The structures of the mantle transition zone(MTZ)are of great significance for studying interactions of the subducted slab and deep mantle and related slab dynamics beneath subduction zones.Here by dense near-source S...The structures of the mantle transition zone(MTZ)are of great significance for studying interactions of the subducted slab and deep mantle and related slab dynamics beneath subduction zones.Here by dense near-source SdP sampling from a large global dataset,we image topographies of transition zone discontinuities such as the 410-km and 660-km discontinuities(410 and 660)beneath the Kamchatka and conduct cross-section comparisons with the seismicity.Compared with the IASP91 model,the 410 exhibits apparent uplifts of 45-65 km with an average of 55 km in a horizontal width of~130 km,corresponding to lowtemperature anomalies of 750-1083 K with an average of 916 K.In contrast,the 660 shows depressions of 15-37 km with an average of 25 km together with downward deflections in a width of~260 km,implying low-temperature anomalies of 161-397 K with an average of 268 K.Thus,we confirm a thickened MTZ with a thickness of 325-345 km around the cold descending Pacific slab.We suggest that topographic patterns of transition zone discontinuities imply a Pacific slab that has been significantly heated in the MTZ with broadened thermal effects on the 660.When considered along with other studies,we infer that the slab is possibly heated by hot mantle flows around the torn slab window extended to at least the MTZ range,thus inducing variations in thermal and rheological properties of the slab.Our seismic results can provide more insight into slab dynamics in the northwestern Pacific.展开更多
Melt inclusions in minerals from some volcanoes of the Kurile-Kamchatka region were examined.The studied basaltic andesites and andesites were sampled from volcanoes of the Central Kamchatka depression(Shiveluch and B...Melt inclusions in minerals from some volcanoes of the Kurile-Kamchatka region were examined.The studied basaltic andesites and andesites were sampled from volcanoes of the Central Kamchatka depression(Shiveluch and Bezymyannyi),Eastern Kamchatka volcanic belt(Avachinskii and Karymskii),and Iturup Island,Southern Kuriles(Kudryavyi).Basalts of the 1996 eruption of the Karymskii volcanic center and dacites of Dikii Greben'volcano,Southern Kamchatka were also studied.More than 260 melt inclusions from 31 rock samples were homogenized,and quenched glasses were analyzed using electron and ion microprobes.The compositions of melt inclusions in andesitic phenoerysts vary in silica contents from 56 to 80wt%.Al_2 O_3 ,FeO,MgO,CaO decrease and Na_2O and K_2O increase with increasing SiO_2.Many inclusions(about 80% )are dacitic or rhyolitic.However,the compositions of silicic glasses(>65wt% SiO_2)in andesites significantly differ in TiO2,FeO,MgO,CaO,and K_2O contents from those in dacites and rhyolites.High-potassium melts(K_2O 3.8～6.8wt% )with various SiO_2 from 51.4 to 77.2wt% were found in minerals of all volcanoes studied.This indicates a contribution of a component selectively enriched in potassium to magmas of the whole region.A great compositional diversity of melt inclusions in plagioelase phenocrysts from the Bezymyannyi andesites suggests a complex history of plagioclase crystallization and magma evolution in the andesite formation.Melts from different volcanoes strongly vary in volatile contents.The highest H_2O contents are found in the melts from Shiveluch(3.0～7.2wt%,4.7wt% on average)and Avachinskii (4.7～4.8wt%);while those are lower in melts of Kudryavyi(0.1～2.6wt% ),Dikii Greben'(0.4～1.8wt%),and Bezymyannyi (<1wt%).Chlorine contents are also variable.The lowest values are found in the Bezymyannyi melts(0.09wt% on average),the highest Cl contents are typical of melt inclusions in minerals from the Karymskii andesites(0.26wt% on average).The melts from Avachinskii,Dikii Greben',Kudryavyi,and Shiveluch show intermediate Cl contents(0.13～0.20wt% ).The pressure of 350～1600 bar determined by CO_2 fluid inclusions in plagioclase from the Shiveluch andesites suggests a magma chamber at a depth of 1.5～6 km. Concentrations of 17 elements were determined in glasses of melt inclusions in plagioclases from five volcanoes(Avachinskii, Bezymyannyi,Dikii Greben',Kudryavyi,and Shiveluch).The studied melts show similar trace-element patterns with Nb and Ti minima and B,K,Be,and Li maxima.The melts are close to typical island arc magmas by Sr/Y,La/Yb,K/Ti,and Ca/St ratios, and have some specific regional geochemical features.REE patterns sensitive to degree of magma differentiation indicate that Kudryavyi magmas are most primitive,while Shiveluch magmas are most evolved.展开更多
Materials deposited in low-temperature environments are characterized by their small particle size.The activity of microorganisms in aqueous sedimentary environments may have effective impacts on the geochemical
The great mantle plume debate(GPD) has been going on for ~15 years(Foulger and Natland, 2003;Anderson, 2004; Niu, 2005; Davies, 2005; Foulger, 2005; Campbell, 2005; Campbell and Davies, 2006),centered on whether mantl...The great mantle plume debate(GPD) has been going on for ~15 years(Foulger and Natland, 2003;Anderson, 2004; Niu, 2005; Davies, 2005; Foulger, 2005; Campbell, 2005; Campbell and Davies, 2006),centered on whether mantle plumes exist as a result of Earth's cooling or whether their existence is purely required for convenience in explaining certain Earth phenomena(Niu, 2005). Despite the mounting evidence that many of the so-called plumes may be localized melting anomalies, the debate is likely to continue. We recognize that the slow progress of the debate results from communication difficulties.Many debaters may not truly appreciate(1) what the mantle plume hypothesis actually is, and(2) none of the petrological, geochemical and geophysical methods widely used can actually provide smoking-gun evidence for or against mantle plume hypothesis. In this short paper, we clarify these issues, and elaborate a geologically effective approach to test the hypothesis. According to the mantle plume hypothesis, a thermal mantle plume must originate from the thermal boundary layer at the core-mantle boundary(CMB), and a large mantle plume head is required to carry the material from the deep mantle to the surface. The plume head product in ocean basins is the oceanic plateau, which is a lithospheric terrane that is large(1000's km across), thick(>200 km), shallow(2–4 km high above the surrounding seafloors), buoyant(~1% less dense than the surrounding lithosphere), and thus must be preserved in the surface geology(Niu et al., 2003). The Hawaiian volcanism has been considered as the surface expression of a type mantle plume, but it does not seem to have a(known) plume head product. If this is true, the Hawaiian mantle plume in particular and the mantle plume hypothesis in general must be questioned. Therefore, whether there is an oceanic plateau-like product for the Hawaiian volcanism is key to testing the mantle plume hypothesis, and the Kamchatka-Okhotsk Sea basement is the best candidate to find out if it is indeed the Hawaiian mantle plume head product or not(Niu et al., 2003; Niu, 2004).展开更多
Volcanic lakes in the Kuril-Kamchatka region are difficult to access,and for this reason,they remain poorly studied,with only scattered and brief data available.The authors have conducted a study of 10 lake basins usi...Volcanic lakes in the Kuril-Kamchatka region are difficult to access,and for this reason,they remain poorly studied,with only scattered and brief data available.The authors have conducted a study of 10 lake basins using modern digital echolocation survey techniques and have also compiled and summarized published data for 15 lakes in the region,calculating their main morphometric characteristics.It has been established that many caldera lake basins are modified by young explosive funnels,extrusive or effusive domes,and exhibit traces of hydrothermal activity.While lakes of the same genetic type in the Kuril-Kamchatka region are similar in depth and depression forms,the group of caldera lakes shows less homogeneity across all morphometric indicators.It was found that the absolute heights of the reservoirs on Kamchatka Peninsula are generally greater than those on the Kuril Islands,as is often the case with the size of their basins.The volcanic lakes under study can rapidly change their volume and shape under the influence of endogenous processes.For the first time for this region,on the base of repeated observations,underwater extrusive dome rate growth and the approximate rates of 2 lake level changes were calculated.Repeated observations of lakes in the Ksudach calderas(Kamchatka)and on Simushir Island indicate approximate rates of level changes:a decrease ranging within 0.5-0.6 m per year(over a 27-year observation interval)and an increase reaching up to 0.26 m per year(over a 48-year interval).The growth rate of the underwater extrusive dome in Lake Shtyubel has averaged 1-1.6 m per year over the past 25 years.This analysis has facilitated the first generalization regarding the morphology and developmental features of crater and caldera lakes in the Kuril-Kamchatka region of Russia,representing an important step in their study.The results obtained will provide a solid foundation for subsequent research in this region and may be of interest to researchers studying other volcanic lakes.展开更多
The purpose of this study was to estimate the Coniacian latitudinal thermal gradient in the Northern Hemisphere. Both hemipelagic （ammonoids） and benthic （brachiopods and bivalves） δ18O and δ^13C records were us...The purpose of this study was to estimate the Coniacian latitudinal thermal gradient in the Northern Hemisphere. Both hemipelagic （ammonoids） and benthic （brachiopods and bivalves） δ18O and δ^13C records were used. They originated from Coniacian shallow-water sequences across a wide range of paleolatitudes, from the Koryak upland （northern Kamchatka, Russian Far East） in the north, to Hokkaido （Japan） in the south. Among Coniacian ammonoids, both migrants from Hokkaido living in high latitudes （Kamchatka） and endemic forms dwelling in middle-low latitudes （Hokkaido） indicate seemingly close optimal growth temperatures. Nevertheless, certain differences in climatic conditions, prevailing during high-latitude coldest seasons, undoubtedly provoked growth cessation in some groups of ammonites. Our isotopic study suggests latitudinal temperature changes of only 0.12 ℃ per degree of latitude for the Northern Hemisphere in Coniacian times, while the average annual temperature in North Kamchatka seems about 3.3 ℃ lower than that in Hokkaido.展开更多
基金supported by the Central Public-interest Scientific Institution Basal Research Fund(No.CEAIEF 20220201)the National Natural Science Foundation of China(Nos.42374113 and 42074101)the Central Publicinterest Scientific Institution Basal Research Fund(No.CEAIEF20230204).
文摘The structures of the mantle transition zone(MTZ)are of great significance for studying interactions of the subducted slab and deep mantle and related slab dynamics beneath subduction zones.Here by dense near-source SdP sampling from a large global dataset,we image topographies of transition zone discontinuities such as the 410-km and 660-km discontinuities(410 and 660)beneath the Kamchatka and conduct cross-section comparisons with the seismicity.Compared with the IASP91 model,the 410 exhibits apparent uplifts of 45-65 km with an average of 55 km in a horizontal width of~130 km,corresponding to lowtemperature anomalies of 750-1083 K with an average of 916 K.In contrast,the 660 shows depressions of 15-37 km with an average of 25 km together with downward deflections in a width of~260 km,implying low-temperature anomalies of 161-397 K with an average of 268 K.Thus,we confirm a thickened MTZ with a thickness of 325-345 km around the cold descending Pacific slab.We suggest that topographic patterns of transition zone discontinuities imply a Pacific slab that has been significantly heated in the MTZ with broadened thermal effects on the 660.When considered along with other studies,we infer that the slab is possibly heated by hot mantle flows around the torn slab window extended to at least the MTZ range,thus inducing variations in thermal and rheological properties of the slab.Our seismic results can provide more insight into slab dynamics in the northwestern Pacific.
文摘Melt inclusions in minerals from some volcanoes of the Kurile-Kamchatka region were examined.The studied basaltic andesites and andesites were sampled from volcanoes of the Central Kamchatka depression(Shiveluch and Bezymyannyi),Eastern Kamchatka volcanic belt(Avachinskii and Karymskii),and Iturup Island,Southern Kuriles(Kudryavyi).Basalts of the 1996 eruption of the Karymskii volcanic center and dacites of Dikii Greben'volcano,Southern Kamchatka were also studied.More than 260 melt inclusions from 31 rock samples were homogenized,and quenched glasses were analyzed using electron and ion microprobes.The compositions of melt inclusions in andesitic phenoerysts vary in silica contents from 56 to 80wt%.Al_2 O_3 ,FeO,MgO,CaO decrease and Na_2O and K_2O increase with increasing SiO_2.Many inclusions(about 80% )are dacitic or rhyolitic.However,the compositions of silicic glasses(>65wt% SiO_2)in andesites significantly differ in TiO2,FeO,MgO,CaO,and K_2O contents from those in dacites and rhyolites.High-potassium melts(K_2O 3.8～6.8wt% )with various SiO_2 from 51.4 to 77.2wt% were found in minerals of all volcanoes studied.This indicates a contribution of a component selectively enriched in potassium to magmas of the whole region.A great compositional diversity of melt inclusions in plagioelase phenocrysts from the Bezymyannyi andesites suggests a complex history of plagioclase crystallization and magma evolution in the andesite formation.Melts from different volcanoes strongly vary in volatile contents.The highest H_2O contents are found in the melts from Shiveluch(3.0～7.2wt%,4.7wt% on average)and Avachinskii (4.7～4.8wt%);while those are lower in melts of Kudryavyi(0.1～2.6wt% ),Dikii Greben'(0.4～1.8wt%),and Bezymyannyi (<1wt%).Chlorine contents are also variable.The lowest values are found in the Bezymyannyi melts(0.09wt% on average),the highest Cl contents are typical of melt inclusions in minerals from the Karymskii andesites(0.26wt% on average).The melts from Avachinskii,Dikii Greben',Kudryavyi,and Shiveluch show intermediate Cl contents(0.13～0.20wt% ).The pressure of 350～1600 bar determined by CO_2 fluid inclusions in plagioclase from the Shiveluch andesites suggests a magma chamber at a depth of 1.5～6 km. Concentrations of 17 elements were determined in glasses of melt inclusions in plagioclases from five volcanoes(Avachinskii, Bezymyannyi,Dikii Greben',Kudryavyi,and Shiveluch).The studied melts show similar trace-element patterns with Nb and Ti minima and B,K,Be,and Li maxima.The melts are close to typical island arc magmas by Sr/Y,La/Yb,K/Ti,and Ca/St ratios, and have some specific regional geochemical features.REE patterns sensitive to degree of magma differentiation indicate that Kudryavyi magmas are most primitive,while Shiveluch magmas are most evolved.
基金financially supported by Research Grants Council of Hong Kong (HKU 703911P)
文摘Materials deposited in low-temperature environments are characterized by their small particle size.The activity of microorganisms in aqueous sedimentary environments may have effective impacts on the geochemical
基金supported by the National Natural Science Foundation of China (41130314, 41630968)Chinese Academy of Sciences Innovation (Y42217101L)+1 种基金grants from Qingdao National Laboratory for Marine Science and Technology (2015ASKJ03)the NSFC-Shandong Joint Fund for Marine Science Research Centers (U1606401)
文摘The great mantle plume debate(GPD) has been going on for ~15 years(Foulger and Natland, 2003;Anderson, 2004; Niu, 2005; Davies, 2005; Foulger, 2005; Campbell, 2005; Campbell and Davies, 2006),centered on whether mantle plumes exist as a result of Earth's cooling or whether their existence is purely required for convenience in explaining certain Earth phenomena(Niu, 2005). Despite the mounting evidence that many of the so-called plumes may be localized melting anomalies, the debate is likely to continue. We recognize that the slow progress of the debate results from communication difficulties.Many debaters may not truly appreciate(1) what the mantle plume hypothesis actually is, and(2) none of the petrological, geochemical and geophysical methods widely used can actually provide smoking-gun evidence for or against mantle plume hypothesis. In this short paper, we clarify these issues, and elaborate a geologically effective approach to test the hypothesis. According to the mantle plume hypothesis, a thermal mantle plume must originate from the thermal boundary layer at the core-mantle boundary(CMB), and a large mantle plume head is required to carry the material from the deep mantle to the surface. The plume head product in ocean basins is the oceanic plateau, which is a lithospheric terrane that is large(1000's km across), thick(>200 km), shallow(2–4 km high above the surrounding seafloors), buoyant(~1% less dense than the surrounding lithosphere), and thus must be preserved in the surface geology(Niu et al., 2003). The Hawaiian volcanism has been considered as the surface expression of a type mantle plume, but it does not seem to have a(known) plume head product. If this is true, the Hawaiian mantle plume in particular and the mantle plume hypothesis in general must be questioned. Therefore, whether there is an oceanic plateau-like product for the Hawaiian volcanism is key to testing the mantle plume hypothesis, and the Kamchatka-Okhotsk Sea basement is the best candidate to find out if it is indeed the Hawaiian mantle plume head product or not(Niu et al., 2003; Niu, 2004).
基金support of the State Assignments of the Institute of Marine Geology and Geophysics,Far Eastern Branch of the Russian Academy of Sciences and the Institute of Geography of the Russian Academy of Sciences(FMWS-2024-0005).
文摘Volcanic lakes in the Kuril-Kamchatka region are difficult to access,and for this reason,they remain poorly studied,with only scattered and brief data available.The authors have conducted a study of 10 lake basins using modern digital echolocation survey techniques and have also compiled and summarized published data for 15 lakes in the region,calculating their main morphometric characteristics.It has been established that many caldera lake basins are modified by young explosive funnels,extrusive or effusive domes,and exhibit traces of hydrothermal activity.While lakes of the same genetic type in the Kuril-Kamchatka region are similar in depth and depression forms,the group of caldera lakes shows less homogeneity across all morphometric indicators.It was found that the absolute heights of the reservoirs on Kamchatka Peninsula are generally greater than those on the Kuril Islands,as is often the case with the size of their basins.The volcanic lakes under study can rapidly change their volume and shape under the influence of endogenous processes.For the first time for this region,on the base of repeated observations,underwater extrusive dome rate growth and the approximate rates of 2 lake level changes were calculated.Repeated observations of lakes in the Ksudach calderas(Kamchatka)and on Simushir Island indicate approximate rates of level changes:a decrease ranging within 0.5-0.6 m per year(over a 27-year observation interval)and an increase reaching up to 0.26 m per year(over a 48-year interval).The growth rate of the underwater extrusive dome in Lake Shtyubel has averaged 1-1.6 m per year over the past 25 years.This analysis has facilitated the first generalization regarding the morphology and developmental features of crater and caldera lakes in the Kuril-Kamchatka region of Russia,representing an important step in their study.The results obtained will provide a solid foundation for subsequent research in this region and may be of interest to researchers studying other volcanic lakes.
基金supported by the International Field Expedition Programme of Japan (No. 10041109)DVO RAN (No. 09-III-A-08-402)
文摘The purpose of this study was to estimate the Coniacian latitudinal thermal gradient in the Northern Hemisphere. Both hemipelagic （ammonoids） and benthic （brachiopods and bivalves） δ18O and δ^13C records were used. They originated from Coniacian shallow-water sequences across a wide range of paleolatitudes, from the Koryak upland （northern Kamchatka, Russian Far East） in the north, to Hokkaido （Japan） in the south. Among Coniacian ammonoids, both migrants from Hokkaido living in high latitudes （Kamchatka） and endemic forms dwelling in middle-low latitudes （Hokkaido） indicate seemingly close optimal growth temperatures. Nevertheless, certain differences in climatic conditions, prevailing during high-latitude coldest seasons, undoubtedly provoked growth cessation in some groups of ammonites. Our isotopic study suggests latitudinal temperature changes of only 0.12 ℃ per degree of latitude for the Northern Hemisphere in Coniacian times, while the average annual temperature in North Kamchatka seems about 3.3 ℃ lower than that in Hokkaido.
基金supported by the NSF Microbial Observatory Program(JW CRS)the Environmental Remediation Sciences Division of the Office of Biological and Environmental Research,U.S.+1 种基金Department of Energy through the Financial As-sistant Award no.DE-FC09-96SR 18546 to the Univer-sity of Georgia Research Foundation(CSR,CM,and CLZ)supported by the Education Department of Jiangsu Province for Geo-chemistry discipline construction.
