It is widely acknowledged that olivine-hosted melt inclusions retain compositional information un... more It is widely acknowledged that olivine-hosted melt inclusions retain compositional information unavailable from the study of bulk-rock samples alone. Whether or not the compositions of melt inclusions are truly representative of geologically significant melt bodies has, however, been called into question; isotopic data are critical to resolving this debate but the rare existing data are contradictory. Previous studies of Pb
Multi-stage formation of tourmaline occurs in the Hnilec granite-related hydrothermal tin mineral... more Multi-stage formation of tourmaline occurs in the Hnilec granite-related hydrothermal tin mineralisation system from the Western Carpathians, Slovakia. The tourmalines belong to the schorl-dravite series and have two major stages of formation: the majority crystallized during the first stage (defined as M-stage), forming zoned tourmaline crystals with the cores being generally more Fe, Al, and Mn rich than the rims. During the second stage (defined as L-stage), tourmaline formed as small veins or irregular patches along fractures and cracks in the M-stage tourmaline grains. In the contact metapelites near the granite body, the L-stage tourmalines are more Mg-rich and Fe, Al, Mn depleted than the M-stage tourmalines. In the granites, the L-stage tourmalines have generally similar compositions to those of the M-stage tourmaline rims. The boron isotopic compositions of the M-stage tourmalines vary from −10.3‰ to −15.4‰; with no clear variation between the cores and the rims, however, some of the tourmaline grains from the contact metapelites show a slightly higher δ 11 B in the cores than in the rims. The L-stage tourmalines have lower δ 11 B value of −16.0‰ to −17.1‰. We suggest that these trends reflect a changing fluid source from a dominant magmatic-hydrothermal fluid derived from the granites to a late-stage metamorphic fluid derived from the regional metamorphism (chlorite and biotite zone) in the metapelites. The significantly higher Fe 3+ in the L-stage than the M-stage tourmalines reflect changing redox conditions towards a more oxidising environment. This redox condition change may have important implications for the hydrothermal tin mineralisation in the area.
It is widely acknowledged that olivine-hosted melt inclusions retain compositional information un... more It is widely acknowledged that olivine-hosted melt inclusions retain compositional information unavailable from the study of bulk-rock samples alone. Whether or not the compositions of melt inclusions are truly representative of geologically significant melt bodies has, however, been called into question; isotopic data are critical to resolving this debate but the rare existing data are contradictory. Previous studies of Pb
... 500C. The calculated cooling rate, assuming a garnet SmNd clo sure temperature similar to tha... more ... 500C. The calculated cooling rate, assuming a garnet SmNd clo sure temperature similar to that of hornblende to Ar MAH Maboko, E. Nakamura Precambrian Research 74 (1995) 195202 201 diffusion, is about 23C Ma. This ...
In order to facilitate the understanding of the geological evolution of the Kalahari Craton and i... more In order to facilitate the understanding of the geological evolution of the Kalahari Craton and its relation to South America, the provenance of the first large-scale cratonic cover sequence of the craton,
While exposure to fibers and particles has been proposed to be associated with several different ... more While exposure to fibers and particles has been proposed to be associated with several different lung malignancies including mesothelioma, the mechanism for the carcinogenesis is not fully understood. Along with mineralogical observation, we have analyzed forty-four major and trace elements in extracted asbestos bodies (fibers and proteins attached to them) with coexisting fiber-free ferruginous protein bodies from extirpative lungs of individuals with malignant mesothelioma. These observations together with patients' characteristics suggest that inhaled iron-rich asbestos fibers and dust particles, and excess iron deposited by continuous cigarette smoking would induce ferruginous protein body formation resulting in ferritin aggregates in lung tissue. Chemical analysis of ferruginous protein bodies extracted from lung tissues reveals anomalously high concentrations of radioactive radium, reaching millions of times higher concentration than that of seawater. Continuous and prolonged internal exposure to hotspot ionizing radiation from radium and its daughter nuclides could cause strong and frequent DNA damage in lung tissue, initiate different types of tumour cells, including malignant mesothelioma cells, and may cause cancers.
Proceedings of the Japan Academy. Ser. B: Physical and Biological Sciences, 1995
In order to examine the behavior of elements under the control of aqueous fluid through slab-mant... more In order to examine the behavior of elements under the control of aqueous fluid through slab-mantle interactions, a series of high-pressure and high-temperature experiments was carried out at
AT convergent margins, the subducting oceanic slab is thought to dehydrate, producing fluids whic... more AT convergent margins, the subducting oceanic slab is thought to dehydrate, producing fluids which metasomatize the overlying mantle wedge where island-arc magma forms. However, the nature and origin of the metasomatizing fluid, its source composition and its relation to the genesis of the chemical characteristics of arc magmas are largely controversial. Across-arc variation in the chemistry of arc lavas provides
Multi-stage formation of tourmaline occurs in the Hnilec granite-related hydrothermal tin mineral... more Multi-stage formation of tourmaline occurs in the Hnilec granite-related hydrothermal tin mineralisation system from the Western Carpathians, Slovakia. The tourmalines belong to the schorl-dravite series and have two major stages of formation: the majority crystallized during the first stage (defined as M-stage), forming zoned tourmaline crystals with the cores being generally more Fe, Al, and Mn rich than the rims. During the second stage (defined as L-stage), tourmaline formed as small veins or irregular patches along fractures and cracks in the M-stage tourmaline grains. In the contact metapelites near the granite body, the L-stage tourmalines are more Mg-rich and Fe, Al, Mn depleted than the M-stage tourmalines. In the granites, the L-stage tourmalines have generally similar compositions to those of the M-stage tourmaline rims. The boron isotopic compositions of the M-stage tourmalines vary from −10.3‰ to −15.4‰; with no clear variation between the cores and the rims, however, some of the tourmaline grains from the contact metapelites show a slightly higher δ 11 B in the cores than in the rims. The L-stage tourmalines have lower δ 11 B value of −16.0‰ to −17.1‰. We suggest that these trends reflect a changing fluid source from a dominant magmatic-hydrothermal fluid derived from the granites to a late-stage metamorphic fluid derived from the regional metamorphism (chlorite and biotite zone) in the metapelites. The significantly higher Fe 3+ in the L-stage than the M-stage tourmalines reflect changing redox conditions towards a more oxidising environment. This redox condition change may have important implications for the hydrothermal tin mineralisation in the area.
Journal of Mineralogical and Petrological Sciences, 2008
Eclogites of the Kaghan valley, Pakistan Himalaya were investigated petrographically and geochemi... more Eclogites of the Kaghan valley, Pakistan Himalaya were investigated petrographically and geochemically. Based on petrography, geochemistry and mineral compositions, metamorphic history and a reasonable tectonic model are proposed. Eclogites exposed in the Kaghan valley are classified into two groups. Group I eclogites appear as massive and Group II are lenstype. Group I eclogites have a mineral assemblage of garnet, omphacitic clinopyroxene, quartz, symplectite with rare epidote and phengite. Accessory minerals include abundant zircon, rutile, ilmenite, and rare apatite. Group II eclogites have a mineral assemblage of garnet, omphacitic clinopyroxene, phengite, quartz/coesite, epidote, and symplectite. In accessory minerals rutile and ilmenite are common while zircon and apatite are rare. Different types of protolith are proposed for these eclogites. Group I eclogites have higher FeO and TiO 2 contents and trace element contents, and seem to be derived from gabbroic protolith. Group II eclogites have lower FeO and TiO 2 and trace element contents and were derived from basalts. Pressuretemperaturetime path was constructed for the Kaghan valley eclogites using various mineral assemblages along with textural relationship and inclusions study. At least three distinct metamorphic stages were identified. The first stage is the prograde garnet growth stage deduced from the inclusion paragenesis in garnet core. The second stage records the ultrahighpressure metamorphic stage deduced from the presence of coesite inclusions in omphacitic clinopyroxene. The third stage is the decompression stage and is deduced from the quartzalbiteamphibole symplectite portions. These petrological and geochemical results combined with isotopic ages reported elsewhere indicate that basalts and associated gabbroic dikes were emplaced at about 267 Ma when the Indian plate was moving northward and passing above an unknown hot spot. The closure of the Tethys and initiation of collision of the Indian plate with the Kohistan -Ladakh Island Arc is reported from 65 -50 Ma. After that the leadingedge of the Indian plate underwent eclogite facies metamorphism at 49 Ma and when it reached to depths of about 100 km, the ultrahighpressure metamorphic event took place at 46 Ma.
Isotopic compositions of Pb, Sr, and Nd and concentrations of trace elements were determined for ... more Isotopic compositions of Pb, Sr, and Nd and concentrations of trace elements were determined for Quaternary island arc basaltic rocks from northeastern Japan. Sr and Pb isotopic ratios decrease, and Nd isotopic ratios increase from the volcanic front toward the back arc. The isotopic compositions nearest the back arc side are nearly identical to those of mid-ocean ridge basalt (MORB). The high field strength elements and heavy rare earth elements show homogeneous and MORB-like characteristics. These observations indicate that the mantle wedge beneath northeastern Japan originally had a MORB-type mantle composition that was homogeneous across the arc. Pb isotope compositions show a mixing relationship between mantle wedge and oceanic sediments reflecting the introduction of subduction component into the mantle wedge. Across-arc isotopic variations were caused by interaction between MORB-type mantle wedge and the subducting slab, and the amount of subduction component correlates with the depth to the slab. The isotopic compositions of subduction component are expressed by bulk mixing of 15 wt % of oceanic sediment and 85 wt % of altered MORB. Inversion analyses of isotopic compositions using two-component mixing relationships show that the Sr/Nd and Pb/Nd ratios in subduction component decrease with increasing depth to the slab, while the Sr/Pb ratio is nearly constant. These changes can be explained only by a preferential discharge of the elements into the wedge mantle associated with continuous dehydration of the subducting slab. The present study further demonstrates that a very wide range of isotopic and elemental compositions in island arc magmas is a consequence of the interaction between subducting slab and mantle wedge without the involvement of an oceanic island basalts component, and the slab can carry water and supply a subduction component as a fluid to the overlying mantle wedge to depths exceeding 150 km. introduction The nature of the subducting slab, including oceanic crus• and oceanic sediment, has been a focus of attention since ,4rmstrong [1968] because it is critical to understanding mantle-crust recycling. The subduction process is a unique mechanism whereby crustal components can be introduced back into the mantic, and therefore investigation of the interaction between subducting slab and mantle wedge is important for understanding not only island arc magma genesis but also •hc chemical evolution of the Earth. It is believed generally that slab-derived materials (melts and/or fluids) are added to the mantle wedge from the Subducting slab, and subsequently, these components induce generation of island arc magma. Recently, it has been argued that the subduction component is an aqueous fluid derived by dehydration of the subducting slab. This argument is based on the abundance ratios of mobile and immobile elements in , aqueous fluids, such as K* value [Nakamura et al., 198•], abundance ratios of large ion lithophilc elements (LILEs, ; Ryan et ai., 1995]. Two possible mechanisms of slab dehydration have been recognized: (1) continuous dehydration of the subducting slab from the volcanic front to the back arc side with a continuous release of fluid to the overlying mantle wedge [Nakamura et al., 1990; Ishikawa and Nakamura, 1994; Ryan et at., 1995], and (2) stepwise dehydration of the mantle wedge where fluid exchanged between the slab and overlying mantle occurs at discreet depths depending on the stability ranges of hydrou.s mineral [Tatsumi, 1989]. Furthermore, the chemical characteristics of the mantle wedge are also ambiguous, with a mid-ocean ridge basalt (MORB)-type mantle wedge being recognized by some [e.g., Perfit et al., 1980; Nakamura et at., 1985; Sakuyama and Nesbitt, 1986; Woodhead, 1989; Ishikawa and Nakarnura, 1994] and an oceanic island basalt (OIB)type mantle wedge caused by interaction between depleted (MORB-type) mantle and enriched mantle component recognized by others [e.g., Morris and Hart, 1983; Ito and Stern, 1985]. 8051
ABSTRACT A double-spike multicollector ICP-MS (DS-MC-ICP-MS) technique for Pb isotope analysis wi... more ABSTRACT A double-spike multicollector ICP-MS (DS-MC-ICP-MS) technique for Pb isotope analysis without Tl addition is established and its analytical performance is examined in detail. This simple DS-MC-ICP-MS technique using 20 ng ml sup(-1) gave averages of 16.9417, 15.4988 and 36.7196 with reproducibilities of 0.007, 0.008 and 0.009 % (RSD, n = 35), respectively, for sup(206) Pb / sup(204)Pb, sup(207) Pb / sup(204) Pb and sup(208) Pb / sup(204) Pb in NIST 981 solution, corresponding to consumption of 4 ng of Pb in a pair of spiked and non-spiked measurements. The average is consistent with those obtained by previous studies by DS-TIMS and DS-MC-ICP-MS with Tl addition. The reproducibility (RSD %) of sup(206) Pb / sup(204) Pb, sup(207) Pb / sup(204) Pb and sup(208) Pb / sup(204) Pb improves from 0.26, 0.54 and 0.69 % to 0.0022, 0.0030 and 0.0029 % as the Pb consumption during analysis increases from 20 pg to 11 ng. The reproducibility with 11 ng is similar to or even better than those by DS-TIMS, MC-ICP-MS with Tl addition, or with DS-Tl addition. The accuracy of the simple DS-MC-ICP-MS technique for Pb, including the column chemistry, is further confirmed by analysis of actual silicate sample, JB-3.
Lithium is an excellent geochemical tracer in understanding hydrothermal processes, island arc vo... more Lithium is an excellent geochemical tracer in understanding hydrothermal processes, island arc volcanism and crust-mantle recycling (e.
Vol. 30 -N°3 p . 2 4 5 -2 7 1 A method for the determination of major, minor and trace elements i... more Vol. 30 -N°3 p . 2 4 5 -2 7 1 A method for the determination of major, minor and trace elements in silicate samples by ICP-QMS and ICP-SFMS applying isotope dilution-internal standardisation (ID-IS) and multi-stage internal standardisation has been developed. Samples with an enriched isotope of 149 Sm (spike) were decomposed by a HF/HClO 4 mixture and stepwise drying and finally diluted. In ID-IS for trace element analyses by Q-pole type ICP-MS (ICP-QMS), the Sm concentration was determined by ID, while other trace elements (Li, Be, Rb, were determined using the 149 Sm intensity as an internal standard. Major and minor elements were determined by multi-stage internal standardisation, with Na, Mg, Al, P, Ca, V, Mn, Fe and Co measured by sector magnetic field type ICP-MS (ICP-SFMS) at middle resolution (MR; M/∆M = ~ 3000) using Sr determined by ICP-QMS in the sample as the internal standard. Potassium, Sc, Ni, Cu, Zn and Ga were measured at high resolution (HR; M/∆M ~7500) using the Sr concentration obtained by ICP-QMS or the Mn concentration obtained by ICP-SFMS at MR as internal standard. The merit of ID-IS is that accurate dilution of the sample is not required. Matrix effects on elemental ratios down to a dilution factor (DF) of 600 were not observed in either types of mass spectrometry. Pseudo-flow injection (FI), where transient signals were integrated, was used in ICP-QMS, while conventional continuous sample introduction was used in ICP-SFMS, resulting in total required sample solutions of 0.026 ml and 0.08 ml, respectively. Detection limits were low enough to determine these elements in depleted ultramafic rocks, and typical Une méthode permettant la détermination des éléments majeurs, mineurs et en trace dans les échantillons silicatés par ICP-QMS et ICP-SFMS a été développée. Elle combine la standardisation interne par dilution isotopique (ID-IS) et la standardisation interne en deux étapes. Les échantillons, auxquels est ajouté un spike enrichi en 149 Sm, sont décomposés par une mixture HF/HClO 4 , séchés progressivement puis dilués. Dans la phase de standardisation interne par dilution isotopique avec un ICP-MS à quadrupôle (ICP-QMS), la concentration en Sm est déterminée par dilution isotopique tandis que les autres éléments en trace
Structural, petrological, and geochronological data from the middle Korean peninsula indicate tha... more Structural, petrological, and geochronological data from the middle Korean peninsula indicate that the Qinling-Dabie-Sulu collisional belt of east-central China crosses the Yellow Sea and extends into the Imjingang belt. The Yeoncheon complex, first identified as the western Imjingang belt, comprises primarily northdipping metamorphic sequences: (1) the northern Jingok unit, consisting of Barrovian-type metapelites, and (2) the southern Samgot unit, consisting of calc-silicate and amphibolitic rocks. South-vergent structures with reverse-sense shearing are dominant in the Jingok unit, whereas late normal-sense shearing is pervasive in the Samgot unit and the deformed granitoid to the south. These structural patterns are interpreted to correspond to extensional deformation associated with uplift following compression in a collisional belt. Pressure-temperature (P-T) estimates from the amphibolites suggest a high-P amphibolite-facies metamorphism (8 -13 kbar and 630 -790 ؇C), possibly evolving from eclogite facies conditions along a clockwise P-T path. Sm-Nd and Rb-Sr geochronological data suggest that the amphibolites emplaced in Late Proterozoic time were metamorphosed during Permian-Triassic time.
It is widely acknowledged that olivine-hosted melt inclusions retain compositional information un... more It is widely acknowledged that olivine-hosted melt inclusions retain compositional information unavailable from the study of bulk-rock samples alone. Whether or not the compositions of melt inclusions are truly representative of geologically significant melt bodies has, however, been called into question; isotopic data are critical to resolving this debate but the rare existing data are contradictory. Previous studies of Pb
Multi-stage formation of tourmaline occurs in the Hnilec granite-related hydrothermal tin mineral... more Multi-stage formation of tourmaline occurs in the Hnilec granite-related hydrothermal tin mineralisation system from the Western Carpathians, Slovakia. The tourmalines belong to the schorl-dravite series and have two major stages of formation: the majority crystallized during the first stage (defined as M-stage), forming zoned tourmaline crystals with the cores being generally more Fe, Al, and Mn rich than the rims. During the second stage (defined as L-stage), tourmaline formed as small veins or irregular patches along fractures and cracks in the M-stage tourmaline grains. In the contact metapelites near the granite body, the L-stage tourmalines are more Mg-rich and Fe, Al, Mn depleted than the M-stage tourmalines. In the granites, the L-stage tourmalines have generally similar compositions to those of the M-stage tourmaline rims. The boron isotopic compositions of the M-stage tourmalines vary from −10.3‰ to −15.4‰; with no clear variation between the cores and the rims, however, some of the tourmaline grains from the contact metapelites show a slightly higher δ 11 B in the cores than in the rims. The L-stage tourmalines have lower δ 11 B value of −16.0‰ to −17.1‰. We suggest that these trends reflect a changing fluid source from a dominant magmatic-hydrothermal fluid derived from the granites to a late-stage metamorphic fluid derived from the regional metamorphism (chlorite and biotite zone) in the metapelites. The significantly higher Fe 3+ in the L-stage than the M-stage tourmalines reflect changing redox conditions towards a more oxidising environment. This redox condition change may have important implications for the hydrothermal tin mineralisation in the area.
It is widely acknowledged that olivine-hosted melt inclusions retain compositional information un... more It is widely acknowledged that olivine-hosted melt inclusions retain compositional information unavailable from the study of bulk-rock samples alone. Whether or not the compositions of melt inclusions are truly representative of geologically significant melt bodies has, however, been called into question; isotopic data are critical to resolving this debate but the rare existing data are contradictory. Previous studies of Pb
... 500C. The calculated cooling rate, assuming a garnet SmNd clo sure temperature similar to tha... more ... 500C. The calculated cooling rate, assuming a garnet SmNd clo sure temperature similar to that of hornblende to Ar MAH Maboko, E. Nakamura Precambrian Research 74 (1995) 195202 201 diffusion, is about 23C Ma. This ...
In order to facilitate the understanding of the geological evolution of the Kalahari Craton and i... more In order to facilitate the understanding of the geological evolution of the Kalahari Craton and its relation to South America, the provenance of the first large-scale cratonic cover sequence of the craton,
While exposure to fibers and particles has been proposed to be associated with several different ... more While exposure to fibers and particles has been proposed to be associated with several different lung malignancies including mesothelioma, the mechanism for the carcinogenesis is not fully understood. Along with mineralogical observation, we have analyzed forty-four major and trace elements in extracted asbestos bodies (fibers and proteins attached to them) with coexisting fiber-free ferruginous protein bodies from extirpative lungs of individuals with malignant mesothelioma. These observations together with patients' characteristics suggest that inhaled iron-rich asbestos fibers and dust particles, and excess iron deposited by continuous cigarette smoking would induce ferruginous protein body formation resulting in ferritin aggregates in lung tissue. Chemical analysis of ferruginous protein bodies extracted from lung tissues reveals anomalously high concentrations of radioactive radium, reaching millions of times higher concentration than that of seawater. Continuous and prolonged internal exposure to hotspot ionizing radiation from radium and its daughter nuclides could cause strong and frequent DNA damage in lung tissue, initiate different types of tumour cells, including malignant mesothelioma cells, and may cause cancers.
Proceedings of the Japan Academy. Ser. B: Physical and Biological Sciences, 1995
In order to examine the behavior of elements under the control of aqueous fluid through slab-mant... more In order to examine the behavior of elements under the control of aqueous fluid through slab-mantle interactions, a series of high-pressure and high-temperature experiments was carried out at
AT convergent margins, the subducting oceanic slab is thought to dehydrate, producing fluids whic... more AT convergent margins, the subducting oceanic slab is thought to dehydrate, producing fluids which metasomatize the overlying mantle wedge where island-arc magma forms. However, the nature and origin of the metasomatizing fluid, its source composition and its relation to the genesis of the chemical characteristics of arc magmas are largely controversial. Across-arc variation in the chemistry of arc lavas provides
Multi-stage formation of tourmaline occurs in the Hnilec granite-related hydrothermal tin mineral... more Multi-stage formation of tourmaline occurs in the Hnilec granite-related hydrothermal tin mineralisation system from the Western Carpathians, Slovakia. The tourmalines belong to the schorl-dravite series and have two major stages of formation: the majority crystallized during the first stage (defined as M-stage), forming zoned tourmaline crystals with the cores being generally more Fe, Al, and Mn rich than the rims. During the second stage (defined as L-stage), tourmaline formed as small veins or irregular patches along fractures and cracks in the M-stage tourmaline grains. In the contact metapelites near the granite body, the L-stage tourmalines are more Mg-rich and Fe, Al, Mn depleted than the M-stage tourmalines. In the granites, the L-stage tourmalines have generally similar compositions to those of the M-stage tourmaline rims. The boron isotopic compositions of the M-stage tourmalines vary from −10.3‰ to −15.4‰; with no clear variation between the cores and the rims, however, some of the tourmaline grains from the contact metapelites show a slightly higher δ 11 B in the cores than in the rims. The L-stage tourmalines have lower δ 11 B value of −16.0‰ to −17.1‰. We suggest that these trends reflect a changing fluid source from a dominant magmatic-hydrothermal fluid derived from the granites to a late-stage metamorphic fluid derived from the regional metamorphism (chlorite and biotite zone) in the metapelites. The significantly higher Fe 3+ in the L-stage than the M-stage tourmalines reflect changing redox conditions towards a more oxidising environment. This redox condition change may have important implications for the hydrothermal tin mineralisation in the area.
Journal of Mineralogical and Petrological Sciences, 2008
Eclogites of the Kaghan valley, Pakistan Himalaya were investigated petrographically and geochemi... more Eclogites of the Kaghan valley, Pakistan Himalaya were investigated petrographically and geochemically. Based on petrography, geochemistry and mineral compositions, metamorphic history and a reasonable tectonic model are proposed. Eclogites exposed in the Kaghan valley are classified into two groups. Group I eclogites appear as massive and Group II are lenstype. Group I eclogites have a mineral assemblage of garnet, omphacitic clinopyroxene, quartz, symplectite with rare epidote and phengite. Accessory minerals include abundant zircon, rutile, ilmenite, and rare apatite. Group II eclogites have a mineral assemblage of garnet, omphacitic clinopyroxene, phengite, quartz/coesite, epidote, and symplectite. In accessory minerals rutile and ilmenite are common while zircon and apatite are rare. Different types of protolith are proposed for these eclogites. Group I eclogites have higher FeO and TiO 2 contents and trace element contents, and seem to be derived from gabbroic protolith. Group II eclogites have lower FeO and TiO 2 and trace element contents and were derived from basalts. Pressuretemperaturetime path was constructed for the Kaghan valley eclogites using various mineral assemblages along with textural relationship and inclusions study. At least three distinct metamorphic stages were identified. The first stage is the prograde garnet growth stage deduced from the inclusion paragenesis in garnet core. The second stage records the ultrahighpressure metamorphic stage deduced from the presence of coesite inclusions in omphacitic clinopyroxene. The third stage is the decompression stage and is deduced from the quartzalbiteamphibole symplectite portions. These petrological and geochemical results combined with isotopic ages reported elsewhere indicate that basalts and associated gabbroic dikes were emplaced at about 267 Ma when the Indian plate was moving northward and passing above an unknown hot spot. The closure of the Tethys and initiation of collision of the Indian plate with the Kohistan -Ladakh Island Arc is reported from 65 -50 Ma. After that the leadingedge of the Indian plate underwent eclogite facies metamorphism at 49 Ma and when it reached to depths of about 100 km, the ultrahighpressure metamorphic event took place at 46 Ma.
Isotopic compositions of Pb, Sr, and Nd and concentrations of trace elements were determined for ... more Isotopic compositions of Pb, Sr, and Nd and concentrations of trace elements were determined for Quaternary island arc basaltic rocks from northeastern Japan. Sr and Pb isotopic ratios decrease, and Nd isotopic ratios increase from the volcanic front toward the back arc. The isotopic compositions nearest the back arc side are nearly identical to those of mid-ocean ridge basalt (MORB). The high field strength elements and heavy rare earth elements show homogeneous and MORB-like characteristics. These observations indicate that the mantle wedge beneath northeastern Japan originally had a MORB-type mantle composition that was homogeneous across the arc. Pb isotope compositions show a mixing relationship between mantle wedge and oceanic sediments reflecting the introduction of subduction component into the mantle wedge. Across-arc isotopic variations were caused by interaction between MORB-type mantle wedge and the subducting slab, and the amount of subduction component correlates with the depth to the slab. The isotopic compositions of subduction component are expressed by bulk mixing of 15 wt % of oceanic sediment and 85 wt % of altered MORB. Inversion analyses of isotopic compositions using two-component mixing relationships show that the Sr/Nd and Pb/Nd ratios in subduction component decrease with increasing depth to the slab, while the Sr/Pb ratio is nearly constant. These changes can be explained only by a preferential discharge of the elements into the wedge mantle associated with continuous dehydration of the subducting slab. The present study further demonstrates that a very wide range of isotopic and elemental compositions in island arc magmas is a consequence of the interaction between subducting slab and mantle wedge without the involvement of an oceanic island basalts component, and the slab can carry water and supply a subduction component as a fluid to the overlying mantle wedge to depths exceeding 150 km. introduction The nature of the subducting slab, including oceanic crus• and oceanic sediment, has been a focus of attention since ,4rmstrong [1968] because it is critical to understanding mantle-crust recycling. The subduction process is a unique mechanism whereby crustal components can be introduced back into the mantic, and therefore investigation of the interaction between subducting slab and mantle wedge is important for understanding not only island arc magma genesis but also •hc chemical evolution of the Earth. It is believed generally that slab-derived materials (melts and/or fluids) are added to the mantle wedge from the Subducting slab, and subsequently, these components induce generation of island arc magma. Recently, it has been argued that the subduction component is an aqueous fluid derived by dehydration of the subducting slab. This argument is based on the abundance ratios of mobile and immobile elements in , aqueous fluids, such as K* value [Nakamura et al., 198•], abundance ratios of large ion lithophilc elements (LILEs, ; Ryan et ai., 1995]. Two possible mechanisms of slab dehydration have been recognized: (1) continuous dehydration of the subducting slab from the volcanic front to the back arc side with a continuous release of fluid to the overlying mantle wedge [Nakamura et al., 1990; Ishikawa and Nakamura, 1994; Ryan et at., 1995], and (2) stepwise dehydration of the mantle wedge where fluid exchanged between the slab and overlying mantle occurs at discreet depths depending on the stability ranges of hydrou.s mineral [Tatsumi, 1989]. Furthermore, the chemical characteristics of the mantle wedge are also ambiguous, with a mid-ocean ridge basalt (MORB)-type mantle wedge being recognized by some [e.g., Perfit et al., 1980; Nakamura et at., 1985; Sakuyama and Nesbitt, 1986; Woodhead, 1989; Ishikawa and Nakarnura, 1994] and an oceanic island basalt (OIB)type mantle wedge caused by interaction between depleted (MORB-type) mantle and enriched mantle component recognized by others [e.g., Morris and Hart, 1983; Ito and Stern, 1985]. 8051
ABSTRACT A double-spike multicollector ICP-MS (DS-MC-ICP-MS) technique for Pb isotope analysis wi... more ABSTRACT A double-spike multicollector ICP-MS (DS-MC-ICP-MS) technique for Pb isotope analysis without Tl addition is established and its analytical performance is examined in detail. This simple DS-MC-ICP-MS technique using 20 ng ml sup(-1) gave averages of 16.9417, 15.4988 and 36.7196 with reproducibilities of 0.007, 0.008 and 0.009 % (RSD, n = 35), respectively, for sup(206) Pb / sup(204)Pb, sup(207) Pb / sup(204) Pb and sup(208) Pb / sup(204) Pb in NIST 981 solution, corresponding to consumption of 4 ng of Pb in a pair of spiked and non-spiked measurements. The average is consistent with those obtained by previous studies by DS-TIMS and DS-MC-ICP-MS with Tl addition. The reproducibility (RSD %) of sup(206) Pb / sup(204) Pb, sup(207) Pb / sup(204) Pb and sup(208) Pb / sup(204) Pb improves from 0.26, 0.54 and 0.69 % to 0.0022, 0.0030 and 0.0029 % as the Pb consumption during analysis increases from 20 pg to 11 ng. The reproducibility with 11 ng is similar to or even better than those by DS-TIMS, MC-ICP-MS with Tl addition, or with DS-Tl addition. The accuracy of the simple DS-MC-ICP-MS technique for Pb, including the column chemistry, is further confirmed by analysis of actual silicate sample, JB-3.
Lithium is an excellent geochemical tracer in understanding hydrothermal processes, island arc vo... more Lithium is an excellent geochemical tracer in understanding hydrothermal processes, island arc volcanism and crust-mantle recycling (e.
Vol. 30 -N°3 p . 2 4 5 -2 7 1 A method for the determination of major, minor and trace elements i... more Vol. 30 -N°3 p . 2 4 5 -2 7 1 A method for the determination of major, minor and trace elements in silicate samples by ICP-QMS and ICP-SFMS applying isotope dilution-internal standardisation (ID-IS) and multi-stage internal standardisation has been developed. Samples with an enriched isotope of 149 Sm (spike) were decomposed by a HF/HClO 4 mixture and stepwise drying and finally diluted. In ID-IS for trace element analyses by Q-pole type ICP-MS (ICP-QMS), the Sm concentration was determined by ID, while other trace elements (Li, Be, Rb, were determined using the 149 Sm intensity as an internal standard. Major and minor elements were determined by multi-stage internal standardisation, with Na, Mg, Al, P, Ca, V, Mn, Fe and Co measured by sector magnetic field type ICP-MS (ICP-SFMS) at middle resolution (MR; M/∆M = ~ 3000) using Sr determined by ICP-QMS in the sample as the internal standard. Potassium, Sc, Ni, Cu, Zn and Ga were measured at high resolution (HR; M/∆M ~7500) using the Sr concentration obtained by ICP-QMS or the Mn concentration obtained by ICP-SFMS at MR as internal standard. The merit of ID-IS is that accurate dilution of the sample is not required. Matrix effects on elemental ratios down to a dilution factor (DF) of 600 were not observed in either types of mass spectrometry. Pseudo-flow injection (FI), where transient signals were integrated, was used in ICP-QMS, while conventional continuous sample introduction was used in ICP-SFMS, resulting in total required sample solutions of 0.026 ml and 0.08 ml, respectively. Detection limits were low enough to determine these elements in depleted ultramafic rocks, and typical Une méthode permettant la détermination des éléments majeurs, mineurs et en trace dans les échantillons silicatés par ICP-QMS et ICP-SFMS a été développée. Elle combine la standardisation interne par dilution isotopique (ID-IS) et la standardisation interne en deux étapes. Les échantillons, auxquels est ajouté un spike enrichi en 149 Sm, sont décomposés par une mixture HF/HClO 4 , séchés progressivement puis dilués. Dans la phase de standardisation interne par dilution isotopique avec un ICP-MS à quadrupôle (ICP-QMS), la concentration en Sm est déterminée par dilution isotopique tandis que les autres éléments en trace
Structural, petrological, and geochronological data from the middle Korean peninsula indicate tha... more Structural, petrological, and geochronological data from the middle Korean peninsula indicate that the Qinling-Dabie-Sulu collisional belt of east-central China crosses the Yellow Sea and extends into the Imjingang belt. The Yeoncheon complex, first identified as the western Imjingang belt, comprises primarily northdipping metamorphic sequences: (1) the northern Jingok unit, consisting of Barrovian-type metapelites, and (2) the southern Samgot unit, consisting of calc-silicate and amphibolitic rocks. South-vergent structures with reverse-sense shearing are dominant in the Jingok unit, whereas late normal-sense shearing is pervasive in the Samgot unit and the deformed granitoid to the south. These structural patterns are interpreted to correspond to extensional deformation associated with uplift following compression in a collisional belt. Pressure-temperature (P-T) estimates from the amphibolites suggest a high-P amphibolite-facies metamorphism (8 -13 kbar and 630 -790 ؇C), possibly evolving from eclogite facies conditions along a clockwise P-T path. Sm-Nd and Rb-Sr geochronological data suggest that the amphibolites emplaced in Late Proterozoic time were metamorphosed during Permian-Triassic time.
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Papers by Eizo Nakamura