Contrasting ages of metamorphism in the Seve nappes: U‐Pb results from the central and northern Swedish Caledonides
Contrasting ages of metamorphism in the Seve nappes: U‐Pb results from the central and northern Swedish Caledonides
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七推覆体变质作用年龄对比：瑞典喀里多尼德中部和北部的 U-Pb 结果
DOI：
10.1080/11035899609546308
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发表时间：
1996
期刊：
影响因子：
1
通讯作者：
L. Albrecht
中科院分区：
文献类型：
--
作者：
L. Gromet;H. Sjöström;S. Bergman;S. Claesson;R. Essex;P. Andreasson;L. Albrecht
A36 GFF 118 Jubilee Issue（1996）较远的下阿洛希顿的耶姆特兰推覆体和向北的下阿洛希顿的极窄边缘。这一地带以其与马和双联体的侧向终止有关的结构而引人注目。这些特征包括侧向斜坡，但也包括非层序逆冲断层和EW向褶皱，这可以用几何复杂性来解释，因为约束马的侧向斜坡并不完全平行于一般构造搬运方向。马在地层下部的机械能力强的碎屑沉积层序中特别发育（Risbäck和Sjoutälven群），其中薄的不合格层位（如Vendian冰碛岩，寒武纪黑色页岩）或基底盖层界面提供拆离层位。因此，马的厚度与岩性单元的厚度直接相关。这一事实，一旦被Gayer & Greiling（1989）和Zachrisson & Greiling（1993）记录下来，就成为场映射的一个有用的工作假设。可以估计逆冲断层的位置和逆冲断层单元的厚度，并且更容易找到暴露逆冲断层的合适位置。相比之下，较不称职的，上部的序列（中寒武纪到奥陶纪页岩和灰岩）是在一个不同的风格，从逆冲断层和/或小叠瓦过渡到（尖）褶皱变形。有时候，水晶基底切片记录了也切入基底的推力。而在该地区的西部，这些基底切片通常主要被Risbäck群arkoses覆盖，arkoses向东楔出，基底切片主要被Sjoutälven群石英岩甚至中寒武纪黑色页岩覆盖。然而，在图2：8的北方边缘向北，新发现了里斯贝克群长石砂岩。这些观察结果表明，构造格局是倾斜的被动边缘和现在的（侵蚀）加里东边缘的预先存在的结构。
A36 GFF118 Jubilee Issue (1996) the Jämtland nappes of the Lower Allochthon farther S and an extremely narrow margin of the Lower Allochthon towards N. This zone is remarkable for its structures related to the lateral terminations of horses and duplexes. Such features comprise lateral ramps but also out-of-sequence thrusts and EW-trending folds, which can be explained by geometric complexities arising from the fact that the lateral ramps which bound the horses are not exactly parallel with the general tectonic transport direction.Horses are particularly well developed within the mechanically competent, clastic sedimentary sequences in the lower part of the stratigraphy (Risbäck and Sjoutälven Groups), where thin, incompetent horizons (eg Vendian tillites, Cambrian black shales) or the basement-cover interface provide detachment horizons. Accordingly, thicknesses of horses are directly related to the thickness of lithologic units. This fact, once it was documented by Gayer & Greiling (1989) and Zachrisson & Greiling (1993), was a useful working hypothesis for the field-mapping. The location of thrusts and thicknesses of thrust units could be estimated and appropriate locations for exposed thrusts were more easy to find. In contrast, the less competent, upper part of the sequence (mid-Cambrian to Ordovician shales and greywackes) is deformed in a different style, with transitions from thrusts and/or minor imbricates into (tip-) folds. Sometimes crystalline basement slices document that thrusts also cut into the basement. Whereas in the western part of the area these basement slices are often primarily overlain by Risbäck Group arkoses, arkoses wedge out towards the east, where basement slices are primarily overlain by Sjoutälven Group quartzites or even mid-Cambrian black shales. However, towards north at the northern margin of Fig. 2: 8, new occurrences of Risbäck Group arkoses have been mapped. These observations point to the fact that the structural pattern is oblique to both the pre-existing structures of the passive margin and to the present (erosional) Caledonian margin.