Research School of Earth Sciences, Australian National University, Canberra 0200, Australia.
School of Geosciences, University of Aberdeen, Aberdeen AB24 3UE, Scotland.
Sci Rep. 2015 Feb 3;5:8218. doi: 10.1038/srep08218.
Simple models involving the gradual outboard accretion of material along curvilinear subduction zones are often inconsistent with field-based evidence. A recent study using 3-D geodynamic modelling has shown that the entrainment of an exotic continental fragment within a simple subduction system can result in a complex phase of growth. Although kinematic models based on structural mapping and high-resolution gravity and magnetic maps indicate that the pre-Carboniferous Tasmanides in southeastern Australia may have been subjected to this process, to date there has been little corroboration from crustal scale geophysical imaging. Here, we apply Bayesian transdimensional tomography to ambient noise data recorded by the WOMBAT transportable seismic array to constrain a detailed (20 km resolution in some areas) 3-D shear velocity model of the crust beneath southeast Australia. We find that many of the velocity variations that emerge from our inversion support the recently developed geodynamic and kinematic models. In particular, the full thickness of the exotic continental block, responsible for orocline formation and the tectonic escape of the back arc region, is imaged here for the first time. Our seismic results provide the first direct evidence that exotic continental fragments may profoundly affect the development of an accretionary orogen.
简单的模型涉及到物质沿着曲线俯冲带逐渐向外堆积，但这些模型通常与基于现场的证据不一致。最近的一项使用三维地球动力学建模的研究表明，在简单的俯冲系统中引入外来大陆碎片会导致一个复杂的生长阶段。尽管基于构造测绘和高分辨率重力和磁图的运动学模型表明，澳大利亚东南部的前石炭纪塔斯曼尼亚可能经历了这一过程，但迄今为止，来自地壳尺度地球物理成像的证据很少。在这里，我们应用贝叶斯跨维层析成像方法，对 WOMBAT 可移动地震阵列记录的环境噪声数据进行处理，以约束澳大利亚东南部地壳的详细（某些地区分辨率为 20 公里）三维剪切速度模型。我们发现，我们反演得出的许多速度变化都支持最近发展的地球动力学和运动学模型。特别是，负责旋卷形成和后弧区构造逃逸的外来大陆块的全厚度首次在这里成像。我们的地震结果提供了第一个直接证据，表明外来大陆碎片可能深刻地影响了增生造山带的发展。
