but deeply eroded since their formation in the Paleozoic. Therefore, deep levels of the mountain belt can be directly studied in the field and complemented with surface and geophysical information from present-day mountain belts into a more complete picture of Himalaya-type collisional mountain-building. The Seve Nappe Complex, an assemblage of thrust sheets from the outer part of the Baltoscandian margin, emplaced towards east over Baltica during the collision with Laurentia at ca. 400 Ma and cropping out over a distance of ca. 1000 km in Sweden and Norway, has most recently been established as an ultrahigh-pressure (UHP) metamorphic terrane by thermobarometry and the finding of microdiamond inclusions. UHP metamorphism in the Seve probably occurred in the Late Ordovician (ca. 460 to 450 Ma), earlier than the UHP metamorphism of the structurally deeper Western Gneiss Complex (ca. 420 to 400 Ma). As a working hypothesis, Seve UHP rocks formed in an arc-continent collision, were exhumed by extraction of the forearc lithosphere block, partly resubducted together with the Western Gneiss Complex during Baltica-Laurentia collision, and exhumed again by extraction of the Iapetus oceanic slab. Analogue processes in the Himalaya would encompass the collision of India with the Kohistan-Ladakh arc and UHP metamorphism in Indian margin rocks, their exhumation by extraction of the overlying mantle wedge, and the presently ongoing subduction of Indian crust to UHP depths, not accessible to direct observation. We will test the hypothesis using the following methods: structural and microstructural work on the HP and UHP units of the Seve in order to establish the deformation history of the terrane; Lu-Hf garnet dating of eclogites; U-Pb zircon dating of exhumation-related melts and pre-, syn-, and posttectonic dikes; step-wise retrodeformation of four cross-sections across the Scandinavian Caledonides.