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

在整个地质时期，弧陆碰撞在大陆汇聚中发挥了关键作用，目前作为大地震和火山爆发的主要来源，对社会构成了重大威胁。然而，对弧-陆碰撞的基本地球动力学了解甚少，缺乏量化。这在一定程度上是由于缺乏对一系列时间尺度上的变形模式的详细测量，而这只有在活动的弧陆碰撞中才有可能。本研究采用多学科的方法，建立了东部舜他弧陆碰撞活动的三维力学模型。调查的目的是通过多种方法的组合来测量整个碰撞带应变的累积和分布，这些方法在时间和空间尺度上都进行了广泛的抽样。该地区的斜向碰撞为研究处于不同发展阶段的演化造山带提供了难得的机会。此外，大多数岛屿周围保存完好的珊瑚阶地的丰富飞行提供了当地和区域应变标记，能够记录10^4到10^6年的时间尺度上的变形模式。这是在以前对这个和其他活跃变形板块边界带的研究中最不具有代表性的时间范围。这个项目正在解决一系列关于应变分配的基本地球动力学问题，例如：在进行性的弧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哪里(以及如何)？是否存在连接相反汇聚带的离散侧向滑动断层？如果是这样，这个连接系统是如何在碰撞中传播的？汇聚率(7-8厘米/年)的比例是多少？是沿着断层定位还是沿着增殖带的韧性构造定位？碰撞区域是否被分割成离散的刚性区块？如果是这样的话，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？涉及构造地质学、地貌学和有限元模拟的综合地球动力学研究正在被用来解决这些问题。将模型与GPS速度场和变形特征(如活动断层和扭曲的珊瑚阶地)的测量结果进行比较，表明了各种构造过程，这些构造过程是变形沿先前存在的和新形成的地质结构重新分布到大陆地区的结果。俯冲和碰撞之间的这种流变行为的广泛转变为研究大陆变形和刚性板块构造之间的差异提供了新的视角。从海沟到弧前和弧后区域的应变分布导致东舜他弧与俯冲的澳大利亚大陆边缘相连，并激活了新的板块边界段。这一过程的模型有助于更好地理解这些与时间相关的流变学方面的常见地球动力学模式，并为整个弧陆碰撞带应变的时间分布提供详细的理论测试。

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.