Browsing by Author "Wang, J."
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Item Alaskan-type nature and PGE mineralization of the Wuxing mafic–ultramafic complex in eastern part of the Central Asian Orogenic belt(Ore Geology Reviews, 2020-05-04) Anani, C.Y.; Cui, M-M.; Su, B-X.; Wang, J.; Chen, K-Y.; Sakyi, P.A.; Tang, D-M.; He, Y-P.; Sun, J-G.; Cui, J.; Gao, D-L.The Wuxing mafic–ultramafic complex is located in the eastern part of the Central Asian Orogenic Belt (CAOB). It consists of hornblende-olivine clinopyroxenite, hornblende clinopyroxenite, clinopyroxenite, gabbro and diorite. Hornblende occurs in all the rock types of the complex and is pargasite in composition. Clinopyroxene is diopsidic in composition with high CaO and low TiO2 contents. The flat REE and sub-parallel trace element patterns of both clinopyroxene and hornblende suggest that these rocks were formed by fractional crystallization from common magma with no significant crustal contamination. Enrichment in large ion lithophile elements relative to high field strength elements of the silicate minerals, together with the variable sulfur isotope compositions (δ34S = -2.55 ~ 11.01‰) of the sulfides, indicate the involvement of subducted oceanic materials into the mantle source. These petrological, mineralogical and geochemical features strongly suggest the Alaskan-type nature of the Wuxing complex. The hydrous parental magma of the Wuxing complex was derived from partial melting of the mantle wedge, which had been metasomatized by subducted melts/fluids. The Wuxing complex is a unique Pt-Pd-rich Ni-Cu sulfide deposit in the CAOB. The ore minerals, which are dominated by pyrite, pyrrhotite, pentlandite, chalcopyrite and platinum-group mineral (PGM), mainly occur in clinopyroxenite and hornblende clinopyroxenite. The sulfide ores are predominantly present as net-textured and disseminated textures. Pentlandite and chalcopyrite associated with pyrrhotite commonly occur in the marginal zone of the pyrrhotite grains. The PGMs occur as interstitial grains at the contact between base-metal sulfides and silicate minerals or along the crack of pyrrhotite or clinopyroxene, or as inclusions in pyrrhotite. The occurrences of sulfides and PGMs in the Wuxing complex, together with sulfur isotope compositions and PGE patterns, reveal that the PGE enrichment of the Alaskan-type complexes can be attributed to the high-degree partial melting of the mantle source, sulfur involvement in the source, and PGE transportation of hydrous melts.Item Inequalities in urban air pollution in sub-Saharan Africa: an empirical modeling of ambient NO and NO2 concentrations in Accra, Ghana(Enviromental Research Letters, 2024) Wang, J.; Ezzati, M.; Hughes, A.F.; et al.Road traffic has become the leading source of air pollution in fast-growing sub-Saharan African cities. Yet, there is a dearth of robust city-wide data for understanding space-time variations and inequalities in combustion related emissions and exposures. We combined nitrogen dioxide (NO2) and nitric oxide (NO) measurement data from 134 locations in the Greater Accra Metropolitan Area (GAMA), with geographical, meteorological, and population factors in spatio-temporal mixed effects models to predict NO2 and NO concentrations at fine spatial (50 m) and temporal (weekly) resolution over the entire GAMA. Model performance was evaluated with 10-fold cross-validation (CV), and predictions were summarized as annual and seasonal (dusty [Harmattan] and rainy [non-Harmattan]) mean concentrations. The predictions were used to examine population distributions of, and socioeconomic inequalities in, exposure at the census enumeration area (EA) level. The models explained 88% and 79% of the spatiotemporal variability in NO2 and NO concentrations, respectively. The mean predicted annual, non-Harmattan and Harmattan NO2 levels were 37 (range: 1–189), 28 (range: 1–170) and 50 (range: 1–195) µg m−3 , respectively. Unlike NO2, NO concentrations were highest in the non-Harmattan season (41 [range: 31–521] µg m−3 ). Road traffic was the dominant factor for both pollutants, but NO2 had higher spatial heterogeneity than NO. For both pollutants, the levels were substantially higher in the city core, where the entire population (100%) was exposed to annual NO2 levels exceeding the World Health Organization (WHO) guideline of 10 µg m−3 . Significant disparities in NO2 concentrations existed across socioeconomic gradients, with residents in the poorest communities exposed to levels about 15 µg m−3 higher compared with the wealthiest (p < 0.001). The results showed the important role of road traffic emissions in air pollution concentrations in the GAMA, which has major implications for the health of the city’s poorest residents. These data could support climate and health impact assessments as well as policy evaluations in the city.Item Ostracod‐based reconstruction of Late Quaternary lake level changes within the Tangra Yumco lake system (southern Tibetan Plateau)(Journal of Quaternary Science, 2018-08) Alivernini, M.; Akita, L.G.; Ahlborn, M.; Börner, N.; Haberzettl, T.; Kasper, T.; Plessen, B.; Peng, P.; Schwalb, A.; Wang, J.; Frenzel, P.Tangra Yumco, a large saline lake located in the central–southern part of the Tibetan Plateau, liesin a hydrologically closed basin and is part of a cascade lake system including Tangqung Co, Tangra Yumco andXuru Co. The extension and position of this lake system makes it valuable for reconstructing palaeoclimaticvariations through the lake history and to compare both with the adjacent lake systems. We reconstructed LateQuaternary lake level changes based on data from two lacustrine sediment cores. A micropalaeontologicalanalysis focusing on Ostracoda was carried out combined with dating (14C,210Pb,137Cs), sedimentology andstable isotope data from bulk sediment. Ostracod analysis involves the quantitative documentation ofassociations. An ostracod-based transfer function for specific conductivity was applied to assess and refine lakelevel changes and to compare the results with other lake level reconstructions from the Tibetan Plateau forevaluating inter-regional climatic patterns. Seven ostracod species were detected, withLeucocytherella sinensisdominating the associations followed byLeucocythere?dorsotuberosa,Limnocythere inopinataandTonnacyprisgyirongensis.Fabaeformiscandona gyirongensis,Candona candidaandCandona xizangensiswere found in onlya few samples and at low percentages. The synthesis of ostracod-based environmental reconstruction andchronology for samples from Tangra Yumco reveals the evolution of the lake system during the past 17 ka. A lowlake level around 17 cal kaBPis followed by a recovering until the reaching of a high stand around 8–9 cal kaBP.Subsequently, between 7.7 and 2.5 cal kaBP, it remained relatively stable with a subsequent short-livinglowstand–highstand cycle at around 2 ka. Thereafter, the ostracod-based conductivity transfer function shows anincrease of conductivity corresponding to a lake level rising phase at around 0.4 ka. The recorded changes areindicators of past climatic conditions and refine the palaeoclimatic models in this area.Copyright#2018 John Wiley & Sons, Ltd.Item Spatial-temporal patterns of ambient fine particulate matter (PM2.5) and black carbon (BC) pollution in Accra(IOP publishing ltd, 2021) Alli, A.S.; Clark, S.N.; Hughes, A.; Nimo, J.; Bedford-Moses, J.; Baah, S.; Wang, J.; Vallarino, J.; Agyemang, E.; Barratt, B.; Beddows, A.; Kelly, F.; Owusu, G.; Baumgartne, J.; Brauer, M.; Ezzati, M.; Agyei-Mensah, S.; Arku, R.E.Sub-Saharan Africa (SSA) is rapidly urbanizing, and ambient air pollution has emerged as a major environmental health concern in growing cities. Yet, effective air quality management is hindered by limited data. We deployed robust, low-cost and low-power devices in a large-scale measurement campaign and characterized within-city variations in fine particulate matter (PM2.5) and black carbon (BC) pollution in Accra, Ghana. Between April 2019 and June 2020, we measured weekly gravimetric (filter-based) and minute-by-minute PM2.5 concentrations at 146 unique locations, comprising of 10 fixed (∼1 year) and 136 rotating (7 day) sites covering a range of land-use and source influences. Filters were weighed for mass, and light absorbance (10−5m−1 ) of the filters was used as proxy for BC concentration. Year-long data at four fixed sites that were monitored in a previous study (2006–2007) were compared to assess changes in PM2.5 concentrations. The mean annual PM2.5 across the fixed sites ranged from 26 µg m−3 at a peri-urban site to 43 µg m−3 at a commercial, business, and industrial (CBI) site. CBI areas had the highest PM2.5 levels (mean: 37 µg m−3 ), followed by high-density residential neighborhoods (mean: 36 µg m−3 ), while peri-urban areas recorded the lowest (mean: 26 µg m−3 ). Both PM2.5 and BC levels were highest during the dry dusty Harmattan period (mean PM2.5: 89 µg m−3 ) compared to non-Harmattan season (mean PM2.5: 23 µg m−3 ). PM2.5 at all sites peaked at dawn and dusk, coinciding with morning and evening heavy traffic. We found about a 50% reduction (71 vs 37 µg m−3 ) in mean annual PM2.5 concentrations when compared to measurements in 2006–2007 in Accra. Ambient PM2.5 concentrations in Accra may have plateaued at levels lower than those seen in large Asian megacities. However, levels are still 2- to 4-fold higher than the WHO guideline. Effective and equitable policies are needed to reduce pollution levels and protect public health.Item Trace elements in olivine: Proxies for petrogenesis, mineralization and discrimination of mafic-ultramafic rocks(Lithos, 2021) Wang, J.; Ben-Xun, Su; Robinson, P.T.; Xiao, Y.; Bai, Y.; Liu, X.; Sakyi, P.A.; Chen, C.; Liang, Z.; Bao, Zhi-An .; Jing, Jie-Jun.Olivine is a ubiquitous mineral inmafic-ultramafic rocks and has been widely used as a mineral marker in various geological processes. However, its development of trace elements is limited. Here we present newly-obtained trace element data 7Li, 27Al, 29Si, 31P, 43Ca, 45Sc, 49Ti, 51V, 53Cr, 55Mn, 59Co, 60Ni, and 66Zn of olivine in typicalmantle xenoliths, mantle peridotites in ophiolites, and plutonic rocks from layered and Alaskan-type intrusions to develop trace element proxies for the petrogenesis, mineralization and discrimination of various mafic-ultramafic rocks. Residual olivine grains in mantle xenoliths and ophiolitic peridotites, which represent residues of mantle melting, have higher Ni/Co (>20) and Ni/Mn (>2) ratios than magmatic olivine (Ni/Co < 20, Ni/Mn < 2), which are consistent with the compatibilities of these elements during partial melting and magma differentiation. Lower Ni content, and lower Ni/Co and Ni/Mn ratios at a given Fo content can distinguish olivine in Alaskantype intrusions from layered intrusions, reflecting the nature of their mantle sources. The V and Sc contents and V/Sc ratios in olivine can distinguish mantle xenoliths (V > 2 ppm, V/Sc > 0.5) from ophiolitic peridotites (V<2 ppm, V/Sc< 0.5), indicating a more reduced state of continental lithospheric mantle compared to the oceanic lithospheric mantle. As a consequence, the four occurrences of mafic-ultramafic rocks can be distinguished by olivine with (Sc × 10)-(Ti × 2)-Zn and V/Sc-(Co/Ni × 2)-(Zn/Mn× 5) ternary diagrams. In addition, Li, Ti and P contents in olivine are good tracers of melt/fluid metasomatism, whereas Ni/Co, Ni/Mn and Mn/Zn ratios are indicators of chromite mineralization. Therefore, trace elements in olivine can be used as chemical proxies to distinguish the origin of various mafic-ultramafic rocks, as well as the processes by which they evolved.