Research
PhD:
"LONG-TERM OFFSET HISTORY OF THE SAN ANDREAS FAULT THROUGH A MULTICHRONOMETER STUDY OF A KEY PIERCING POINT"Abstract coming soon
The San Andreas Fault (SAF) zone has been extensively studied to understand the rates and timing of deformation in transform plate-boundaries. Piercing points are critical to understand displacement on the SAF, however currently proposed piercing points yield total offset estimates ranging from 160 to 240km. This study revisits a key plutonic piercing point, the Triassic megaporphyritic monzogranite bodies of Liebre Mountain and Mill Creek. These two bodies are proposed to represent 160km of total SAF displacement based on pluton crystallization age, chemistry and the presence of K-feldspar megacrysts. This study applies a multichronometer approach to 1) confirm whether the two granitic bodies originate from the same pluton, 2) compare the exhumation histories of the two sites, pinpointing when their cooling histories diverge in relation to SAF inception and 3) determine spatio-temporal trends on either side of the fault.
New zircon U-Pb data from both sites record crystallization ages around 240 Ma with ~1.6 Ga inherited cores, as established by cathodoluminescence, confirming they derive from the same pluton. We also refined the extent of the Liebre Mountain megaporphyritic monzogranite through field mapping and U-Pb geochronology of the Triassic pluton in this area, revealing the presence of cretaceous granitoids (~80 Ma), which reduced the overall extent of the megaporphyritic unit. We present new apatite and zircon (U-Th)/He (aHe, zHe) and apatite fission track (AFT) in conjunction with published thermochronologic data from each site to model the plutons’ exhumation since emplacement and test the relation to SAF movement. Thermochronologic data and thermal history models suggests that the two sites share a common thermal history through zHe closure temperatures. Subsequently, the thermal histories diverged at lower temperatures after ~20Ma, as indicated by both AFT and aHe ages exhibiting a fault-perpendicular younging trend towards the SAF. These results suggest that the two bodies likely originated from the same pluton and remained as a single body until being offset by the San Andreas Fault, with subsequent differential evolution on either side of the fault. This model will be further tested with new samples close to the fault at Liebre Mountain.
"THE TIMING AND RHEOLOGICAL EFFECTS OF MAGNETITE COATED FAULT SURFACES"
Abstract coming soon
M.S. PROJECT: "UTILIZING DIGITAL MAPPING METHODOLOGY TO ANALYZE STRATIGRAPHIC VARIATION IN THE TRIASSIC ISCHIGUALASTO FORMATION, SAN JUAN PROVINCE, ARGENTINA"
Recently developed software and high resolution imagery has made it increasingly possible to derive stratigraphic and structural information remotely. This study explores the viability of such application in the Triassic Ischigualasto basin of northwest Argentina. While much of the work on the Ischigualasto Formation has focused on its abundant paleontological content, other recent research has involved investigating the structural controls on fluvial-channel and overbank deposition and the morphology of paleosols preserved in this ancient continental rift basin. These studies have equated observed changes in fluvial channel/overbank architecture and paleosol morphology with spatial/temporal changes in rates of basin accommodation development due to structural controls (Currie et al., 2009; Colombi et al., 2017). Field observations in 2019 brought these interpretations into question; there was not enough stratigraphic information (i.e. stratigraphic unit thickness measurements) to determine the true controls on sediment deposition.
Using a geologic map created in ArcGIS and a 5m resolution Digital Surface Model (DSM), along-strike stratigraphic-thickness change within the NW trending Ischigualasto Formation was discerned using the Geologic Map Data Extractor (GMDE) computer application (Allmendinger, 2020). Twenty three sections were measured across an along-strike distance of 50 km. Thicknesses increased from ~220 m in the southeast part of the study area to ~870 m in the northwest. These results are similar to published sections from the same area and are in accord with previous interpretations that the observed/calculated stratigraphic thickness changes in the Ischigualasto Formation were primarily controlled by along-strike increases in displacement on the basin-bounding Valle Fértil normal fault during the time of deposition. The methods used in this study can be applied globally to aid in field reconnaissance and computing unit thicknesses on a large scale.