Continent-derived metasediments (Cimes Blanches and Frilihorn) within the ophiolites around Zermatt: relations with the Mischabel backfold and Mont Fort nappe (Pennine Alps)

IF 1.8 2区 地球科学 Q3 GEOSCIENCES, MULTIDISCIPLINARY
Adrien Pantet, Jean-Luc Epard, Henri Masson
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引用次数: 0

Abstract

The region surrounding Zermatt (SW Switzerland and NW Italy) displays some classic examples of imbrications between continental and oceanic units. In particular, the studied units, called Cimes Blanches and Frilihorn or Faisceau Vermiculaire, consist of a set of thin bands of continent-derived metasediments intercalated at different levels within the ocean-derived units. These bands are locally reduced to only one meter thick but can be traced for several tens to more than one hundred kilometers across the Pennine Alps. The mechanisms leading to such imbrications are a long-standing and still-debated question. Based on detailed mapping and structural analysis of key areas, we present new data on the structure and stratigraphy of the Faisceau Vermiculaire in the area surrounding Zermatt, with particular focus on the Täschalpen sector, where the Faisceau Vermiculaire is locally in contact with basement units. Our observations allow: (i) to confirm the presence of widespread breccias of probable Jurassic age in the Faisceau Vermiculaire; (ii) to interpret the contacts between the Faisceau Vermiculaire and the overlying non-ophiolitic Schistes Lustrés (Série Rousse) as stratigraphic; (iii) to show that the stratigraphy of the Faisceau Vermiculaire and associated Série Rousse contrasts strongly with the cover of the Siviez-Mischabel nappe and that these sequences originate from different paleogeographic domains (Prepiemont basin and Briançonnais platform respectively); (iv) to interpret as stratigraphic the contact of the Faisceau Vermiculaire and the Série Rousse with the basement forming the Alphubel anticline; the local unconformity is interpreted as the result of the activity of synsedimentary Jurassic normal paleofaults; (v) to highlight the trace of a major Jurassic normal fault, that should have marked an abrupt thinning of the paleomargin; it corresponds now to the contact between the Faisceau Vermiculaire (and associated Série Rousse) and the Siviez-Mischabel basement in the hinge of the Mischabel backfold. We propose a new tectonic scheme for the structure of the Faisceau Vermiculaire and adjacent units involving an early northward folding of the Faisceau Vermiculaire with the Série Rousse and the ophiolitic Schistes Lustrés of the Tsaté nappe, followed by major backfolding responsible for the southward emplacement of these units above the HP Zermatt-Saas and Monte Rosa nappes. Our study at regional scale shows that the group formed by the Alphubel basement, the Faisceau Vermiculaire and the Série Rousse share a tectonic position and stratigraphic sequences identical to those of the Mont Fort nappe, which outcrops on the other side of the Dent Blanche klippe. It leads to the proposition that this group constitutes the eastern extension of the Mont Fort nappe.
采尔马特周围蛇绿岩中的大陆源变质岩(Cimes Blanches和Frilihorn):与米沙贝尔背褶和蒙特堡岩层(宾夕法尼亚阿尔卑斯山)的关系
采尔马特(瑞士西南部和意大利西北部)周边地区展示了大陆和海洋单元交错的一些典型例子。特别是,所研究的称为 Cimes Blanches 和 Frilihorn 或 Faisceau Vermiculaire 的单元,由一组源于大陆的变质岩薄带组成,这些薄带在不同层面上夹杂在源于海洋的单元中。这些薄带在局部地区厚度仅为一米,但在整个宾夕法尼亚阿尔卑斯山脉却可以追溯几十公里到一百多公里。导致这种交错的机制是一个长期存在且仍有争议的问题。基于对关键区域的详细测绘和结构分析,我们提供了采尔马特周边地区褶皱岩的结构和地层学新数据,尤其侧重于 Täschalpen 地区,在该地区褶皱岩与基底单元局部接触。我们的观测结果有助于(i) 确认在褶皱岩中广泛存在可能是侏罗纪的角砾岩;(ii) 将褶皱岩与上覆非沸石片岩(Série Rousse)之间的接触解释为地层接触;(iii) 表明 Faisceau Vermiculaire 地层和相关的 Série Rousse 地层与 Siviez-Mischabel 断层的覆盖层形成强烈反差,这些地层源自不同的古地理区域(分别为 Prepiemont 盆地和 Briançonnais 平台);(iv) 从地层学角度解释 Faisceau Vermiculaire 和 Série Rousse 与形成 Alphubel 反断裂的基底的接触;将当地的不整合解释为侏罗系合 成岩正常古断层活动的结果;(v) 突出侏罗纪大正断层的痕迹,该断层本应标志着古边际的突然变薄;现在该断层相当于 Faisceau Vermiculaire(及相关的 Série Rousse)与米沙贝尔背褶铰接处的 Siviez-Mischabel 基底之间的接触。我们为 Faisceau Vermiculaire 及其邻近单元的构造提出了一个新的构造方案,其中包括 Faisceau Vermiculaire 早期与 Série Rousse 和 Tsaté 网状地层的蛇绿岩 Schistes Lustrés 一起向北褶皱,随后发生大的反褶,导致这些单元向南隆起于 HP Zermatt-Saas 和 Monte Rosa 网状地层之上。我们在区域范围内进行的研究表明,由阿尔弗贝尔基底、费斯索侏罗纪和塞里鲁兹形成的岩组,其构造位置和地层序列与出露于登特布兰奇地块另一侧的蒙堡岩层相同。由此可以推断,该岩组构成了蒙堡岩层的东延部分。
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来源期刊
Swiss Journal of Geosciences
Swiss Journal of Geosciences 地学-地质学
CiteScore
4.50
自引率
12.90%
发文量
21
审稿时长
>12 weeks
期刊介绍: The Swiss Journal of Geosciences publishes original research and review articles, with a particular focus on the evolution of the Tethys realm and the Alpine/Himalayan orogen. By consolidating the former Eclogae Geologicae Helvetiae and Swiss Bulletin of Mineralogy and Petrology, this international journal covers all disciplines of the solid Earth Sciences, including their practical applications. The journal gives preference to articles that are of wide interest to the international research community, while at the same time recognising the importance of documenting high-quality geoscientific data in a regional context, including the occasional publication of maps.
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