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

收敛的山脉带如何同时发生水平收缩和伸展这一悖论，仍然是大陆动力学中一个基本的、基本上尚未解决的问题。亚平宁代表了同步收敛扩展中最容易接近的“类型局部性”区域之一。回滚--描述俯冲板块从造山带前缘撤退的趋势--通常被用作对同步收敛伸展的解释，但这一想法没有解决俯冲板块的逆行运动是基于地幔的过程如何导致地壳会聚的上覆带水平伸展的问题，特别是考虑到通常与大陆俯冲有关的大增量通量。该项目(项目撤退)的目标是建立一个自洽的同步收敛伸展的动力学模型，将亚平宁北部作为一个天然的实验室。这部分亚平宁造山带自约30 Ma以来一直是相对稳定的正交会聚和2D(平面应变)造山变形的场所。GPS测量表明，目前汇聚是活跃的，层析成像表明，俯冲板块的全长在250公里以下仍然完好无损。同步会聚伸展活动至少在15 Ma以前就开始了。北亚平宁山脉得到了很好的研究，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。项目撤退的具体目标是：1)详细确定横跨造山带的速度场，包括造山楔内的变形、岩石圈板块的运动和周围软流圈地幔中的流场；2)利用这些运动学信息开发和测试造山楔和下地幔中变形的特定动力学模型。将使用的研究方法包括大地测量学、构造地貌学、低温热力学、构造地质学和构造综合学、地震研究和地球动力学模拟。务虚会项目将一个广泛的多学科小组联系在一起，该小组由来自6个机构的11名私人投资机构以及意大利、瑞士、加拿大和法国的约27名外国合作者组成。*

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.***