Pozzolans from the Tombel Plain,Bamileke Plateau,and Noun Plain,3 monogenetic volcanic fields in the central part of the Cameroon Volcanic Line(the Tombel Plain,Bamileke Plateau,and Noun Plain),were explored in order ...Pozzolans from the Tombel Plain,Bamileke Plateau,and Noun Plain,3 monogenetic volcanic fields in the central part of the Cameroon Volcanic Line(the Tombel Plain,Bamileke Plateau,and Noun Plain),were explored in order to constrain their petrology and make some predictions on their pozzolanicity.The rocks in this study include alkaline and subalkaline basalts,trachybasalts,and basanites.Most of these rocks present an overall composition that overlaps with primitive mantle,suggesting rapid ascent of magmas,limited crustal contamination and crystal fractionation of olivine,clinopyroxene,and feldspar.The pozzolans present enrichment of LREE relative to HREE and high chondrite normalized ratios of La/Yb and Tb/Yb.ranging between 7 and 20 and>1.9 respectively,similar to those of Ocean Island Basalts.Like other nearby volcanoes,partial melting in a dominantly garnet-bearing mantle zone can be assumed.Quantitative mineralogy by X-ray diffraction revealed various mineral phases with dominantly plagioclase,augite,olivine,and Fe-Ti oxides.The samples contains important amorphous phase up to 23,51,and 69 wt%in the Tombel Plain,Noun Plain,and Bamileke Plateau,respectively.This elevated amount of amorphous phases together with the sum of SiO2,Al2O3 and total Fe2O3(SAI=68.50-83.50>70 wt%)according to ASTM C618 standard and the sum of CaO,FeO,and MgO(CIM=14.5-30.52 wt%and 23.58-31.08 wt%)suggest interesting pozzolanicity character for the studied pozzolans.展开更多
The Tengchong volcano field(TVF),situated at the southeastern margin of the Tibetan Plateau,holds crucial information regarding Cenozoic volcanic activities and geotectonic evolution of the SE Xizang.To provide new co...The Tengchong volcano field(TVF),situated at the southeastern margin of the Tibetan Plateau,holds crucial information regarding Cenozoic volcanic activities and geotectonic evolution of the SE Xizang.To provide new constraints on petrogenesis and evolution of the Tengchong volcanism,here we conducted copper(Cu)elemental and isotopic analyses on a suite of samples that document the evolution from basalts to andesites in the TVF.The basalts are Cu-depleted(29.7-36.9 ppm)and have higherδ^(65)Cu val-ues(0.19‰-0.40‰,mean=0.31‰±0.05‰;n=11)than those of mid-ocean ridge basalts(MORBs,~0.09‰)and the mantle(~0.06‰)as well as the majority of island arc lavas.Along with the low Cu/Zr ratios,these characteristics are interpreted to reflect the fractionation of isotopically light sulfides in the S-saturated systems during magma ascent,rather than source heterogeneity induced by recycled materials and redox reactions.Compared with the basalts,the andesites have slightly lower Cu contents(14.4-29.4 ppm)and lighter Cu isotopic compositions(mean=-0.14‰±0.06‰;n=13).These differences cannot be attributed to progressive sulfide fractionation of basaltic magmas but require the assimilation of lower crustal materials with lowδ^(65)Cu values during evolution of the andesitic magmas.Our results collectively suggest that Cu isotopes can provide valuable insights into magma origin and evolution.展开更多
Objective The Tengchong volcanic field is situated along the southeastern margin of the Tibetan Plateau and adjacent to the border area of western Yunnan Province of China and Myanmar.Affected by the intense tectonic ...Objective The Tengchong volcanic field is situated along the southeastern margin of the Tibetan Plateau and adjacent to the border area of western Yunnan Province of China and Myanmar.Affected by the intense tectonic stress of subduction of the Indian plate to Eurasian plate,this volcanic field has experienced strong volcanism.展开更多
The Wadi Natash volcanic field(WNVF)in the south of the Eastern Desert of Egypt is a typical example of well-preserved intraplate alkaline magmatism during the Late Cretaceous,i.e.,prior to the Oligo-Miocene Red Sea r...The Wadi Natash volcanic field(WNVF)in the south of the Eastern Desert of Egypt is a typical example of well-preserved intraplate alkaline magmatism during the Late Cretaceous,i.e.,prior to the Oligo-Miocene Red Sea rift.We compiled stratigraphic sections at two sectors;namely East Gabal Nuqra and West Khashm Natash(WKN)where the volcanic flows are intercalated with the Turonian Abu Agag sandstone with occasional paleosols when volcanic activity is intermittent.Peridotite mantle xenoliths are encountered in the first sector whereas flows in the second sector are interrupted by trachyte plugs and ring dykes.On a geochemical basis,the maifc melt originating from the lithospheric mantle beneath the WNVF practiced~5%partial melting of phlogopite-bearing garnet peridotite.Basalts dominate in the two sectors and highly evolved(silicic)rocks are confined to the WKN sector.Rejuvenation of ancient Precambrian fractures following the NW-SE and ENE-WSW trends facilitated the ascend of Late Cretaceous mantle-derived alkaline magma.Structurally,the WNVF developed at the eastern shoulder of the so-called"Kom Ombo-Nuqra-Kharit rift system"that represents a well-defined NW-trending intracontinental rift basin in the southern Eastern Desert.In such a structural setup,the Natash volcanic are confined to half-grabens at the East Gabal Nuqra sector whereas the West Khashm Natash sector is subjected to extensional stresses that propagated eastwards.The WNVF is a typical example of fluvial clastics(Turonian)intercalation with rift-related alkaline volcanic rocks in northeast Africa.展开更多
Seismicity in northern Arizona is concentrated in a northwest-southeast trending belt that stretches from the Utah border south to the edge of the Colorado Plateau. Located within this NASB （Northern Arizona Seismic ...Seismicity in northern Arizona is concentrated in a northwest-southeast trending belt that stretches from the Utah border south to the edge of the Colorado Plateau. Located within this NASB （Northern Arizona Seismic Belt） is the San Francisco volcanic field, classified by the United States Geological Survey as potentially active. The last volcanic event in the field was located at Sunset Crater and occurred less than 1,000 years ago. Eruption intervals in the volcanic field are of the same order of length of time. Seismic monitoring of the volcanic field area has improved greatly since 1985 with the establishment of new network seismic stations. This has allowed for a lowered threshold of detection of seismic events and improved location capabilities. As an example of the result of this improved ability to locate smaller tremors, two swarms have been identified in the field, the 2009 Halloween swarm near Sunset Crater volcano and the 2011 swarm near Flagstaff, the largest urban community in northern Arizona.展开更多
Volcanic eruptions potentially threaten local and global environments,making it crucial to reconstruct their eruption history for risk assessments and forecasts.However,accurately dating of young(e.g.,Holocene)volcano...Volcanic eruptions potentially threaten local and global environments,making it crucial to reconstruct their eruption history for risk assessments and forecasts.However,accurately dating of young(e.g.,Holocene)volcanoes remains challenging.For example,K-Ar and^(40)Ar/^(39)Ar dating are potentially problematic due to the long half-lives of radioisotopes,while radiocarbon dating requires organic materials.The study used optically stimulated luminescence(OSL)dating on quartz to accurately constrain the ages of lava-baked sediments from the Tengchong volcanic field,southeastern margin of the Tibetan Plateau.The results show two types of quartz OSL characteristics in the initial OSL signals.The first type,dominated by the fast component,yields reliable OSL ages.In contrast,the second type,dominated by the medium component,shows a negative correlation between equivalent dose(D_(e))and recuperation,and a decreasing trend in D_(e)over illumination time,providing the underestimated ages due to the influence of the unstable medium component.These underestimated OSL ages are corrected using the D_(e)-recuperation plot.Combining with previous chronological studies,we conclude that Tengchong volcanoes have erupted at least seven times during the Holocene,occurring at 11.6–11.1,≤11.4–10.3,5.9–5.7,5.0–4.8,3.5–2.5,2.0 thousand years ago,and1609 AD.D_(e)spite the current stability of the Tengchong volcanoes,frequent tectonic activities,eruptive history,and the presence of active magma chambers suggest the potential for future volcanic eruptions.展开更多
So far,the nature and evolution of the lower crust under central Spain have been constrained mainly on the basis of a heterogeneous suite of granulite xenoliths from the Spanish Central System(SCS).In recent years,ult...So far,the nature and evolution of the lower crust under central Spain have been constrained mainly on the basis of a heterogeneous suite of granulite xenoliths from the Spanish Central System(SCS).In recent years,ultramafic volcanics from the Calatrava Volcanic Field(CVF)have also provided deep-seated crustal xenoliths which have not been studied in detail.Our data,combining mineral,whole-rock and isotopic geochemistry with U–Pb–Hf isotope ratios in zircons from the CVF and SCS xenoliths,highlight the felsic composition of the lower crust under central Iberia.A number of the Calatrava xenoliths represents Variscan igneous protoliths,which are a minor population in the SCS,and were likely formed by crystallisation of intermediate and felsic melts in the lower crust during the Variscan orogeny(leucodiorite protolith age of 314±3 Ma and leucogranite protolith age of 308±2.5 Ma).U–Pb data of metamorphic zircons show that granulite-facies metamorphism mainly occurred from 299 to 285 Ma in both areas.These ages are slightly younger than those of granitic intrusions that could be genetically related to the granulitic residue,which points to a main role of U–Pb isotope resetting in lower crustal zircons during HT or UHT conditions.The zircon U–Pb–Hf isotopic ratios support the idea that the lower crust in central Iberia consists mainly of Ordovician–Neoproterozoic metaigneous and metasedimentary rocks associated with the Cadomian continental arc of northern Gondwana.These rocks provide evidence of mixing between juvenile magmas and an enriched crustal component,ultimately extracted from an Eburnean crust.Other more evolved components present in detrital zircons are likely related to recycling of Archean crust derived from North Africa cratonic terranes.展开更多
基金Authors are thankful to the ISTerre of Grenoble(France)and Nathaniel Findling for hosting and training the first author on the XRD technique and Rietveld method interpretation as part of his Ph.D.research work.The authors are also thankful to the Ministry of Higher Education of Cameroon for providing Research Modernization Allowance(RMA)that has been very helpful to support part of the field trip and Geochemical analysis expenses.
文摘Pozzolans from the Tombel Plain,Bamileke Plateau,and Noun Plain,3 monogenetic volcanic fields in the central part of the Cameroon Volcanic Line(the Tombel Plain,Bamileke Plateau,and Noun Plain),were explored in order to constrain their petrology and make some predictions on their pozzolanicity.The rocks in this study include alkaline and subalkaline basalts,trachybasalts,and basanites.Most of these rocks present an overall composition that overlaps with primitive mantle,suggesting rapid ascent of magmas,limited crustal contamination and crystal fractionation of olivine,clinopyroxene,and feldspar.The pozzolans present enrichment of LREE relative to HREE and high chondrite normalized ratios of La/Yb and Tb/Yb.ranging between 7 and 20 and>1.9 respectively,similar to those of Ocean Island Basalts.Like other nearby volcanoes,partial melting in a dominantly garnet-bearing mantle zone can be assumed.Quantitative mineralogy by X-ray diffraction revealed various mineral phases with dominantly plagioclase,augite,olivine,and Fe-Ti oxides.The samples contains important amorphous phase up to 23,51,and 69 wt%in the Tombel Plain,Noun Plain,and Bamileke Plateau,respectively.This elevated amount of amorphous phases together with the sum of SiO2,Al2O3 and total Fe2O3(SAI=68.50-83.50>70 wt%)according to ASTM C618 standard and the sum of CaO,FeO,and MgO(CIM=14.5-30.52 wt%and 23.58-31.08 wt%)suggest interesting pozzolanicity character for the studied pozzolans.
基金supported by the National Natural Science Foundation of China(grant 42121002)the National Key R&D Program of China(2019YFA0708400).
文摘The Tengchong volcano field(TVF),situated at the southeastern margin of the Tibetan Plateau,holds crucial information regarding Cenozoic volcanic activities and geotectonic evolution of the SE Xizang.To provide new constraints on petrogenesis and evolution of the Tengchong volcanism,here we conducted copper(Cu)elemental and isotopic analyses on a suite of samples that document the evolution from basalts to andesites in the TVF.The basalts are Cu-depleted(29.7-36.9 ppm)and have higherδ^(65)Cu val-ues(0.19‰-0.40‰,mean=0.31‰±0.05‰;n=11)than those of mid-ocean ridge basalts(MORBs,~0.09‰)and the mantle(~0.06‰)as well as the majority of island arc lavas.Along with the low Cu/Zr ratios,these characteristics are interpreted to reflect the fractionation of isotopically light sulfides in the S-saturated systems during magma ascent,rather than source heterogeneity induced by recycled materials and redox reactions.Compared with the basalts,the andesites have slightly lower Cu contents(14.4-29.4 ppm)and lighter Cu isotopic compositions(mean=-0.14‰±0.06‰;n=13).These differences cannot be attributed to progressive sulfide fractionation of basaltic magmas but require the assimilation of lower crustal materials with lowδ^(65)Cu values during evolution of the andesitic magmas.Our results collectively suggest that Cu isotopes can provide valuable insights into magma origin and evolution.
基金supported by the National Science Foundation of China(grant No.41472305)Special Project of China Earthquake Administration(grant No. 201108001)
文摘Objective The Tengchong volcanic field is situated along the southeastern margin of the Tibetan Plateau and adjacent to the border area of western Yunnan Province of China and Myanmar.Affected by the intense tectonic stress of subduction of the Indian plate to Eurasian plate,this volcanic field has experienced strong volcanism.
文摘The Wadi Natash volcanic field(WNVF)in the south of the Eastern Desert of Egypt is a typical example of well-preserved intraplate alkaline magmatism during the Late Cretaceous,i.e.,prior to the Oligo-Miocene Red Sea rift.We compiled stratigraphic sections at two sectors;namely East Gabal Nuqra and West Khashm Natash(WKN)where the volcanic flows are intercalated with the Turonian Abu Agag sandstone with occasional paleosols when volcanic activity is intermittent.Peridotite mantle xenoliths are encountered in the first sector whereas flows in the second sector are interrupted by trachyte plugs and ring dykes.On a geochemical basis,the maifc melt originating from the lithospheric mantle beneath the WNVF practiced~5%partial melting of phlogopite-bearing garnet peridotite.Basalts dominate in the two sectors and highly evolved(silicic)rocks are confined to the WKN sector.Rejuvenation of ancient Precambrian fractures following the NW-SE and ENE-WSW trends facilitated the ascend of Late Cretaceous mantle-derived alkaline magma.Structurally,the WNVF developed at the eastern shoulder of the so-called"Kom Ombo-Nuqra-Kharit rift system"that represents a well-defined NW-trending intracontinental rift basin in the southern Eastern Desert.In such a structural setup,the Natash volcanic are confined to half-grabens at the East Gabal Nuqra sector whereas the West Khashm Natash sector is subjected to extensional stresses that propagated eastwards.The WNVF is a typical example of fluvial clastics(Turonian)intercalation with rift-related alkaline volcanic rocks in northeast Africa.
文摘Seismicity in northern Arizona is concentrated in a northwest-southeast trending belt that stretches from the Utah border south to the edge of the Colorado Plateau. Located within this NASB （Northern Arizona Seismic Belt） is the San Francisco volcanic field, classified by the United States Geological Survey as potentially active. The last volcanic event in the field was located at Sunset Crater and occurred less than 1,000 years ago. Eruption intervals in the volcanic field are of the same order of length of time. Seismic monitoring of the volcanic field area has improved greatly since 1985 with the establishment of new network seismic stations. This has allowed for a lowered threshold of detection of seismic events and improved location capabilities. As an example of the result of this improved ability to locate smaller tremors, two swarms have been identified in the field, the 2009 Halloween swarm near Sunset Crater volcano and the 2011 swarm near Flagstaff, the largest urban community in northern Arizona.
基金supported by the Research Grant Council of the Hong Kong Special Administrative Region,China(Grant No.17309121)the National Natural Science Foundation of China(Grant No.41303080)+1 种基金the Youth Innovation Promotion Association CAS(Grant No.2018499)the USTC Research Funds of the Double First-Class Initiative(Grant No.YD2110002027)。
文摘Volcanic eruptions potentially threaten local and global environments,making it crucial to reconstruct their eruption history for risk assessments and forecasts.However,accurately dating of young(e.g.,Holocene)volcanoes remains challenging.For example,K-Ar and^(40)Ar/^(39)Ar dating are potentially problematic due to the long half-lives of radioisotopes,while radiocarbon dating requires organic materials.The study used optically stimulated luminescence(OSL)dating on quartz to accurately constrain the ages of lava-baked sediments from the Tengchong volcanic field,southeastern margin of the Tibetan Plateau.The results show two types of quartz OSL characteristics in the initial OSL signals.The first type,dominated by the fast component,yields reliable OSL ages.In contrast,the second type,dominated by the medium component,shows a negative correlation between equivalent dose(D_(e))and recuperation,and a decreasing trend in D_(e)over illumination time,providing the underestimated ages due to the influence of the unstable medium component.These underestimated OSL ages are corrected using the D_(e)-recuperation plot.Combining with previous chronological studies,we conclude that Tengchong volcanoes have erupted at least seven times during the Holocene,occurring at 11.6–11.1,≤11.4–10.3,5.9–5.7,5.0–4.8,3.5–2.5,2.0 thousand years ago,and1609 AD.D_(e)spite the current stability of the Tengchong volcanoes,frequent tectonic activities,eruptive history,and the presence of active magma chambers suggest the potential for future volcanic eruptions.
基金The LA-ICPMS laboratory at the University of Johannesburg was funded by NRF-NEP grant#93208supported by PPM and the CoE DSI-NRF CIMERAsupported by,the PID2020-115980 GB-I00 research project of the Ministerio de Ciencia e Innovación of Spain.
文摘So far,the nature and evolution of the lower crust under central Spain have been constrained mainly on the basis of a heterogeneous suite of granulite xenoliths from the Spanish Central System(SCS).In recent years,ultramafic volcanics from the Calatrava Volcanic Field(CVF)have also provided deep-seated crustal xenoliths which have not been studied in detail.Our data,combining mineral,whole-rock and isotopic geochemistry with U–Pb–Hf isotope ratios in zircons from the CVF and SCS xenoliths,highlight the felsic composition of the lower crust under central Iberia.A number of the Calatrava xenoliths represents Variscan igneous protoliths,which are a minor population in the SCS,and were likely formed by crystallisation of intermediate and felsic melts in the lower crust during the Variscan orogeny(leucodiorite protolith age of 314±3 Ma and leucogranite protolith age of 308±2.5 Ma).U–Pb data of metamorphic zircons show that granulite-facies metamorphism mainly occurred from 299 to 285 Ma in both areas.These ages are slightly younger than those of granitic intrusions that could be genetically related to the granulitic residue,which points to a main role of U–Pb isotope resetting in lower crustal zircons during HT or UHT conditions.The zircon U–Pb–Hf isotopic ratios support the idea that the lower crust in central Iberia consists mainly of Ordovician–Neoproterozoic metaigneous and metasedimentary rocks associated with the Cadomian continental arc of northern Gondwana.These rocks provide evidence of mixing between juvenile magmas and an enriched crustal component,ultimately extracted from an Eburnean crust.Other more evolved components present in detrital zircons are likely related to recycling of Archean crust derived from North Africa cratonic terranes.
