T33A-2914
Linking Anomalously Low Topographic Relief in the Taiwan Arc-Continent Collision to a Submarine Plateau South of the Collision.

Wednesday, 16 December 2015
Poster Hall (Moscone South)
Timothy B Byrne, University of Connecticut, Groton, CT, United States, Andrew T Lin, NCU National Central University of Taiwan, Jhongli, Taiwan, Chih-Chieh Su, NTU National Taiwan University, Institute of Oceanography, Taipei, Taiwan, Jonathan C Lewis, Indiana University of Pennsylvania Main Campus, Geoscience, Indiana, PA, United States, Char-Shine Liu, NTU National Taiwan University, Taipei, Taiwan, William B Ouimet, University of Connecticut, Storrs, CT, United States, Tzu-Ting Chen, IONTU Institute of Oceanography National Taiwan University, Taipei, Taiwan and Chung Huang, Department of Geoscience, National Taiwan University, Taipei, Taiwan
Abstract:
Ouimet et al. (2014; submitted) have recently described broad areas of anomalously low relief and slope that straddle the topographic ridge crest in Taiwan. The areas are anomalous because Taiwan also preserves some of the steepest topography in the world, as expected from the high rates of convergence, exhumation and erosion. In addition, several age-elevation data sets (see Hsu et al. this meeting), using new and previously published ZrnFT, ZrnHe and ApFT ages, show exhumation cooling rates of 3 to 5 mm/yr since ~1.5-2.0 Ma, which is consistent with the exposure of reset zircons beneath the surfaces. Erosion rates of this magnitude, however, are expected to produce significant topographic relief, making it difficult to generate a topographic surface of low slope and low relief centered on the ridge crest. Very young ApFT and ZrnHe ages (e.g., < 0.5 Ma) also suggest a more recent acceleration in exhumation cooling.

A relatively large area of low relief centered on the top of the submarine accretionary prism south of Taiwan may provide a solution for this conundrum. The area covers ca 1000 km2, has a mean elevation of ca 450 m below sea level and appears to be composed of hard, intact rocks rather than unlithified deep sea muds. Several attempts at gravity and piston coring failed to penetrate the substrate and samples retrieved in the core catcher include rounded clasts of quartz and siltstone. Geophysical studies also show high Vp velocities at relatively shallow depths beneath the sea floor, suggesting the removal of a significant volume of sediment and rock, presumably through erosion. We propose that this low relief plateau serves as a modern analog for the formation of the low relief surfaces that currently straddle the ridge crest in Taiwan.

If this interpretation is correct, it suggests a tectonic model in which submarine erosion processes modulate vertical growth of the prism until collision of thick continental crust promotes uplift that outpaces erosion. This requires significant erosion rates (e.g., mm/yr) in the shallow water marine environment. Based on the young ApFT and ZrnHe ages, we propose that emergence of the prism occurred less than about a half a million years ago, and that this hypothesis could be tested by chronologic and thermochronologic data from cores retrieved through submarine drilling.

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