CSU Structural Geology - Recent Projects

Magmatism and polyphase deformation in the Middle Jurassic arc of central Chile

This project focused on the magmatic and structural evolution of the Middle Jurassic Papudo-Quintero plutonic complex, which is spectacularly exposed along the coastline in central Chile (near 32.5°S). Fieldwork was completed during my 2022 sabbatical in collaboration with Chilean geologists Gloria Arancibia, Diego Morata, and Ignacia Perez De La Maza. We documented three deformation events (D1, D2, and D3) and dated all major phases of the plutonic complex via U-Pb geochronology. D1 records three stages of ductile NW‐SE transpressional shortening that overlapped with arc magmatism; D2 and D3 record brittle transtension or strike‐slip deformation in the Late Jurassic to Early Cretaceous. D1 is consistent with regional oblique subduction convergance and localization of plate-driven strain the active magmatic arc, which was an important process in the early Andean orogeny.

Publication: Singleton, J.S., Arancibia, G., Morata, D., and Pérez De La Maza, I., 2024, Magmatism and polyphase deformation in the Middle Jurassic arc of central Chile: Implications for the tectonic development of the early Andean margin: Tectonics, v.43 (8), doi.org/10.1029/2023TC008241. link

Resumen en español

Skyler Mavor along the Taltal fault, northern Chile

Gert Heuser and Skyler Mavor in the Coastal Cordillera, northern Chile

Nikki Seymour along the eastern branch of the Atacama fault system

Structural evolution of the Atacama fault system, northern Chile: Insights into rheology and strain in a magmatic arc during oblique convergence

Funding: NSF Tectonics program (EAR 1822064, $308,743, including $83,298 in total supplements for the NSF INTERN program, 2018–2022)

John Singleton (PI), CSU Students: Nikki Seymour, Skyler Mavor, Rachel Ruthven, Emily Perman, Chilean geologists: Rodrigo Gomila, Gert Heuser, and Gloria Arancibia

This project addressed the structural evolution of the Cretaceous Atacama fault system, which is considered a classic example of an intra-arc strike-slip system. Intra-arc strike-slip fault systems play a critical role in accommodating oblique subduction convergence, yet significant uncertainty remains surrounding their rheology and deformation histories. The main goals of this project were to: a) determine the timing, magnitude, and rate of slip across the AFS, b) determine the spatial and temporal relationship between magmatism and deformation along the AFS, and c) determine the rheology and deformation conditions near the brittle-plastic transition along the AFS. Through a major mapping effort, geo/thermochronology, and microstructural analysis we established the slip history of this structure, identifying the first clear geologic offset markers along the fault (indicating ~54±6 km of sinistral displacement from 133–110 Ma), and we have documented in detail the how plutonism is intimately related to the timing and rheological development of the AFS. In addition, our work has provided new insight into the pre- and post-AFS deformation history in the Coastal Cordillera. Throughout this project we worked closely with Chilean geologists at Pontificia Universidad Católica.

Publications

Seymour, N.M., Singleton, J.S., Gomila, R., Arancibia, G., Ridley. J.,Gevedon, M.L., Stockli, D.F., and Seman, S.M., 2024, Sodic-calcic alteration and transpressional shear along the Atacama fault system during IOCG mineralization, Copiapó, Chile: Mineralium Deposita, doi.org/10.1007/s00126-024-01259-2. link

Mavor, S.P, Singleton, J.S., Heuser, G., Gomila, R., Seymour, N.M., Williams, S., and Arancibia, G.,2022, Sinistral shear during Middle Jurassic emplacement of the Matancilla Plutonic Complex in northern Chile (25.4°S) as evidence of oblique plate convergence during the early Andean orogeny: Journal of

South American Earth Science, v.120, 104047 link

Seymour, N.M., Singleton, J.S., Gomila. R., Mavor, S.P., Heuser, G., Arancibia, G., Williams, S., and Stockli, D.F., 2021, Magnitude, timing, and rate of slip along the Atacama fault system, northern Chile: Implications for Early Cretaceous slip partitioning and plate convergence: Journal of the Geological Society, v.178 link

Mavor, S.P., Singleton, J.S., Gomila, R., Heuser, G., Seymour, N.M., Williams, S.A., Arancibia, G., Johnston, S.M., Kylander-Clark, A.R.C., and Stockli, D.F., 2020, Timing, kinematics, and displacement of the Taltal fault system, northern Chile: Implications for the Cretaceous tectonic evolution of the Andean margin: Tectonics, v.39 link

Seymour, N.M., Singleton, J.S., Mavor, S.P., Gomila, R., Stockli, D.F., Heuser, G., and Arancibia, G., 2020, The relationship between magmatism and deformation along the intra-arc strike-slip Atacama fault system, northern Chile: Tectonics, v.39 link

Ruthven, R., Singleton, J., Seymour, N., Gomila, R., Arancibia, G., Stockli, D.F., Ridley, J., Magloughlin, J., 2020, The geometry, kinematics, and timing of deformation along the southern segment of the Paposo fault zone, Atacama fault system, northern Chile: Journal of South American Earth Sciences, v.97 link

Folded bedding in the evaporite décollemont, Sierra Madre Oriental

Structural evolution of shortening in the Potosi uplift, Sierra Madre Oriental, Mexico

Funding: PRF New Directions program (56057-ND8, $110,000, 2016–2019; PI: John Singleton)

This project involved geologic mapping, field-based structural analysis, and zircon (U-Th)/He thermochronology to investigate how deformation in the Sierra Madre Oriental near Galeana (Nuevo Leon) transitioned from thin-skinned shortening above an evaporite décollement to thick-skinned shortening involving subdécollemont strata.

Publication: Williams, S.A., Singleton, J.S., Prior, M.G., Mavor, S.P., Cross, G.E., and Stockli, D.F., 2021, The early Palaeogene transition from thin-skinned to thick-skinned shortening in the Potosí uplift, Sierra Madre Oriental, northeastern Mexico: International Geology Review, v.63 (2), p.233-263. link

Antietam Formation quartzite in the Virginia Blue Ridge (photomicrograph)

Rheology of brittle-plastic deformation in quartzite from the Virginia Blue Ridge

John Singleton (CSU), Jeffrey Rahl (Washington & Lee), Kenneth Befus (Baylor)

This project involved detailed field and microstructural analysis, EBSD, FTIR, strain analysis, and thermal modelling to investigate brittle-plastic deformation in coaxial shear zone involving Cambrian quartzite in the Virginia Blue Ridge. We demonstrate that dislocation creep at low temperatures (250–280°C) and strain localization was facilitated by low strain rates (~10-15/s) and hydrolytic weakening. An extension of this project led by Jeff Rahl investigated the relationships between crystallographic preferred orientation, water content, and strain.

Publications: Singleton, J.S., Rahl, J.M., and Befus, K.S., 2020, Rheology of a coaxial shear zone in the Virginia Blue Ridge: Wet quartzite dislocation creep at ~250–280°C: Journal of Structural Geology, v.140. link

Rahl, J.M., Moehringer, B., Befus, K.S., and Singleton, J.S., Influence of water on

crystallographic preferred orientation patterns in a naturally-deformed quartzite: Solid Earth,

v.15, p. 1233-1240. link

Zircon U-Pb data from the northern Plomosa Mountains (Seymour et al., 2018)

Orocopia Schist in the Plomosa Mountains, Arizona: A Laramide subduction complex exhumed in a Miocene metamorphic core complex

John Singleton (CSU), Evan Strickland (CSU), Nikki Seymour (CSU), Gordon Haxel (USGS), Danny Stockli (UT Austin)

Funding: USGS EDMAP (G16AC00142), NSF Tectonics program (1557265), and CSU start-up funds

This project in the northern Plomosa Mountains originated as an EDMAP project led by MS student Evan Strickland, which led to the remarkable discovery of one of the farthest inland exposures of Orocopia Schist – a Laramide subduction complex that includes blocks of metasomatized peridotite encased within quartzofeldspathic schist derived from trench sediments. We demonstrated that the northern Plomosa Mountains represents a Miocene metamorphic core complex dominated by mylonitic Orocopia Schist and early Miocene intrusions. Using zircon LA-ICP-MS geochronology we also determined that the Orocopia Schist was subducted at ca. 73 Ma and metamorphosed during Laramide underplating and Paleogene exhumation from 73 to 47 Ma, before assimilation into Miocene plutons and final exhumation during core complex extension.

Publications:

Strickland, E.D., Singleton, J.S., Haxel, G.B., 2018, Orocopia Schist in the northern Plomosa Mountains, west-central Arizona: A Laramide subduction complex exhumed in a Miocene metamorphic core complex: Lithosphere, v. 10, p. 723–742. link

Seymour, N.M., Strickland, E.D., Singleton, J.S., Stockli, D.F., and Wong, M.S., 2018,

Laramide subduction and metamorphism of the Orocopia Schist, northern Plomosa Mountains, west-central Arizona: Insights from zircon U-Pb geochronology: Geology, v.46, p. 847–850. link

Strickland, E.D., Singleton, J.S., Griffin, A.T.B. and Seymour, N.M., 2017, Geologic Map of the Northern Plomosa Mountains Metamorphic Core Complex, Arizona. Arizona Geological Survey Contributed Map CM-17-A, 1 map sheet, scale 1:10,000. link

Singleton, J.S., Seymour, N.M., and Strickland, E.D., 2022, The Buckskin-Rawhide and northern Plomosa Mountains metamorphic core complexes, west-central Arizona, USA, in Jiang, G., and Dehler, C., eds., Field Excursions from Las Vegas, Nevada: Guides to the 2022 GSA Cordilleran and Rocky Mountain Joint Section Meeting: Geological Society of America Field Guide 63, p. 85–107.

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