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首页> 外文期刊>Contributions to Mineralogy and Petrology >Middle Ordovician subduction of continental crust in the Scandinavian Caledonides: an example from Tjeliken, Seve Nappe Complex, Sweden
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Middle Ordovician subduction of continental crust in the Scandinavian Caledonides: an example from Tjeliken, Seve Nappe Complex, Sweden

机译：中间奥陶诺迪亚·斯堪的纳维亚喀茶岛大陆地壳介绍：瑞典的Tjeliken的一个例子，Seve Nappe Complex，Seve Nappe Complex

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摘要

The Seve Nappe Complex of the Scandinavian Caledonides is thought to be derived from the distal passive margin of Baltica which collided with Laurentia in the Scandian Phase of the Caledonian Orogeny at 430-400 Ma. Parts of the Seve Nappe Complex were affected by pre-Scandian high-and ultrahigh-pressure metamorphism, in a tectonic framework that is still unclear, partly due to uncertainties about the exact timing. Previous age determinations yielded between similar to 505 and similar to 446 Ma, with a general trend of older ages in the North (Norrbotten) than in the South (Jamtland). New age determinations were performed on eclogite and garnet-phengite gneiss at Tjeliken in northern Jamtland. Thermodynamic modelling yielded peak metamorphic conditions of 25-27 kbar/680-760 degrees C for the garnet-phengite gneiss, similar to published peak metamorphic conditions of the eclogite (25-26 kbar/650-700 degrees C). Metamorphic rims of zircons from the garnet-phengite gneiss were dated using secondary ion mass spectrometry and yielded a concordia age of 458.9 +/- 2.5 Ma. Lu-Hf garnet-whole rock dating yielded 458 +/- 1.0 Ma for the eclogite. Garnet in the eclogite shows prograde major-element zoning and concentration of Lu in the cores, indicating that this age is related to garnet growth during pressure increase, i.e. subduction. The identical ages from both rock types, coinciding with published Sm-Nd ages from the eclogite, confirm subduction of the Seve Nappe Complex in Northern Jamtland during the Middle Ordovician in a fast subduction-exhumation cycle.
机译：斯堪的纳维亚喀茶岛的Seve Nappe综合体被认为是巴尔的辛的远端被动边缘，它与洛杉矶山脉的康乃馨阶段的斯科尼亚相撞，在430-400 mA。 Seve Nappe Complex的部分受到斯堪的舞蹈前高和超高压变质的影响，在一个仍然不清楚的构造框架中，部分原因是由于关于确切时序的不确定性。以前的年龄测定产生与505之间相似，类似于446 mA，北北（Norbotten）的一般趋势超过南部（贾姆特兰）。在贾姆特兰北部的Tjeliken对Eclogite和Garnet-Phengite Gneiss进行了新的年龄测定。 Garnet-phengite环味的热力学建模产生25-27 kBar / 680-760℃的峰变质条件，类似于Eclogite的公布峰变质条件（25-26 kbar / 650-700c）。使用二次离子质谱法测定来自石榴石 - 峰锭的Zircons的变质轮，并产生458.9 +/- 2.5 mA的协和症。 Lu-HF石榴石整体摇滚可供eClogite产生458 +/- 1.0 mA。 eClogite中的石榴石显示了核心中Lu的促进主要元素分区和Lu的浓度，表明该年龄与压力增加期间的石榴石生长有关，即俯冲。两种岩石类型的相同年龄，与Eclogite的公布的SM-ND年龄恰逢，在快速俯冲送达周期中确认在中奥陶氏岛北部Jamtland的Seve Nappe综合体的俯冲。

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