| 1. |
- Plasman, M., et al.
(författare)
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Lithospheric low-velocity zones associated with a magmatic segment of the Tanzanian Rift, East Africa
- 2017
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Ingår i: Geophysical Journal International. - : OXFORD UNIV PRESS. - 0956-540X .- 1365-246X. ; 210:1, s. 465-481
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Tidskriftsartikel (refereegranskat)abstract
- Rifting in a cratonic lithosphere is strongly controlled by several interacting processes including crust/mantle rheology, magmatism, inherited structure and stress regime. In order to better understand how these physical parameters interact, a 2 yr long seismological experiment has been carried out in the North Tanzanian Divergence (NTD), at the southern tip of the eastern magmatic branch of the East African rift, where the southward-propagating continental rift is at its earliest stage. We analyse teleseismic data from 38 broad-band stations ca. 25 km spaced and present here results from their receiver function (RF) analysis. The crustal thickness and Vp/Vs ratio are retrieved over a ca. 200 x 200 km(2) area encompassing the South Kenya magmatic rift, the NTD and the Ngorongoro-Kilimanjaro transverse volcanic chain. Cratonic nature of the lithosphere is clearly evinced through thick (up to ca. 40 km) homogeneous crust beneath the rift shoulders. Where rifting is present, Moho rises up to 27 km depth and the crust is strongly layered with clear velocity contrasts in the RF signal. The Vp/Vs ratio reaches its highest values (ca. 1.9) beneath volcanic edifices location and thinner crust, advocating for melting within the crust. We also clearly identify two major low-velocity zones (LVZs) within the NTD, one in the lower crust and the second in the upper part of the mantle. The first one starts at 15-18 km depth and correlates well with recent tomographic models. This LVZ does not always coexist with high Vp/Vs ratio, pleading for a supplementary source of velocity decrease, such as temperature or composition. At a greater depth of ca. 60 km, a midlithospheric discontinuity roughly mimics the step-like and symmetrically outward-dipping geometry of the Moho butwith a more slanting direction (NE-SW) compared to theNS rift. By comparison with synthetic RF, we estimate the associated velocity reduction to be 8-9 per cent. We relate this interface to melt ponding, possibly favouring here deformation process such as grain-boundary sliding (EAGBS) due to lithospheric strain. Its geometry might have been controlled by inherited lithospheric fabrics and heterogeneous upper mantle structure. We evidence that crustal and mantle magmatic processes represent first order mechanisms to ease and locate the deformation during the first stage of a cratonic lithospheric breakup.
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| 2. |
- Tiberi, C., et al.
(författare)
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Lithospheric modification by extension and magmatism at the craton-orogenic boundary : North Tanzania Divergence, East Africa
- 2019
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Ingår i: Geophysical Journal International. - : OXFORD UNIV PRESS. - 0956-540X .- 1365-246X. ; 216:3, s. 1693-1710
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Tidskriftsartikel (refereegranskat)abstract
- We present a joint analysis of newly acquired gravity and teleseismic data in the North Tanzanian Divergence, where the lithospheric break-up is at its earliest stage. The impact of a mantle upwelling in more mature branches of the East African Rift has been extensively studied at a lithospheric scale. However, few studies have been completed that relate the deep-seated mantle anomaly detected in broad regional seismic tomography with the surface deformation observed in the thick Archaean Pan-African suture zone located in North Tanzania. Our joint inversion closes the gap between local and regional geophysical studies, providing velocity and density structures from the surface down to ca. 250 km depth with new details. Our results support the idea of a broad mantle upwelling rising up to the lithosphere and creating a thermal modification along its path. However, our study clearly presents an increasing amplitude of the associated anomaly both in velocity and density above 200 km depth, which cannot be solely explained by a temperature rise. We infer from our images the combined impact of melt (2-3 per cent), composition and hydration that accompany the modification of a thick heterogenous cratonic lithosphere are a response to the hot mantle rising. The detailed images we obtained in density and velocity assert that Archaean and Proterozoic units interact with the mantle upwelling to restrict the lithosphere modifications within the Magadi-Natron-Manyara rift arm. The composition and hydration variations associated with those units equilibrate the thermal erosion of the craton root and allow for its stability between 100 and 200 km depth. Above 80 km depth, the crustal part is strongly affected by intruding bodies (melt and gas) which produces large negative anomalies in both velocity and density beneath the main magmatic centres. In addition to the global impact of a superplume, the velocity and density anomaly pattern suggests a 3-D distribution of the crust and mantle lithospheric stretching, which is likely to be controlled by inherited fabrics and enhanced by lateral compositional and hydration variations at the Tanzanian craton-orogenic belt boundary.
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| 3. |
- Krum, H., et al.
(författare)
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Prognostic benefit of beta-blockers in patients not receiving ACE-Inhibitors
- 2005
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Ingår i: Eur Heart J. - : Oxford University Press (OUP). - 0195-668X. ; 26:20, s. 2154-8
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Tidskriftsartikel (refereegranskat)abstract
- AIMS: Beta-blockers (BBs) confer significant prognostic benefit in patients (pts) with systolic chronic heart failure (CHF). However, major trials have thus far studied BBs mainly in addition to ACE-Inhibitors or angiotensin receptor blockers (ARBs) as background therapy. The magnitude of the prognostic benefit of BBs in the absence of ACE-I or ARB has not as yet been determined. METHODS AND RESULTS: We performed a meta-analysis of all placebo-controlled BB studies in patients with CHF (n>200). Trials were identified via Medline literature searches, meeting abstracts, and contact with study organizations. Results for all-cause mortality and death or heart failure hospitalization were pooled using the Mantel-Haenszel (fixed effects) method. The impact of BB therapy on all-cause mortality in CHF, in the absence (4.8%) and presence (95.2%) of ACE-I (or ARB), was determined from six trials of 13 370 patients. The risk ratio (RR) for BBs vs. placebo was 0.73 [95% confidence interval (CI) 0.53-1.02] in the absence of ACE-I or ARB at baseline, compared with a RR of 0.76 (95% CI 0.71-0.83) in the presence of these agents. When ACE-Inhibitors were analysed in the same way (pre-BB), a RR of 0.89 (0.80-0.99) vs. placebo was observed in studies of >90 days. The impact of BB therapy on death or HF hospitalization in systolic CHF, in the absence and presence of ACE-I, was determined from three trials of 8988 patients. The RR for BBs vs. placebo was 0.81 (95% CI 0.61-1.08) in the absence of ACE-I or ARB at baseline, compared with a RR of 0.78 (95% CI 0.74-0.83) in the presence of these agents. When ACE-Is were analysed in the same way (pre-BB), a RR of 0.85 (95% CI 0.78-0.93) vs. placebo was observed in studies of >90 days. CONCLUSION: The magnitude of the prognostic benefit conferred by BBs in the absence of ACE-I appears to be similar to those of ACE-Is in systolic CHF. These data therefore suggest that either ACE-Is or BBs could be used as first-line neurohormonal therapy in patients with systolic CHF. Prospective studies directly comparing these agents are required to definitively address this issue.
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| 4. |
- Metra, M., et al.
(författare)
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Effects of low-dose oral enoximone administration on mortality, morbidity, and exercise capacity in patients with advanced heart failure: the randomized, double-blind, placebo-controlled, parallel group ESSENTIAL trials
- 2009
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Ingår i: European Journal of Heart Failure. - 1522-9645. ; 30:24, s. 3015-26
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Tidskriftsartikel (refereegranskat)abstract
- AIMS: Use of inotropic agents in patients with heart failure (HF) has been limited by adverse effects on outcomes. However, administration of positive inotropes at lower doses and concomitant treatment with beta-blockers might increase benefit-risk ratio. We investigated the effects of low doses of the positive inotrope enoximone on symptoms, exercise capacity, and major clinical outcomes in patients with advanced HF who were also treated with beta-blockers and other guideline-recommended background therapy. METHODS AND RESULTS: The Studies of Oral Enoximone Therapy in Advanced HF (ESSENTIAL) programme consisted of two identical, randomized, double-blind, placebo-controlled trials that differed only by geographic location (North and South America: ESSENTIAL-I; Europe: ESSENTIAL-II). Patients with New York Heart Association class III-IV HF symptoms, left ventricular ejection fraction < or = 30%, and one hospitalization or two ambulatory visits for worsening HF in the previous year were eligible for participation in the trials. The trials had three co-primary endpoints: (i) the composite of time to all-cause mortality or cardiovascular hospitalization, analysed in the two ESSENTIAL trials combined; (ii) the 6 month change from baseline in the 6 min walk test distance (6MWTD); and (iii) the Patient Global Assessment (PGA) at 6 months, both analysed in each trial separately. ESSENTIAL-I and -II randomized 1854 subjects at 211 sites in 16 countries. In the combined trials, all-cause mortality and the composite, first co-primary endpoint did not differ between the two treatment groups [hazard ratio (HR) 0.97; 95% confidence interval (CI) 0.80-1.17; and HR 0.98; 95% CI 0.86-1.12, respectively, for enoximone vs. placebo]. The two other co-primary endpoints were analysed separately in the two ESSENTIAL trials, as prospectively designed in the protocol. The 6MWTD increased with enoximone, compared with placebo, in ESSENTIAL-I (P = 0.025, not reaching, however, the pre-specified criterion for statistical significance of P < 0.020), but not in ESSENTIAL-II. No difference in PGA was observed in either trial. CONCLUSION: Although low-dose enoximone appears to be safe in patients with advanced HF, major clinical outcomes are not improved.
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