Eocene fault-controlled fluid flow and mineralization in the Paradox Basin, United States

Sedimentary rocks of the Paradox Basin of the Colorado Plateau (southwestern USA) record widespread manifestations of paleo–fluid flow and fluid-rock reactions including Cu, U-V, and Fe-Mn mineral deposits, Si and Ca metasomatism, hydrocarbon accumulations, and bleached sandstones. Many of these are spatially associated with faults. Here we show evidence for a widespread phase of fault-related fluid migration and mineralization at 41–48 Ma in the Paradox Basin. We measured K-Ar dates of multiple size fractions of clay-rich fault gouge, yielding statistically overlapping dates of authigenic (1Md) illite for the Salt Valley (47.0 ± 3.0 Ma), Kane Springs (47.7 ± 3.8 Ma), Cliffdweller (43.4 ± 4.6 Ma), Courthouse (41.9 ± 2.3 Ma), Lisbon Valley (45.3 ± 0.9 Ma), and GTO (48.1 ± 2.6 Ma) faults. The latter two have an illite Rb-Sr isochron age of 50.9 ± 3.5 Ma, and fault-adjacent bornite has a Re-Os isochron age of 47.5 ± 1.5 Ma. Authigenic illite from a paleo–oil reservoir near the Courthouse fault formed from the interaction of reduced fluids with oxidized red-bed sandstones at 41.1 ± 2.5 Ma. The Moab and Keystone faults have older authigenic illite ages of 59.1 ± 5.7 Ma and 65.2 ± 1.0 Ma, respectively. Our results show a close temporal relationship between fault gouge formation, red-bed bleaching, and Cu mineralization during an enigmatic time interval, raising questions about drivers of Eocene fluid flow.

Late pleistocene movement of Nam O - Nam Dong fault: evidence from electron spin resonance dating of fault gouge in the Western Da Nang city

The Nam O - Nam Dong fault is rated as one of the most seismic source zones in Central Vietnam. Field investigation in the mountainous areas in the Cam Le and Hoa Vang districts (Da Nang city), which is a part of the Nam O - Nam Dong fault zone, the authors have discovered fault gouge zone of 5-40 cm width within the Dai Loc granitic rock. Two fault gouge samples were collected for Electron spin resonance (ESR) dating. The results from the ESR dating on the quartz grains from the fault gouge samples showed the youngest age from the smallest fraction, probably indicating that ESR signals in the fractions were completely zeroed at the time of faulting due to frictional heat. The preliminary results from the ESR dating on the quartz grains from the fault gouge indicate that the last major faulting in this site was later the ages of 15.05±3.55 ka to 18.21±4.06 ka ago. Multiple actives during the late Pleistocene - Holocene of this fault had uplifted the fault gouge from a depth-seated to the present-day locality. These data suggest that this fault zone can be classified as a potentially active fault zone and presents some seismic hazards.