The Umbria-Marche Apennines as a Double Orogen: Observations and hypotheses
The Umbria-Marche Apennines as a Double Orogen: Observations and hypotheses
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翁布里亚-马尔凯亚平宁山脉作为双造山带：观察和假设
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发表时间：
2012
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通讯作者：
D. Shimabukuro
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作者：
M. Barchi;W. Álvarez;D. Shimabukuro
翁布里亚-马尔什亚平宁山脉是一条向东凸出且辐辏的弧形褶皱冲断带，形成北亚平宁山脉的外部。 20 世纪 80 年代中期，翁布里亚-马尔凯亚平宁山脉被一些人解释为经典的薄皮褶皱冲断带，冲断片从造山带的内部到外部以顺序、背负式的方式安置在三叠纪蒸发岩的主要基底分离层上。在这种建筑物的力学中，褶皱和逆冲将在棱柱形或锥形楔形内发展，其底部以未变形的基底为界，该基底具有向内陆倾斜的区域单斜线，而顶部以通常向前陆倾斜的地形和结构斜坡为界。其他作者认为翁布里亚-马尔什亚平宁山脉是一个更复杂的造山带，有基底参与、可能的构造反转和无序逆冲。在本文中，翁布里亚-马尔凯亚平宁山脉的几何形状、结构和构造沉积演化与经典薄皮模型进行了比较。我们认为该褶皱逆冲带可以纵向分为两个扇区。链的东部部分，包括轴带的高中生代碳酸盐岩背斜脊和马尔凯外部褶皱，与经典模型非常吻合，但西部部分，包括翁布里亚前亚平宁山脉，显示出显着的差异。翁布里亚-马尔凯亚平宁山脉东部和西部之间的边界在这里被称为谢贾-福利尼奥线（SFL）。这条线以东，东翁布里亚-马尔什亚平宁山脉在未变形的基底和上表面之间呈现出向东的锥度，基底向西倾斜，上表面的地形和结构高程都向东降低。相比之下，在斯凯吉亚-福利尼奥线以西，地震反射剖面和地下数据显示基底参与了浅层的逆冲作用，而与该线更东的部分相比，地形和构造高程都异常低。斯凯吉亚-福利尼奥线的前深盆地演化也存在显着的不连续性，在翁布里亚前亚平宁山脉和外部马尔凯带（分别为马尔诺索-竞技场和马尔凯普利奥-更新世），前深盆地发育良好，而在托尔托阶-墨西尼期，轴向带仅发育逆冲顶盆地。可以援引各种机制（并非全部相互排斥）来解释谢贾-福利尼奥线的不连续性。这些可能的解释包括与该地区的沉积和构造演化有关的局部特征的原因，涉及稳态条件的偶发性偏离，从而中断了增生楔的正常生长。然而，翁布里亚-马尔凯亚平宁山脉西部和东部也有可能代表完全不同的造山系统，其成因可能不同，前者可能与科西嘉-亚德里亚碰撞有关，后者可能与亚得里亚海岩石圈的板块回滚有关。无论哪种情况，这项研究都证明了北亚平宁山脉演化的复杂性，相邻区域在历史和变形方式上表现出突变，很难将其纳入单一、统一的地球动力学模型中。
The Umbria-Marche Apennines, an arc-shaped fold and thrust belt with eastward convexity and vergence, form the external part of the Northern Apennines. In the middle 1980s, the Umbria-Marche Apennines were interpreted by some as a classical thin-skinned foldthrust belt, with thrust sheets emplaced in an in-sequence, piggyback mode, from the interior to the exterior of the orogen, over a main, basal detachment in the Triassic evaporites. In the mechanics of this kind of edifice, the folds and thrusts would develop within a prism or tapered wedge, bounded at the base by an undeformed basement with a regional monocline dipping toward the hinterland, and at the top by a topographic and structural slope generally dipping toward the foreland. Other authors saw the Umbria-Marche Apennines as a more complex orogen, with basement involvement, possible tectonic inversions, and out-of-sequence thrusts. In the present paper, the geometry, structure, and tectono-sedimentary evolution of the Umbria-Marche Apennines are compared with the classical thin-skinned model. We suggest that this fold-thrust belt can be divided longitudinally into two sectors. The eastern part of the chain, comprising the high Mesozoic carbonate anticlinal ridges of the axial zone together with the Marche external folds, fits the classical model well, but the western part, comprising the Umbrian Pre-Apennines, shows striking differences. The boundary between the eastern and western parts of the Umbria-Marche Apennines is here termed the Scheggia-Foligno Line (SFL). East of this line, the Eastern Umbria-Marche Apennines show an eastward taper between the undeformed basement, dipping gently west, and an upper surface in which both topographic and structural elevation decrease toward the east. West of the Scheggia-Foligno Line, by contrast, seismic reflection profiles and subsurface data show basement involvement in the thrusting at shallow depths, while both the topographic and structural elevations are anomalously low compared to the more easterly parts of the chain. There is also a notable discontinuity in foredeep-basin evolution at the Scheggia-Foligno Line, with welldeveloped foredeep basins in the Umbrian Pre-Apennines and the external Marche belt (the Marnoso-arenacea and Marche Plio-Pleistocene, respectively), whereas only thrust-top basins developed in the axial zone, during the Tortonian-Messinian interval. Various mechanisms, not all mutually exclusive, might be invoked to explain the discontinuity at the Scheggia-Foligno Line. These possible explanations include causes of local character, linked to the sedimentary and tectonic evolution of the region, involving episodic departures from steady-state conditions, interrupting the regular growth of the accretionary wedge. However, it also possible that the Western and Eastern Umbria-Marche Apennines represent completely different orogenic systems, with different causes possibly with the former related to Corsica-Adria collision and the latter due to slab rollback of Adriatic lithosphere. In either case, this study demonstrates the complexity of evolution of the Northern Apennines, with adjacent zones showing abrupt variations in their history and style of deformation, which are difficult to incorporate in a single, unified geodynamic model.