Modes of orogen-parallel stretching and extensional exhumation in response to microplate indentation and roll-back subduction (Tauern Window, Eastern Alps)
Modes of orogen-parallel stretching and extensional exhumation in response to microplate indentation and roll-back subduction (Tauern Window, Eastern Alps)
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DOI：
10.1007/s00531-013-0894-4
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发表时间：
2013-05
影响因子：
2.3
通讯作者：
Andreas Scharf;M. Handy;S. Favaro;Stefan M. Schmid;A. Bertrand
中科院分区：
文献类型：
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作者：
Andreas Scharf;M. Handy;S. Favaro;Stefan M. Schmid;A. Bertrand
陶恩窗暴露了由高度变质的大洋（阿尔卑斯特提斯）和大陆（远欧洲边缘）逆冲岩席组成的古近纪推覆体。在这个窗口的东部，这个推覆体叠层（东陶恩亚穹隆，ETD）是由新近纪剪切系统（Katschberg剪切带系统，KSZS），容纳造山带平行拉伸，造山带正常缩短，并折返相对于结构上覆的Austroalpine单位（亚得里亚海边缘）。KSZS包括一个厚度≤5 km的退积糜棱岩带，其中段是一个东南倾斜的低角度伸展剪切带，具有脆性叠加（Katschberg正断层，KNF）。在该中段的北方和南端，KSZS失去了其脆性叠加，并围绕ETD的两个角摆动，成为近垂直、右旋和左旋走滑断层。后者代表伸展断层，其位移向西减小至接近零。沿着KSZS中央低角度伸展部分的自上而下的自上而下至东南方向的韧性剪切运动学连续性及其陡端的走滑剪切，结合KNF下盘ETD推覆体的最大构造缺失，表明南北缩短、平行造山带伸展和正断层是同时代的。地层学和放射性年龄约束折返的褶皱推覆复合体在下盘的KSZS已开始在23-21马，导致快速冷却之间的21和16马。这种折返作用包括伸展剪切、直立褶皱和侵蚀剥蚀引起的构造去顶作用。构造去顶的贡献是最大的沿着中央段的KSZS和减少西部的中部的陶恩窗。KSZS形成于半刚性Austroalpine基底的楔形块体位于南阿尔卑斯山压头的前面，是亚得里亚海微板块的一部分。向北运动的这个压头沿着左朱迪卡里带抵消了亚得里亚海周围的断层，并引发了快速折返的造山地壳内的整个陶恩窗。折返涉及走滑和正常的断层，容纳约100公里的造山带平行的延伸，是同期约30公里的造山带垂直，南北缩短的ETD。延伸的潘诺尼亚盆地有关的滚回俯冲在喀尔巴阡山脉开始于20马，但没有影响到东阿尔卑斯山前约17马。这一延伸的效果是减少横向阻力，向东地壳流动远离最大增厚区在陶恩窗地区。因此，我们建议，回滚俯冲暂时增强，而不是触发折返和造山带平行运动在东阿尔卑斯山。在东阿尔卑斯山的横向挤压和造山带平行的延伸，从12到10 Ma的持续到现在，并驱动向北的阿德里亚推。
The Tauern Window exposes a Paleogene nappe stack consisting of highly metamorphosed oceanic (Alpine Tethys) and continental (distal European margin) thrust sheets. In the eastern part of this window, this nappe stack (Eastern Tauern Subdome, ETD) is bounded by a Neogene system of shear (the Katschberg Shear Zone System, KSZS) that accommodated orogen-parallel stretching, orogen-normal shortening, and exhumation with respect to the structurally overlying Austroalpine units (Adriatic margin). The KSZS comprises a ≤5-km-thick belt of retrograde mylonite, the central segment of which is a southeast-dipping, low-angle extensional shear zone with a brittle overprint (Katschberg Normal Fault, KNF). At the northern and southern ends of this central segment, the KSZS loses its brittle overprint and swings around both corners of the ETD to become subvertical, dextral, and sinistral strike-slip faults. The latter represent stretching faults whose displacements decrease westward to near zero. The kinematic continuity of top-east to top-southeast ductile shearing along the central, low-angle extensional part of the KSZS with strike-slip shearing along its steep ends, combined with maximum tectonic omission of nappes of the ETD in the footwall of the KNF, indicates that north–south shortening, orogen-parallel stretching, and normal faulting were coeval. Stratigraphic and radiometric ages constrain exhumation of the folded nappe complex in the footwall of the KSZS to have begun at 23–21 Ma, leading to rapid cooling between 21 and 16 Ma. This exhumation involved a combination of tectonic unroofing by extensional shearing, upright folding, and erosional denudation. The contribution of tectonic unroofing is greatest along the central segment of the KSZS and decreases westward to the central part of the Tauern Window. The KSZS formed in response to the indentation of wedge-shaped blocks of semi-rigid Austroalpine basement located in front of the South-Alpine indenter that was part of the Adriatic microplate. Northward motion of this indenter along the sinistral Giudicarie Belt offsets the Periadriatic Fault and triggered rapid exhumation of orogenic crust within the entire Tauern Window. Exhumation involved strike-slip and normal faulting that accommodated about 100 km of orogen-parallel extension and was contemporaneous with about 30 km of orogen-perpendicular, north–south shortening of the ETD. Extension of the Pannonian Basin related to roll-back subduction in the Carpathians began at 20 Ma, but did not affect the Eastern Alps before about 17 Ma. The effect of this extension was to reduce the lateral resistance to eastward crustal flow away from the zone of greatest thickening in the Tauern Window area. Therefore, we propose that roll-back subduction temporarily enhanced rather than triggered exhumation and orogen-parallel motion in the Eastern Alps. Lateral extrusion and orogen-parallel extension in the Eastern Alps have continued from 12 to 10 Ma to the present and are driven by northward push of Adria.