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Title: Active faulting and deformation of the Mongolian Altay Mountains
Author: Gregory, Laura C.
Awarding Body: University of Oxford
Current Institution: University of Oxford
Date of Award: 2012
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In this thesis, I use multiple techniques to investigate the active faulting and deformation of the Altay Mountains, Western Mongolia. The Altay are an intracontinental transpressional mountain range, which are deforming in the far-field of the India-Asia collision. An anastomosing network of dextral faults strikes NNW-SSE, and accommodates NE-SW oriented shortening by rotating anticlockwise about vertical axes. I begin by characterising the Altay faults, and add to what is already known about their surface expression with new observations of active faulting and three previously undescribed ancient earthquake ruptures. I use 10Be cosmogenic dating and uranium-series dating on pedogenic carbonate to estimate the average Quaternary rate of slip for two of the major fault zones in the Altay. The slip rate on the Ölgiy fault is constrained to 0.3-2.1 mm/yr-1. Results from the Hovd fault are ambiguous, demonstrating the complications encountered with application of Quaternary dating techniques. I measure palaeomagnetic directions from Cretaceous to Pliocene-aged sediments in the eastern Altay to constrain the degree of anticlockwise rotation. Results from thermal demagnetisation of specimens indicate that the eastern Altay has not undergone significant rotation, in contrast with previous studies from the Siberian Altay that reveal almost 40 degrees of anticlockwise rotation. This suggests that the eastern-most Altay fault is too young to have experienced significant rotation, or is kinematically different from the Siberian Altay. I apply apatite fission track (AFT) dating and track length modeling to the central Altay. Results from AFT dating show rapid cooling in the late Cretaceous due to the distal assembly of Central Asia, suggesting that there was pre-existing topography at the start of the Late Cenozoic phase of deformation, the timing of which is constrained to have initiated at least 20 Myr ago. My work demonstrates that combining results from techniques that cover a variety of time scales quantifies the evolution of active faulting and deformation in the region.
Supervisor: Walker, Richard T. ; Mac Niocaill, Conall Sponsor: Clarendon Fund
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: Earthquakes and tectonics ; Palaeomagnetism and rock magnetism ; earth sciences ; active tectonics ; faulting and earthquakes ; geochronology