Occurrence and significance of inverted metamorphic gradients in the western Scandinavian Caledonides
Occurrence and significance of inverted metamorphic gradients in the western Scandinavian Caledonides
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斯堪的纳维亚喀里多尼德西部地区逆变质梯度的发生及其意义
DOI：
10.1144/gsjgs.137.3.0219
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发表时间：
1980
影响因子：
2.7
通讯作者：
B. Lagerblad
中科院分区：
文献类型：
--
作者：
P. Andreasson;B. Lagerblad
在斯堪的纳维亚的加里东地区，基底与覆盖沉积物的薄单板可以追溯到从前线的原地远西向造山带的中心。可以记录变质程度的变化，并与上覆推覆体的变质程度进行对比。这些盖层沉积物的变质性质进行了检查，在最深的结构水平的两个窗口，200公里的加里东前线的W。盖层之上推覆体的侵位导致了绿片岩相条件下的渐进重结晶，共生体中石英+珍珠云母+白云母、石英+云母+白云母和石英+白色云母+石墨的发育，确定了与推覆体位移有关的穿透叶理。最终上覆岩层压力估计为6-8 kb。推覆体就位后，温度首先在550°C左右达到峰值。尽管西风的情况和深构造地层水平的变质沉积物，其变质历史是不相容的位置靠近造山带内部。上覆盖层序列显示出至少2次变质分带的反转。这些开发的高品位推覆体以上的低品位或未变质的单位，与不完整的后续恢复的热剖面，并在逆冲推覆过程中集中应变的催化作用的结果。西部窗口热剖面的锯齿状印记表明，斯堪的纳维亚西部的这一部分存在构造不连续性，一些地质学家认为这是造山带的轴带。这也表明，隆起和形成的晚期区域同形和反形后不久，或同时，后期平移的加里东前外来体。
In the Scandinavian Caledonides, the basement with a thin veneer of cover sediments can be traced from the frontal autochthon far westwards towards the centre of the orogen. The changing metamorphic grade can be recorded and compared with that of the overlying nappes. The metamorphic nature of these cover sediments is examined in the deepest structural levels of two windows, 200 km to the W of the Caledonian front. The emplacement of nappes above the cover caused a progressive recrystallization under greenschist facies conditions, with development of quartz + margarite + muscovite, quartz + chlorite + muscovite and quartz + white mica + graphite among parageneses defining the penetrative foliation related to the nappe displacement. The final overburden pressure is estimated to be 6–8 kb. Temperatures reached peak values around 550°C first after nappe emplacement. Despite the westerly situation and deep tectono-stratigraphic level of the metasediments, their metamorphic history is incompatible with a location close to an orogenic interior. The overlying cover sequence displays at least 2 inversions of metamorphic zonation. These developed as a result of the emplacement of high-grade nappes above low-grade or unmetamorphosed units, with incomplete subsequent restoration of the thermal profile, and in response to the catalytic effect of concentrated strain during thrusting. The imprinted saw-tooth pattern of the thermal profile in the western windows requires that tectonic discontinuities exist in this part of the western Scandes, considered by some geologists the axial zone of the orogen. It also suggests that the uplift and the formation of late regional syn- and antiforms followed soon after, or were simultaneous with, the late translation of the Caledonian front allochthon.