The East African Rift system (EARS) provides a unique system with the juxtaposition of two contrasting yet simultaneously formed rift branches, the eastern, magma-rich, and the western, magma-poor, on either sides o...The East African Rift system (EARS) provides a unique system with the juxtaposition of two contrasting yet simultaneously formed rift branches, the eastern, magma-rich, and the western, magma-poor, on either sides of the old thick Tanzanian craton embedded in a younger lithosphere. Data on the pre-rifr, syn-rift and post-rift far-field volcanic and tectonic activity show that the EARS formed in the context of the interaction between a deep mantle plume and a horizontally and vertically heterogeneous lithosphere under far-field tectonic extension. We bring quantitative insights into this evolution by implementing high-resolution 3D thermo-mechanical numerical deformation models of a lithosphere of realistic rheology. The models focus on the central part of the EARS. We explore scenarios of plumelithosphere interaction with plumes of various size and initial position rising beneath a tectonically pre-stretched lithosphere. We test the impact of the inherited rheological discontinuities (suture zones) along the craton borders, of the rheological structure, of lithosphere plate thickness variations, and of physical and mechanical contrasts between the craton and the embedding lithosphere. Our experiments indicate that the ascending plume material is deflected by the cratonic keel and preferentially channeled along one of its sides, leading to the formation of a large rift zone along the eastern side of the craton, with significant magmatic activity and substantial melt amount derived from the mantle plume material. We show that the observed asymmetry of the central EARS, with coeval amagmatic (western) and magmatic (eastern) branches, can be explained by the splitting of warm material rising from a broad plume head whose initial position is slightly shifted to the eastern side of the craton. In that case, neither a mechanical weakness of the contact between the craton and the embedding lithosphere nor the presence of second plume are required to produce simulations that match observations. This result reconciles the passive and active rift models and demonstrates the possibility of development of both magmatic and amagmatic rifts in identical geotectonic environments.展开更多
The East African Rift System(EARS)is located in East Africa,separating into two main branches,the eastern branch and the western branch.It is considered as an intracontinental ridge system,which meets the Red Sea and
IT’S difficult to talk about Southern Sudan in 2011 without bringing up the historic referendum that will determine whether the south of Africa’s largest country will secede from the rest of the country. "The r...IT’S difficult to talk about Southern Sudan in 2011 without bringing up the historic referendum that will determine whether the south of Africa’s largest country will secede from the rest of the country. "The referendum in Southern Sudan is the most important event in the calendar of Africa after the(2010) World Cup(held in South Africa),because it has the consequence of introducing a new member state in Africa,and also has the consequence of returning this region back to war."展开更多
The East African Rift extending across Djibouti, Ethiopia and Kenya is characterized by low level of economic development,high level of poverty,increasing population,scarce natural resources(land,water, and environmen...The East African Rift extending across Djibouti, Ethiopia and Kenya is characterized by low level of economic development,high level of poverty,increasing population,scarce natural resources(land,water, and environment),complex and rich ecosystems, increasing desertification and degrading biodiversity, underdeveloped regional trade and market,water resources mainly stored in groundwater and展开更多
The East African Community is a regional block that brings together Kenya, Uganda, Tanzania, Rwanda, Burundi and South Sudan into various forms of economic partnership, the eventual dream being to achieve political fe...The East African Community is a regional block that brings together Kenya, Uganda, Tanzania, Rwanda, Burundi and South Sudan into various forms of economic partnership, the eventual dream being to achieve political federation. The current activities within this community, plus the block’s further development, require the generation and sharing of much geo-information to support the attendant decision-making. Such geo-information can be best served through a harmonized cartographic service with common standards. Such a harmonized service is not only lacking, but even the status of the current national services is also largely unknown. This paper reports on a study undertaken to establish this status, as represented by twelve elements of a cartographic service that the authors are able to establish. Results of the study have shown that the present national services are characterized by inadequate basic datasets that remain largely analogue. In addition, there are non-uniform spatial reference systems, inadequate cartographic human resources and lack of common mapping standards;further, funding for mapping activities remains low in national budgets. Given that over 80% of decisions are influenced by geo-spatial data, these findings point to an urgent need to improve, harmonize and digitize these services as the way forward, if the East African Community is to remain globally competitive.展开更多
Human Leukocyte Antigens (HLAs) play an important role in host immune responses to infectious pathogens, and influence organ transplantation, cancer and autoimmune diseases. In this study we conducted a high resolutio...Human Leukocyte Antigens (HLAs) play an important role in host immune responses to infectious pathogens, and influence organ transplantation, cancer and autoimmune diseases. In this study we conducted a high resolution, sequence-based genotyping of HLA class I and class II genes of more than 2000 women from Kenya, eastern Tanzania and southern Uganda around Lake Victoria and analyzed their allele, phenotype and haplotype frequencies. A considerable genetic diversity was observed at both class I and II loci. A total of 79 HLA-A, 113 HLA-B, 53 HLA-C, 25 HLA-DPA1, 60 HLA-DPB1, 15 HLA-DQA1, 44 HLA-DQB1 and 38 HLA-DRB1 alleles have been identified. The most common class I alleles were A * 02:01:01 (10.90%), B * 58:02 (8.79%), and C * 06:02:01 (16.98%). The most common class II alleles were DPA1*01:03:01 (40.60%), DPB1 * 01:01:01 (23.45%), DQA1 * 01:02:01 (31.03%), DQB1 * 03:01:01 (21.79%), DRB1 * 11:01:02 (11.65%), DRB3 * 02:02:01 (31.65%), DRB4 * 01:01:01 (10.50%), and DRB5 * 01:01:01 (10.50%). Higher than expected homozygosity was observed at HLA-B (P = 0.022), DQA1 (P = 0.004), DQB1 (P = 0.023), and DRB1 (P = 0.0006) loci. The allele frequency distribution of this population is very similar to the ones observed in other sub-Saharan populations with the exception of lower frequencies of A * 23 (5.55% versus 11.21%) and DQA1 * 03 (4.79% versus 11.72%), and higher frequencies of DPB1 * 30 (2.26% versus 0.37%) and DRB1 * 11 (21.51% versus 15.89%). The knowledge of the diversity and allele/ phenotype frequencies of the HLA alleles of this east African population, can contribute to the understanding of how host genetic factors influence disease susceptibility and effective anti-retroviral treatment of HIV infections and future vaccine trials.展开更多
China's increasing exports have prompted research to examine whether Chinese exports displace those that originate from elsewhere.In this paper we focus on the growth of China's exports to the East African Com...China's increasing exports have prompted research to examine whether Chinese exports displace those that originate from elsewhere.In this paper we focus on the growth of China's exports to the East African Community(EAC)countries and show how they have afected exports from the European Union(EU).Our methodological contribution to the literature is a set of total and relative displacement estimates based on different specifications of the gravity model where we control for country-year fixed effects so as to avoid the error of not accounting for time-varying"multilateral resistance."Our empirical findings do not support the hypothesis that Chinese exports have displaced exports from other countries including those from the EU.These results suggest that competition in the EAC market has not been a zero-sum game among different exporting countries.展开更多
The granitic plutons associated with the Glito-Kpatala shear zone are composed of biotite and amphibole granodiorites, biotite granites, two-mica granites and aplitic granites, which are very poorly represented. The c...The granitic plutons associated with the Glito-Kpatala shear zone are composed of biotite and amphibole granodiorites, biotite granites, two-mica granites and aplitic granites, which are very poorly represented. The chemical and mineralogical compositions of these facies indicate that they are I type and belong to high-K calc-alkaline series, with a chemical metaluminous character displayed by the granodiorites relative to the biotite and two-mica facies whose chemical compositions vary between metaluminous and peraluminous caracter. The Th/Ta (14.04 - 43.82 ppm, mean = 26.05), Th/U (2.58 to 15.05 ppm, mean = 5.85 ppm), Zr/Hf (25.27 to 37.21, mean = 30.67 ppm) and Rb/Sr (0.16 to 4.32;mean = 1.67 ppm) ratios of these granitoids reveal a strong crustal involvement in their magmatogenesis. Variations in CaO/Na<sub>2</sub>O (0.47 - 1.44 ppm), Rb/Sr (0.14 - 0.27 ppm), Rb/Ba (0.07 - 0.14 ppm) and Sr/Y (38.21 - 174.42 ppm) ratios indicate that biotite and amphibole granodiorites with their excessive Ni (135.37 - 139.51 ppm) and Cr (395.73 - 447.74 ppm) were derived from a mafic to intermediate lower continental crust where garnet and/or amphibole were stable residual assemblage minerals. The moderate Sr/Y ratios (1.81 - 9.47 ppm) and low transition elements Ni (1 - 6.44 ppm) and Cr (7.89 - 13.47 ppm) contents in both the two-mica and biotite granites are consistent with their emplacement at relatively shallow depths in the upper to mean continental crust, at pressures below 10 Kbar. In the two-mica granites, moderate CaO/Na<sub>2</sub>O (0.20 - 0.57 ppm, mean = 0.38 ppm) and Rb/Ba (0.39 - 1.37, mean = 0.84 ppm) ratios and quite varied Rb/Sr (1.53 - 4.23 ppm, mean = 2.85 ppm) ratios indicate a predominant derivation from psammitic and pelitic metasediments rather than metagreywackes. These low ratios (0.25 ≤ CaO/Na<sub>2</sub>O ≤ 0.32, mean = 0.28 ppm;0.31 ≤ Rb/Ba ≤ 0.44, mean = 0.39 ppm;1.11 ≤ Rb/Sr ≤ 1.78, mean = 0.39 ppm) in biotite granites are more consistent with melting from a metagreywacke-derived source. Evidence for the contribution of mantle-derived mafic magma with granitic magma in the plutons studied is materialized by the presence of magmatic enclaves in both granodiorites and two-mica granites, the volcanic arc geochemical signatures displayed by the plutons in geotectonic diagrams and Nb/Ta ratios (14.14 - 34.61 ppm) closer to mantle estimates. Geochemical data and radiometric dating elements suggest that the granitoids studied can be integrated into the pan-African late magmatic episode, which corresponds between 606 and 583 Ma, to the activity of transcurrent ductile strike-slips and to the synchronous emplacement of high K calc-alkaline plutons in a post-collisional context.展开更多
The Pan-African event is widely distributed in East Antarctica (EA) craton, including both the coastal regions and interior of the EA. From aspects of the shear zones, granites, pegmatites, time of high-grade meta...The Pan-African event is widely distributed in East Antarctica (EA) craton, including both the coastal regions and interior of the EA. From aspects of the shear zones, granites, pegmatites, time of high-grade metamorphism and detrital zircon age peaks of the downflowing sediments from the inland, the Pan-African event in the EA and adjacent areas in the Gondwana reconstruction, like SE Africa, southern India and SW Australia, was described in the paper. The water or fluid available along the shear zones was responsible for retrogression of the earlier, e.g., Grenville age, high-grade outcrops to later Pan-African amphibolite to granulite facies metamorphism. In geochemistry, the granites are generally anorogenic, ocassionally with some gabbros or dolerite dykes, showing sign of bimodal feature. Meanwhile, the event has influenced most isotopic systems, including the U-Pb, Sm-Nd, Rb-Sr and Ar-Ar systems, giving Pan-African apparent ages. Spatially, the Pan-African event is demonstrated from possibly local granitic magmatism, to wider medium-high grade metamorphism, and mostly widespread in resetting for some isotope systems, suggesting the prevailing thermal effect of the event. Before Gondwana formation, local depressions in the EA may have been filled with sediments, implying the initial breakup period of the Rodinia. The later Pan-Gondwana counterrotating cogs shaped the interstitial fold belts between the continent blocks and formed a set of shear zones. The mafic underplating in the Gondwana may be responsible for the typical features of the Pan-African event. The event may be an overwhelmingly extensional and transcurrent tectonics in mechanism and is a possible response of the plate movement surrounding the continent swarms in the non-stable interior of the yet consolidated Gondwana.展开更多
Objective:To understand the epidemiology of the East,Central and South African(ECSA) genotype of Chikungunya virus(CHIKV) in terms of emerging and re-emerging infections,this study has been aimed at investigating the ...Objective:To understand the epidemiology of the East,Central and South African(ECSA) genotype of Chikungunya virus(CHIKV) in terms of emerging and re-emerging infections,this study has been aimed at investigating the evolutionary parameters,genomic signatures and molecular tracking of the CHIKV ECSA genotype in South-east Asia and coastal areas of the Indian Ocean between 2006 and 2009 by using phylogenetie analysis and the Bayesian Markov Chain Monte Carlo(BMCMC) evolutionary estimation.Methods:Nearly complete genome sequences of 53 CHIKV isolates from all genotypes were subjected to phylogenetie analysis and evolutionary parameter estimation.The amino acids of 67 of ECSA genotype during 2006 to 2009 were compared for finding molecular signature tracking.The ECSA genotype signatures were visualized to find the possible transmission root was projected onto a geographic map.Results: Phylogenetie analysis showed the ECSA genotype was divided into 2 groups.The first group comprises viruses from India and Southeast Asian countries.The second group consists of strains typically circulating in Sri Lanka in 2008.The evolutionary parameters of these groups depicted the time of the most recent common ancestor at approximately 7.5 years ago.The genomic signatures revealed the positions of amino acid variation in each group.Conclusions:The molecular evolution projected onto a geographical map showed the routes of CHIKV transmission from 2006 to 2009.Molecular tracking will assist in understanding transmission routes, epidemiology and molecular evolution of CHIKV.展开更多
The Grove Mountains, 400 km south of the Chinese Antarctic Zhongshan Station, are an inland continuation of the Pan-African-aged (i.e., Late Neoproterozoic/Cambrian) Prydz Belt, East Antarctica. In this paper we car...The Grove Mountains, 400 km south of the Chinese Antarctic Zhongshan Station, are an inland continuation of the Pan-African-aged (i.e., Late Neoproterozoic/Cambrian) Prydz Belt, East Antarctica. In this paper we carried out a combined U-Th-Pb monazite and Sm-Nd mineral-whole-rock dating on para- and orthogneisses from bedrock in the Grove Mountains. U-Th-Pb monazite dating of a cordierite-bearing pelitic paragneiss yields ages of 523 ? 4 Ma for the cores and 508 ? 6 Ma for the rims. Sm-Nd mineral-whole-rock isotopic analyses yield isochron ages of 536 ? 3 Ma for a coarse-grained felsic orthogneiss and 507 ? 30 Ma for a fine-grained quartzofeldspathic paragneiss. Combined with previously published age data in the Grove Mountains and adjacent areas, the older age of ~530 Ma is interpreted as the time of regional medium- to low-pressure granulite-facies metamorphism, and the younger age of ~510 Ma as the cooling age of the granulite terrane. The absence of evidence for a Grenville-aged (i.e., Late Mesoproterozoic/Early Neoproterozoic) metamorphic event indicates that the Grove Mountains have experienced only a single metamorphic cycle, i.e., Pan-African-aged, which distinguishes them from other polymetamorphic terranes in the Prydz Belt. This will provide important constraints on the controversial nature of the Prydz Belt.展开更多
The Grove Mountains are an inland continuation of the Prydz Belt in East Antarctica. Detailed metamorphic petrological and zircon U-Pb geochronological studies are performed on the high-pressure (HP) pelitic granu...The Grove Mountains are an inland continuation of the Prydz Belt in East Antarctica. Detailed metamorphic petrological and zircon U-Pb geochronological studies are performed on the high-pressure (HP) pelitic granulites from glacial moraines in the Grove Mountains. The metamorphic peak mineral assemblage of the HP pelitic granulites is characterized by garnet + kyanite + K-feldspar + biotite + plagioclase + quartz, and the subsequent medium-pressure (MP) granulite facies retrogression is characterized by sillimanite replacing kyanite, the formation of the biolite + sillimanite symplectite in the matrix. These mineral assemblages and their P-T estimates based on the P-T pseudosection constructed in MnNCKFMASHT system define a clockwise P-T path involving metamorphic peak of 11.6–13.6 kbar at 817–834°C followed by a near-isothermal decompression of 6.7–7.5 kbar at 806–828°C, comparable with those of associated HP mafic granulites from glacial moraines in the Grove Mountains. Zircon U-Pb dating, coupled with available metamorphic age data obtained for HP mafic granulites, reveals HP metamorphism occurred at 540–545 Ma. Combining the previous research results, the HP pelitic granulites and contemporary HP mafic granulites were widely distributed in glacial moraines from the Grove Mountains, suggesting at least part of the Grove Subglacial Highlands underwent Pan-Afrian HP granulite facies metamorphism, which provides new evidence for a collisional tectonic setting of the Pan-Afrian Prydz Belt.展开更多
基金co-funded by a U.S.National Science Foundation(Grant EAR-0538119)to E.Calaisthe Advanced ERC(Grant 290864 RHEOLITH)to E.Burov and A.Koptev+2 种基金the Royal Academy of Netherlands visiting professor grant to E.Burovthe UPMC visiting professor grant to S.Cloetinghperformed on the ERC-funded SGI Ulysse cluster of ISTEP
文摘The East African Rift system (EARS) provides a unique system with the juxtaposition of two contrasting yet simultaneously formed rift branches, the eastern, magma-rich, and the western, magma-poor, on either sides of the old thick Tanzanian craton embedded in a younger lithosphere. Data on the pre-rifr, syn-rift and post-rift far-field volcanic and tectonic activity show that the EARS formed in the context of the interaction between a deep mantle plume and a horizontally and vertically heterogeneous lithosphere under far-field tectonic extension. We bring quantitative insights into this evolution by implementing high-resolution 3D thermo-mechanical numerical deformation models of a lithosphere of realistic rheology. The models focus on the central part of the EARS. We explore scenarios of plumelithosphere interaction with plumes of various size and initial position rising beneath a tectonically pre-stretched lithosphere. We test the impact of the inherited rheological discontinuities (suture zones) along the craton borders, of the rheological structure, of lithosphere plate thickness variations, and of physical and mechanical contrasts between the craton and the embedding lithosphere. Our experiments indicate that the ascending plume material is deflected by the cratonic keel and preferentially channeled along one of its sides, leading to the formation of a large rift zone along the eastern side of the craton, with significant magmatic activity and substantial melt amount derived from the mantle plume material. We show that the observed asymmetry of the central EARS, with coeval amagmatic (western) and magmatic (eastern) branches, can be explained by the splitting of warm material rising from a broad plume head whose initial position is slightly shifted to the eastern side of the craton. In that case, neither a mechanical weakness of the contact between the craton and the embedding lithosphere nor the presence of second plume are required to produce simulations that match observations. This result reconciles the passive and active rift models and demonstrates the possibility of development of both magmatic and amagmatic rifts in identical geotectonic environments.
文摘The East African Rift System(EARS)is located in East Africa,separating into two main branches,the eastern branch and the western branch.It is considered as an intracontinental ridge system,which meets the Red Sea and
文摘IT’S difficult to talk about Southern Sudan in 2011 without bringing up the historic referendum that will determine whether the south of Africa’s largest country will secede from the rest of the country. "The referendum in Southern Sudan is the most important event in the calendar of Africa after the(2010) World Cup(held in South Africa),because it has the consequence of introducing a new member state in Africa,and also has the consequence of returning this region back to war."
文摘The East African Rift extending across Djibouti, Ethiopia and Kenya is characterized by low level of economic development,high level of poverty,increasing population,scarce natural resources(land,water, and environment),complex and rich ecosystems, increasing desertification and degrading biodiversity, underdeveloped regional trade and market,water resources mainly stored in groundwater and
文摘The East African Community is a regional block that brings together Kenya, Uganda, Tanzania, Rwanda, Burundi and South Sudan into various forms of economic partnership, the eventual dream being to achieve political federation. The current activities within this community, plus the block’s further development, require the generation and sharing of much geo-information to support the attendant decision-making. Such geo-information can be best served through a harmonized cartographic service with common standards. Such a harmonized service is not only lacking, but even the status of the current national services is also largely unknown. This paper reports on a study undertaken to establish this status, as represented by twelve elements of a cartographic service that the authors are able to establish. Results of the study have shown that the present national services are characterized by inadequate basic datasets that remain largely analogue. In addition, there are non-uniform spatial reference systems, inadequate cartographic human resources and lack of common mapping standards;further, funding for mapping activities remains low in national budgets. Given that over 80% of decisions are influenced by geo-spatial data, these findings point to an urgent need to improve, harmonize and digitize these services as the way forward, if the East African Community is to remain globally competitive.
文摘Human Leukocyte Antigens (HLAs) play an important role in host immune responses to infectious pathogens, and influence organ transplantation, cancer and autoimmune diseases. In this study we conducted a high resolution, sequence-based genotyping of HLA class I and class II genes of more than 2000 women from Kenya, eastern Tanzania and southern Uganda around Lake Victoria and analyzed their allele, phenotype and haplotype frequencies. A considerable genetic diversity was observed at both class I and II loci. A total of 79 HLA-A, 113 HLA-B, 53 HLA-C, 25 HLA-DPA1, 60 HLA-DPB1, 15 HLA-DQA1, 44 HLA-DQB1 and 38 HLA-DRB1 alleles have been identified. The most common class I alleles were A * 02:01:01 (10.90%), B * 58:02 (8.79%), and C * 06:02:01 (16.98%). The most common class II alleles were DPA1*01:03:01 (40.60%), DPB1 * 01:01:01 (23.45%), DQA1 * 01:02:01 (31.03%), DQB1 * 03:01:01 (21.79%), DRB1 * 11:01:02 (11.65%), DRB3 * 02:02:01 (31.65%), DRB4 * 01:01:01 (10.50%), and DRB5 * 01:01:01 (10.50%). Higher than expected homozygosity was observed at HLA-B (P = 0.022), DQA1 (P = 0.004), DQB1 (P = 0.023), and DRB1 (P = 0.0006) loci. The allele frequency distribution of this population is very similar to the ones observed in other sub-Saharan populations with the exception of lower frequencies of A * 23 (5.55% versus 11.21%) and DQA1 * 03 (4.79% versus 11.72%), and higher frequencies of DPB1 * 30 (2.26% versus 0.37%) and DRB1 * 11 (21.51% versus 15.89%). The knowledge of the diversity and allele/ phenotype frequencies of the HLA alleles of this east African population, can contribute to the understanding of how host genetic factors influence disease susceptibility and effective anti-retroviral treatment of HIV infections and future vaccine trials.
文摘China's increasing exports have prompted research to examine whether Chinese exports displace those that originate from elsewhere.In this paper we focus on the growth of China's exports to the East African Community(EAC)countries and show how they have afected exports from the European Union(EU).Our methodological contribution to the literature is a set of total and relative displacement estimates based on different specifications of the gravity model where we control for country-year fixed effects so as to avoid the error of not accounting for time-varying"multilateral resistance."Our empirical findings do not support the hypothesis that Chinese exports have displaced exports from other countries including those from the EU.These results suggest that competition in the EAC market has not been a zero-sum game among different exporting countries.
文摘The granitic plutons associated with the Glito-Kpatala shear zone are composed of biotite and amphibole granodiorites, biotite granites, two-mica granites and aplitic granites, which are very poorly represented. The chemical and mineralogical compositions of these facies indicate that they are I type and belong to high-K calc-alkaline series, with a chemical metaluminous character displayed by the granodiorites relative to the biotite and two-mica facies whose chemical compositions vary between metaluminous and peraluminous caracter. The Th/Ta (14.04 - 43.82 ppm, mean = 26.05), Th/U (2.58 to 15.05 ppm, mean = 5.85 ppm), Zr/Hf (25.27 to 37.21, mean = 30.67 ppm) and Rb/Sr (0.16 to 4.32;mean = 1.67 ppm) ratios of these granitoids reveal a strong crustal involvement in their magmatogenesis. Variations in CaO/Na<sub>2</sub>O (0.47 - 1.44 ppm), Rb/Sr (0.14 - 0.27 ppm), Rb/Ba (0.07 - 0.14 ppm) and Sr/Y (38.21 - 174.42 ppm) ratios indicate that biotite and amphibole granodiorites with their excessive Ni (135.37 - 139.51 ppm) and Cr (395.73 - 447.74 ppm) were derived from a mafic to intermediate lower continental crust where garnet and/or amphibole were stable residual assemblage minerals. The moderate Sr/Y ratios (1.81 - 9.47 ppm) and low transition elements Ni (1 - 6.44 ppm) and Cr (7.89 - 13.47 ppm) contents in both the two-mica and biotite granites are consistent with their emplacement at relatively shallow depths in the upper to mean continental crust, at pressures below 10 Kbar. In the two-mica granites, moderate CaO/Na<sub>2</sub>O (0.20 - 0.57 ppm, mean = 0.38 ppm) and Rb/Ba (0.39 - 1.37, mean = 0.84 ppm) ratios and quite varied Rb/Sr (1.53 - 4.23 ppm, mean = 2.85 ppm) ratios indicate a predominant derivation from psammitic and pelitic metasediments rather than metagreywackes. These low ratios (0.25 ≤ CaO/Na<sub>2</sub>O ≤ 0.32, mean = 0.28 ppm;0.31 ≤ Rb/Ba ≤ 0.44, mean = 0.39 ppm;1.11 ≤ Rb/Sr ≤ 1.78, mean = 0.39 ppm) in biotite granites are more consistent with melting from a metagreywacke-derived source. Evidence for the contribution of mantle-derived mafic magma with granitic magma in the plutons studied is materialized by the presence of magmatic enclaves in both granodiorites and two-mica granites, the volcanic arc geochemical signatures displayed by the plutons in geotectonic diagrams and Nb/Ta ratios (14.14 - 34.61 ppm) closer to mantle estimates. Geochemical data and radiometric dating elements suggest that the granitoids studied can be integrated into the pan-African late magmatic episode, which corresponds between 606 and 583 Ma, to the activity of transcurrent ductile strike-slips and to the synchronous emplacement of high K calc-alkaline plutons in a post-collisional context.
基金financially supported by the National Natural Science Foundation of China (Grant nos.41472172,41530209)the Chinese Polar Environment Comprehensive Investigation and Assessment Programme (Grant no.CHINARE2015-02-05)
文摘The Pan-African event is widely distributed in East Antarctica (EA) craton, including both the coastal regions and interior of the EA. From aspects of the shear zones, granites, pegmatites, time of high-grade metamorphism and detrital zircon age peaks of the downflowing sediments from the inland, the Pan-African event in the EA and adjacent areas in the Gondwana reconstruction, like SE Africa, southern India and SW Australia, was described in the paper. The water or fluid available along the shear zones was responsible for retrogression of the earlier, e.g., Grenville age, high-grade outcrops to later Pan-African amphibolite to granulite facies metamorphism. In geochemistry, the granites are generally anorogenic, ocassionally with some gabbros or dolerite dykes, showing sign of bimodal feature. Meanwhile, the event has influenced most isotopic systems, including the U-Pb, Sm-Nd, Rb-Sr and Ar-Ar systems, giving Pan-African apparent ages. Spatially, the Pan-African event is demonstrated from possibly local granitic magmatism, to wider medium-high grade metamorphism, and mostly widespread in resetting for some isotope systems, suggesting the prevailing thermal effect of the event. Before Gondwana formation, local depressions in the EA may have been filled with sediments, implying the initial breakup period of the Rodinia. The later Pan-Gondwana counterrotating cogs shaped the interstitial fold belts between the continent blocks and formed a set of shear zones. The mafic underplating in the Gondwana may be responsible for the typical features of the Pan-African event. The event may be an overwhelmingly extensional and transcurrent tectonics in mechanism and is a possible response of the plate movement surrounding the continent swarms in the non-stable interior of the yet consolidated Gondwana.
基金supported by the Commission on Higher Education,Ministry of Education,The Center of Excellence Research FundCU Centenary Academic Development Project+1 种基金Chulalongkorn University,King Chulalongkorn Memorial Hospital,MK Restaurant Company Limited and the National Research University Project of CHEthe Ratchadaphiseksomphot Endowment Fund(HR1155A)
文摘Objective:To understand the epidemiology of the East,Central and South African(ECSA) genotype of Chikungunya virus(CHIKV) in terms of emerging and re-emerging infections,this study has been aimed at investigating the evolutionary parameters,genomic signatures and molecular tracking of the CHIKV ECSA genotype in South-east Asia and coastal areas of the Indian Ocean between 2006 and 2009 by using phylogenetie analysis and the Bayesian Markov Chain Monte Carlo(BMCMC) evolutionary estimation.Methods:Nearly complete genome sequences of 53 CHIKV isolates from all genotypes were subjected to phylogenetie analysis and evolutionary parameter estimation.The amino acids of 67 of ECSA genotype during 2006 to 2009 were compared for finding molecular signature tracking.The ECSA genotype signatures were visualized to find the possible transmission root was projected onto a geographic map.Results: Phylogenetie analysis showed the ECSA genotype was divided into 2 groups.The first group comprises viruses from India and Southeast Asian countries.The second group consists of strains typically circulating in Sri Lanka in 2008.The evolutionary parameters of these groups depicted the time of the most recent common ancestor at approximately 7.5 years ago.The genomic signatures revealed the positions of amino acid variation in each group.Conclusions:The molecular evolution projected onto a geographical map showed the routes of CHIKV transmission from 2006 to 2009.Molecular tracking will assist in understanding transmission routes, epidemiology and molecular evolution of CHIKV.
基金financial support from the National Natural Science Foundation of China (Grant no.41530209)the Central Public-Interest Scientific Institution Basal Research Fund (Grant no.JYYWF201819)
文摘The Grove Mountains, 400 km south of the Chinese Antarctic Zhongshan Station, are an inland continuation of the Pan-African-aged (i.e., Late Neoproterozoic/Cambrian) Prydz Belt, East Antarctica. In this paper we carried out a combined U-Th-Pb monazite and Sm-Nd mineral-whole-rock dating on para- and orthogneisses from bedrock in the Grove Mountains. U-Th-Pb monazite dating of a cordierite-bearing pelitic paragneiss yields ages of 523 ? 4 Ma for the cores and 508 ? 6 Ma for the rims. Sm-Nd mineral-whole-rock isotopic analyses yield isochron ages of 536 ? 3 Ma for a coarse-grained felsic orthogneiss and 507 ? 30 Ma for a fine-grained quartzofeldspathic paragneiss. Combined with previously published age data in the Grove Mountains and adjacent areas, the older age of ~530 Ma is interpreted as the time of regional medium- to low-pressure granulite-facies metamorphism, and the younger age of ~510 Ma as the cooling age of the granulite terrane. The absence of evidence for a Grenville-aged (i.e., Late Mesoproterozoic/Early Neoproterozoic) metamorphic event indicates that the Grove Mountains have experienced only a single metamorphic cycle, i.e., Pan-African-aged, which distinguishes them from other polymetamorphic terranes in the Prydz Belt. This will provide important constraints on the controversial nature of the Prydz Belt.
基金financial support from the National Natural Science Foundation of China (Grant no.41530209)the Central Public-Interest Scientific Institution Basal Research Fund (Grant no.JYYWF201819)+1 种基金the Chinese Polar Environment Comprehensive Investi-gation&Assessment Programs (Grant no.CHINARE2015-02-05)the Geological Investigation Project of the China Geological Survey (Grant no.12120113019000)
文摘The Grove Mountains are an inland continuation of the Prydz Belt in East Antarctica. Detailed metamorphic petrological and zircon U-Pb geochronological studies are performed on the high-pressure (HP) pelitic granulites from glacial moraines in the Grove Mountains. The metamorphic peak mineral assemblage of the HP pelitic granulites is characterized by garnet + kyanite + K-feldspar + biotite + plagioclase + quartz, and the subsequent medium-pressure (MP) granulite facies retrogression is characterized by sillimanite replacing kyanite, the formation of the biolite + sillimanite symplectite in the matrix. These mineral assemblages and their P-T estimates based on the P-T pseudosection constructed in MnNCKFMASHT system define a clockwise P-T path involving metamorphic peak of 11.6–13.6 kbar at 817–834°C followed by a near-isothermal decompression of 6.7–7.5 kbar at 806–828°C, comparable with those of associated HP mafic granulites from glacial moraines in the Grove Mountains. Zircon U-Pb dating, coupled with available metamorphic age data obtained for HP mafic granulites, reveals HP metamorphism occurred at 540–545 Ma. Combining the previous research results, the HP pelitic granulites and contemporary HP mafic granulites were widely distributed in glacial moraines from the Grove Mountains, suggesting at least part of the Grove Subglacial Highlands underwent Pan-Afrian HP granulite facies metamorphism, which provides new evidence for a collisional tectonic setting of the Pan-Afrian Prydz Belt.