Some low-chloride pore waters observed in accretionary complexes are thought to result from clay dehydration and subsequent migration of the released water along faults or sand layers. We test this hypothesis with a two-dimensional flow and transport model for a cross section of the northern Barbados accretionary complex. The model flow system is driven by consolidation of the accreted sediments and by fluids from smectite clay dehydration. Steady state simulations result in concentrations that are too high along the d6collement fault and too low near the seafloor. In a transient model we simulate buildup and release of fluids by assuming that strain or hydrofracture along the fault causes an instantaneous increase in d6collement permeability of 2-3 orders of magnitude. With such an increase, the observed concentrations can be achieved in 100-1000 years.Also pressures along the fault rise to near lithostatic values in 10-100 years and remain high for 1000-10,000 years. This pressure rise may represent a mechanism for sustaining high fault permeabilities long after the initial increase. A steady source of pore fluids enters an accretionary complex with the accreted seafloor sediments. These fluids may then affect a variety of geologic processes. For example, high pore pressures affect fault strength and seismicity [Magee and Zoback, 1993], and fluid-rock interactions influence metamorphic reactions [Peacock, 1990]. In a thorough review of fluid Paper number 95WR02569. 0043-1397/95/95WR-02569505.00 flow in accretionary prisms, Moore and Vrolijk [1992] described two processes that drive the flow system. One is the very high mechanical loading rate on the saturated sediments as they are either incorporated into or underthrust below the complex. This loading rate is up to 15 times the maximum due to sedimentary basin subsidence [Moore and Vrolijk, 1992; Neuzil, 1995]. The resulting consolidation is often limited by low permeabilities, leading to near-lithostatic pore pressures. A second process is the dehydration of minerals and generation of hydrocarbons as sediments buried deep in the complex are subjected to higher temperatures. Anomalously low chloride and high methane concentrations in pore waters suggest that this is occurring in many accretionary complexes [Kastner et al., 1991]. The elevated temperatures and exotic chemical signatures of the pore fluids indicate that the flow systems supplying the vents may extend, in some cases, for 50-100 km. However, the source of heat and solutes is still poorly understood. Figure lc shows pore water chloride and methane concentration changes with depth at Ocean Drilling Program (ODP) site 671 in the Barbados Ridge complex. The pore waters are almost 10% lower in chloride than seawater at the depth of the d6collement fault. In addition, more recent chloride concentrations from the dficollement at ODP site 948 (near site 671) were 20% lower than that of seawater [Kastner et al., 1994]. Gieskes et al. [1990] discussed clay membrane filtration, hydrate dissolution, and the de...
Low chloride pore fluids observed along faults in clay‐rich accretionary complexes are commonly attributed to the release of interlayer water during the smectite to illite transformation. However, to date, there has been no thorough analysis of the location and quantity of fluids that may be generated by this mechanism. To address this problem, a temperature and time dependent rate expression describing the dehydration reaction was coupled to a kinematic model of the northern Barbados accretionary complex. Temperatures in the complex were estimated by modeling heat flow through the prism sediments as they thicken arcward. The sediments' temperature‐time histories were computed using a model for the velocities of sediment motion through the complex. In this model the prism sediments follow uniformly diverging paths from the toe, while the underthrust sediments undergo uniaxial strain. The model predictions are validated against clay mineralogy data from Barbados Island mudstones. Our results show that the location of the peak dehydration rate is 20 km farther arcward in the underthrust sediments than in the prism complex. The fresh water produced by the reaction results in pore waters that are 10–30% fresher at a distance of 50–70 km from the prism toe. This constraint indicates a probable fluid migration path of more than 50 km from the reaction zone to the sites where freshened pore fluids have been observed. The peak rate of fluid production when expressed as the volume of fluid per volume of sediment per second is 2×l0−15.
Much of what patients are seeking in integrative medical care is likely universally shared: a strong therapeutic relationship with providers who listen and provide time and knowledgeable advice. Users believe a combined approach of CAM and conventional medicine is better than either alone and want to be able to discuss CAM use with their providers.
An estimated one third of adults used prayer for health concerns in 1998. Most respondents did not discuss prayer with their physicians. Prayer was used frequently for common medical conditions, and users reported high levels of perceived helpfulness.
Abstract:The purpose of this study was to examine the benefits associated with complementary and alternative medicine (CAM) treatments from the patients' perspective using a whole systems research approach as a guiding framework. We conducted five focus groups of six to eight participants each, with users of CAM recruited through experienced CAM providers and clinics. Eligible participants were aged 21 or older, had used CAM in the last 12 months, and believed the treatment to be beneficial. The focus group discussions were digitally recorded, transcribed, and analyzed through a qualitative content analysis. Responses were inductively coded for common themes, and then placed into broader conceptual categories reflecting the CAM outcome domains suggested by Verhoef and colleagues. Participants described physical health benefits including symptom relief and improved function, and positive psychological benefits such as improved coping and resilience. Social health benefits that arose from the positive aspects of the patient-practitioner relationship were also reported, including support and advocacy. In addition, participants identified empowerment, increased hope and spiritual growth as results of receiving CAM treatments. A new behavioral health outcome domain emerged as participants reported that CAM use had fostered behavioral changes such as increased exercise, smoking cessation and improving their diets. These patient-reported benefits of CAM treatment are consistent with the outcome model proposed by Verhoef and colleagues, and extend this model by identifying a new outcome domain-behavioral health outcome. The findings provide insight and direction for the development of outcome and process measures to evaluate CAM treatment effects.
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