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

Franklin And Marshall College, Lancaster PA

Investigators

Abstract

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.