Protolith ages and exhumation histories of (ultra)high-pressure rocks across the Western Gneiss Region, Norway
Protolith ages and exhumation histories of (ultra)high-pressure rocks across the Western Gneiss Region, Norway
复制标题
挪威西部片麻岩地区（超）高压岩石的原岩年龄和折返历史
DOI：
10.1130/b25817.1
复制
发表时间：
2007
影响因子：
4.9
通讯作者：
G. Gehrels
中科院分区：
文献类型：
--
作者：
E. Walsh;B. Hacker;P. Gans;M. Grove;G. Gehrels
使用 U/Pb 锆石、Th/Pb 独居石和 40 Ar/ 39 Ar 白云母年龄评估了挪威西部片麻岩地区东部超高压到高压单元的原岩形成时间、超高压 (UHP) 俯冲以及随后的折返。榴辉岩的 U/Pb 锆石年龄表明，在整个物质俯冲到（超）高压之前，海洋和大陆异地岩就已经安置在波罗的海基底上。整个西部片麻岩地区的外来岩中的榴辉岩都是加里东期的，并且显示出一定程度的锆石（重）结晶，该程度随着峰值压力的增加而增加，从而可以解释整个地区经历了同步俯冲。 40 Ar/ 39 Ar白云母年龄为399 Ma，表明西部片麻岩地区的东部已被挖掘到浅地壳水平，而超高压变质作用正在更远的西部进行，表明板片向西倾斜。 40 Ar/ 39 Ar白云母年龄在整个西部片麻岩区也显示出明显的从东到西的梯度，表明西部片麻岩区在399和390 Ma之间从东到西穿时地上升到地壳水平。
The timing of protolith formation, ultrahigh-pressure (UHP) subduction, and subsequent exhumation for the ultrahigh-pressure to high-pressure units across the eastern part of the Western Gneiss Region, Norway, were assessed using U/Pb zircon, Th/Pb monazite, and 40 Ar/ 39 Ar white mica ages. U/Pb zircon ages from eclogites demonstrate that oceanic and continental allochthons were emplaced onto the Baltica basement before the entire mass was subducted to (ultra)high pressure. Eclogites within the allochthons across the entire Western Gneiss Region are Caledonian and show a degree of zircon (re)crystallization that increases with peak pressure, permitting the interpretation that the entire region underwent synchronous subduction. 40 Ar/ 39 Ar white mica ages of 399 Ma indicate that the eastern part of the Western Gneiss Region had been exhumed to shallow crustal levels while UHP metamorphism was ongoing farther west, indicating a westward dip to the slab. The 40 Ar/ 39 Ar white mica ages also show a clear east-to-west gradient across the entire Western Gneiss Region, indicating that the Western Gneiss Region rose diachronously to crustal levels from east to west between 399 and 390 Ma.