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

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 investigates the relationships between crystallographic preferred orientation, intragranular 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 et al. 2022 GSA abstract

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.