Reassessing the structural and geomorphic evolution of a 'classic' Atlantic type passive margin: an integrated study of the Namaqualand sector of the South African continental margin

The origin of high elevation topography at so-called “passive” continental margins and their interior hinterlands has been an outstanding question in geoscience for decades. An important step towards answering this question is to improve our understanding of the response of the landscape to deformation of the lithosphere over different length scales. During continental rifting, elevated rift flanks may develop as a result of lateral extension of the lithosphere combined with vertical movements of the lithosphere driven by isostasy or convection of buoyant mantle flow. However, mechanisms capable of maintaining rift-related topography over geological timescales or driving post-rift rejuvenation of margin topography remain largely speculative and are strongly dependent on theoretical models. By constraining the timing and magnitude of major erosional events that have occurred across a particular margin using suitable empirical data we can begin to unravel the geomorphic development of the margin and identify the forces driving surface uplift. Apatite fission track (AFT) and apatite (U-Th-Sm)/He (AHe) thermochronometry has the unique ability to deliver these constraints by providing information on the cooling of rocks through temperatures of c. 120 – 40°C as they are exhumed from depth (c. 4 – 6 km) by erosion of overlying rock. Along the western continental margin of South Africa recent insights from thermochronology, structural geology and geomorphology has revealed that the margin may have experienced a more complex post-rift tectonic history than is to be expected for a “passive” margin. In this study, AFT and AHe analysis was performed on samples collected across the high relief escarpment zone along the continental margin (Namaqualand Highlands) and across the continental interior plateau (Bushmanland Plateau) to determine the post-break up cooling history of the continental margin. Sampling was undertaken from a structural perspective by sampling individual fault blocks within the heavily faulted Namaqualand Highlands and by collecting a profile of samples, from the interior plateau, that crosses major structural features at the boundary of the Kaapvaal craton. The approach for AHe analysis was to obtain multiple single grain age measurements (up to 20 grains per sample) for selected samples in order to investigate and exploit the primary causes of natural dispersion of AHe single grain ages and the influence of this dispersion on thermal history modelling. AFT and AHe data from 56 outcrop samples are jointly inverted using a Bayesian transdimensional approach incorporating the compositional influence on fission track annealing and radiation damage enhanced He retention. Two major discrete cooling episodes are recorded in thermal history models at c. 150 – 130 Ma and 110 – 90 Ma, respectively. These cooling episodes are broadly coeval with periods of enhanced deposition in the offshore Orange Basin and are therefore linked to discrete periods of enhanced continental erosion. The first phase of erosion is believed to involve the progressive destruction of syn-rift topography which prevailed across the developing continental margin and inland to the SW boundary of the Kaapvaal craton. The second phase of erosion is proposed to have been induced by regional uplift of southern Africa coupled with localised reactivation of basement structures at the continental margin and craton boundary. A vertical thickness of at least c. 3 – 5 km of material was eroded across the continental margin during the Cretaceous with only minor erosion (typically < 0.5km) occurring during the Cenozoic. There is now considerable support from the low temperature thermochronology record that km-scale denudation has occurred regionally across South Africa during the Mid-Late Cretaceous, long after the end of continental rifting in the South Atlantic. Data from this study reveals a more localised structural component to this regional event and more complexity in the spatial and temporal distribution of denudation during this period. The mechanisms driving this denudation are still uncertain but it is proposed here that regional dynamic uplift of South Africa has occurred due to the presence of an underlying upwelling of buoyant mantle, while in-plane horizontal stresses have triggered reactivation of basement structures. It now seems appropriate to revise the classification of the southwest African continental margin as being “passive” in a tectonic sense and consider the implications this has for our understanding of global plate tectonics

Intracontinental deformation in southern Africa during the late Cretaceous

Intracontinental deformation accommodated along major lithospheric scale shear zone systems and within associated extensional basins has been well documented within West, Central and East Africa during the Late Cretaceous. The nature of this deformation has been established by studies of the tectonic architecture of sedimentary basins preserved in this part of Africa. In southern Africa, where the post break-up history has been dominated by major erosion, little evidence for post-break-up tectonics has been preserved in the onshore geology. Here we present the results of 38 new apatite fission track analyses from the Damara region of northern Namibia and integrate these new data with our previous results that were focused on specific regions or sections only to comprehensively document the thermo-tectonic history of this region since continental break-up in the Early Cretaceous. The apatite fission track ages range from 449 ± 20 Ma to 59 ± 3 Ma, with mean confined track lengths between 14.61 ± 0.1 μm (SD 0.95 μm) to 10.83 ± 0.33 μm (SD 2.84 μm). The youngest ages (c. 80-60 Ma) yield the shortest mean track lengths, and combined with their spatial distribution, indicate major cooling during the latest Cretaceous. A simple numerical thermal model is used to demonstrate that this cooling is consistent with the combined effects of heating caused by magmatic underplating, related to the Etendeka continental flood volcanism associated with rifting and the opening of the South Atlantic, and enhanced erosion caused by major reactivation of major lithospheric structures within southern Africa during a key period of plate kinematic change that occurred in the South Atlantic and SW Indian ocean basins between 87-56 Ma. This phase of intraplate tectonism in northern Namibia, focused in discrete structurally defined zones, is coeval with similar phases elsewhere in Africa and suggests some form of trans-continental linkage between these lithospheric zones

Urinary ATP and visualization of intracellular bacteria: a superior diagnostic marker for recurrent UTI in renal transplant recipients?

Renal transplant recipients (RTR) are highly susceptible to urinary tract infections (UTIs) with over 50% of patients having at least one UTI within the first year. Yet it is generally acknowledged that there is considerable insensitivity and inaccuracy in routine urinalysis when screening for UTIs. Thus a large number of transplant patients with genuine urine infections may go undiagnosed and develop chronic recalcitrant infections, which can be associated with graft loss and morbidity. Given a recent study demonstrating ATP is released by urothelial cells in response to bacteria exposure, possibly acting at metabotropic P2Y receptors mediating a proinflammatory response, we have investigated alternative, and possibly more appropriate, urinalysis techniques in a cohort of RTRs.Mid-stream urine (MSU) samples were collected from 53 outpatient RTRs. Conventional leukocyte esterase and nitrite dipstick tests, and microscopic pyuria counts (in 1 ?l), ATP concentration measurements, and identification of intracellular bacteria in shed urothelial cells, were performed on fresh unspun samples and compared to ‘gold-standard’ bacterial culture results.Of the 53 RTRs, 22% were deemed to have a UTI by ‘gold-standard’ conventional bacteria culture, whereas 87%, 8% and 4% showed evidence of UTIs according to leukocyte esterase dipstick, nitrite dipstick, and a combination of both dipsticks, respectively. Intracellular bacteria were visualized in shed urothelial cells of 44% of RTRs, however only 1 of the 23 RTRs (44%) was deemed to have a UTI by conventional bacteria culture. A significant association of the ‘gold-standard’ test with urinary ATP concentration combined with visualization of intracellular bacteria in shed urothelial cells was determined using the Fisher’s exact test.It is apparent that standard bedside tests for UTIs give variable results and that seemingly quiescent bacteria in urothelial cells are very common in RTRs and may represent a focus of subclinical infection. Furthermore, our results suggest urinary ATP concentration combined with detection of intracellular bacteria in shed urinary epithelial cells may be a sensitive means by which to detect ‘occult’ infection in RTRs

The chronology and tectonic style of landscape evolution along the elevated Atlantic continental margin of South Africa resolved by joint apatite fission track and (U-Th-Sm)/He thermochronology

Atlantic-type continental margins have long been considered “passive” tectonic settings throughout the entire postrift phase. Recent studies question the long-term stability of these margins and have shown that postrift uplift and reactivation of preexisting structures may be a common feature of a continental margin's evolution. The Namaqualand sector of the western continental margin of South Africa is characterized by a ubiquitously faulted basement but lacks preservation of younger geological strata to constrain postrift tectonic fault activity. Here we present the first systematic study using joint apatite fission track and apatite (U-Th-Sm)/He thermochronology to achieve a better understanding on the chronology and tectonic style of landscape evolution across this region. Apatite fission track ages range from 58.3 ± 2.6 to 132.2 ± 3.6 Ma, with mean track lengths between 10.9 ± 0.19 and 14.35 ± 0.22 µm, and mean (U-Th-Sm)/He sample ages range from 55.8 ± 31.3 to 120.6 ± 31.4 Ma. Joint inverse modeling of these data reveals two distinct episodes of cooling at approximately 150–130 Ma and 110–90 Ma with limited cooling during the Cenozoic. Estimates of denudation based on these thermal histories predict approximately 1–3 km of denudation coinciding with two major tectonic events. The first event, during the Early Cretaceous, was driven by continental rifting and the development and removal of synrift topography. The second event, during the Late Cretaceous, includes localized reactivation of basement structures as well as regional mantle-driven uplift. Relative tectonic stability prevailed during the Cenozoic, and regional denudation over this time is constrained to be less than 1 km

Projected impact of polypill use among US adults: Medication use, cardiovascular risk reduction, and side effects

Background Polypills, which include multiple medications for reducing cardiovascular disease (CVD) risk in a single pill, have been proposed for population-wide use. The number of US adults eligible for polypills and potential benefits are unknown. Methods The National Health and Nutrition Examination Survey 2003-2004 and 2007-2008 were analyzed to estimate treatment rates for medications proposed for inclusion in polypills (aspirin, statin, an angiotensin-converting enzyme [ACE] inhibitor, and a thiazide-type diuretic for those without and a β-blocker for those with a history of myocardial infarction) among US adults. The number of coronary heart disease (CHD) and stroke events potentially prevented through polypill use was projected by published meta-analyses and 3 large population-based cohort studies. Two polypill eligibility criteria were analyzed: (1) US adults ≥55 years and (2) US adults with a history of CVD. Results There are 67.6 million US adults ≥55 years and 15.4 million US adults with a history of CVD and, thus, eligible for polypills using the 2 outlined criteria. In 2007 to 2008, 37.3% of US adults ≥55 years and 57.0% of those with a history of CVD were taking statins. Use of other polypill medications was also low. Polypill use by US adults aged ≥55 years is projected to potentially prevent 3.2 million CHD events and 1.7 million strokes over 10 years. Among those with a history of CVD, the potential to prevent of 0.9 million CHD events and 0.5 million strokes is projected. Conclusions Polypills have the potential to lower CVD incidence substantially among US adults

Towards digital metal additive manufacturing via high-temperature drop-on-demand jetting

Drop-on-demand jetting of metals offers a fully digital manufacturing approach to surpass the limitations of the current generation powder-based additive manufacturing technologies. However, research on this topic has been restricted mainly to near-net shaping of relatively low melting temperature metals. Here it is proposed a novel approach to jet molten metals at high-temperatures (>1000 °C) to enable the direct digital additive fabrication of micro- to macro-scale objects. The technique used in our research – “MetalJet” - is discussed by studying the ejection and the deposition of two example metals, tin and silver. The applicability of this new technology to additive manufacturing is evaluated through the study of the interface formed between the droplets and the substrate, the inter-droplets bonding, the microstructure and the geometrical fidelity of the printed objects. The research shows that the integrity of the samples (in terms of density as well as metallurgy) varies dramatically in the two investigated materials due to the different conditions that are required to melt the interface of the stacked droplets. Nevertheless the research shows that by a careful choice of the jetting strategy and sintering treatments 3D structures of various complexity can be formed. This research paves the way towards the next generation metal additive manufacturing where various printing resolutions and multi-material capabilities could be used to obtain functional components for applications in printed electronics, medicine and the automotive sectors

The Dopamine D 3 Receptor Gene and Posttraumatic Stress Disorder

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/108358/1/jts21937.pd

Thermal history modeling techniques and interpretation strategies: applications using QTQt

Advances in low-temperature thermochronology have made it applicable to a plethora of geoscience investigations. The development of modeling programs (e.g., QTQt and HeFTy) that extract thermal histories from thermochronologic data has facilitated growth of this field. However, the increasingly wide range of scientists who apply these tools requires an accessible entry point to thermal history modeling and how these models develop our understanding of complex geological processes. This contribution offers a discussion of modeling strategies, using QTQt, including making decisions about model design, data input, kinetic parameters, and other factors that may influence the model output. We present a suite of synthetic data sets derived from known thermal histories with accompanying tutorial exercises in the Supplemental Material. These data sets illustrate the opportunities and limitations of thermal history modeling. Examining these synthetic data helps to develop intuition about which thermochronometric data are most sensitive to different thermal events and to what extent user decisions on data handling and model setup can control the recovery of the true solution. We also use real data to demonstrate the importance of incorporating sensitivity testing into thermal history modeling and suggest several best practices for exploring model sensitivity to factors including, but not limited to, the model design or inversion algorithm, geologic constraints, data trends, the spatial relationship between samples, or the choice of kinetics model. Finally, we provide a detailed and explicit workflow and an applied example for a method of interrogating vague model results or low observation-prediction fits that we call the “Path Structure Approach.” Our explicit examination of thermal history modeling practices is designed to guide modelers to identify the factors controlling model results and demonstrate reproducible approaches for the interpretation of thermal histories