Syncing fault rock clocks; direct comparison of U-Pb carbonate and K-Ar illite fault dating methods

• Published in: Geology (Boulder) 2020-12, Vol.48 (12), p.1179-1183
• Main Authors: Mottram, C. M, Kellett, D. A, Barresi, T, Zwingmann, H, Friend, M, Todd, A, Percival, J. B
• Format: Article
• Language: English
• Subjects: absolute age; Aseismic zones; Big Creek Fault; brittle deformation; Brittleness; Canada; Canadian Cordillera; Carbonates; Cenozoic; Clay minerals; Clocks; Coastal inlets; Computational fluid dynamics; Cretaceous; crust; dates; Dating; Dating techniques; deformation; Earth crust; Eocene; Fault lines; Fault zones; Faults; Fluid flow; fracturing; Geochronology; Geological faults; Geology; gouge; Hydrothermal solutions; Illite; Illites; K/Ar; Lead; Mesozoic; Methods; North America; North American Cordillera; Palaeocene; Paleocene; Paleogene; Potassium-argon dating; Radiometric dating; sheet silicates; silicates; Slip; strike-slip faults; Structural geology; Tertiary; U/Pb; upper crust; Western Canada; Yukon Territory
• ISSN: 0091-7613; 1943-2682
• DOI: 10.1130/G47778.1

The timing of slip on brittle faults in Earth's upper crust is difficult to constrain, and direct radiometric dating of fault-generated materials is the most explicit approach. Here we make a direct comparison between K-Ar dating of fault gouge clay (authigenic illite) and U-Pb dating of carbonate slickenfibers and veins from the same fault. We have dated fault generated materials from the Big Creek fault, a northwest-striking, dextral strike-slip fault system in Yukon Territory, Canadian Cordillera. Both methods yielded dates at ca. 73 Ma and ca. 60-57 Ma, representing at least two periods of fault slip that form part of a complex fault and fluid-flow history. The Cretaceous result lies within previous indirect estimates for major slip on the fault. The Paleocene-Eocene result coincides with the estimated timing of slip of the nearby Tintina and Denali faults, which are crustal-scale, northwest-striking dextral faults, indicating Big Creek fault reactivation during regional faulting. The coincidence of periods of carbonate-crystallizing fracturing and fluid flow with intervals of seismic, gouge-generating slip supports the fault valve model, where fault strength is mediated by fluid pressures, and fluid emplacement requires seismic pumping in otherwise impermeable aseismic fault zones. The reproducibility of slip periods for distinct fault-generated materials using different decay systems indicates that these methods provide complimentary results and can be reliably applied to date brittle fault slip, opening new opportunities for investigating fault conditions with associated mineralizing fluid events.