Current and ongoing research
Titanite deformation chronometry
Directly dating ductile deformation is a critical, unresolved challenge in tectonics and geochronology. Methods to directly constrain the timing, duration, and conditions of ductile deformation will transform conceptual and quantitative models of how the deep lithosphere deforms. Using examples from exhumed ductile shear zones, I am one of several researchers developing "titanite deformation chronometry" to directly date high-temperature (i.e., >500 °C) deformation. The approach integrates titanite U-Pb geochronology with individual grain microstructure, zoning, and trace-element geochemistry to determine if and when grains recrystallized during ductile shearing.
Our work in the Coast shear zone, British Columbia, directly ties titanite U-Pb dates to the timing of shearing and fluid flow along a crustal-scale shear zone (see example to right, published in Contributions to Mineralogy and Petrology). Titanite in the Anita Shear Zone, New Zealand, document the end of Alpine Fault Zone-related, amphibolite-facies deformation at ~11 Ma (manuscript in prep for the Journal of Metamorphic Geology). In m-scale shear zones in southern California, titanite record cooling and the evolution of fluid compositions during a punctuated deformation event (published in G-Cubed). |
Above: Date vs. misorientation plots for four titanite grains deformed in the Coast shear zone, British Columbia. Insets are EBSD misorientation maps showing increasing misorientation (warmer colors) relative to point in center of grain. Each scale bar is 100 microns. After Moser et al. 2022.
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Experimental constraints on dating deformation
The above examples from natural shear zones illustrate that titanite deformation chronometry is a powerful approach to directly date the timing of events in ductile shear zones. However, the multitude of processes that may be simultaneously active during ductile deformation (e.g., thermally mediated volume diffusion, neocrystallization, fluid-mediated recrystallization) make it challenging to evaluate if dislocation glide and climb alone reset dates and trace-element distributions. In my NSF postdoc, I use high-temperature, high-pressure titanite deformation experiments to evaluate the relative roles of dislocations and fluids in resetting U-Pb dates. The ultimate goal is to develop best practices for dating deformation with titanite. Collaborators for this work include Dr. Chloë Bonamici at the University of Wisconsin-Madison and Dr. Matej Pec at the Massachusetts Institute of Technology.
Left: Backscattered electron image of a titanite grain that preserves evidence of fluid-mediated recrystallization (dark rim) from a Cretaceous shear zone in SE California. After Cawood, Moser et al. (2022) in GSA Bulletin. |
How do sediments become lower continental crust?
Many models that explain the formation of the lower continental crust assume that these rocks are predominantly mafic. However, several exhumed sections of lower continental crust contain voluminous, felsic, metamorphosed sediments. For a complete model of the processes that create and modify Earth’s crust, we must understand how sediments become lower continental crust. The Ivrea-Verbano Zone is an intact section of primarily metasedimentary lower continental crust exposed in the southernmost Italian Alps. I use detrital zircon U-Pb geochronology to link the high-grade history of these rocks to the tectonic processes responsible for their deposition and subsequent burial to lower-crustal depths. Our results demonstrate that rapid timescales from deposition to metamorphism are not required to explain the formation of felsic, lower continental crust. A manuscript incorporating these data is currently in preparation for Earth and Planetary Science Letters.
Right: Garnetiferous metapelite exposed in the lower continental crust of the Ivrea Zone, Italy. Photo from fall 2019 field work with Josh Garber and Charlotte Connop. |
Prior research
Spatiotemporal patterns of deformation and exhumation along the southernmost San Andreas Fault
My prior research integrated low-temperature thermochronology with field observations of fault damage zones and microtextural observations of fault surfaces to elucidate the spatiotemporal patterns of crystalline basement exhumation in the Mecca Hills, southern California. These data revealed a multiphase history of Oligocene–Miocene and Pliocene–Pleistocene fluid flow, deformation, and fault-related exhumation tied to slip on the Orocopia Mountains detachment fault and the San Andreas fault system. My research interests in the record of tectonic processes preserved in mineral microtextures and radioisotopic systems in the deep crust are directly informed by my prior research on these fault systems in southern California. See our publications in EPSL, Chemical Geology, and Tectonics to learn more!
Left: Exposure of the Platform fault in the Mecca Hills. Inset: hematite-coated slip surface from basement-hosted damage zones in the Mecca Hills. |
For more on my research, view my google scholar page.