Tectonic evolution of accretionary prism in the arc-continent collision of Taiwan as imaged by broadband magnetotelluric transects

Category Geophysic
Group GSI.IR
Location International Geological Congress,oslo 2008
Author Chen, Chow-Son
Holding Date 03 September 2008

Taiwan is the typical example of an arc-continent collision, in which the Luzon arc is actively being accreted onto the southeast China continental margin. Arc accretion is widely regarded as the fundamental mode by which continents grow. Due to the oblique nature of convergence between the arc and margin, Taiwan offers a unique opportunity to investigate the evolution of this important process in both time and space: variations along strike can be viewed as ’’snapshots’’ of various stages in orogenic evolution. Thus, a major goal is to identify various modes of crustal deformation as a function of depth, especially the orogenic processes of Taiwan, three transects cross the island of Taiwan by using broadband magnetotelluric soundings were initiated during the past two year. Profiles almost perpendicular to the regional strike of Taiwan were obtained. Based on 2-D various constrained inversion, where static shift and ocean effect were also a model parameter, various modes of crustal deformation as a function of depth were identified. Each profile model is characterized by two main relative high resistivity anomalies in the mid-crust to account for the response of Taiwan tectonics, the Luzon arc to the east and the southeast China continental margin to the west. Correlation of the resistivity structure to the seismicity, the heat flow, GPS velocity field and surface geology of Taiwan, some key questions as to how continents accrete and mountains evolve could be displayed in the resistivity profiles to some how. By looking at sections from south to north, we can trace the collision feature at differ crustal components (upper, lower, continental, oceanic) in the undeformed state through the orogenic system. The oceanic Philippine Sea plate act as an indenter to the generally weaker continental margin. The foreland was deformation thin-skinned to west, but was basement deformation to the east, the divider is at the topographic divide of Taiwan. Moreover, the oblique collision of the Luzon arc with the Chinese continental margin, resulting in southwestward propagating collision through time, the pre-collision and incipient-collision stages of Taiwan can be viewed in the resistivity profiles. In Taiwan, continental crust within the collision is accreted in the prowedge facing Asia, but is advected eastward into the east-verging retrowedge, where the most deeply exhumed rocks are exposed. The crustal deformation, as expressed in the surface geology, ultimately root into the mantle.


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