285-7 Crustal Conditions of a Collisional Orogen: Using Electron Backscatter Diffraction (EBSD) to Understand Deformation in Taiwan

Session: Rock Deformation and the Dynamics of Mountain Building: A Session Honoring the Scientific Contributions of John P. Platt, Part II

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The island of Taiwan is an orogen built by a southward-propagating collision between the north-south trending Luzon volcanic arc and the northeast-trending passive Eurasian margin. The propagating nature of the collision makes Taiwan a suitable place to examine how deformation varies during progressive collision, from a juvenile collision to a mature one. Here, we conduct electron backscatter diffraction (EBSD) analysis on 42 samples collected from the Eastern Central Range, to determine the mechanism, stress, and temperature of deformation along the length of the orogen in Taiwan. Our results indicate that both higher-temperature dislocation creep and lower-temperature pressure solution are active in Taiwan, with increasing activation of pressure solution towards the southern end of the orogen. Where dislocation creep dominates, deformation is accomplished primarily by a combination of prism <a>, rhomb <a>, and pi <a> slip, although there is regional significance of prism <c> and basal <a> to the north and south, respectively. The trends in deformation mechanism and slip system indicate deformation temperature decreases from north to south. We apply an EBSD-calibrated piezometer and find flow stress in the Eastern Central Range varies from 35 to 110 MPa. We construct a crustal strength profile by combining estimates of flow stress and deformation temperature. Our results suggest a peak crustal strength between 80 and 150 MPa. Additionally, our crustal profile suggests the brittle-ductile transition may be fairly shallow, ranging from 3 to 7 km deep. The results presented here provide important constraints on the conditions of the crust during progressive collision, and the microstructural fabrics suggest that deformation varies in active slip system, temperature, and stress as collision proceeds, ultimately resulting in a moderately strong crust with a potentially very shallow brittle-ductile transition.

Geological Society of America Abstracts with Program. Vol. 57, No. 6, 2025

doi: 10.1130/abs/2025AM-11042

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