SUMMARY

Since the Mesozoic, central and eastern European tectonics have been dominated by the closure of the Tethyan Ocean as the African and European plates collided. In the Miocene, the edge of the East European Craton and Moesian Platform were reworked in collision during the Carpathian orogeny and lithospheric extension formed the Pannonian Basin. To investigate the mantle deformation signatures associated with this complex collisional-extensional system, we carry out SKS splitting analysis at 123 broad-band seismic stations in the region. We compare our measurements with estimates of lithospheric thickness and recent seismic tomography models to test for correlation with mantle heterogeneities. Reviewing splitting delay times in light of xenolith measurements of anisotropy yields estimates of anisotropic layer thickness. Fast polarization directions are mostly NW–SE oriented across the seismically slow West Carpathians and Pannonian Basin and are independent of geological boundaries, absolute plate motion direction or an expected palaeo-slab roll-back path. Instead, they are systematically orthogonal to maximum stress directions, implying that the indenting Adria Plate, the leading deformational force in Central Europe, reset the upper-mantle mineral fabric in the past 5 Ma beneath the Pannonian Basin, overprinting the anisotropic signature of earlier tectonic events. Towards the east, fast polarization directions are perpendicular to steep gradients of lithospheric thickness and align along the edges of fast seismic anomalies beneath the Precambrian-aged Moesian Platform in the South Carpathians and the East European Craton, supporting the idea that craton roots exert a strong influence on the surrounding mantle flow. Within the Moesian Platform, SKS measurements become more variable with Fresnel zone arguments indicating a shallow fossil lithospheric source of anisotropy likely caused by older tectonic deformation frozen in the Precambrian. In the Southeast Carpathian corner, in the Vrancea Seismic Zone, a lithospheric fragment that sinks into the mantle is sandwiched between two slow anomalies, but smaller SKS delay times reveal weaker anisotropy occurs mainly to the NW side, consistent with asymmetric upwelling adjacent to a slab, slower mantle velocities and recent volcanism.

中文翻译：

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基于SKS各向异性分析的喀尔巴阡-潘诺尼地区克拉通-造山带相互作用的上地幔变形特征

概要

自中生代以来，随着非洲板块和欧洲板块的碰撞，特提斯洋的封闭主导了中欧和东欧的构造。在中新世，在喀尔巴阡山造山运动和岩石圈扩张形成潘诺尼盆地的过程中，东欧克拉通和莫斯平台的边缘发生了碰撞。为了研究与此复杂的碰撞-伸展系统相关的地幔变形特征，我们在该地区的123个宽带地震台站进行了SKS分裂分析。我们将测量结果与岩石圈厚度估计值和最新的地震层析成像模型进行比较，以测试与地幔非均质性的相关性。根据异质岩的各向异性测量来回顾分裂延迟时间，可以得出各向异性层厚度的估计值。快极化方向大部分在地震缓慢的西喀尔巴阡山脉和Pannonian盆地上为NW-SE方向，并且与地质边界，绝对板块运动方向或预期的古板块回滚路径无关。取而代之的是，它们系统地正交于最大应力方向，这暗示着凹陷的阿德里亚板块（中欧地区的主要变形力）使潘诺尼亚盆地下方过去5 Ma的上地幔矿物结构复位，覆盖了早期构造的各向异性特征事件。向东，快速极化方向垂直于岩石圈厚度的陡峭梯度，并沿着南喀尔巴阡山脉和东欧克拉通前寒武纪时代的Moesian台下的快速地震异常的边缘排列，支持克拉通根对周围的地幔流产生强烈影响的观点。在Moesian平台内，SKS的测量变得更加可变，因为菲涅耳带的论证表明，浅层化石岩石圈各向异性的源可能是由前寒武纪中较旧的构造变形引起的。在喀尔巴阡山脉东南角的Vrancea地震带中，岩石深陷于地幔中的碎片夹在两个缓慢的异常之间，但是较小的SKS延迟时间表明各向异性较弱，主要发生在西北侧，与板块附近的不对称上升相一致。 ，地幔速度下降和最近的火山活动。菲涅耳带的论据表明，浅层化石岩石圈各向异性源可能是由前寒武纪中冻结的较旧的构造变形引起的，因此SKS测量变得更加可变。在喀尔巴阡山脉东南角的Vrancea地震带中，岩石深陷于地幔中的碎片夹在两个缓慢的异常之间，但较小的SKS延迟时间表明各向异性较弱，主要发生在西北侧，这与板块附近的不对称上升相一致。 ，地幔速度下降和最近的火山活动。菲涅耳带的论据表明，浅层化石岩石圈各向异性源可能是由前寒武纪中冻结的较旧的构造变形引起的，因此SKS测量变得更加可变。在喀尔巴阡山脉东南角的Vrancea地震带中，岩石深陷于地幔中的碎片夹在两个缓慢的异常之间，但较小的SKS延迟时间表明各向异性较弱，主要发生在西北侧，这与板块附近的不对称上升相一致。 ，地幔速度下降和最近的火山活动。