Active tectonics of the Yakutat – North America collision zone : GPS and geomorphology contribution to the study of strain partitioning

• Main Author: Maréchal, Anaïs
• Other Authors: Géosciences Montpellier, Institut national des sciences de l'Univers (INSU - CNRS)-Université de Montpellier (UM)-Université des Antilles (UA)-Centre National de la Recherche Scientifique (CNRS), Université Montpellier, Stéphane Mazzotti
• Format: Doctoral or Postdoctoral Thesis
• Language: French
• Published: HAL CCSD 2015
• Subjects: Strain; Partition; Gps; Indentor; Morphotectonics; Structural heritage; Déformation; Indenteur; Morphotectonique; Héritage structural; [SDU.STU]Sciences of the Universe [physics]/Earth Sciences; Yukon; Pacific; Queen Charlotte; Fairweather; Duke River; Yakutat; Alaska
• Online Access: https://tel.archives-ouvertes.fr/tel-03215203; https://tel.archives-ouvertes.fr/tel-03215203/document; https://tel.archives-ouvertes.fr/tel-03215203/file/MARECHAL_2015_archivage_cor.pdf

In SW Yukon – SE Alaska, the boundary between the Pacific and North America plates is characterized by a syntaxis at the transition between the Aleutian subduction to the W and the Fairweather – Queen Charlotte strike-slip faults to the SE. The relative motion is oblique to the main fault structures, and the area is marked by the Yakutat block collision. From the Chugach – Saint Elias mountains in the plate boundary zone (up to 6 000 m high) to the intraplate strike-slip faults, markers of the present-day deformation give information on its partition in the system.During my PhD, I first measure surface deformation using a dense GPS network, deployed up to 500 km inland the North America plate. After precise processing and corrections of transient effects in the area (postseismic and glacial isostatic rebound), a new residual velocity field is produced for the syntaxis area, from which I derive strain rates. Those data allow me to quantify the fault slip rates for Fairweather and southern Denali strike-slip faults, and to characterize a bi-modal deformation pattern: Along the plate boundary, the deformation is localized on large-scale structures (accretionary prism to the W, Fairweather to the E); In the syntaxis area, strain rates are the highest and the GPS data shows a diffuse intraplate deformation, similar to an indentor pattern. The Yakutat block seems to strongly drive the North America plate deformation.This indentor pattern induces strong lateral variations on the large intraplate faults: the Denali – Totschunda – Duke River system. In a second part, I realize a regional geomorphological study to characterize the role and slip rate of those faults. From very high-resolution Digital Elevation Models (~ 1 m), a detailed cartography is done. On the basis of fieldwork observations, I measure offsets of fluvial and glacial markers, which are sampled for dating. A dextral cumulative deformation is highlighted on the northern Denali Fault, where as all southern Denali is marked by vertical deformation. This ...