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首页> 外文学位 >Exhumation of deep mountain roots: lessons from the Western Tatra Mountains, northern Slovakia.
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Exhumation of deep mountain roots: lessons from the Western Tatra Mountains, northern Slovakia.

机译：挖掘深山根源：来自斯洛伐克北部塔特拉山西部的课程。

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摘要

The Tatric crystalline unit of the Western Carpathians in northern Slovakia displays an inverted metamorphic sequence where high-grade migmatite and orthogneiss units are overlying lower-grade mica schists. Enclosed within the migmatites are lenses of eclogite-bearing amphibolites. Conventional geothermobarometry coupled with isochemical modeling constrained P-T paths that exhibit contrasting metamorphic histories for rock units that are now heterogeneously interleaved. Relict eclogite facies assemblages with occasionally preserved omphacite record post-peak pressure conditions of 1.7-1.8 GPa followed by near isothermal decompression at ∼750°C leading to intensive re-equilibration of eclogites at high-pressure granulite facies conditions and development of diopside + plagioclase symplectitic textures. New ID-TIMS Sm-Nd dating of garnet separated from the omphacite-bearing eclogite yields a whole rock-garnet isochron age of 337 +/- 10 Ma, with an epsilon Nd isotopic composition of +8.3. While major element profiles across the garnets display little variation, the trace element distribution shows a typical HREE enrichment profile and a slight core to rim disparity with LREE and MREE concentrations higher in the cores and higher HREE in the rims. Granulite-facies migmatites that host the eclogite boudins record lower pressure metamorphic conditions of 1.2 GPa at ∼750°C and a similar retrograde path. The lower-grade micaschists reached metamorphic conditions of 0.8 GPa at ∼650°C. Monazite U-Pb analysis from a migmatite surrounding the eclogite boudins yields one population of ca. 380 Ma age. Another migmatite away from the eclogite yields two populations monazite ages. A robust 340 +/- 11 Ma monazite U-Pb age is indistinguishable from our garnet age and U-Pb SIMS age of zircons in the anatectic leucosome of the migmatite (347 +/- 7 Ma). We interpret the ca. 340 Ma ages to represent the exhumation of the deep crustal root of the Variscan orogen into the middle crust coeval with anatexis. A younger monazite U-Pb age of 300 +/- 16 Ma is consistent with 40Ar/39Ar thermochronology data of ca. 310 Ma that is likely indicative of the Late Carboniferous I-type magmatism and cooling in the Tatric block. Cooling rates calculated by garnet diffusion modeling yield estimates of ∼30 °/Ma. This exhumation was likely tectonically forced by the action of a rigid indentor which prompted the weak lower crust to be heterogeneously extruded to mid-crustal levels at a time coeval with anatexis and subsequently extruded with mid-crustal material to the upper crust.
机译：斯洛伐克北部西喀尔巴阡山脉的塔特拉晶体单元显示出一个倒置的变质层序，其中高等级的蒙脱石和生铁片单元覆盖着低级的云母片岩。蒙脱石中包裹着含榴辉岩的角闪石晶状体。常规的地热气压测量法与等化学建模相结合，限制了P-T路径，这些路径表现出现在异质交错的岩石单元的对比变质历史。遗迹榴辉岩相组合，偶尔保留的辉绿岩记录的峰后压力条件为1.7-1.8 GPa，随后在约750°C等温减压，导致在高压粒岩相条件下榴辉岩强烈地重新平衡，并形成透辉石+斜长石象征性的纹理。从含绿辉石的榴辉岩中分离出的石榴石的新ID-TIMS Sm-Nd测年结果表明，整个岩石-石榴石的等时年龄为337 +/- 10 Ma，εNd同位素组成为+8.3。虽然整个石榴石上的主要元素分布几乎没有变化，但痕量元素分布却显示出典型的HREE富集分布，并且芯与轮缘之间的差异很小，其中芯中的LREE和MREE浓度较高，而轮缘中的HREE较高。拥有榴辉岩布丁的粒岩相辉石记录了在约750°C和类似的逆行路径下较低的1.2 GPa变质条件。低品位的云母在〜650°C达到0.8 GPa的变质条件。从围绕榴辉岩布丁的辉石中的独居石U-Pb分析可得出大约一个种群。 380 Ma年龄。远离榴辉岩的另一个辉长岩产生两个族群独居石年龄。稳固的340 +/- 11 Ma独居石的U-Pb年龄与我们的石榴石年龄和辉石的钙质白质体的锆石的U-Pb SIMS年龄（347 +/- 7 Ma）没有区别。我们解释ca。 340 Ma年龄代表了瓦里斯卡造山带的深地壳发掘到带有后足的中地壳的同时期。年龄小于300 +/- 16 Ma的独居石U-Pb年龄与大约40 Ar / 39Ar的热年代学数据一致。 310 Ma可能指示了塔塔克块体的晚石炭世I型岩浆作用和冷却。通过石榴石扩散模型计算出的冷却速率估计约为30°/ Ma。这种发掘可能是由于刚性压头的作用而引起的，它促使薄弱的下地壳在与食蚁兽同时出现时被异质地挤出到中地壳水平，随后又用中地壳材料挤出到上地壳。

著录项

  • 作者

    Moussallam, Yves.;

  • 作者单位

    University of Ottawa (Canada).;

  • 授予单位 University of Ottawa (Canada).;
  • 学科 Geology.;Mineralogy.
  • 学位 M.Sc.
  • 年度 2010
  • 页码 92 p.
  • 总页数 92
  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类
  • 关键词

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