Geological and geochemical variations in Mid-Tertiary Ethiopian Flood Basalt Province, Maychew, Tigray Region, Ethiopia

The paper presents the results of a comprehensive major element, trace element, and Sr-Nd-Pb-Hf isotopic study of Mid-Tertiary volcanic sequences from the northwestern flood basalt province in Ethiopia. The volcanic rocks studied range in composition from basanites, alkaline basalts, and ankaramites, which form the 1st three sequences at the base associated with basaltic agglomerate (sequence 1, 2 and 3) to transitional and tholeiitic basalts and picrites confined to the upper three sequences (sequences 4, 5 and 6). Sequence 5 is bimodal with intermediate-felsic pyroclastic rocks intercalating the transitional-tholeiitic basalts. There is a good correlation of sequences with geochemical enrichments, such as an increase La/LuN with TiO2, and decrease in Al2O3 and SiO2 towards the base. The smooth increase of La/LuN ratios in lower sequences reflect the general decrease of degree of partial melting that sampled heterogeneous packages of mantle plume materials. In the Sr-Nd isotopic diagram two clusters are formed one with restricted and low- Sr- (0.70356-0.70345) and Nd- (0.51290-0.51284) isotopic compositions, defined by sequence 1, and the other cluster with relatively higher 87Sr/86Sr (0.7052-0.7036) and 143Nd/144Nd (0.51296-0.5127) isotopic compositions defined by samples from sequence 2, and most other sequences with little scatter. The Pb-isotopic compositions vary systematically within each sequence (from base to top), and each sequence clustered systematically in a different Pb–Pb– isotopic space with the highest 206Pb/204Pb (19.10-19.30) and 207Pb/204Pb (15.60-15.65) measured in sequence 1, quite differently from other sequences and from previously reported for northwestern Ethiopian flood basalt province, and the lowest 206Pb/204Pb (18.20-18.56) and 207Pb/204Pb (15.51-15.55) measured in sequence 4. Sequence 2 and 3 lavas display a similar 206Pb/204Pb and 207Pb/204Pb ranges falling between sequence 1 and 4. In contrast, sequence 6 samples displayed towards higher 206Pb/204Pb than sequence 2, 3, and 4, but with lower and higher 207Pb/204Pb than sequence 1 and 5 respectively. The lavas of sequence 1 and 4 have relatively less radiogenic 176Hf/177Hf than other sequences with slight scatter. The systematic geochemical variations in lavas are remarkable and reflects three mantle end component mixing with minimal crustal in put as a fourth component. The enriched sequence 1 has very similar geochemistry to HIMU-type ocean island basalts (OIBs), and this end member ascribed to be the most enriched Afar plume component 1, which is the most enriched Afar Plume component during initial continental break. The second enriched component is defined by sequence 2 and 3 samples and may reflect the second enriched component in Ethiopian flood basalt, previously reported for the high-Ti2 basalts assumed to be the enriched Afar Plume component, whereas the third component is the depleted component defined by sequence 4 partly overlap the range previously reported for low-Ti basalts. Keywords: Flood basalts, Geochemistry, Sr-Nd, Pb-Pb, Hf-Hf isotopes, Afar Plume, Partial melting, Crustal inpu

Compositional Differences between Felsic Volcanic rocks from the Margin and Center of the Northern Main Ethiopian Rift

Pliocene felsic rift margin and Quaternary rift center volcanic rocks from the northern Main Ethiopian Rift (MER) exhibit contrasts in major and trace element contents and Sr-Nd isotopic ratios. Quaternary rift center felsic volcanic rocks are mainly peralkaline trachytes and rhyolites, whereas Pliocene felsic rift margin volcanic rocks are represented by benmoreites, weakly peralkaline trachytes and rare rhyolites. Most of the felsic rift margin volcanic rocks have greater Al2O3, K2O, Nb, Zr, Rb, and Sr, and lesser CaO, Zr/Nb, and CaO/Al2O3 than rift center volcanic rocks. These contrasts may have been inherited from differences in the compositions of their parental basic magmas, which were produced by variable degrees of partial melting. In both series, the felsic volcanic rocks generally have higher initial Sr- isotopic (0.7038-0.7073) ratios than their basic equivalents (0.7035-0.7046). Nd- isotopic ratios of most felsic rift center samples (0.5129-0.5126) are similar to their associated basic volcanic rocks. In contrast, the Nd-isotopic ratios (0.5128-0.5124) of felsic rift margin volcanic rocks are commonly lower than their companion basic volcanic rocks (0.512806-0.512893), and are relatively lower than rift center equivalents. The elemental and Sr-Nd isotopic compositions of the volcanic rocks suggest that fractional crystallization from differing basic parents accompanied by a limited assimilation (AFC) was the dominant process controlling the genesis of the MER felsic volcanic rocks. Keywords: Ethiopia; Northern Main Ethiopian Rift; Bimodal Volcanism; parental difference; Sr-Nd Isotopes, Fractional Crystallisatio

Preliminary study on geology, mineral potential and characteristics of hot springs from Dallol area, Afar rift, northeastern Ethiopia: Implications for natural resource exploration

Dallol area is located in Afar region of northeastern Ethiopia. From west to east, the geology of the area is characterized by: i) Neoproterozoic metavolcanics and metasediments, ii) Quaternary alluvial fan deposits and red beds, iii) a transitional zone of mud and salt mixture, and iv) evaporites, which consist of rock salt (commonly halite and potash) and sulfur/sulfides. The metavolcanic-sedimentary rocks of the area are sheared and locally affected by pervasive chloritization, silicification, and carbonatization as well as quartz-carbonate veining suggesting that it has a good potential for orogenic gold mineralization. The around 5 m thick alluvial sediments of Gehartu and Musely Fans are also favorable for the occurrence of placer gold deposits. This study reveals that industrial minerals such as kaolin and mica are also encountered in the Dallol area in addition to the already known sulfur and salt deposits. In surrounding areas of mount Dallol, hot springs of varying temperature and extent are being erupted forming semicircular to circular ponds. In this study, two types of hot springs, light-yellowish and yellowish brines are recognized which are contaminated with mud. Field observations show that both brines have indications for the presence of oil as sensed by greasy feelings. To know the general compositions of the hot springs and test the presence of liquid hydrocarbons, 8 water samples were collected and analyzed for major element contents, sulfide, sulfate and Total Organic Carbon (TOC) concentrations. The preliminary results show that TOC values are moderately low (94 to 902 ppm). Sulfate (19 to 60 ppm) and sulfide (27 to 111 ppm) concentrations are low except for one sample with higher concentrations for both complexes. Their low sulfide and sulfate content suggest that these compounds are converted into sulfur/sulfide by bacterial reduction of magmatic and/or sea water SO2 or sulfate. Therefore, the Dallol hot springs are interpreted to be derived from heated groundwater mixed with sulfides/sulfates of magmatic and/or sea water origin. Although low, the up to 902 ppm TOC concentrations in the hydrothermal fluids could suggest the presence of hydrocarbon containing rocks at depth and/or fluid mixing with laterally and/or vertically migrating hydrocarbon fluids. Generally, the Dallol area contains huge metallic and non metallic resources, which warrant detailed exploration and further scientific study

Cognitive health among older adults in the United States and in England

<p>Abstract</p> <p>Background</p> <p>Cognitive function is a key determinant of independence and quality of life among older adults. Compared to adults in England, US adults have a greater prevalence of cardiovascular risk factors and disease that may lead to poorer cognitive function. We compared cognitive performance of older adults in the US and England, and sought to identify sociodemographic and medical factors associated with differences in cognitive function between the two countries.</p> <p>Methods</p> <p>Data were from the 2002 waves of the US Health and Retirement Study (HRS) (n = 8,299) and the English Longitudinal Study of Ageing (ELSA) (n = 5,276), nationally representative population-based studies designed to facilitate direct comparisons of health, wealth, and well-being. There were differences in the administration of the HRS and ELSA surveys, including use of both telephone and in-person administration of the HRS compared to only in-person administration of the ELSA, and a significantly higher response rate for the HRS (87% for the HRS vs. 67% for the ELSA). In each country, we assessed cognitive performance in non-hispanic whites aged 65 and over using the same tests of memory and orientation (0 to 24 point scale).</p> <p>Results</p> <p>US adults scored significantly better than English adults on the 24-point cognitive scale (unadjusted mean: 12.8 vs. 11.4, P < .001; age- and sex-adjusted: 13.2 vs. 11.7, P < .001). The US cognitive advantage was apparent even though US adults had a significantly higher prevalence of cardiovascular risk factors and disease. In a series of OLS regression analyses that controlled for a range of sociodemographic and medical factors, higher levels of education and wealth, and lower levels of depressive symptoms, accounted for some of the US cognitive advantage. US adults were also more likely to be taking medications for hypertension, and hypertension treatment was associated with significantly better cognitive function in the US, but not in England (P = .014 for treatment × country interaction).</p> <p>Conclusion</p> <p>Despite methodological differences in the administration of the surveys in the two countries, US adults aged ≥ 65 appeared to be cognitively healthier than English adults, even though they had a higher burden of cardiovascular risk factors and disease. Given the growing number of older adults worldwide, future cross-national studies aimed at identifying the medical and social factors that might prevent or delay cognitive decline in older adults would make important and valuable contributions to public health.</p