Collaborative Research: Retreating-Trench, Extension, and Accretion Tectonics (RETREAT): A Multi-Disciplinary Study of the Northern Apennines

0208461 Okaya水平收缩和伸展如何在会聚山脉中同时发生的悖论仍然是大陆动力学中一个基本的和基本上未解决的问题。亚平宁山脉代表了同向收敛扩张的最易接近的“典型局部性”区域之一。 回滚--描述俯冲板块从造山前缘后退的趋势--通常被用来解释同会聚伸展，但这种想法并没有解决俯冲板块的逆行运动是如何引起地壳会聚上覆带的水平伸展的，特别是考虑到与大陆俯冲有关的典型的大的加积通量。（项目RETREAT）的目的是利用北方亚平宁山脉作为自然实验室，建立一个自洽的同向收敛扩展的动态模型。亚平宁造山带的这一部分自~30 Ma以来一直是相对稳定的正交会聚和二维（平面应变）造山变形的场所。 全球定位系统的测量结果表明，目前的收敛是活跃的，和层析成像表明，俯冲板片的全长仍然完好无损的深度为250公里。 自15 Ma以来，同会聚伸展一直很活跃。 北方亚平宁山脉已被充分研究，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。RETREAT项目的具体目标是：1）详细确定造山带的速度场，包括造山楔的变形、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发展和检验造山楔和下伏地幔变形的特定动力学模型。 将使用的研究技术包括：大地测量学、构造地貌学、低温热年代学、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六个机构的11名PI以及意大利、瑞士、加拿大和法国的约27名外国合作者联系在一起。

0208461OkayaThe 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.