Collaborative Research: Retreating-trench, extension, and accretion tectonics (RETREAT): a multidisciplinary study of the northern Apennines

[20829 . 99]在收敛的山带中，水平收缩和伸展如何同时发生，这一悖论仍然是大陆动力学中一个基本的、基本上没有解决的问题。亚平宁山脉是最容易接近的同收敛扩展的“类型局部性”区域之一。“回滚”——描述了俯冲板块从造山带前缘撤退的趋势——通常被用来解释同辐合伸展，但这一观点并没有解释俯冲板块的逆行运动是如何导致地壳辐合上覆带的水平伸展的，这是一个以地幔为基础的过程，特别是考虑到通常与大陆俯冲有关的大量增生通量。该项目（项目RETREAT）的目标是利用亚平宁山脉北部作为自然实验室，开发一个自一致的同步收敛扩展动态模型。自~30 Ma以来，亚平宁造山带的这一部分是相对稳定的正交辐合和二维（平面应变）造山变形的场所。GPS测量表明，目前辐合活动很活跃，断层扫描显示，俯冲板块的全长到250公里深处仍然完好无损。自至少15 Ma以来，同辐合伸展一直活跃。人们对北亚平宁山脉进行了很好的研究，造山带的所有重要特征都在陆地上，因此可以直接进行详细的地质和地球物理研究。该项目的具体目标是：1)详细确定整个造山带的速度场，包括造山带楔的变形、岩石圈板块的运动和周围软流圈地幔的流场；2)利用这些运动学信息开发和测试造山带楔和下伏地幔变形的特定动力学模型。研究方法包括：大地测量学、构造地貌学、低温测时学、构造地质学和构造综合、地震研究和地球动力学建模。RETREAT项目将一个广泛的多学科小组与来自6个机构的11名pi以及来自意大利、瑞士、加拿大和法国的约27名外国合作者联系在一起

0208299CowanThe paradox of how horizontal contraction and extension can occur simultaneously in convergent mountain belts remains a fundamental and largely unresolved problem in continental dynamics. The Apennines represent one of the most accessible "type locality" areas of syn-convergent extension. Rollback - which describes the tendency of a subducting plate to retreat from the orogenic front - is commonly invoked as an explanation for syn-convergent extension, but this idea does not address how the retrograde motion of the subducting plate, which is a mantle-based process, causes horizontal extension in the overlying zone of crustal convergence, especially in light of the large accretionary fluxes typically associated with continental subduction.The goal of the project (project RETREAT) is to develop a self-consistent dynamic model of syn-convergent extension, using the Northern Apennines as a natural laboratory. This part of the Apennine orogen has been the site of relatively steady orthogonal convergence and 2D (plane strain) orogenic deformation since ~30 Ma. GPS measurements indicate that convergence is presently active, and tomography indicates that the full length of subducted slab is still intact to depths of 250 km. Syn-convergent extension has been active since at least 15 Ma. The Northern Apennines are well studied, and all important features of the orogen are onland and thus directly accessible for detailed geological and geophysical research.The specific objectives of project RETREAT are 1) to determine in detail the velocity field across the orogen, including deformation in the orogenic wedge, the motion of lithospheric plates, and the flow fields in the surrounding asthenospheric mantle, and 2) to use this kinematic information to develop and test specific dynamic models for deformation in the orogenic wedge and underlying mantle. The research techniques to be used include; geodesy, tectonic geomorphology, low-temperature thermochronometry, structural geology and tectonic syntheses, seismic studies, and geodynamic modeling. The RETREAT project links together a broad multidisciplinary group with eleven PIs from six institutions, plus some 27 foreign collaborators in Italy, Switzerland, Canada, and France.***