Collisional Reactivation of Rift Margin Fracture Zones, Taiwan and the Taconic Allochthon

<p><strong>Chapter I. Transverse Topographic Development due to the Reactivation of a Partially-Subducted Fracture Zone: The Southwest Hsüehshan Range, Central Taiwan</strong></p> <p><strong><em>Abstract — </em></strong>The southwest flank of the Hsüehshan Range is defined by a topographic break which cuts across regionally mapped structures in central Taiwan. The mountain front trends ~345°, slightly oblique to the Sanyi-Puli seismic zone which has been previously interpreted as a reactivated continental margin fracture zone. Structural data collected along the length of the topographic break reveal two populations of cross-cutting faults with distinct fault-zone materials and a series of southwest-plunging folds. Paleostress axes were reconstructed using the P-B-T axes, right dihedra, and Gauss paleostress methods. Stress inversion results yield an azimuth of maximum horizontal shortening for early-stage faults of 315°, subparallel to the current relative plate convergence vector, and 252° for late-stage faults, approximately normal to the topographic break. In addition, rock uplift rates were examined by extracting normalized steepness indices from streams with catchments ≥ 10 km²within the Tachia, Peikang, and Mei River basins. With the incorporation of precise leveling data, zones of equal steepness coincide with increases in rock uplift rates from 5.15 ± 1.55 mm/yr in the Puli basin to 15.9 ± 1.88 mm/yr west of the Lishan fault zone, delineating a northwest-trending boundary consistent with the late-stage maximum compressive stress orientation. These results suggest that spatial variations in uplift rates across the topographic break are accommodated by the late-stage fault population. We propose that the formation of these late-stage structures is causally linked to the partial-subduction of a continental margin promontory and fracture zone.</p> <p><strong>Chapter II. Spatial Variation of Slaty Cleavage and Stretching Lineation Orientation in the Taconic Allochthon, Vermont and New York</strong></p> <p><strong><em>Abstract —</em></strong> New and previously collected structural data were compiled to produce detailed maps of slaty cleavage (S₂) and stretching lineation (L₂) orientation in the Taconic slate belt. The area of study encompasses a ~360 km² area between N43° 43’ and N43° 22’ along the Vermont and New York border. In total, ~1500 measurements of S₂ were compiled at 120 sites and 145 oriented samples were analyzed at 90 sites to determine the orientation of L₂. Kriging maps of the strike and dip of S₂ and the rake and trend of L₂ were constructed from these data. The kriging maps delineate three structural domains previously recognized from along-strike changes in the orientation of the axial traces of F₂ folds. The boundaries between domains are transitional; for domains 1 and 2 the boundary is located at approximately N43° 34’ and for domains 2 and 3, the boundary is located at approximately N43° 26’. In domain 1, the mean orientations of S₂and L₂ are 013, 31 E and 111, 29, respectively. The mean rake of L₂on S₂ is 82° from the south. In domain 2, the mean orientations of S₂and L₂are 354, 42 E and 124, 36, respectively. The mean rake of L₂on S₂is 50° from the south. In domain 3, the mean orientations of S₂and L₂are 013, 32 E and 111, 35, respectively. The mean rake of L₂on S₂is 82° from the south. The kriging maps show a correlation between the strike of S₂, dip of S₂, and rake and trend of L₂ along strike of the entire study area. The central part of domain 2 shows the most extreme values of strike, dip, rake, and trend. The overall change in S₂ and L₂ orientation from north to south has been previously interpreted as resulting from transport of domain 2 across an Iapetan transform fault and related along-strike variation in orientation of the shear zone in which S₂ and L₂ formed.</p>

Name thesis:degree_name

Master of Science

Discipline thesis:degree_discipline

Geological Sciences

Year dc:date.available

2011

Author dc:creator

• Mirakian, David C

Contributors dc:contributor

• Timothy Byrne; William Ouimet
• Jean Crespi

• Taiwan
• geology
• tectonics
• structural
• geomorphology
• Taconic
• orogenic curvature
• reactivation
• transfer
• fault

Repository record dc:identifier

https://digitalcommons.lib.uconn.edu/gs_theses/206

OAI identifier oai:identifier

oai:digitalcommons.lib.uconn.edu:gs_theses-1233