Deformation inside a paleosubduction channel – Insights from microstructures and crystallographic preferred orientations of eclogites and metasediments from the Tauern Window, Austria
Deformation inside a paleosubduction channel – Insights from microstructures and crystallographic preferred orientations of eclogites and metasediments from the Tauern Window, Austria
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DOI：
10.1016/j.jsg.2015.11.006
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发表时间：
2016
影响因子：
3.1
通讯作者：
R. Keppler;M. Stipp;J. Behrmann;K. Ullemeyer;F. Heidelbach
中科院分区：
文献类型：
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作者：
R. Keppler;M. Stipp;J. Behrmann;K. Ullemeyer;F. Heidelbach
陶恩窗的榴辉岩带是一个折返的俯冲通道，由高压变质沉积物基质中具有不同退变质程度的榴辉岩组成。岩石暴露于600 °C和20-25千巴，然后在折返过程中退变质，首先在蓝片岩相下，后来在角闪岩相变质下。为了深入了解俯冲和折返过程中的俯冲通道内的变形，新鲜和退变质榴辉岩，以及周围的变质沉积物进行了研究，相对于他们的变形显微结构和晶体学择优取向（CPOs）。原始榴辉岩和退变质榴辉岩在绿辉石中具有晶界迁移和亚晶旋转重结晶显微结构。取向差轴分析揭示了互补变形机制的活动，包括晶界滑动和位错蠕变。榴辉岩的绿辉石CPO对应于占主导地位的SL-面料的平面应变变形的特点，虽然有局部变平或收缩的古俯冲通道内。退变质榴辉岩中的蓝闪石CPO与绿辉石相匹配，表明在蓝片岩相条件下折返过程中持续存在恒定的应变几何形状。寄主高压变质沉积物的塑性变形持续时间超过榴辉岩，如白色云母织物和石英CPO所示。后者是一贯不对称的，指向非同轴变形的操作。显微结构和CPO数据表明，一个连续的塑性变形循环与榴辉岩和蓝片岩相变质有关的俯冲和折返的不同岩石单元。
The Eclogite Zone, of the Tauern Window is an exhumed subduction channel comprising eclogites with different grades of retrogression in a matrix of high-pressure metasediments. The rocks were exposed to 600 °C and 20–25 kbars, and then retrogressed during their exhumation, first under blueschist facies and later under amphibolite facies metamorphism. To gain insights into the deformation within the subduction channel during subduction and exhumation, both fresh and retrogressed eclogites, as well as the surrounding metasediments were investigated with respect to their deformation microstructures and crystallographic preferred orientations (CPOs). Pristine and retrogressed eclogites show grain boundary migration and subgrain rotation recrystallization microstructures in omphacite. A misorientation axes analysis reveals the activity of complementary deformation mechanisms including grain boundary sliding and dislocation creep. The omphacite CPOs of the eclogites correspond to dominant SL-fabrics characteristic of plane strain deformation, though there are local variations towards flattening or constriction within the paleosubduction channel. The glaucophane CPOs in retrogressed eclogites match those of omphacite, suggesting that a constant strain geometry persisted during exhumation at blueschist facies conditions. Plastic deformation of the host high-pressure metasediments outlasted that of the eclogites, as indicated by white mica fabrics and quartz CPO. The latter is consistently asymmetric, pointing to the operation of non-coaxial deformation. The microstructures and CPO data indicate a continuous plastic deformation cycle with eclogite and blueschist facies metamorphism related to subduction and exhumation of the different rock units.