The full text of this item is not available at this time because the student has placed this item under an embargo for a period of time. The Libraries are not authorized to provide a copy of this work during the embargo period, even for Texas A&M users with NetID.
Investigating the Roles of Cordilleran Cyclicity and Subduction Zone Geometry on Erosional and Depositional Processes in the Central Andes
Abstract
The link between subduction zone dynamics, orogenesis, and surface processes remains unclear. Two proposed drivers are cyclical process within the upper plate as proposed by the Cordilleran Cyclicity Model and changing subducting plate geometries from the Slab Geometry Model. The Cusco stratigraphic section in the Central Andes spans Cenozoic Andean orogenesis, including the 45–27 Ma shallow subduction phase. This study applies U-Pb geochronology and (U-Th)/He thermochronology double dating to detrital zircons at 7 horizons from the Cusco Section to determine upsection lag time trends (the difference between depositional and cooling ages). Each model makes unique predictions using Critical Wedge Theory for lag time trends. 164 new (U-Th)/He ages were returned, and 2 stratigraphic samples were partially reset and offer no information on cooling age or lag time. Age distributions of non-reset samples support the onset of Andean orogenesis at 80 Ma. Cooling age was selected as the peak age of the (U-Th)/He age distribution. Lag time trends of non-partially samples decrease from 41-9 Ma, indicating subcritical wedge state supported by geologic evidence of distributed deformation, surface uplift, and increased exhumation of Eastern Cordillera. This is followed by increasing lag time from 9-7.4 Ma, representing supercritical wedge state and constraining the deformation advancement to Subandean Zone at least 7.4 Ma, consistent with broader SAZ advancement timing. Western Escarpment extensional fault timing also supports supercritical state. Results do not support the Cordilleran Cyclicity Model after the onset of the shallow slab as the high flux event is not followed by deformation advancement and increased lag time at ~25 Ma but rather continued out-of-sequence deformation and decreasing lag time trends. The shallowing slab disrupted predicted cycles and concluded that subduction zone dynamics are the primary driver on orogenesis, deformation, and surfaces processes at cordilleran margins.
Citation
Schroeder, Rachel M (2022). Investigating the Roles of Cordilleran Cyclicity and Subduction Zone Geometry on Erosional and Depositional Processes in the Central Andes. Master's thesis, Texas A&M University. Available electronically from https : / /hdl .handle .net /1969 .1 /197880.