Collaborative Research: Geodynamic Evolution of an Active Arc-Continent Collision, Eastern Sunda Arc, Indonesia

弧-陆碰撞在整个地质时期的大陆组装中发挥了关键作用，目前作为大地震和爆炸性火山爆发的主要来源，对社会构成了重大威胁。 然而，弧-陆碰撞的基本地球动力学知之甚少，缺乏量化。 这部分是由于缺乏在一系列时间尺度上对变形模式的详细测量，而这只有在活跃的弧-大陆碰撞中才有可能。本研究采用多学科方法构建了活动性东巽他弧-大陆碰撞的三维力学模型。 调查的目的是通过综合各种方法，对广泛的时间和空间尺度进行取样，测量整个碰撞区的应变积累和分布情况。该地区的斜向碰撞为研究处于不同发展阶段的不断演变的造山带提供了难得的机会。此外，在大多数岛屿的边缘都有大量保存完好的隆起珊瑚阶地，这些阶地提供了局部和区域性的应变标志，能够记录10^4~10^6年时间尺度上的变形模式。 这是在以前的研究中，这个和其他活跃变形板块边界带的时间范围最少代表。 该项目正在解决一系列关于应变分区的基本地球动力学问题，例如：在进行性弧-大陆碰撞和俯冲极性反转期间，板块会聚从海沟转移到弧后的何处（以及如何）？是否有离散的侧向滑动断层连接着反向汇聚带？ 如果是这样的话，这个连接系统是如何随着碰撞传播的？收敛速度（7 - 8厘米/年）是局限于沿着断层还是增生带的韧性结构？ 碰撞区域是否被分割成离散的刚性块体？ 如果是这样，区块边界的性质是什么，它们是如何演变的？板块边界重组在不同的时间尺度上是如何表现的？综合地球动力学调查，包括结构地质学，地貌学和有限元建模正在被用来解决这些问题。将模型与GPS速度场和变形特征（如活动断层和翘曲珊瑚阶地）的测量结果进行比较，可以看出变形沿沿着先前存在的和新形成的地质结构重新分布到大陆区域所产生的各种构造过程。 俯冲和碰撞之间流变行为的这种广泛转变为大陆变形和刚性板块构造之间的差异提供了新的视角。应变分布远离海沟到弧前和弧后地区的原因，巽他弧东部增生的俯冲澳大利亚大陆边缘和激活新的板块边界段。这一过程的模型有助于更好地了解这些共同的地球动力学模式的时间依赖的流变学，并提供了一个详细的测试理论的时间分布的应变在整个弧-大陆碰撞带。

Arc-continent collision has played a key role in the assembly of continents throughout geologic time and currently poses a significant threat to society as a major source of large earthquakes and explosive volcanic eruptions. However, the fundamental geodynamics of arc-continent collision is poorly understood and lacks quantification. This is due in part to the lack of detailed measurements of deformation patterns at a range of temporal scales, which is only possible from active arc-continent collisions. This study is using a multidisciplinary approach to construct a 3-D mechanical model of the active eastern Sunda arc-continent collision. The aim of the investigation is to measure the accumulation and distribution of strain throughout the collision zone by a combination of methods that sample a wide range of temporal and spatial scales. Oblique collision in the region provides a rare opportunity to examine an evolving orogen at different stages of development. In addition, the abundance of well-preserved flights of uplifted coral terraces fringing most islands provide local and regional strain markers capable of recording deformation patterns over time scales of 10^4 to 10^6 years. This is the temporal range least represented in previous studies of this and other actively deforming plate boundary zones. This project is addressing a series of fundamental geodynamic questions about strain partitioning, such as: where (and how) is plate convergence from the trench transferred to the back arc during progressive arc-continent collision and subduction polarity reversal? Are there discrete lateral-slip faults that link zones of opposing convergence? If so, how does this connective system propagate with the collision? What proportion of the rate of convergence (7-8 cm/yr.) is localized along faults versus ductile structures of the accretionary zone? Is the collision zone segmented into discrete, rigid blocks? If so, what is the nature of the block boundaries and how do they evolve? How is plate boundary reorganization represented at different temporal scales?Integrated geodynamic investigations involving structural geology, geomorphology, and finite element modeling are being used to address these questions. Comparing models with measurements of the GPS velocity field and deformational features, such as active faults and warped coral terraces, demonstrates a variety of tectonic processes that result from the redistribution of deformation into continental regions along preexisting and newly forming geologic structures. This broad transition in rheological behavior between subduction and collision provides new perspectives into differences between continental deformation and rigid-plate tectonics. The distribution of strain away from the trench into the forearc and backarc regions causes the eastern Sunda arc to accrete to the underthrust Australian continental margin and activate new plate boundary segments. Models of this process help better understand these common geodynamic patterns in terms of a time-dependant rheology, and provide a detailed test of theories for the temporal distribution of strain throughout a arc-continent collision zone.