From ocean formation to mountain evolution in alpine-type orogens,Swiss Journal of Geosciences

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From ocean formation to mountain evolution in alpine-type orogens
Swiss Journal of Geosciences ( IF 3.1 ) Pub Date : 2017-04-26 , DOI: 10.1007/s00015-017-0273-4
Christian Sue , Stefan M. Schmid

The 12th Alpine Workshop, organized by Christian Sue, Gianreto Manatschal and Raymond Cirio, was held in the Montgenèvre resort, located next-door to one of the best-preserved ocean floor sequences exposed in the Western Alps, known as the Chenaillet ophiolite. As all the previous bi-annual series of Alpine workshops this conference was again held in a friendly and stimulating atmosphere.

Before introducing the collection of papers received after the conference we take the opportunity to mention the locations and dates of the previous conferences. The first Alpine Workshop conference was held in Grenoble (France) in 1993, and was followed by Basel (Switzerland) in 1995, Oropa (Italy) in 1997, Tübingen (Germany) in 1999, Obergurgl (Austria) in 2001, Sopron (Hungary) in 2003, Opatja (Croatia) in 2005, Davos (Switzerland) in 2007, Cogne (Italy) in 2009, Saint-Florent (Corsica, France) in 2011, Schladming (Austria) in 2013, and Montgenèvre-Briançon (France) in 2015.

In 2013, this informal series of conferences acquired an official character, being held under the auspices of the European Geosciences Union for the first time under the name “Emile Argand Conference on Alpine Geological Studies”, in honour of the famous Swiss geologist, Emile Argand (1879–1940), who first linked plate tectonics and dynamics of orogeny (e.g. Argand 1924). The aim of the conferences is to promote the discussion of new data and interpretations based on studies addressing the structural, tectonic, metamorphic and sedimentary evolution of the Alps, and adjacent Mediterranean Alpine-type orogens, in an informal and friendly atmosphere by bringing senior researchers together with young scientists, including numerous PhD students.

A first group of papers arising from the 12th Alpine Workshop focuses on a topic that recently received a lot of attention by the international community, including oil companies working in off-shore areas of passive margin environments. Such environments are characterised by highly extended continental crust grading into adjacent oceanic areas formed along slow spreading (Atlantic) type ridges, the fossil equivalents of which are exposed in the Alps. The paper by M. E. Epin, G. Manatschal and M. Amann analyses well preserved structures still inherited from rift-related tectonism in an area of intense Alpine deformation related to the subsequent closing of Alpine Tethys. Their case study carried out in the Err and Platta nappes of southeastern Switzerland, representing an ocean-continent transition, focuses on the discussion as to how much rift-inheritance controls the architecture of a collisional orogen such as the Alps. They point out that retro-deformation of Alpine shortening inevitably results in a template of non-layer cake rift structures in the internal most parts of a collisional orogen. N. Incerpi, L. Martire, G. Manatschal and S. M. Bernasconi also present a study carried out in the same area; they specifically focus on hydrothermal fluid circulation in pre- and syn-tectonic sediments associated with detachment faults in order to improve our knowledge on thermal regimes in hyperextended continental margins. Their study reveals the complexity of the evolution of hyperextended continental rift domains and, at the same time, highlights the importance of studying fossil analogues in order to better constrain and understand present-day passive margin features. T. Mateeva, G. A. Wolf, G. Manatschal, S. Picazo, N. J. Kuzmir and J. Wheeler analysed the content of organic matter in the Totalp serpentinites of southeastern Switzerland, formed at another location preserving a fossil ocean continent transition zone. They provide evidences for the preservation of traces of organic matter originally deposited in a reducing marine environment in serpentinized mantle rocks and overlying sediments. Although they searched for biomarkers or molecular remains of former living organisms they found no indication that the organic matter was generated from methanotrophic bio-systems. The paper of M. R. Renna, R. Tribuzio, A. Sanfilippo and M. Tiepolo focuses on a geochronological analysis of yet another continent-near ophiolitic unit, the Balagne ophiolite in Corsica, in dating oceanic lower crustal plagiogranite, as well as associated quartzo-feldspathic clastic sediments. They found surprisingly young ages of crystallization for the plagiogranites (Oxfordian) suggesting that these rocks could possibly represent one of the youngest pieces of lower oceanic crust found in the Alpine orogen, while the quartzo-feldspathic clastics from the nearby continent revealed Permian ages.

A classical and very detailed structural-petrological field study is presented by F. Kirst, who studied multiple reactivations of the basal thrust zone of the Dent Blanche continental klippe overlying the Piedmont-Liguria ophiolites. Repeated shearing of the fault rocks associated with this tectonic contact occurred during a very long time interval (43–32 Ma) under ductile conditions. The shearing took place initially under blueschist facies conditions, with changes from thrusting to normal sense shearing and back to thrusting under greenschist facies conditions, before being affected by normal faulting again, after 32 Ma, under semi-brittle to brittle conditions.

Two papers investigate the role of inherited pre-orogenic faulting and paleogeographical disposition on the early stages of orogeny using alternative approaches. A. Bauville and S. M. Schmalholz present an inspiring numerical modelling study that investigates the initiation of shear zones in the Helvetic nappes. They demonstrate that the differences in viscosity between crystalline basement and the sediments found in half-grabens play a major role by initiating strain localization during nappe formation, while rheological softening mechanisms might have further intensified subsequent shear localization. For the purpose of comparison with the Alps C. Bell and R. Butler present a study that analyses 3D seismic sections and drill holes from the Kamchia basin (Black Sea), caught between the Balkan orogen and the relatively mildly deformed Moesian platform being relatively mildly deformed. Their study provides key observations focusing on the role of the transition between weakly and strongly rifted continental crust during early stages of orogeny. Such observations cannot be made in an orogenic system such as the Alps proper, whose internal zones have subsequently become too strongly deformed.

Another two papers, again very contrasting in terms of methodology, analyse present-day and late-stage brittle faulting in the Alps and their foreland, respectively. N. Vouillamoz, J. Mosar and N. Deichmann present a seismic hazard assessment of a very prominent line source of seismic activity: the Fribourg lineament hosted in the molasse foreland of the Alps. They use a novel approach by monitoring very low magnitude events and dense spacing of stations (down to ML = −2.0). Integration of the data in a 3D model provides evidence that this lineament is only active within the sedimentary cover; but the authors cannot exclude future activity also in the basement that could potentially lead to a magnitude 6 earthquake. For the first time A. Bertrand and C. Sue studied late-stage (Miocene) brittle faulting at the scale of the entire Alpine chain by providing overall homogeneous orogen-scale mapping of late Alpine brittle deformations, combined with thermochronological data. They found that orogen-parallel extension was surprisingly stable at the scale of the orogen and discuss a possible coupling of this extension with the directions of mantle flow as revealed by SKS anisotropy axes, also oriented subparallel to the orogen.

Finally, S. M. Schmid, E. Kissling, T. Diehl, D. J. J. van Hinsbergen and G. Molli provide another orogen-scale study that addresses the kinematics of the formation of the arc of the Western Alps, based on existing structural data combined with a series of new and revised geophysical transects along the entire arc, and on the results of a 3D-model of p-wave velocities derived from crustal tomography. Their discussion of the Alps–Apennines transition suggests that substantial parts of the Northern Apennines formerly suffered Alpine-type shortening associated with an E-dipping Alpine subduction zone being back-thrusted to the NE during Apenninic orogeny, after a reversal in subduction polarity that commenced in the Oligocene.

The editors of this collection of papers gratefully acknowledge the colleagues who kindly accepted to review the manuscripts, and who provided accurate and fruitful comments. We also warmly thank the chief editor of the Swiss Journal of Geosciences, A. G. Milnes, who helped us to organize this special volume and to actually publish it, as was announced at the Montgenèvre-Briancon Alpine Workshop. Finally, we wish to dedicate this collection of papers to the memory of Marco Beltrando.

Argand, E. (1924). La Tectonique de l’Asie. In Extrait du Compte-rendu (Ed.), du XIIIe Congrès Géologique International de Bruxelles (pp. 171–372). Liège: Imprimerie Vaillant-Carmanne.
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Affiliations

Université de Franche-Comté, Chrono-environnement, 16 route de Gray 2503, Besançon, France
- Christian Sue
Institute of Geophysics, ETH Zürich, Sonneggstrasse 5, 8092, Zurich, Switzerland
- Stefan M. Schmid

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Correspondence to Stefan M. Schmid.

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Sue, C., Schmid, S.M. From ocean formation to mountain evolution in alpine-type orogens. Swiss J Geosci 110, 417–418 (2017). https://doi.org/10.1007/s00015-017-0273-4

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Received: 18 March 2017
Accepted: 30 March 2017
Published: 26 April 2017
Issue Date: June 2017
DOI: https://doi.org/10.1007/s00015-017-0273-4

中文翻译：

从海洋形成到高山型造山带的山体演化

由Christian Sue，Gianreto Manatschal和Raymond Cirio组织的第12届高山讲习班在Montgenèvre度假胜地举行，该度假胜地毗邻西部阿尔卑斯山中保存最完好的海底序列之一，被称为Chenaillet蛇绿岩。与以前的每两年一次的高山培训班系列一样，本次会议再次在友好和令人兴奋的气氛中举行。

在介绍会议之后收到的论文集之前，我们将借此机会提及以前会议的地点和日期。第一次高山研讨会于1993年在法国格勒诺布尔举行，随后是1995年在瑞士的巴塞尔，1997年在意大利的Oropa，1999年在德国的蒂宾根，2001年在奥地利的Obergurgl，在匈牙利的Sopron ），2003年的奥帕蒂亚（克罗地亚），2007年的达沃斯（瑞士），2009年的科涅（意大利），2011年的圣弗洛朗（法国科西嘉），2013年的施拉德明（奥地利）和蒙格涅夫尔-布里安松（法国）在2015年。

2013年，这一系列非正式会议获得了正式资格，这是在欧洲地球科学联合会的主持下首次举行的，名称为“阿尔卑斯地质研究埃米尔·阿尔甘德会议”，以纪念著名的瑞士地质学家埃米尔·阿尔甘德（1879–1940），他首先将板块构造与造山运动动力学联系起来（例如Argand 1924）。会议的目的是在非正式和友好的气氛中，通过吸引高级研究人员，探讨有关阿尔卑斯山以及邻近地中海阿尔卑斯型造山带的结构，构造，变质和沉积演化的研究，从而促进对新数据和解释的讨论。与年轻科学家，包括众多博士生一起。

第十二届高山讲习班的第一批论文集中于国际社会最近关注的一个话题，包括在被动边际环境的近海工作的石油公司。这种环境的特征是大陆壳高度扩展，并沿着缓慢扩展的（大西洋）型山脊形成相邻的海洋区域，这些化石的等价物暴露在阿尔卑斯山中。ME Epin，G.Manatschal和M.Amann的论文分析了仍然保存于裂谷相关构造的保存完好的结构，该区域在与随后的高山特提斯山闭合有关的强烈高山变形区域中。他们在瑞士东南部的Err和Platta纳普斯进行的个案研究代表了欧洲大陆的过渡，重点是关于多少裂谷遗传控制了碰撞造山带（如阿尔卑斯山）的结构的讨论。他们指出，高山起酥油的逆向变形不可避免地导致在碰撞造山带的大部分内部形成非层状蛋糕裂谷结构的模板。N. Incerpi，L.蒂雷，G. Manatschal和SM贝尔纳斯科尼还提出了在同一地区进行的一项研究；他们特别关注与分离断层有关的前，中构造沉积物中的热液循环，以增进我们对超伸展大陆边缘热力状况的了解。他们的研究揭示了超伸展大陆裂谷域演化的复杂性，同时强调了研究化石类似物的重要性，以便更好地限制和理解当今的被动边缘特征。T. Mateeva，GA Wolf，G.Manatschal，S.Picazo，NJ Kuzmir和J.Wheeler分析了瑞士东南部的Totalp蛇纹岩中有机物的含量，该蛇形岩是在另一个保存化石海洋大陆过渡带的地点形成的。它们提供了证据，证明了原始的痕迹有机物的保存，这些痕迹最初沉积在蛇形化的地幔岩石和上覆沉积物中，处于海洋环境的还原性之中。尽管他们寻找以前的活生物体的生物标记或分子残留物，但他们没有发现有机物是由甲烷营养生物系统产生的。Renna先生，R.Tribuzio，A.Sanfilippo和M.Tiepolo的论文侧重于对下一个近地壳的岩相单元科西嘉岛的Balagne蛇绿岩进行大地年代学分析，以对海洋下地壳斜长花岗岩以及相关的石英长石碎屑沉积进行定年。他们发现斜长花岗岩（牛津）的结晶年龄年轻得令人惊讶，这表明这些岩石可能代表了高山造山带中发现的最年轻的下部洋壳碎片之一，而附近大陆的石英长石碎屑则显示出二叠纪年龄。

F. Kirst提出了一个经典且非常详细的结构岩石学野外研究，他研究了覆盖在皮埃蒙特-利古里亚蛇绿岩上的登特布兰奇大陆飞来峰基部逆冲带的多次活化。在延性条件下，在很长的时间间隔（43-32 Ma）内，与这种构造接触有关的断层岩石反复被剪切。剪切最初是在蓝片岩相条件下发生的，从推力变到正常意义上的剪切，再在绿片岩相条件下变回推力，然后在32Ma之后，在半脆性至脆性条件下再次受到正断层的影响。

两篇论文使用替代方法研究了造山带前期断裂和古地理分布在造山带早期的作用。A. Bauville和SM Schmalholz提出了一个启发性的数值模型研究，该研究研究了Helvetic尿布中剪切区的形成。他们证明，在结晶质基底和沉积物中发现的半粘性成分之间的粘度差异起着重要作用，这是通过在油层形成过程中引发应变局部化而引起的，而流变软化机制可能会进一步加剧随后的剪切局部化。为了与阿尔卑斯山比较C. Bell和R. Butler目前的一项研究分析了位于巴尔干造山带与相对轻度变形的Moesian平台之间的3D地震剖面和来自Kamchia盆地（黑海）的钻孔。他们的研究提供了关键的观察结果，重点关注在造山运动的早期阶段，软壳和强裂谷大陆壳之间过渡的作用。不能在诸如阿尔卑斯山之类的造山系统中进行这样的观测，而造山系统的内部区域随后变得太强烈变形。

另外两篇论文在方法论上也有很大的不同，分别分析了阿尔卑斯山及其前陆的现今和后期的脆性断层。N. Vouillamoz，J。Mosar和N. Deichmann介绍了一个非常重要的地震活动线源的地震危险性评估：弗里堡（Fribourg）阵线位于阿尔卑斯山的糖蜜前陆。他们通过监视非常低的事件和密集的站点间隔（低至ML = -2.0）来使用新颖的方法。将数据集成到3D模型中可提供证据，表明该谱系仅在沉积盖层中有效。但是作者不能排除地下室将来可能会导致6级地震的活动。A. Bertrand和C. Sue第一次通过提供晚高山脆性变形的整体均质造山带规模作图，并结合热年代学数据，研究了整个高山链规模的晚期（中新世）脆性断层。他们发现，造山带平行扩展在造山带规模上出乎意料地稳定，并讨论了这种扩展与地幔流动方向的可能耦合，如SKS各向异性轴所揭示的，也定向为与造山带平行。

最后，SM Schmid，E。Kissling，T。Diehl，DJJ van Hinsbergen和G. Molli根据现有的结构数据和一系列资料，提供了另一种造山带规模的研究，研究西阿尔卑斯山弧形成的运动学。沿整个弧线的新的和经修改的地球物理样条线，以及基于地壳层析成像的p波速度3D模型的结果。他们对阿尔卑斯山-亚平宁山脉过渡的讨论表明，北亚平宁山脉的大部分地区以前曾经历过阿尔卑斯型的缩短，这与在亚平宁造山运动中在俯冲极性反转后向北向东北逆冲推高了一个E浸入的高山俯冲带有关。在渐新世。

这些论文的编辑非常感谢同事们的诚意，他们审阅了稿件，并提供了准确而富有成果的评论。我们还要热烈感谢《瑞士地球科学杂志》的首席编辑米尔尼斯（AG Milnes），他如Montgenèvre-Briancon高山讲习班所宣布的那样，帮助我们组织了这本特别的书并实际出版。最后，我们希望将这些论文集献给Marco Beltrando。