Estimating displacement along the Brenner Fault and orogen-parallel extension in the Eastern Alps
Estimating displacement along the Brenner Fault and orogen-parallel extension in the Eastern Alps
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估计沿布伦纳断层和东阿尔卑斯山造山带平行延伸的位移
DOI：
10.1007/s00531-011-0645-3
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发表时间：
2011
影响因子：
2.3
通讯作者：
Garcia
中科院分区：
文献类型：
--
作者：
Rosenberg;Garcia
在东阿尔卑斯，容纳造山带平行伸展的主要构造是布伦纳断裂，它形成了陶恩窗的西部边界。沿这条断层的估计延伸量从最小10-20公里到最大100 - 70公里不等。所有试图限制这种扩展量的研究都计算了在重力测量的约束下恢复下盘和上盘之间结构水平差所需的断平面平行位移。然而，这些计算忽略了由于褶皱和侵蚀引起的下盘挖掘的成分。因此，总的伸展位移量被系统地高估了。在本研究中，我们从Brenner断裂下盘和上盘投影了一个构造标志面到一个北向的横截面上。该标志面为下盘Patscherkofel单元基底和上盘Ötztal基底基底，推断其在Brenner断裂活动前在上盘和下盘处于同一构造水平。因此，下盘和上盘投影的标记高度差是Brenner断层垂直偏移的度量。该构造表明，Brenner断层两侧标志层的垂直偏移量沿Brenner断层走向变化强烈且连续，在褶皱下盘的铰链处（Tauern Dome）达到最大值15 km。垂向偏移量的沿向变化可以解释为Brenner断裂下盘的大规模垂直褶皱，但不影响上盘。因此，布伦纳山口地区与因斯布鲁克以南地区之间10公里垂直偏移量的差异对应于下盘发掘的缩短（垂直折叠）成分。其余5公里的垂直偏移必须归因于伸展变形。布伦纳断裂本身几乎没有褶皱，倾角在20 ~ 70°之间，横切了西陶伦窗的直立褶皱。在偏移量为5 km的情况下，断层倾角限制了伸展位移在2 ~ 14 km之间。我们得出的结论是，陶恩之窗主要是由褶皱和侵蚀挖掘出来的，而不是由伸展拆顶挖掘出来的。
The major structure accommodating orogen-parallel extension in the Eastern Alps is inferred to be the Brenner Fault, which forms the western boundary of the Tauern Window. The estimated amount of extension along this fault varies from a minimum of 10–20 km to a maximum of >70 km. All investigations that have attempted to constrain this amount of extension have calculated the fault plane parallel displacement required to restore the difference in structural level between footwall and hanging wall as constrained by geobarometry. However, these calculations neglected the component of exhumation of the footwall resulting from folding and erosion. Therefore, the total amount of extensional displacement was systematically overestimated. In the present study, we project a tectonic marker surface from the footwall and hanging wall of the Brenner Fault onto a N–S-striking cross section. This marker surface, which is the base of the Patscherkofel unit in the footwall and the base of the Ötztal basement in the hanging wall, is inferred to have occupied the same structural level in the hanging wall and footwall of the Brenner Fault before its activity. Therefore, the difference in height between the marker projected from the footwall and from the hanging wall is a measure of the vertical offset across the Brenner Fault. This construction shows that the vertical offset of the marker horizon on both sides of the Brenner Fault varies strongly and continuously along strike of the Brenner Fault, attaining a maximum value of 15 km at the hinge of the folded footwall (Tauern Dome). The along-strike change of vertical offset is explained by large-scale upright folding of the footwall that did not affect the hanging wall of the Brenner Fault. Therefore, the difference in vertical offset of 10 km between the area of the Brenner Pass and the area immediately south of Innsbruck corresponds to the shortening (upright folding) component of exhumation of the footwall. The remaining 5 km of vertical offset must be attributed to extensional deformation. The Brenner Fault itself is barely folded, its dip varies between 20 and 70°, and it crosscuts the upright folds of the western Tauern Window. Given the offset of 5 km, the dip of the fault constrains the extensional displacement to be between 2 and 14 km. We conclude that the Tauern Window was exhumed primarily by folding and erosion, not by extensional unroofing.
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