Characterization and geodynamic implications of contrasting metamorphic evolution in juxtaposed high-pressure units of the western Erzgebirge (Saxony, Germany)
Characterization and geodynamic implications of contrasting metamorphic evolution in juxtaposed high-pressure units of the western Erzgebirge (Saxony, Germany)
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DOI：
10.1127/ejm/10/2/0261
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发表时间：
1998-03
影响因子：
2.1
通讯作者：
K. Rötzler;R. Schumacher;W. Maresch;A. Willner
中科院分区：
文献类型：
--
作者：
K. Rötzler;R. Schumacher;W. Maresch;A. Willner
西厄尔日格由三个构造变质推覆体单元组成，它们在挖掘过程中和挖掘后并置，具有不同的P-T历史。构造上由下至上依次为云母片岩单元、石榴石-千层岩单元和千层岩单元。这三个单元围绕着一个反形的核心形成了同心圆带，该反形由厄尔斯格的两个构造最低的单元组成，即红-灰色片麻岩单元和上覆片麻岩-榴辉岩单元。本文对西额尔齐格云母片岩单元和石榴石千层岩单元的样品进行了详细的研究，以阐明该地区的地球动力学历史。不同世代的矿物组合可以与变质压力-温度条件以及岩石组构的发育相关联。常规的热气压测量以及基于内部一致的热力学数据集的计算表明，最底层的云母片岩-辉绿岩单元是在高压、中温条件下形成的。根据保存下来的遗迹矿物组合，得到了不同类型云母片岩和正长石在470 ~ 560℃温度下的最低压力为12 kbar。在7-8 kbar和500-630 oe的条件下，第二阶段的平衡发生在主叶理形成期间。在450-500℃和2-3 kbar的条件下，在第三次变形事件期间，表明了平衡的后期阶段。在大约470°C和9 kbar的条件下，获得了明确的P-T平衡条件。云母-片岩-榴辉岩单元和石榴石-千层岩单元的P-T路径为顺时针方向，最大压力先于热顶。千层岩单元的P-T条件没有得到很好的约束，但表明压力约为2kbar。石英显微结构表明，该装置的温度超过300°C。这些结果反映了一个复杂的变质历史，其特征是由Variscan大陆-大陆碰撞引起的压缩，随后是一个多阶段的伸展事件。关键词：西额尔齐格，压力-温度路径，热气压计，瓦里斯坎大陆碰撞，地壳伸展掘出。
The Western Erzgebirge consists of a sequence of three tectonometamorphic nappe units with contrasting P-T histories that became juxtaposed during and after exhumation. From the tectonically lowermost to the uppermost these units are the Mica-SchistlEc1ogite Unit, the Garnet-Phyllite Unit and the Phyllite Unit. These three units form concentric zones around the core of an antiform composed of the two tectonically lowermost units of the Erzgebirge, the Red-and-Grey-Gneiss Unit and the overlying GneisslEclogite Unit. SampIes from the Mica-SchistlEclogite Unit and the Garnet-Phyllite Unit of the Western Erzgebirge have been investigated in detail, in order to elucidate the geodynamic history of the region. Different generations of mineral assemblages can be correlated with metamorphic pressure-temperature conditions as weil as with the development of the rock fabric. Conventional thermobarometry as weil as calculations based on an internally consistent thermodynamic data set suggest that the lowermost Mica-SchistlEclogite Unit formed under high pressure, intermediate-temperature conditions. Based on preserved relic mineral assemblages , minimum pres sures of 12 kbar at temperatures of 470-560 °C were obtained for different types of mica schist and orthogneiss. A second stage of equilibration occurred during the formation of the main foliation under conditions of about 7-8 kbar and 500-630 oe. A late stage of equilibration is indicated under conditions of 450-500°C and 2-3 kbar during the third deformational event. Well-defined P-T conditions of equilibration at approximately 470°C and 9 kbar were obtained for the Garnet-Phyllite Unit. P-T paths of the Mica-SchistlEclogite Unit and the Garnet-Phyllite Unit are clockwise, with maximum pressures preceding the thermal c1imax. P-T conditions for the Phyllite Unit are poorly constrained, but pressures of approximately 2 kbar are indicated. The quartz microtexture suggests temperatures in excess of 300°C for this unit. These results reflect a complex metamor phic history within a tectonic framework characterized by compression due to Variscan continent-continent collision, followed by a multistage extensionaJ event. Key-words: Western Erzgebirge, pressure-temperature path, thermobarometry, Variscan continent-continent collision, exhumation by crustal extension.