Broad-band Magnetotelluric to Image the Electrical Structure beneath Taiwan Orogen
Speaker: Irwan
Abstract
Taiwan is the type example of an arc-continent collision. Arc-continent collisions are a fundamental plate tectonic process that control continental growth, orogen development and the distribution of natural hazards and natural resources. This process actively occurs in Taiwan where the Luzon Volcanic Arc collides obliquely with the passive margin of the Eurasian Plate. Numerous tectonic models have been proposed for this orogen, and include both thin-skinned and thick-skinned lithospheric deformation. These models predict very different structures at middle and lower crustal depths, but insufficient geophysical data exist to unequivocally distinguish between them. Long-period Broad-band Magnetotelluric (MT) data were collected in Taiwan at 84 sites included one of remote station at Penghu island. Tensor decomposition, three- dimensional forward, and two-dimensional inversion were applied to the MT data. A two-dimensional inversion of these Broad-band Magnetotelluric data revealed a prominent electrical conductor that extends across the decollement predicted by the thin-skinned model in central Taiwan. This feature is interpreted to be due to 1%–2% saline fluids, and is inconsistent with the thin-skinned model. In contrast, the thick-skinned model predicts this feature since fluids are generated in the crustal root through metamorphism. Quantitative correlation of the resistivity and seismic velocity models supports small-volume, high-salinity fluids in a thickened crust as the cause of this conductor. A similar feature was observed in southern Taiwan, but with a higher fluid content. The conductor in southern Taiwan extends to lower crustal depths and is likely caused by fluids generated by metamorphic reactions in a thickened crust. Together the central and southern Taiwan MT profiles show a crustal root beneath the Central Range.
Reference
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