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Exhumation of the High‐Pressure Tsäkkok Lens, Swedish Caledonides: Insights From the Structural and White Mica 40Ar/39Ar Geochronological Record
Tectonics ( IF 4.2 ) Pub Date : 2020-07-21 , DOI: 10.1029/2020tc006242
C. J. Barnes 1 , P. Jeanneret 2, 3 , K. Kullerud 4, 5 , J. Majka 1, 2 , D. A. Schneider 6 , M. Bukała 1 , I. Klonowska 1
Affiliation  

Integrated structural, geochemical, and geochronological investigations were conducted on metasedimentary rocks in the eclogite‐bearing Tsäkkok Lens of the Seve Nappe Complex (Scandinavian Caledonides) to resolve its exhumation history. Three deformation events are defined. D1 is likely related to the prograde to peak‐metamorphic stages, represented by a locally preserved S1. D2 resulted in vertical shortening and is defined by a pervasive S2 and cm‐/m‐scale F2 closed folds. D2 terminated with Scandian thrusting, which emplaced the overlying Köli Nappe Complex. D3 records NE‐SW shortening and constitutes m‐/km‐scale F3 open folds that deformed the Tsäkkok Lens and Köli Nappe Complex together. In situ white mica 40Ar/39Ar geochronology was conducted on select metasedimentary samples possessing S1 or S2 to resolve the timing of exhumation. Postdecompression cooling of the Tsäkkok Lens is best recorded by samples containing S1 or S2 that yield homogeneous white mica chemistry and 40Ar/39Ar dates. The timing of cooling is resolved to 477.2 ± 4.1 Ma (S1) and 475.3 ± 3.5 Ma (S2). Vertical shortening of the lens during exhumation may have proceeded until 458.1 ± 9.0 Ma. Later‐stage deformation during Scandian thrusting penetrated the Tsäkkok Lens at 429.9 ± 9.0 Ma, or younger. This resulted in noncoaxial deformation of the metasedimentary rocks, producing heterogeneous white mica chemistry and partially reset the older 40Ar/39Ar cooling record. Temperatures for deformation are resolved to the upper greenschist‐lower amphibolite facies. Altogether, the Tsäkkok Lens records rapid exhumation from eclogite‐facies conditions to midcrustal depths or shallower, followed by emplacement of the overlying Köli Nappe Complex.

中文翻译:

瑞典喀里多尼德群岛Tsäkkok透镜的发掘:来自结构云母和白云母40Ar / 39Ar年代记录的见解

在Seve Nappe复合体(斯堪的纳维亚喀里多尼德)的含榴辉岩的Tsäkkok晶状体中的准沉积岩上进行了综合的结构,地球化学和地质年代研究,以解决其发掘历史。定义了三个变形事件。D1可能与升级到峰变态阶段有关,以局部保存的S1表示。D2导致垂直缩短,并由普遍的S2和cm / m级F2闭合褶皱定义。D2因斯堪的纳斯冲刺而终止,将其冲上了上覆的KöliNappe建筑群。D3记录NE‐SW缩短,并构成m / km尺度的F3褶皱,使TsäkkokLens和KöliNappe Complex一起变形。原位白云母40 Ar / 39对拥有S1或S2的选定沉积沉积样品进行了Ar年代学研究,以解决尸体挖掘的时间。Tsäkkok透镜的减压后冷却最好通过含有S1或S2的样品来记录,这些样品产生均一的白云母化学成分和40 Ar / 39 Ar日期。冷却时间定为477.2±4.1 Ma(S1)和475.3±3.5 Ma(S2)。掘尸期间晶状体的垂直缩短可能已经进行到458.1±9.0 Ma。在斯堪的纳斯冲刺过程中,后期变形以429.9±9.0 Ma或更小深度穿透了Tsäkkok透镜。这导致了准沉积岩的非同轴变形,产生了异质的白云母化学成分,并使部分较旧的40 Ar / 39复位。氩气冷却记录。变形温度解析为上部绿片岩-下部闪石岩相。总的来说,Tsäkkok镜头记录了从榴辉岩相状态到中地壳深度或更浅处的快速发掘出土,然后覆盖了上覆的KöliNappe综合体。
更新日期:2020-07-21
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