Evidence for the ~ 1.4 Ga Picuris orogeny in the central Colorado Front Range

We present the first evidence for sedimentation and new evidence for penetrative deformation and metamorphism in the central Colorado Front Range associated with the ~ 1.48–1.35 Ga Picuris orogeny. This orogeny has recently been recognized in New Mexico, Arizona and southern Colorado and may be part of a larger active accretionary margin that includes the ~ 1.51–1.46 Ga Pinware and Baraboo events, in eastern Canada and central US respectively, that preceded the amalgamation of the Rodinian supercontinent. We demonstrate that in addition to ~ 1.4 Ga reactivation of northeast-trending Paleoproterozoic shear zones, regional folding occurred in an area south of Mt. Evans, away from these shear zones. Detrital zircon from one quartzite yielded U–Pb laser ablation inductively coupled mass spectrometry (LAICPMS) major age populations of ~ 1.81–1.61 Ga and ~ 1.49–1.38 Ga, and minor ones of ~ 1.90 Ga and ~ 1.56 Ga. The Paleoproterozoic and ~ 1.49–1.38 Ga populations have numerous local and regional sources. The ~ 1.56 Ga age population may represent a minor exotic population as recognized in Defiance, Arizona the Yankee Joe and Blackjack Formations in Arizona, the Four Peaks area in Arizona, and the Tusas and Picuris Mountains in New Mexico. Alternatively it may be a result of mixing between zircon age domains reflecting the older and younger populations, or Pb loss from 1.81 to 1.61 Ga zircon. In-situ LA-ICPMS U–Pb analysis on monazite from four biotite schist samples yielded ~ 1.74 Ga and ~ 1.42 Ga age populations, and separate populations that show ~ 1.68–1.47 Ga and ~ 1.39–1.33 Ga age spreads. The ~ 1.74 Ga and ~ 1.68–1.47 Ga populations may be detrital or metamorphic. Monazite ages between ~ 1.6 Ga and ~ 1.5 Ga may be due to the mixing of age domains or Pb loss, because metamorphism during that time has not been recognized in Laurentia. The ~ 1.42 Ga and ~ 1.39–1.33 Ga populations are most likely metamorphic and consistent with the age of the ~ 1.48–1.35 Ga Picuris orogeny. The evidence for ~ 1.4 Ga sedimentation, and especially regional folding and metamorphism in the central Colorado Front Range indicate that the impact and extent of the Picuris orogeny in the southwestern U.S. are larger than previously thought

Перспективы развития рынка еврокапитала в современных условиях

Clinical and research staff who work around magnetic resonance imaging (MRI) scanners are exposed to the static magnetic stray fields of these scanners. Although the past decade has seen strong developments in the assessment of occupational exposure to electromagnetic fields from MRI scanners, there is insufficient insight into the exposure variability that characterizes routine MRI work practice. However, this is an essential component of risk assessment and epidemiological studies. This paper describes the results of a measurement survey of shift-based personal exposure to static magnetic fields (SMF) (B) and motion-induced time-varying magnetic fields (dB/dt) among workers at 15 MRI facilities in the Netherlands. With the use of portable magnetic field dosimeters, >400 full-shift and partial shift exposure measurements were collected among various jobs involved in clinical and research MRI. Various full-shift exposure metrics for B and motion-induced dB/dt exposure were calculated from the measurements, including instantaneous peak exposure and time-weighted average (TWA) exposures. We found strong correlations between levels of static (B) and time-varying (dB/dt) exposure (r = 0.88–0.92) and between different metrics (i.e. peak exposure, TWA exposure) to express full-shift exposure (r = 0.69–0.78). On average, participants were exposed to MRI-related SMFs during only 3.7% of their work shift. Average and peak B and dB/dt exposure levels during the work inside the MRI scanner room were highest among technical staff, research staff, and radiographers. Average and peak B exposure levels were lowest among cleaners, while dB/dt levels were lowest among anaesthesiology staff. Although modest exposure variability between workplaces and occupations was observed, variation between individuals of the same occupation was substantial, especially among research staff. This relatively large variability between workers with the same job suggests that exposure classification based solely on job title may not be an optimal grouping strategy for epidemiological purposes