A lower crustal perspective on the stabilization and reactivation of continental lithosphere in the western Canadian shield

Thesis (Sc. D.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 2005."September 2005."Includes bibliographical references.New geochronological, thermochronological, geological and isotopic data from an extensive (> 20,000 km²) exposure of high-pressure granulites (0.8 to > 1.5 GPa, >750 ⁰C) in the East Lake Athabasca region of the Snowbird tectonic zone provide important constraints on the stabilization, reactivation and exhumation of continental lithosphere in the western Canadian Shield. The exhumed lower crust of this craton comprises several disparate domains that preserve a complex record of tectonic, magmatic and metamorphic processes from formation to exhumation. U-Pb zircon geochronology documents two episodes of metamorphic zircon growth at 2.55 Ga and 1.9 Ga, linked with two high-pressure granulite facies assemblages preserved in Chipman domain mafic granulites. The intervening 650 m.y. of relative quiescence implies a period of lithospheric stability during which the granulites continued to reside in the deep crust. Disruption of the stable Archean craton at 1.9 Ga broadly coincides with the assembly of the Laurentian supercontinent. The correlation of 1.9 Ga mafic magmatism and metamorphism in the Chipman domain with contemporaneous mafic magmatism along > 1200 km strike-length of the Snowbird tectonic zone indicates that regional asthenospheric upwelling was an important aspect of this reactivation event.(cont.) UL-Pb (titanite, apatite, rutile), ⁴⁰Ar/³⁹Ar (hornblende, muscovite, apatite) and (U-Th)/He (zircon, apatite) thermochronometry documents the cooling history of domains in the East Lake Athabasca region during the 200 m.y. multistage history of unroofing following 1.9 Ga metamorphism. Linkage of reconstructed temperature-time histories with existing pressure-temperature-deformation paths reveals spatial and temporal heterogeneity in exhumation patterns, with domain juxtaposition during episodes of unroofing separated by intervals of crustal residence. Low temperature (U-Th)/He zircon and apatite dates are the oldest reported for terrestrial rocks, and confirm the protracted residence of rocks at shallow (< [or equal to] 2 km) crustal depths following the re-attainment of a stable lithospheric configuration in the western Canadian shield at ca. 1.7 Ga.by Rebecca M. Flowers.Sc.D

Perspectives on pre-exposure prophylaxis for people who inject drugs in the context of an HIV outbreak: a qualitative study

Background: There is an ongoing HIV outbreak amongst people who inject drugs (PWID) in Glasgow, Scotland, and one response which has not yet been widely implemented is the provision of Pre-exposure prophylaxis (PrEP). PrEP is the use of HIV anti-retrovirals prior to HIV infection to provide a barrier to infection. This has been shown to be effective amongst various at-risk populations in preventing HIV spread. The present study aimed to explore views of PWID who might benefit from PrEP provision and Service Providers working with PWID to understand will to use PrEP and literacy of PrEP, contributing to the development of a PrEP service. Methods: A qualitative approach was taken, with semi structured interviews conducted in Glasgow at two third sector service sites. 11 Service Providers and 21 PWID participated in the study. Data was analysed thematically. Results: Participants, both PWID and Service Providers, were keen to engage with PrEP and perceived substantial potential benefits of PrEP for this population. Potential barriers to engagement were identified as a lack of health literacy, motivation, and self-ascribed risk, as well as the overwhelming unpredictability of substance use. Participants wanted PrEP to be provided within already existing structures, particularly community pharmacies, and for promotion and provision to involve peers. Conclusion: This sample reported willingness to engage with PrEP, and suggested there is a specific need amongst PWID for PrEP. However, PWID have specific lived experienced contexts and needs, and are burdened by social and economic marginalisation and inequality at every level. This contrasts them from other populations currently being provided with PrEP, and must be considered in the development of provision

The AGeS2 (Awards for Geochronology Student research 2) Program: Supporting Community Geochronology Needs and Interdisciplinary Science

Geochronology is essential in the geosciences. It is used to resolve the durations and rates of earth processes, as well as test causative relationships among events. Such data are increasingly required to conduct cutting-edge, transformative, earth-science research. The growing need for geochronology is accompanied by strong demand to enhance the ability of labs to meet this pressure and to increase community awareness of how these data are produced and interpreted. For example, a 2015 National Science Foundation (NSF) report on opportunities and challenges for U.S. geochronology research noted: While there has never been a time when users have had greater access to geo-chronologic data, they remain, by and large, dissatisfied with the available style/ quantity/cost/efficiency (Harrison et al., 2015, p. 1). And the 2012 National Research Council NROES (New Research Opportunities in the Earth Sciences) report (Lay et al., 2012, p. 82) recommended: [NSF] EAR should explore new mechanisms for geochronology laboratories that will service the geochronology requirements of the broad suite of research opportunities while sustaining technical advances in methodologies. The AGeS (Awards for Geochronology Student research) program is one way that these calls are being answered

Mechanisms affecting the implementation of a national antimicrobial stewardship programme; multi-professional perspectives explained using normalisation process theory.

Background: Antimicrobial stewardship (AMS) describes activities concerned with safe-guarding antibiotics for the future, reducing drivers for the major global public health threat of antimicrobial resistance (AMR), whereby antibiotics are less effective in preventing and treating infections. Appropriate antibiotic prescribing is central to AMS. Whilst previous studies have explored the effectiveness of specific AMS interventions, largely from uni-professional perspectives, our literature search could not find any existing evidence evaluating the processes of implementing an integrated national AMS programme from multi-professional perspectives. Methods: This study sought to explain mechanisms affecting the implementation of a national antimicrobial stewardship programme, from multi-professional perspectives. Data collection involved in-depth qualitative telephone interviews with 27 implementation lead clinicians from 14/15 Scottish Health Boards and 15 focus groups with doctors, nurses and clinical pharmacists (n = 72) from five Health Boards, purposively selected for reported prescribing variation. Data was first thematically analysed, barriers and enablers were then categorised, and Normalisation Process Theory (NPT) was used as an interpretive lens to explain mechanisms affecting the implementation process. Analysis addressed the NPT questions 'which group of actors have which problems, in which domains, and what sort of problems impact on the normalisation of AMS into everyday hospital practice'. Results: Results indicated that major barriers relate to organisational context and resource availability. AMS had coherence for implementation leads and prescribing doctors; less so for consultants and nurses who may not access training. Conflicting priorities made obtaining buy-in from some consultants difficult; limited role perceptions meant few nurses or clinical pharmacists engaged with AMS. Collective individual and team action to implement AMS could be constrained by lack of medical continuity and hierarchical relationships. Reflexive monitoring based on audit results was limited by the capacity of AMS Leads to provide direct feedback to practitioners. Conclusions: This study provides original evidence of barriers and enablers to the implementation of a national AMS programme, from multi-professional, multi-organisational perspectives. The use of a robust theoretical framework (NPT) added methodological rigour to the findings. Our results are of international significance to healthcare policy makers and practitioners seeking to strengthen the sustainable implementation of hospital AMS programmes in comparable contexts

How can we make self-sampling packs for sexually transmitted infections and bloodborne viruses more inclusive? a qualitative study with people with mild learning disabilities and low health literacy

Objectives: 1.5 million people in the UK have mild to moderate learning disabilities. STIs and bloodborne viruses (BBVs) are over-represented in people experiencing broader health inequalities, which include those with mild learning disabilities. Self-managed care, including self-sampling for STIs/BBVs, is increasingly commonplace, requiring agency and health literacy. To inform the development of a partner notification trial, we explored barriers and facilitators to correct use of an STI/BBV self-sampling pack among people with mild learning disabilities. Methods: Using purposive and convenience sampling we conducted four interviews and five gender-specific focus groups with 25 people (13 women, 12 men) with mild learning disabilities (July-August 2018) in Scotland. We balanced deductive and inductive thematic analyses of audio transcripts to explore issues associated with barriers and facilitators to correct use of the pack. Results: All participants found at least one element of the pack challenging or impossible, but welcomed the opportunity to undertake sexual health screening without attending a clinic and welcomed the inclusion of condoms. Reported barriers to correct use included perceived overly complex STI/BBV information and instructions, feeling overwhelmed and the manual dexterity required for blood sampling. Many women struggled interpreting anatomical diagrams depicting vulvovaginal self-swabbing. Facilitators included pre-existing STI/BBV knowledge, familiarity with self-management, good social support and knowing that the service afforded privacy. Conclusion: In the first study to explore the usability of self-sampling packs for STI/BBV in people with learning disabilities, participants found it challenging to use the pack. Limiting information to the minimum required to inform decision-making, € easy read' formats, simple language, large font sizes and simpler diagrams could improve acceptability. However, some people will remain unable to engage with self-sampling at all. To avoid widening health inequalities, face-to-face options should continue to be provided for those unable or unwilling to engage with self-managed care

An Imbalancing Act: The Delayed Dynamic Response of the Kaskawulsh Glacier to Sustained Mass Loss

The Kaskawulsh Glacier is an iconic outlet draining the icefields of the St. Elias Mountains in Yukon, Canada. We determine and attempt to interpret its catchment-wide mass budget since 2007. Using SPOT5/6/7 data we estimate a 2007–18 geodetic balance of −0.46 ± 0.17 m w.e. a−1. We then compute balance fluxes and observed ice fluxes at nine flux gates to examine the discrepancy between the climatic mass balance and internal mass redistribution by glacier flow. Balance fluxes are computed using a fully distributed mass-balance model driven by downscaled and bias-corrected climate-reanalysis data. Observed fluxes are calculated using NASA ITS_LIVE surface velocities and glacier cross-sectional areas derived from ice-penetrating radar data. We find the glacier is still in the early stages of dynamic adjustment to its mass imbalance. We estimate a committed terminus retreat of ~23 km under the 2007–18 climate and a lower bound of 46 km3 of committed ice loss, equivalent to ~15% of the total glacier volume

Post-Laramide, Eocene epeirogeny in central Colorado—The result of a mantle drip?

The Southern Rocky Mountains first rose during the Laramide Orogeny (ca. 75–45 Ma), but today's mountains and adjacent Great Plains owe their current height to later epeirogenic surface uplift. When and why epeirogeny affected the region are controversial. Sedimentation histories in two central Colorado basins, the South Park–High Park and Denver basins, shifted at 56–54 Ma from an orogenic to an epeirogenic pattern, suggesting central Colorado experienced epeirogeny at that time. To interrogate that hypothesis, we analyzed thermal histories for seven samples from central Colorado's Arkansas Hills and High Park using thermochronometers with closure temperatures below ~180 °C, enabling us to track sample exhumation from ~5–7 km depth. Three samples are from the Cretaceous Whitehorn pluton, and four are Precambrian granitoids. All zircon and titanite (U-Th)/He dates (ZHe and THe) and one apatite fission-track (AFT) date are similar to the 67 Ma pluton emplacement age. Whitehorn dates using the lower-temperature apatite (U-Th)/He (AHe) thermochronometer are 55–41 Ma. These data require two exhumation episodes, one ca. 67–60 Ma, the second beginning at 54–46 Ma. The pluton reached the surface by 37 Ma, based on the age of volcanic tuff filling a pluton-cutting paleovalley. The Precambrian samples do not further refine this thermal history owing to the comparatively higher He closure temperature of their more radiation-damaged apatite. Laramide crustal shortening caused 67–60 Ma exhumation. Arkansas Hills shortening ended before 67 Ma, so shortening could not have caused the exhumation event that began 54–46 Ma; thermochronology supports the Eocene epeirogeny hypothesis. Epeirogeny affected &gt;2.0 × 104 km2, from the Sawatch Range to the Denver Basin. We attribute epeirogeny to an Eocene mantle drip that likely triggered subsequent drips, causing younger exhumation events in adjacent areas

Cumulative Probability of False-Positive Recall or Biopsy Recommendation After 10 Years of Screening Mammography: A Cohort Study

False-positive mammography results are common. Biennial screening may decrease the cumulative probability of false-positive results across many years of repeat screening but could also delay cancer diagnosis

Cenozoic Exhumation Across the High Plains of Southeastern Colorado from (U-Th)/He Thermochronology

Colorado&rsquo;s High Plains stand at anomalously high elevations (~1300&ndash;2100 m) for their continental interior setting, but when and why this region became elevated is poorly understood. The Cenozoic history of the High Plains is also likely linked with that of the Rocky Mountains, where the timing and cause(s) of uplift are similarly debated. We present apatite (U-Th)/He (AHe) data for 10 samples from Tertiary intrusives along a ~200 km west-to-east transect across the High Plains of southeastern Colorado to constrain the timing of exhumation and to gain insight into when and why regional elevation gain occurred. Mean sample AHe dates for the ~24&ndash;22 Ma East Spanish Peak pluton and associated radial dikes from the westernmost High Plains are 18.8 &plusmn; 1.4 to 14.1 &plusmn; 1.7 Ma, recording substantial postemplacement erosion. AHe results for the mafic to ultramafic Apishapa Dikes (oldest ~37 Ma, youngest ~14 Ma) located ~20&ndash;40 km farther north and east on the High Plains range from 12.0 &plusmn; 1.4 to 6.2 &plusmn; 1.9 Ma, documenting continued exhumation on the western High Plains during the ~12&ndash;5 Ma deposition of the Ogallala Formation farther east and suggesting that the western limit of Ogallala deposition was east of the Apishapa Dikes. In far southeastern Colorado, the Two Buttes lamprophyre was emplaced at 36.8 &plusmn; 0.4 Ma and yields a Late Oligocene AHe date of 27.1 &plusmn; 4 Ma. Here, the Ogallala Formation unconformably overlies Two Buttes, indicating that the regional ~12 Ma age for the base of the Ogallala is a minimum age for the exposure of the pluton at the surface. The AHe data presented here document that kilometer-scale erosion affected all of the southeastern Colorado High Plains in Oligo-Miocene time. While exhumation can have multiple possible causes, we favor contemporaneous surface uplift capable of elevating the region to modern heights. &nbsp;</p