Three monogenetic cones in the Baossi–Warack area, Ngaoundéré, Adamawa Plateau forming part of the Cameroon Volcanic Line(CVL) are documented in this study. Basaltic lavas(<1 km^3) scattered around these...Three monogenetic cones in the Baossi–Warack area, Ngaoundéré, Adamawa Plateau forming part of the Cameroon Volcanic Line(CVL) are documented in this study. Basaltic lavas(<1 km^3) scattered around these vents and restricted volcaniclastic deposits were emplaced by Hawaiian and mild strombolian style eruptions. The lavas are porphyritic, mainly composed of olivine(chrysolite) and clinopyroxene(diopside and augite) phenocrysts and plagioclase(andesine) microphenocrysts. Accessory minerals include titano-magnetite and titano-hematite, nepheline,apatite and amphibole xenocrysts. Sanidine occurs in some samples and sodi-potassic albite in others. Some olivines and clinopyroxenes exhibit resorbed margins and thin reaction rims while plagioclase displays oscillatory zoning, and sieved textures as a result of magma mixing. Whole-rock geochemistry data indicates that the lavas are silica-undersaturated, composed of basanites and basalts, showing little compositional variations(SiO_2: 39.20 wt.%–48.01 wt.%,MgO: 5.29 wt.%–9.70 wt.%). Trace elements patterns of these lavas suggest they are enriched in LILE including Pb,probably due to crustal contamination. REE patterns suggest cogenetic magmas below Baossi 1 and Baossi 2 volcanoes,and distinct sources below Warack volcano and nearby lavas.The lavas studied show affinity to high-μ(HIMU), enriched type Ⅰ(EM1) and Oceanic Island Basalt(OIB)-like mantle signatures and thus indicate a heterogeneous mantle source underneath the vents as noted at other monogenetic and polygenetic volcanoes along the CVL. Primary melts derived from low degrees of partial melting(0.5%–2%) and encountered low rates of fractionation, and crustal contamination coupled with magma mixing. These melts evolved independently through structural weaknesses in the basement.展开更多
This study was conducted in the region of Tahoua the northeastern part of the Southern Illulemeden sedimentary basin. In this region the transboundary aquifer system of Continental Intercalaire (CI) and the Continenta...This study was conducted in the region of Tahoua the northeastern part of the Southern Illulemeden sedimentary basin. In this region the transboundary aquifer system of Continental Intercalaire (CI) and the Continental Hamadien (CH) are potentially rich in underground water especially in free and captive aquifers. More, this water is the main source of drinking water for the populations, the animals and for agriculture and extractive industries. However, the population growth, the agricultural development, and the climate change have a real impact on the dynamics of groundwater and the exploitation of these resources. Hence, this study aims at analyzing the behavior of aquifers and assessing the impact of various natural and anthropogenic factors. Especially it matters to analyze the drilling parameters and cuttings, logging data and pumping test of nine new boreholes. The results reveal that the depths equipped with boreholes catching the CI/CH complex vary from 70 to 800 meters from East to West while the average thickness of the reservoir CH is 50 meters and it mainly consists of coarse sandstone. Drilling penetrated more than 100 meters into the CI without reaching the base. The CI tank is composed of several layers of gravel and clay whilst the CI/CH aquifers flow rates range from 0.2 to 22.8 m3/h/m. So this is cause of great variability of the water potential within this aquifer. Lastly, the transmissivity coefficients are more important in the CH than in the CI, and the water flow average rates range respectively from 29 m/year to 7 m/year.展开更多
Numerous mantle xenoliths 6–12 cm in size and sub-angular to rounded in shape occur within Mio-Pliocene basanite lavas of the monogenic volcano of HosséréSédé in the Adamawa plateau.Xenoliths of s...Numerous mantle xenoliths 6–12 cm in size and sub-angular to rounded in shape occur within Mio-Pliocene basanite lavas of the monogenic volcano of HosséréSédé in the Adamawa plateau.Xenoliths of spinel lherzolite exhibit protogranular,equigranular or porphyroclastic texture.Microprobe chemical analyses show that olivine is highly magnesian(Fo_(88-90)),clinopyroxene crystals are diopside and augite(Wo_(41.6–49.6)En_(45.3–53.7)Fs_(4.2–6.2)),orthopyroxene crystals are enstatite(Wo 1.4–1.5 En_(88.6–89.0)Fs_(9.6–9.9))and spinel crystals are mainly Al-spinel associ-ated to minor Cr-spinel.Estimated temperatures and pressures through empirical formulas show that HosséréSédé noliths have equilibrated between 1085 and 1204℃and 1.08 to 1.57 GPa,corresponding to sampling depths of 36 and 52 km.Detailed petrographical and mineral chemistry of HosséréSédénoliths evidences the com-plex nature and composition of the subcontinental lithosphere under the Adamawa plateau.This may involve a probable uplift of the whole area after a limited exten-sional event,possible metasomatism through melt infiltration during shearing of the lithospheric mantle along the Pan African strike-slip fault system.展开更多
The Temtebasement in North Cameroon is crosscut by dyke swarms with N 20°–40°trending,including dykes 15–30 m wide,up to 3 km-long.Representative rocks exhibit intersertal to sub-ophitic textures.Electron ...The Temtebasement in North Cameroon is crosscut by dyke swarms with N 20°–40°trending,including dykes 15–30 m wide,up to 3 km-long.Representative rocks exhibit intersertal to sub-ophitic textures.Electron microprobe analyses identified diopside,augite,pargasite,biotite,Ti-magnetite,plagioclase,and sanidine.Whole-rock ICP-MS and ICP-AES chemical analyses showed compositions of basaltic andesite,basaltic trachyandesite and trachyandesite in composition.Igneous differentiation was likely governed by fractional crystallization associated with limited fluid metasomatism.Some lavas could have been moderately contaminated by crustal materials during feeding of local cracks through turbulent magma flows.Discrimination geochemical diagrams and immobile trace and REE element ratios show that the mantle source of Temtedolerites was a deep phlogopitebearing EMII mantle component and has undergone moderate to high partial melting rate.Correlations of fieldwork and analytical data with previous results evidence the Temtedolerite dyke swarms as fingerprints of crustal extension accompanying regional uplift in an active continental margin when early rifting led to the formation of the Poli marginal basin.展开更多
The Admiralty Mountains region forms the northern termination of the northern Victoria Land,Antarctica.Few quantitative data are available to reconstruct the Cenozoic morpho-tectonic evolution of this sector of the An...The Admiralty Mountains region forms the northern termination of the northern Victoria Land,Antarctica.Few quantitative data are available to reconstruct the Cenozoic morpho-tectonic evolution of this sector of the Antarctic plate,where the Admiralty Mountains region forms the northern termination of the western shoulder of the Mesozoic-Cenozoic West Antarctica Rift System.In this study we combine new low-temperature thermochronological data(apatite fission-track and(U-Th-Sm)/He analyses)with structural and topography analysis.The regional pattern of the fission-track ages shows a general tendency to older ages(80-60 Ma)associated with shortened mean track-lengths in the interior,and younger fission-track ages clustering at 38-26 Ma with long mean track-lengths in the coastal region.Differently from other regions of Victoria Land,the younger ages are found as far as 50-70 km inland.Single grain apatite(U-Th-Sm)/He ages cluster at 50-30 Ma with younger ages in the coastal domain.Topography analysis reveals that the Admiralty Mountains has high local relief,with an area close to the coast,180 km long and 70 km large,having the highest local relief of>2500 m.This coincides with the location of the youngest fission-track ages.The shape of the area with highest local relief matches the shape of a recently detected low velocity zone beneath the northern TAM,indicating that high topography of the Admiralty Mountains region is likely sustained by a mantle thermal anomaly.We used the obtained constraints on the amount of removed crustal section to reconstruct back-eroded profiles and calculate the erosional load in order to test flexural uplift models.We found that our back-eroded profiles are better reproduced by a constant elastic thickness of intermediate values(Te=20-30 km).This suggests that,beneath the Admiralty Mountains,the elastic properties of the lithosphere are different with respect to other TAM sectors,likely due to a stationary Cenozoic upper mantle thermal anomaly in the region.展开更多
Distributed temperature sensing is known to provide sharp signals which are very efficient for mapping hydraulically active fractures in wellbores. High-resolution temperature sensing has specifically demonstrated its...Distributed temperature sensing is known to provide sharp signals which are very efficient for mapping hydraulically active fractures in wellbores. High-resolution temperature sensing has specifically demonstrated its capacity to characterize very low flows in wellbores. But as sharp as they can be, temperature profiles are often difficult to decipher. The aim of the present work is to provide and to test the “Borehole Heat Budget Calculator” (BHB Calculator), which is implemented as a fast and easy to use tool for the quantitative analysis of depth-temperature profiles. The Calculator is suitable for most pumping and draining configurations, as the heat budget is generalized for modelling multidirectional flow systems within the same wellbore. The formatted worksheet allows the quick exploitation of temperature logs, and is applicable for the characterization of distributed fractures in long screened wellbores. Objectives of the heat modelling are to enhance the readability of complex depth-temperature data, as well as to quantify distribution of inflow intensities and temperatures with depth. The use of heat budget helps to clearly visualize how heat conduction and heat advection contributions are distributed along wellbores profiles. Calculations of inflow temperatures and their evolution through pumping duration is a prerequisite to infer about the nature of aquifer properties (i.e. conduits, distributed or discrete fractures, porous media), as well as to give insight information about the mapping of effective flow paths draining the aquifer. The efficiency and limitations of the BHB Calculator are being tested through high-resolution temperature logging, along with complementary flowmetering and televiewing logging in fractured aquifers located in the St-Lawrence Lowlands, Quebec, Canada.展开更多
Atmospheric composition is an important indicator of habitability and life.The presence or absence of a large exomoon around an Earth-size exoplanet could have important consequences for planet climate stability.Thus ...Atmospheric composition is an important indicator of habitability and life.The presence or absence of a large exomoon around an Earth-size exoplanet could have important consequences for planet climate stability.Thus the detection of exomoons and retrieval of information regarding atmospheric composition of Earth-size exoplanets are important goals of future exoplanet observations.Here a data analysis method is developed to achieve both goals simultaneously,based on reflection spectra of exoplanet-exomoon systems.We show that the existence of exomoons,the size of exomoons,and the concentrations of some atomic and molecular species in the atmospheres of their hosting Earth-like exoplanets can be retrieved with high levels of reliability.In addition,the method can provide well-constrained fractions of basic surface types on the targets because of the characteristic spectral features of atmospheric species and surface types in the analyzed spectral range.展开更多
The Action Group called‘Standardized methods across Permafrost Landscapes:from Arctic Soils to Hydrosystems’(SPLASH)is a community-driven effort aiming to provide a suite of standardized field strategies for samplin...The Action Group called‘Standardized methods across Permafrost Landscapes:from Arctic Soils to Hydrosystems’(SPLASH)is a community-driven effort aiming to provide a suite of standardized field strategies for sampling mineral and organic components in soils,sediments,and water across permafrost landscapes.This unified approach will allow data from different landscape interfaces,field locations and seasons to be shared and compared,thus improving our understanding of the processes occurring during lateral transport in circumpolar Arctic watersheds.展开更多
The distribution of oil and gas resources is intricately connected to the underlying structure of the lithosphere.Therefore,investigating the characteristics of lithospheric thickness and its correlation with oil and ...The distribution of oil and gas resources is intricately connected to the underlying structure of the lithosphere.Therefore,investigating the characteristics of lithospheric thickness and its correlation with oil and gas basins is highly important.This research utilizes recently enhanced geological–geophysical data,including topographic,geoid,rock layer thickness,variable rock layer density,and interface depth data.Employing the principles of lithospheric isostasy and heat conduction,we compute the laterally varying lithospheric thickness in the China seas and adjacent areas.From these results,two pivotal parameters for different types of oil and gas basins were statistically analyzed:the minimum lithospheric thickness and the relative fluctuation in lithospheric thickness.A semiquantitative analysis was used to explore the connection between these parameters and the hydrocarbon abundance within the oil and gas basins.This study unveils distinct variations in lithospheric thickness among basins,with oil and gas rich basins exhibiting a thicker lithosphere in the superimposed basins of central China and a thinner lithosphere in the rift basins of eastern China.Notably,the relative fluctuations in lithospheric thickness in basins demonstrate significant disparities:basins rich in oil and gas often exhibit greater thickness fluctuations.Additionally,in the offshore basins of China,a conspicuous negative linear correlation is observed between the minimum lithospheric thickness and the relative fluctuation in lithospheric thickness.This study posits that deep-seated thermal upwelling results in lithospheric undulations and extensional thinning in oil and gas basins.Concurrently,sustained deep-seated heat influences sedimentary materials in basins,creating favorable conditions for oil and gas generation.The insights derived from this study contribute to a quantitative understanding of the intricate relationships between deep lithospheric structures and oil and gas basins.These findings provide valuable guidance for future oil and gas exploration in the studied areas.展开更多
The Cambrian-lower Ordovician volcanic units of the South Armorican and Occitan domains are ana- lysed in a tectonostratigraphic survey of the French Variscan Belt. The South Armorican lavas consist of continental tho...The Cambrian-lower Ordovician volcanic units of the South Armorican and Occitan domains are ana- lysed in a tectonostratigraphic survey of the French Variscan Belt. The South Armorican lavas consist of continental tholeiites in middle Camhrian-Furongian sequences related to continental break-up. A significant volcanic activity occurred in the Tremadocian, dominated by crustal melted rhyolitic lavas and initial rifting tholeiites. The Occitan lavas are distributed into five volcanic phases： （I） basal Cambrian rhyolites, （2） upper lower Cambrian Mg-rich tholeiites close to N-MORBs but crustal contaminated, （3） upper lower-middle Cambrian continental tholeiites, （4） Tremadocian rhyolites, and （5） upper lower Ordovician initial rift tholeiites. A rifting event linked to asthenosphere upwelling took place in the late early Cambrian but did not evolve. It renewed in the Tremadocian with abundant crustal melting due to underplating of mixed asthenospheric and lithospheric magmas. This main tectono-magmatic conti- nental rift is termed the ＂Tremadocian Tectonic Belt＂ underlined by a chain of rhyolitic volcanoes from Occitan and South Armorican domains to Central Iberia. It evolved with the setting of syn-rift coarse siliciclastic deposits overlain by post-rift deep water shales in a suite of sedimentary basins that fore- casted the South Armorican-Medio-European Ocean as a part of the Palaeotethys Ocean.展开更多
This study aims to identify from geo-electrics the areas favorable to the in-stallation of drinking water supply(AEP)drilling in the sub-prefecture of Gbangbégouiné-Yati in order to contribute to a better di...This study aims to identify from geo-electrics the areas favorable to the in-stallation of drinking water supply(AEP)drilling in the sub-prefecture of Gbangbégouiné-Yati in order to contribute to a better distribution and manage-ment of water tables in the Department of Man.To achieve these objectives,pi ezometric maps and electrical resistivity maps were produced to understand the functioning of groundwater and to have the imaging of the subsoil.The piezometric maps revealed a regressive trend in the water level in the period from February 2024 to April 2024 and flow towards the lowlands in the north and,more mainly,in the east.Electrical resistivity imaging reveals three types of formations:conductive formations(resistivities between 100 and 1000 Ohm.m),medium resistivity formations(1000 to 3200 Ohm.m),and resistive formations(3200 to 6000 Ohm.m).Low resistivity formations likely to contain water in this locality are located between depths of 40 m and 50 m.展开更多
Côte d’Ivoire is made up of more than 97%bedrock.The majority of water resources are contained in the fractured bedrock,where drilling has a high failure rate.It is therefore important to better understand these...Côte d’Ivoire is made up of more than 97%bedrock.The majority of water resources are contained in the fractured bedrock,where drilling has a high failure rate.It is therefore important to better understand these water reser-voirs,as their hydrogeological significance is considerable.This study is con-ducted from this perspective and covers the sub-prefecture of Togoniéré(North of Côte d’Ivoire)where the water problem is acute.Its objective is to charac-terize the geometry of the aquifers in the sub-prefecture by using electrical resistivity tomography.The results highlight an anisotropy of the underground formations,more pronounced with depth,represented by a succession of re-sistant-conductive-resistant terrains.They reveal conductive formations in-terpreted as lateritic aquifers,located between 20 and 75 m deep and generally with thicknesses of 30 to 50 m.They have a triangular shape and lateral exten-sions of about 85 m.Other conductive formations(3 to 10 m),which have a NW-SE and NE-SW dip and a 45˚inclination,suggest a network of fractures facilitating the infiltration and storage of water.Their reach does not exceed 85 m but can extend to 185 m in length.These aquifers result from regional tectonics or local alteration.展开更多
Understanding fault activity over time provides valuable insights for reconstructing the tectonic history of an orogen,assessing seismological risks and understanding mineralization processes.In the Western Alps,one o...Understanding fault activity over time provides valuable insights for reconstructing the tectonic history of an orogen,assessing seismological risks and understanding mineralization processes.In the Western Alps,one of the main controversies in existing tectonic models is the understanding of syn-orogenic extension.Seismological evidence shows widespread extensional deformation related to the reactivation of major lithospheric structures,such as the Penninic Frontal Thrust(PFT).However,the onset age and origin of extension are still debated due to the lack of suitable geochronological data.Fault hematite and calcite geochronology as well as clumped isotope data can be used to relate fluid regimes to fault activity.The analysis of calcite brecciae from extensional faults above the PFT shows that two distinct fluid regimes were present.The first regime,occurring before 2 Ma is associated with upwelling of deep fluids and is recorded by fault calcite at a temperature>110°C.The second fluid regime is characterized by a meteoric signature and temperatures around 36°C,representing crystallization since 2 Ma.This study presents a new model for the Miocene tectonic history of the Western Alps that combines(U-Th)/He and U-Pb geochronology on fault hematite(13.3±0.8 to<0.8 Ma)and calcite(5.3±0.6 Ma).Results demonstrate a progression of extensional fault activity from east to west,from the Middle Miocene(ca.13 Ma)to the Quaternary.The onset of extension in the inner part of the belt coincides with the development of the fold and thrust belt in the western Alpine foreland.Our new model proposes that extension occurs in the hanging wall of a large top-to-the-west thrust,known as the Alpine Frontal Thrust.This thrust,located to the west of the External Crystalline Massifs gives rise to their uplifting and extension at the rear.展开更多
IN recent years, much progress has been made in the research of the temporal and spatial changes of East Asian monsoon. To research the environmental evolution and monsoon variations in Holocene in the region of South...IN recent years, much progress has been made in the research of the temporal and spatial changes of East Asian monsoon. To research the environmental evolution and monsoon variations in Holocene in the region of Southwest China, a 310-cm continuous lake sediments core in Erhai Lake, Yunnan Province was sampled with Livingston sampler on July 6, 1996. The lake sediments were separated at 2-cm intervals and the core samples were analyzed with chronology, stable isotope ratios of organic carbon and diatoms determination. Three <sup>14</sup>C ages are （4 473±40）a B.P. （98—102 cm）, （5 825±85） a B. P. （144—148 cm） and （7 754±45） a B.P. （198—202 cm）. By <sup>137</sup>Cs dating, the sedimentation rate is about 0.3 mm/a and this result is close to the <sup>14</sup>C dating results. The average sedimentation rates展开更多
nhanced silicate weathering induced by the uplift of the Himalayan-Tibetan Plateau(HTP)has been considered as the major cause of pCO_(2)decline and Cenozoic cooling.However,this hypothesis remains to be validated,larg...nhanced silicate weathering induced by the uplift of the Himalayan-Tibetan Plateau(HTP)has been considered as the major cause of pCO_(2)decline and Cenozoic cooling.However,this hypothesis remains to be validated,largely due to the lack of a reliable reconstruction of the HTP weathering flux.Here,we present a 37-million-year record of the difference in the seawater radiogenic neodymium isotopic composition(△ε_(Nd))of Ocean Drilling Program(ODP)sites and Fe-Mn crusts between the northern and central Indian Ocean,which indicates the contribution of regional weathering input from the South Asian continent to the Indian Ocean.The results show a long-term increase in△ε_(Nd)and thus provide the first critical evidence of enhanced South Asian weathering input since the late Eocene.The evolution coincided well with major pulses of surface uplift in the HTP and global climatic transitions.Our foraminiferal eNd record suggests that tectonic uplift and silicate weathering in South Asia,especially in the Himalayas,might have played a significant role in the late Cenozoic cooling.展开更多
The formation and evolution of permafrost in China during the last 20 ka were reconstructed on the basis of large amount of paleo-permafrost remains and paleo-periglacial evidence, as well as paleo-glacial landforms, ...The formation and evolution of permafrost in China during the last 20 ka were reconstructed on the basis of large amount of paleo-permafrost remains and paleo-periglacial evidence, as well as paleo-glacial landforms, paleo-flora and paleofauna records. The results indicate that, during the local Last Glacial Maximum(LLGM) or local Last Permafrost Maximum(LLPMax), the extent of permafrost of China reached 5.3×106-5.4×106 km2, or thrice that of today, but permafrost shrank to only0.80×106-0.85×106 km2, or 50% that of present, during the local Holocene Megathermal Period(LHMP), or the local Last Permafrost Minimum(LLPMin). On the basis of the dating of periglacial remains and their distributive features, the extent of permafrost in China was delineated for the two periods of LLGM(LLPMax) and LHMP(LLPMin), and the evolution of permafrost in China was divided into seven periods as follows:(1) LLGM in Late Pleistocene(ca. 20000 to 13000-10800 a BP)with extensive evidence for the presence of intensive ice-wedge expansion for outlining its LLPMax extent;(2) A period of dramatically changing climate during the early Holocene(10800 to 8500-7000 a BP) when permafrost remained relatively stable but with a general trend of shrinking areal extent;(3) The LHMP in the Mid-Holocene(8500-7000 to 4000-3000 a BP)when permafrost degraded intensively and extensively, and shrank to the LLPMin;(4) Neoglaciation during the late Holocene(4000-3000 to 1000 a BP, when permafrost again expanded;(5) Medieval Warming Period(MWP) in the late Holocene(1000-500 a BP) when permafrost was in a relative decline;(6) Little Ice Age(LIA) in the late Holocene(500-100 a BP), when permafrost relatively expanded, and;(7) Recent warming(during the 20 th century), when permafrost continuously degraded and still is degrading. The paleo-climate, geography and paleopermafrost extents and other features were reconstructed for each of these seven periods.展开更多
基金financially supported by the Ministry of Higher Education, Cameroon, through the Special Allocation for the Modernization of Research (SAMR) granted to the first author
文摘Three monogenetic cones in the Baossi–Warack area, Ngaoundéré, Adamawa Plateau forming part of the Cameroon Volcanic Line(CVL) are documented in this study. Basaltic lavas(<1 km^3) scattered around these vents and restricted volcaniclastic deposits were emplaced by Hawaiian and mild strombolian style eruptions. The lavas are porphyritic, mainly composed of olivine(chrysolite) and clinopyroxene(diopside and augite) phenocrysts and plagioclase(andesine) microphenocrysts. Accessory minerals include titano-magnetite and titano-hematite, nepheline,apatite and amphibole xenocrysts. Sanidine occurs in some samples and sodi-potassic albite in others. Some olivines and clinopyroxenes exhibit resorbed margins and thin reaction rims while plagioclase displays oscillatory zoning, and sieved textures as a result of magma mixing. Whole-rock geochemistry data indicates that the lavas are silica-undersaturated, composed of basanites and basalts, showing little compositional variations(SiO_2: 39.20 wt.%–48.01 wt.%,MgO: 5.29 wt.%–9.70 wt.%). Trace elements patterns of these lavas suggest they are enriched in LILE including Pb,probably due to crustal contamination. REE patterns suggest cogenetic magmas below Baossi 1 and Baossi 2 volcanoes,and distinct sources below Warack volcano and nearby lavas.The lavas studied show affinity to high-μ(HIMU), enriched type Ⅰ(EM1) and Oceanic Island Basalt(OIB)-like mantle signatures and thus indicate a heterogeneous mantle source underneath the vents as noted at other monogenetic and polygenetic volcanoes along the CVL. Primary melts derived from low degrees of partial melting(0.5%–2%) and encountered low rates of fractionation, and crustal contamination coupled with magma mixing. These melts evolved independently through structural weaknesses in the basement.
文摘This study was conducted in the region of Tahoua the northeastern part of the Southern Illulemeden sedimentary basin. In this region the transboundary aquifer system of Continental Intercalaire (CI) and the Continental Hamadien (CH) are potentially rich in underground water especially in free and captive aquifers. More, this water is the main source of drinking water for the populations, the animals and for agriculture and extractive industries. However, the population growth, the agricultural development, and the climate change have a real impact on the dynamics of groundwater and the exploitation of these resources. Hence, this study aims at analyzing the behavior of aquifers and assessing the impact of various natural and anthropogenic factors. Especially it matters to analyze the drilling parameters and cuttings, logging data and pumping test of nine new boreholes. The results reveal that the depths equipped with boreholes catching the CI/CH complex vary from 70 to 800 meters from East to West while the average thickness of the reservoir CH is 50 meters and it mainly consists of coarse sandstone. Drilling penetrated more than 100 meters into the CI without reaching the base. The CI tank is composed of several layers of gravel and clay whilst the CI/CH aquifers flow rates range from 0.2 to 22.8 m3/h/m. So this is cause of great variability of the water potential within this aquifer. Lastly, the transmissivity coefficients are more important in the CH than in the CI, and the water flow average rates range respectively from 29 m/year to 7 m/year.
文摘Numerous mantle xenoliths 6–12 cm in size and sub-angular to rounded in shape occur within Mio-Pliocene basanite lavas of the monogenic volcano of HosséréSédé in the Adamawa plateau.Xenoliths of spinel lherzolite exhibit protogranular,equigranular or porphyroclastic texture.Microprobe chemical analyses show that olivine is highly magnesian(Fo_(88-90)),clinopyroxene crystals are diopside and augite(Wo_(41.6–49.6)En_(45.3–53.7)Fs_(4.2–6.2)),orthopyroxene crystals are enstatite(Wo 1.4–1.5 En_(88.6–89.0)Fs_(9.6–9.9))and spinel crystals are mainly Al-spinel associ-ated to minor Cr-spinel.Estimated temperatures and pressures through empirical formulas show that HosséréSédé noliths have equilibrated between 1085 and 1204℃and 1.08 to 1.57 GPa,corresponding to sampling depths of 36 and 52 km.Detailed petrographical and mineral chemistry of HosséréSédénoliths evidences the com-plex nature and composition of the subcontinental lithosphere under the Adamawa plateau.This may involve a probable uplift of the whole area after a limited exten-sional event,possible metasomatism through melt infiltration during shearing of the lithospheric mantle along the Pan African strike-slip fault system.
基金"Agence Universitaire de la Francophonie (AUF)" through the BAGL (Bureau Afrique Centrale et des Grands Lacs) for financial support of Le Projet de soutien aux équipes de recherche 2012/2013 (No 51110SU201) for supplement analyses"Laboratoire GEOPS" of the University Paris-Saclay is thanked for financial support of thin sections and electron microprobe analyses。
文摘The Temtebasement in North Cameroon is crosscut by dyke swarms with N 20°–40°trending,including dykes 15–30 m wide,up to 3 km-long.Representative rocks exhibit intersertal to sub-ophitic textures.Electron microprobe analyses identified diopside,augite,pargasite,biotite,Ti-magnetite,plagioclase,and sanidine.Whole-rock ICP-MS and ICP-AES chemical analyses showed compositions of basaltic andesite,basaltic trachyandesite and trachyandesite in composition.Igneous differentiation was likely governed by fractional crystallization associated with limited fluid metasomatism.Some lavas could have been moderately contaminated by crustal materials during feeding of local cracks through turbulent magma flows.Discrimination geochemical diagrams and immobile trace and REE element ratios show that the mantle source of Temtedolerites was a deep phlogopitebearing EMII mantle component and has undergone moderate to high partial melting rate.Correlations of fieldwork and analytical data with previous results evidence the Temtedolerite dyke swarms as fingerprints of crustal extension accompanying regional uplift in an active continental margin when early rifting led to the formation of the Poli marginal basin.
基金carried out in the framework of the research projects PDR2013/AZ2.07(coordinated by F.Rossetti)PNRA16_00263(coordinated by V.Olivetti)funded by PNRA(Italian Research Program in Antarctica)。
文摘The Admiralty Mountains region forms the northern termination of the northern Victoria Land,Antarctica.Few quantitative data are available to reconstruct the Cenozoic morpho-tectonic evolution of this sector of the Antarctic plate,where the Admiralty Mountains region forms the northern termination of the western shoulder of the Mesozoic-Cenozoic West Antarctica Rift System.In this study we combine new low-temperature thermochronological data(apatite fission-track and(U-Th-Sm)/He analyses)with structural and topography analysis.The regional pattern of the fission-track ages shows a general tendency to older ages(80-60 Ma)associated with shortened mean track-lengths in the interior,and younger fission-track ages clustering at 38-26 Ma with long mean track-lengths in the coastal region.Differently from other regions of Victoria Land,the younger ages are found as far as 50-70 km inland.Single grain apatite(U-Th-Sm)/He ages cluster at 50-30 Ma with younger ages in the coastal domain.Topography analysis reveals that the Admiralty Mountains has high local relief,with an area close to the coast,180 km long and 70 km large,having the highest local relief of>2500 m.This coincides with the location of the youngest fission-track ages.The shape of the area with highest local relief matches the shape of a recently detected low velocity zone beneath the northern TAM,indicating that high topography of the Admiralty Mountains region is likely sustained by a mantle thermal anomaly.We used the obtained constraints on the amount of removed crustal section to reconstruct back-eroded profiles and calculate the erosional load in order to test flexural uplift models.We found that our back-eroded profiles are better reproduced by a constant elastic thickness of intermediate values(Te=20-30 km).This suggests that,beneath the Admiralty Mountains,the elastic properties of the lithosphere are different with respect to other TAM sectors,likely due to a stationary Cenozoic upper mantle thermal anomaly in the region.
文摘Distributed temperature sensing is known to provide sharp signals which are very efficient for mapping hydraulically active fractures in wellbores. High-resolution temperature sensing has specifically demonstrated its capacity to characterize very low flows in wellbores. But as sharp as they can be, temperature profiles are often difficult to decipher. The aim of the present work is to provide and to test the “Borehole Heat Budget Calculator” (BHB Calculator), which is implemented as a fast and easy to use tool for the quantitative analysis of depth-temperature profiles. The Calculator is suitable for most pumping and draining configurations, as the heat budget is generalized for modelling multidirectional flow systems within the same wellbore. The formatted worksheet allows the quick exploitation of temperature logs, and is applicable for the characterization of distributed fractures in long screened wellbores. Objectives of the heat modelling are to enhance the readability of complex depth-temperature data, as well as to quantify distribution of inflow intensities and temperatures with depth. The use of heat budget helps to clearly visualize how heat conduction and heat advection contributions are distributed along wellbores profiles. Calculations of inflow temperatures and their evolution through pumping duration is a prerequisite to infer about the nature of aquifer properties (i.e. conduits, distributed or discrete fractures, porous media), as well as to give insight information about the mapping of effective flow paths draining the aquifer. The efficiency and limitations of the BHB Calculator are being tested through high-resolution temperature logging, along with complementary flowmetering and televiewing logging in fractured aquifers located in the St-Lawrence Lowlands, Quebec, Canada.
基金supported by the National Natural Science Foundation of China(1166116101,4164104)supported by the National Natural Science Foundation of China(41375102)+5 种基金support from the Spark Program,Tsinghua Universitysupport from "Institute National des Sciences de l’Univers"(INSU)the "Centre National de la Recherche Scientifique"(CNRS) and "Centre National d’Etude Spatiale"(CNES),through the "Programme National de Planétologie"the PICS programMEX/OMEGAMEX/PFS programs
文摘Atmospheric composition is an important indicator of habitability and life.The presence or absence of a large exomoon around an Earth-size exoplanet could have important consequences for planet climate stability.Thus the detection of exomoons and retrieval of information regarding atmospheric composition of Earth-size exoplanets are important goals of future exoplanet observations.Here a data analysis method is developed to achieve both goals simultaneously,based on reflection spectra of exoplanet-exomoon systems.We show that the existence of exomoons,the size of exomoons,and the concentrations of some atomic and molecular species in the atmospheres of their hosting Earth-like exoplanets can be retrieved with high levels of reliability.In addition,the method can provide well-constrained fractions of basic surface types on the targets because of the characteristic spectral features of atmospheric species and surface types in the analyzed spectral range.
文摘The Action Group called‘Standardized methods across Permafrost Landscapes:from Arctic Soils to Hydrosystems’(SPLASH)is a community-driven effort aiming to provide a suite of standardized field strategies for sampling mineral and organic components in soils,sediments,and water across permafrost landscapes.This unified approach will allow data from different landscape interfaces,field locations and seasons to be shared and compared,thus improving our understanding of the processes occurring during lateral transport in circumpolar Arctic watersheds.
基金supported by the National Key Research and Development Plan project“Research on Comprehensive Processing and Interpretation Methods of Aeronautical Geophysical Data and Soft ware Development”under contract No.2017YFC0602202。
文摘The distribution of oil and gas resources is intricately connected to the underlying structure of the lithosphere.Therefore,investigating the characteristics of lithospheric thickness and its correlation with oil and gas basins is highly important.This research utilizes recently enhanced geological–geophysical data,including topographic,geoid,rock layer thickness,variable rock layer density,and interface depth data.Employing the principles of lithospheric isostasy and heat conduction,we compute the laterally varying lithospheric thickness in the China seas and adjacent areas.From these results,two pivotal parameters for different types of oil and gas basins were statistically analyzed:the minimum lithospheric thickness and the relative fluctuation in lithospheric thickness.A semiquantitative analysis was used to explore the connection between these parameters and the hydrocarbon abundance within the oil and gas basins.This study unveils distinct variations in lithospheric thickness among basins,with oil and gas rich basins exhibiting a thicker lithosphere in the superimposed basins of central China and a thinner lithosphere in the rift basins of eastern China.Notably,the relative fluctuations in lithospheric thickness in basins demonstrate significant disparities:basins rich in oil and gas often exhibit greater thickness fluctuations.Additionally,in the offshore basins of China,a conspicuous negative linear correlation is observed between the minimum lithospheric thickness and the relative fluctuation in lithospheric thickness.This study posits that deep-seated thermal upwelling results in lithospheric undulations and extensional thinning in oil and gas basins.Concurrently,sustained deep-seated heat influences sedimentary materials in basins,creating favorable conditions for oil and gas generation.The insights derived from this study contribute to a quantitative understanding of the intricate relationships between deep lithospheric structures and oil and gas basins.These findings provide valuable guidance for future oil and gas exploration in the studied areas.
基金funded by project CGL2013-48877-P from Spanish MINECO
文摘The Cambrian-lower Ordovician volcanic units of the South Armorican and Occitan domains are ana- lysed in a tectonostratigraphic survey of the French Variscan Belt. The South Armorican lavas consist of continental tholeiites in middle Camhrian-Furongian sequences related to continental break-up. A significant volcanic activity occurred in the Tremadocian, dominated by crustal melted rhyolitic lavas and initial rifting tholeiites. The Occitan lavas are distributed into five volcanic phases： （I） basal Cambrian rhyolites, （2） upper lower Cambrian Mg-rich tholeiites close to N-MORBs but crustal contaminated, （3） upper lower-middle Cambrian continental tholeiites, （4） Tremadocian rhyolites, and （5） upper lower Ordovician initial rift tholeiites. A rifting event linked to asthenosphere upwelling took place in the late early Cambrian but did not evolve. It renewed in the Tremadocian with abundant crustal melting due to underplating of mixed asthenospheric and lithospheric magmas. This main tectono-magmatic conti- nental rift is termed the ＂Tremadocian Tectonic Belt＂ underlined by a chain of rhyolitic volcanoes from Occitan and South Armorican domains to Central Iberia. It evolved with the setting of syn-rift coarse siliciclastic deposits overlain by post-rift deep water shales in a suite of sedimentary basins that fore- casted the South Armorican-Medio-European Ocean as a part of the Palaeotethys Ocean.
文摘This study aims to identify from geo-electrics the areas favorable to the in-stallation of drinking water supply(AEP)drilling in the sub-prefecture of Gbangbégouiné-Yati in order to contribute to a better distribution and manage-ment of water tables in the Department of Man.To achieve these objectives,pi ezometric maps and electrical resistivity maps were produced to understand the functioning of groundwater and to have the imaging of the subsoil.The piezometric maps revealed a regressive trend in the water level in the period from February 2024 to April 2024 and flow towards the lowlands in the north and,more mainly,in the east.Electrical resistivity imaging reveals three types of formations:conductive formations(resistivities between 100 and 1000 Ohm.m),medium resistivity formations(1000 to 3200 Ohm.m),and resistive formations(3200 to 6000 Ohm.m).Low resistivity formations likely to contain water in this locality are located between depths of 40 m and 50 m.
文摘Côte d’Ivoire is made up of more than 97%bedrock.The majority of water resources are contained in the fractured bedrock,where drilling has a high failure rate.It is therefore important to better understand these water reser-voirs,as their hydrogeological significance is considerable.This study is con-ducted from this perspective and covers the sub-prefecture of Togoniéré(North of Côte d’Ivoire)where the water problem is acute.Its objective is to charac-terize the geometry of the aquifers in the sub-prefecture by using electrical resistivity tomography.The results highlight an anisotropy of the underground formations,more pronounced with depth,represented by a succession of re-sistant-conductive-resistant terrains.They reveal conductive formations in-terpreted as lateritic aquifers,located between 20 and 75 m deep and generally with thicknesses of 30 to 50 m.They have a triangular shape and lateral exten-sions of about 85 m.Other conductive formations(3 to 10 m),which have a NW-SE and NE-SW dip and a 45˚inclination,suggest a network of fractures facilitating the infiltration and storage of water.Their reach does not exceed 85 m but can extend to 185 m in length.These aquifers result from regional tectonics or local alteration.
基金This work forms part of the first author’s Ph.D.project funded by the French BRGM in the frame of the RGF-Alps program(Référentiel Géologique de la France)The LA-ICP-MS hosted by the ENVITOP platform at CEREGE has received funding from the“Excellence Initiative”of the Aix Marseille University A*MIDEX–project DATCARB,a french“Investissement d’avenir”programSpecial thanks to Fayçal Soufi and Pierre-Luigi Canepa for their preparation of polished thin-section。
文摘Understanding fault activity over time provides valuable insights for reconstructing the tectonic history of an orogen,assessing seismological risks and understanding mineralization processes.In the Western Alps,one of the main controversies in existing tectonic models is the understanding of syn-orogenic extension.Seismological evidence shows widespread extensional deformation related to the reactivation of major lithospheric structures,such as the Penninic Frontal Thrust(PFT).However,the onset age and origin of extension are still debated due to the lack of suitable geochronological data.Fault hematite and calcite geochronology as well as clumped isotope data can be used to relate fluid regimes to fault activity.The analysis of calcite brecciae from extensional faults above the PFT shows that two distinct fluid regimes were present.The first regime,occurring before 2 Ma is associated with upwelling of deep fluids and is recorded by fault calcite at a temperature>110°C.The second fluid regime is characterized by a meteoric signature and temperatures around 36°C,representing crystallization since 2 Ma.This study presents a new model for the Miocene tectonic history of the Western Alps that combines(U-Th)/He and U-Pb geochronology on fault hematite(13.3±0.8 to<0.8 Ma)and calcite(5.3±0.6 Ma).Results demonstrate a progression of extensional fault activity from east to west,from the Middle Miocene(ca.13 Ma)to the Quaternary.The onset of extension in the inner part of the belt coincides with the development of the fold and thrust belt in the western Alpine foreland.Our new model proposes that extension occurs in the hanging wall of a large top-to-the-west thrust,known as the Alpine Frontal Thrust.This thrust,located to the west of the External Crystalline Massifs gives rise to their uplifting and extension at the rear.
文摘IN recent years, much progress has been made in the research of the temporal and spatial changes of East Asian monsoon. To research the environmental evolution and monsoon variations in Holocene in the region of Southwest China, a 310-cm continuous lake sediments core in Erhai Lake, Yunnan Province was sampled with Livingston sampler on July 6, 1996. The lake sediments were separated at 2-cm intervals and the core samples were analyzed with chronology, stable isotope ratios of organic carbon and diatoms determination. Three <sup>14</sup>C ages are （4 473±40）a B.P. （98—102 cm）, （5 825±85） a B. P. （144—148 cm） and （7 754±45） a B.P. （198—202 cm）. By <sup>137</sup>Cs dating, the sedimentation rate is about 0.3 mm/a and this result is close to the <sup>14</sup>C dating results. The average sedimentation rates
文摘nhanced silicate weathering induced by the uplift of the Himalayan-Tibetan Plateau(HTP)has been considered as the major cause of pCO_(2)decline and Cenozoic cooling.However,this hypothesis remains to be validated,largely due to the lack of a reliable reconstruction of the HTP weathering flux.Here,we present a 37-million-year record of the difference in the seawater radiogenic neodymium isotopic composition(△ε_(Nd))of Ocean Drilling Program(ODP)sites and Fe-Mn crusts between the northern and central Indian Ocean,which indicates the contribution of regional weathering input from the South Asian continent to the Indian Ocean.The results show a long-term increase in△ε_(Nd)and thus provide the first critical evidence of enhanced South Asian weathering input since the late Eocene.The evolution coincided well with major pulses of surface uplift in the HTP and global climatic transitions.Our foraminiferal eNd record suggests that tectonic uplift and silicate weathering in South Asia,especially in the Himalayas,might have played a significant role in the late Cenozoic cooling.
基金supported by the National Natural Science Foundation of China and Russian Foundation for Basic Research (FRBR) on “Formation, evolution and changes of Pleistocene cryogenic deposits in Eastern Asia” (Grant No. 41811530093)the Key Program of the Department of International Cooperation of the Chinese Academy of Sciences (Assessment of changes in permafrost in China, Russia and Mongolia and their impacts on key engineering infrastructures), (Permafrost extent in China during the Last Glaciation Maximum and Megathermal) of the Strategic Pilot Science and Technology Program of the Chinese Academy of Sciences (Grant No. XDA05120302)the CAS Overseas Professorship of Sergey S. Marchenko, and under the auspices of the International Permafrost Association Working Group on Global Permafrost Extent During the Last Permafrost Maximum (LPM)
文摘The formation and evolution of permafrost in China during the last 20 ka were reconstructed on the basis of large amount of paleo-permafrost remains and paleo-periglacial evidence, as well as paleo-glacial landforms, paleo-flora and paleofauna records. The results indicate that, during the local Last Glacial Maximum(LLGM) or local Last Permafrost Maximum(LLPMax), the extent of permafrost of China reached 5.3×106-5.4×106 km2, or thrice that of today, but permafrost shrank to only0.80×106-0.85×106 km2, or 50% that of present, during the local Holocene Megathermal Period(LHMP), or the local Last Permafrost Minimum(LLPMin). On the basis of the dating of periglacial remains and their distributive features, the extent of permafrost in China was delineated for the two periods of LLGM(LLPMax) and LHMP(LLPMin), and the evolution of permafrost in China was divided into seven periods as follows:(1) LLGM in Late Pleistocene(ca. 20000 to 13000-10800 a BP)with extensive evidence for the presence of intensive ice-wedge expansion for outlining its LLPMax extent;(2) A period of dramatically changing climate during the early Holocene(10800 to 8500-7000 a BP) when permafrost remained relatively stable but with a general trend of shrinking areal extent;(3) The LHMP in the Mid-Holocene(8500-7000 to 4000-3000 a BP)when permafrost degraded intensively and extensively, and shrank to the LLPMin;(4) Neoglaciation during the late Holocene(4000-3000 to 1000 a BP, when permafrost again expanded;(5) Medieval Warming Period(MWP) in the late Holocene(1000-500 a BP) when permafrost was in a relative decline;(6) Little Ice Age(LIA) in the late Holocene(500-100 a BP), when permafrost relatively expanded, and;(7) Recent warming(during the 20 th century), when permafrost continuously degraded and still is degrading. The paleo-climate, geography and paleopermafrost extents and other features were reconstructed for each of these seven periods.
