Basaltic partial melts are produced in a range of tectonic settings, including fluid-assisted melting above subduction zones, decompression melting at ridges and thermally driven melting above mantle plumes. To examine the role of partial melting on Zn, isotope and abundance data are reported for modern large-degree partial melts of the mantle represented by 22 mid-ocean ridge basalts (MORB) from three ocean basins and the first data for boninites. Boninites have some of the lowest Zn abundances of all terrestrial basalts and Zn isotope compositions ( δ 66 Zn = þ 0.21 ± 0.06 ‰ ), generally lighter than for MORB ( δ 66 Zn = þ 0.28 ± 0.06 ‰ ). Accounting for partial melting, komatiites, boninites and MORB derive from mantle sources with δ 66 Zn of ∼ 0.16 ± 0.06 ‰ . Lower-degree partial melts, such as alkali basalts, can have higher δ 66 Zn, with up to ∼ 0.4 ‰ variation possible from partial melting of distinct peridotite mantle sources. Partial melting of fertile lherzolitic and depleted harzburgitic mantle sources can generate significant Zn isotope variability and should be evaluated prior to ascribing crustal, enriched or lithological components to mantle reservoirs from Zn compositions of planetary basalts.
{"title":"A partial melting control on the Zn isotope composition of basalts","authors":"J. Day, F. Moynier, O. Ishizuka","doi":"10.7185/geochemlet.2230","DOIUrl":"https://doi.org/10.7185/geochemlet.2230","url":null,"abstract":"Basaltic partial melts are produced in a range of tectonic settings, including fluid-assisted melting above subduction zones, decompression melting at ridges and thermally driven melting above mantle plumes. To examine the role of partial melting on Zn, isotope and abundance data are reported for modern large-degree partial melts of the mantle represented by 22 mid-ocean ridge basalts (MORB) from three ocean basins and the first data for boninites. Boninites have some of the lowest Zn abundances of all terrestrial basalts and Zn isotope compositions ( δ 66 Zn = þ 0.21 ± 0.06 ‰ ), generally lighter than for MORB ( δ 66 Zn = þ 0.28 ± 0.06 ‰ ). Accounting for partial melting, komatiites, boninites and MORB derive from mantle sources with δ 66 Zn of ∼ 0.16 ± 0.06 ‰ . Lower-degree partial melts, such as alkali basalts, can have higher δ 66 Zn, with up to ∼ 0.4 ‰ variation possible from partial melting of distinct peridotite mantle sources. Partial melting of fertile lherzolitic and depleted harzburgitic mantle sources can generate significant Zn isotope variability and should be evaluated prior to ascribing crustal, enriched or lithological components to mantle reservoirs from Zn compositions of planetary basalts.","PeriodicalId":12613,"journal":{"name":"Geochemical Perspectives Letters","volume":" ","pages":""},"PeriodicalIF":4.9,"publicationDate":"2022-09-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"46460824","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
B. Laurent, L. Remusat, J. Viennet, R. Brunetto, L. Binet, M. Holin, M. Ciocco, C. Bouvier, A. Brunelle, S. Bernard
Mighei-type carbonaceous chondrites (CM) figure among the most primitive objects in the solar system. Yet, they all have experienced various degrees of aqueous alteration having modified their insoluble organic matter (IOM), in a sequence that remains to be accurately constrained. Here, we exposed the IOM of Paris, the least altered CM available, to hydrothermal conditions at 150 °C for 49 days and compared the experimental residue to the IOM of two altered CMs likely originating from the same parent body as Paris, namely Aguas Zarcas and Mukundpura. The experimental residue shows a chemical and isotopic composition similar to those of Aguas Zarcas and Mukundpura IOMs, confirming that these CMs can be seen as altered counterparts of Paris. The abundance of organic radicals also increases significantly during the experiment. Isotopic hotspots do not seem to have been lost during the experiment, suggesting that the hotspots generally observed within the CM IOMs may date back from pre-accretion era. Of note, the Raman signature of the residue differs from that of the CM IOMs, highlighting the need for further experiments better mimicking asteroidal-like conditions.
{"title":"reservation of the isotope signatures in chondritic IOM during aqueous alteration","authors":"B. Laurent, L. Remusat, J. Viennet, R. Brunetto, L. Binet, M. Holin, M. Ciocco, C. Bouvier, A. Brunelle, S. Bernard","doi":"10.7185/geochemlet.2233","DOIUrl":"https://doi.org/10.7185/geochemlet.2233","url":null,"abstract":"Mighei-type carbonaceous chondrites (CM) figure among the most primitive objects in the solar system. Yet, they all have experienced various degrees of aqueous alteration having modified their insoluble organic matter (IOM), in a sequence that remains to be accurately constrained. Here, we exposed the IOM of Paris, the least altered CM available, to hydrothermal conditions at 150 °C for 49 days and compared the experimental residue to the IOM of two altered CMs likely originating from the same parent body as Paris, namely Aguas Zarcas and Mukundpura. The experimental residue shows a chemical and isotopic composition similar to those of Aguas Zarcas and Mukundpura IOMs, confirming that these CMs can be seen as altered counterparts of Paris. The abundance of organic radicals also increases significantly during the experiment. Isotopic hotspots do not seem to have been lost during the experiment, suggesting that the hotspots generally observed within the CM IOMs may date back from pre-accretion era. Of note, the Raman signature of the residue differs from that of the CM IOMs, highlighting the need for further experiments better mimicking asteroidal-like conditions.","PeriodicalId":12613,"journal":{"name":"Geochemical Perspectives Letters","volume":" ","pages":""},"PeriodicalIF":4.9,"publicationDate":"2022-09-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"48969267","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
L. Nana Yobo, A. Brandon, L.M. Lauckner, J. Eldrett, S. Bergman, D. Minisini
The emplacement of a Large Igneous Province (LIP) is implicated in the triggering of the Cenomanian-Turonian Oceanic Anoxic Event 2 (OAE 2). Evidence for a similar initiation mechanism for the mid-Cenomanian Event (MCE) is unclear. In this study, a reconstruction of mid-Cenomanian seawater 187 Os/ 188 Os, the first for the Western Interior Seaway, tests the competing roles of LIP versus continental weathering activity in triggering the MCE. The absence of a prolonged unradiogenic Os isotope excursion (low 187 Os/ 188 Os) at the onset of the MCE interval argues against LIP involvement in the event ’ s initiation. Rather, more radiogenic 187 Os/ 188 Os at the onset, that continues to rise to the middle of the MCE, indicates that the event was triggered by increased continental weathering. The combination of decreasing 187 Os/ 188 Os from the middle of the MCE onward, coincident with a 40 Ar/ 39 Ar age of 96.4 Ma of basalts from Ellesmere Island, Canada, is consistent with High Arctic LIP-related volcanic activity that may have contributed to the end of the MCE. These new data on the MCE thus indicate that LIP activity is not always the trigger for carbon cycle perturbation and associated climate change.
{"title":"Enhanced continental weathering activity at the onset of the mid-Cenomanian Event (MCE)","authors":"L. Nana Yobo, A. Brandon, L.M. Lauckner, J. Eldrett, S. Bergman, D. Minisini","doi":"10.7185/geochemlet.2231","DOIUrl":"https://doi.org/10.7185/geochemlet.2231","url":null,"abstract":"The emplacement of a Large Igneous Province (LIP) is implicated in the triggering of the Cenomanian-Turonian Oceanic Anoxic Event 2 (OAE 2). Evidence for a similar initiation mechanism for the mid-Cenomanian Event (MCE) is unclear. In this study, a reconstruction of mid-Cenomanian seawater 187 Os/ 188 Os, the first for the Western Interior Seaway, tests the competing roles of LIP versus continental weathering activity in triggering the MCE. The absence of a prolonged unradiogenic Os isotope excursion (low 187 Os/ 188 Os) at the onset of the MCE interval argues against LIP involvement in the event ’ s initiation. Rather, more radiogenic 187 Os/ 188 Os at the onset, that continues to rise to the middle of the MCE, indicates that the event was triggered by increased continental weathering. The combination of decreasing 187 Os/ 188 Os from the middle of the MCE onward, coincident with a 40 Ar/ 39 Ar age of 96.4 Ma of basalts from Ellesmere Island, Canada, is consistent with High Arctic LIP-related volcanic activity that may have contributed to the end of the MCE. These new data on the MCE thus indicate that LIP activity is not always the trigger for carbon cycle perturbation and associated climate change.","PeriodicalId":12613,"journal":{"name":"Geochemical Perspectives Letters","volume":" ","pages":""},"PeriodicalIF":4.9,"publicationDate":"2022-09-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"44299202","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
New 87 Rb- 87 Sr data are reported for emeralds from Gravelotte, South Africa and Muzo, Colombia, the first such data in 30 years. The Gravelotte deposit is inferred to be the world ’ s oldest emerald deposit from the ∼ 2.97 Ga U-Pb age of the associated pegmatite. The majority of Gravelotte emeralds plot on an 87 Rb- 87 Sr errorchron with an age of 2883 ± 131 Ma, close to the pegmatite age, demonstrating that the emeralds are Mesoarchean in age. The Muzo emerald data, when combined with data from nearby Colombian emerald deposits, define an age of ∼ 48 Ma, younger than muscovite Ar-Ar ages (65 – 62 Ma), likely reflecting the resetting of 87 Rb- 87 Sr in some emeralds. The initial Sr isotopic composition for Gravelotte emeralds is radiogenic ( 87 Sr/ 86 Sr i = 0.841), and their trace element signatures support their formation from a mature, high Rb/Sr, felsic continental crustal protolith in the Mesoarchean. Direct 87 Rb- 87 Sr dating of emeralds holds promise for offering constraints on both mineralisation ages and source compositions.
报道了南非Gravelotte和哥伦比亚Muzo祖母绿的87 Rb- 87 Sr数据，这是30年来首次获得此类数据。根据其伴生伟晶岩的~ 2.97 Ga U-Pb年龄推断，该砾石矿床是世界上最古老的祖母绿矿床。砾石型祖母绿的锆石年龄为2883±131 Ma，与伟晶岩的锆石年龄接近，属于中太古代。Muzo祖母绿数据与附近哥伦比亚祖母绿矿床的数据相结合，确定了~ 48 Ma的年龄，比白云母Ar-Ar年龄(65 - 62 Ma)年轻，可能反映了一些祖母绿中87 Rb- 87 Sr的重置。砾石祖母绿的初始Sr同位素组成为放射性成因(87 Sr/ 86 Sr i = 0.841)，其微量元素特征支持其形成于中太古代成熟的高Rb/Sr长英质大陆地壳原岩。祖母绿的直接87 Rb- 87 Sr定年有望提供矿化年龄和来源成分的限制。
{"title":"Archean age and radiogenic source for the world’s oldest emeralds","authors":"R. Nicklas, J. Day, R. Alonso-Pérez","doi":"10.7185/geochemlet.2232","DOIUrl":"https://doi.org/10.7185/geochemlet.2232","url":null,"abstract":"New 87 Rb- 87 Sr data are reported for emeralds from Gravelotte, South Africa and Muzo, Colombia, the first such data in 30 years. The Gravelotte deposit is inferred to be the world ’ s oldest emerald deposit from the ∼ 2.97 Ga U-Pb age of the associated pegmatite. The majority of Gravelotte emeralds plot on an 87 Rb- 87 Sr errorchron with an age of 2883 ± 131 Ma, close to the pegmatite age, demonstrating that the emeralds are Mesoarchean in age. The Muzo emerald data, when combined with data from nearby Colombian emerald deposits, define an age of ∼ 48 Ma, younger than muscovite Ar-Ar ages (65 – 62 Ma), likely reflecting the resetting of 87 Rb- 87 Sr in some emeralds. The initial Sr isotopic composition for Gravelotte emeralds is radiogenic ( 87 Sr/ 86 Sr i = 0.841), and their trace element signatures support their formation from a mature, high Rb/Sr, felsic continental crustal protolith in the Mesoarchean. Direct 87 Rb- 87 Sr dating of emeralds holds promise for offering constraints on both mineralisation ages and source compositions.","PeriodicalId":12613,"journal":{"name":"Geochemical Perspectives Letters","volume":" ","pages":""},"PeriodicalIF":4.9,"publicationDate":"2022-09-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"42208891","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2022-08-01DOI: 10.7185/geochemlet.2226cor
X.-N. Liu, R. Hin, C. Coath, M. van Soest, E. Melekhova, T. Elliott
{"title":"Corrigendum to “Equilibrium olivine-melt Mg isotopic fractionation explains high δ26Mg values in arc lavas” by Liu et al., 2022","authors":"X.-N. Liu, R. Hin, C. Coath, M. van Soest, E. Melekhova, T. Elliott","doi":"10.7185/geochemlet.2226cor","DOIUrl":"https://doi.org/10.7185/geochemlet.2226cor","url":null,"abstract":"","PeriodicalId":12613,"journal":{"name":"Geochemical Perspectives Letters","volume":" ","pages":""},"PeriodicalIF":4.9,"publicationDate":"2022-08-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"46266099","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2022-08-01DOI: 10.7185/geochemlet.2132cor
T.A. Halamka, J. McFarlin, A. Younkin, J. Depoy, N. Dildar, S. Kopf
{"title":"Corrigendum to “Oxygen limitation can trigger the production of branched GDGTs in culture” by Halamka et al., 2021","authors":"T.A. Halamka, J. McFarlin, A. Younkin, J. Depoy, N. Dildar, S. Kopf","doi":"10.7185/geochemlet.2132cor","DOIUrl":"https://doi.org/10.7185/geochemlet.2132cor","url":null,"abstract":"","PeriodicalId":12613,"journal":{"name":"Geochemical Perspectives Letters","volume":" ","pages":""},"PeriodicalIF":4.9,"publicationDate":"2022-08-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"47937298","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Carbonaceous chondrites are pristine witnesses of the formation of the solar system. Among them, the carbon-rich Tarda and Tagish Lake meteorites are thought to have sampled very distant regions of the outer circumsolar disk (Hiroi et al ., 2001). Here, we show that their noble gas isotopic compositions (especially 129 Xe excesses) are similar, implying their formation in comparable environments. Combined with literature data, we show that the radiogenic excesses of 129 Xe relative to solar wind in carbonaceous chondrites define anti-correlations with their respective iodine and carbon contents. These trends do not result from the heterogeneous distribution of 129 I in the disk but rather evidence a xenon dilution effect; the radiogenic 129 Xe excesses being dominated by trapped xenon in the most carbon-rich carbonaceous chondrites. Our data also suggest that both Tarda and Tagish Lake accreted beyond 10 astronomical units, in regions of the disk that were cold enough for CO 2 to condense.
{"title":"Origin of radiogenic 129Xe variations in carbonaceous chondrites","authors":"G. Avice, M. Meier, Y. Marrocchi","doi":"10.7185/geochemlet.2228","DOIUrl":"https://doi.org/10.7185/geochemlet.2228","url":null,"abstract":"Carbonaceous chondrites are pristine witnesses of the formation of the solar system. Among them, the carbon-rich Tarda and Tagish Lake meteorites are thought to have sampled very distant regions of the outer circumsolar disk (Hiroi et al ., 2001). Here, we show that their noble gas isotopic compositions (especially 129 Xe excesses) are similar, implying their formation in comparable environments. Combined with literature data, we show that the radiogenic excesses of 129 Xe relative to solar wind in carbonaceous chondrites define anti-correlations with their respective iodine and carbon contents. These trends do not result from the heterogeneous distribution of 129 I in the disk but rather evidence a xenon dilution effect; the radiogenic 129 Xe excesses being dominated by trapped xenon in the most carbon-rich carbonaceous chondrites. Our data also suggest that both Tarda and Tagish Lake accreted beyond 10 astronomical units, in regions of the disk that were cold enough for CO 2 to condense.","PeriodicalId":12613,"journal":{"name":"Geochemical Perspectives Letters","volume":" ","pages":""},"PeriodicalIF":4.9,"publicationDate":"2022-08-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"41778478","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
{"title":"Siderophores and the formation of cerium anomalies in anoxic environments","authors":"D. Kraemer, M. Bau","doi":"10.7185/geochemlet.2227","DOIUrl":"https://doi.org/10.7185/geochemlet.2227","url":null,"abstract":"","PeriodicalId":12613,"journal":{"name":"Geochemical Perspectives Letters","volume":" ","pages":""},"PeriodicalIF":4.9,"publicationDate":"2022-08-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"43321961","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
B. Laurent, J. Maillard, C. Afonso, G. Danger, P. Giusti, L. Remusat
Primitive carbonaceous chondrites exhibit an unparalleled diversity in terms of their organic content, in addition to a variable degree of hydrothermal alteration. Whether this diversity results from the circulation of fluids or from a multiplicity of precursors remains an open question of prime interest to understand the formation of carbonaceous asteroids. We applied laser desorption ionization Fourier transform ion cyclotron resonance mass spectrometry (LDI-FTICR-MS) on the macromolecular carbon of recent CM carbonaceous chondrite falls, as well as Orgueil (CI) and Tarda (C2). We probed the diversity of molecular fragments released under low power laser beam. The abundance of the chemical families is correlated to the extent of aqueous alteration, which promotes a structural aromatisation. The weakly altered Paris has retained the largest chemical heterogeneity, whilst it is lost in more altered chondrites. Orgueil and Tarda insoluble organic matter share similarities; this is consistent with Tarda and Orgueil originating from the outer belt region. Applied to returned asteroidal samples, FTICR-MS may help unravelling the origin and evolution of organic compounds during the early stages of the solar system.
{"title":"Diversity of chondritic organic matter probed by ultra-high resolution mass spectrometry","authors":"B. Laurent, J. Maillard, C. Afonso, G. Danger, P. Giusti, L. Remusat","doi":"10.7185/geochemlet.2224","DOIUrl":"https://doi.org/10.7185/geochemlet.2224","url":null,"abstract":"Primitive carbonaceous chondrites exhibit an unparalleled diversity in terms of their organic content, in addition to a variable degree of hydrothermal alteration. Whether this diversity results from the circulation of fluids or from a multiplicity of precursors remains an open question of prime interest to understand the formation of carbonaceous asteroids. We applied laser desorption ionization Fourier transform ion cyclotron resonance mass spectrometry (LDI-FTICR-MS) on the macromolecular carbon of recent CM carbonaceous chondrite falls, as well as Orgueil (CI) and Tarda (C2). We probed the diversity of molecular fragments released under low power laser beam. The abundance of the chemical families is correlated to the extent of aqueous alteration, which promotes a structural aromatisation. The weakly altered Paris has retained the largest chemical heterogeneity, whilst it is lost in more altered chondrites. Orgueil and Tarda insoluble organic matter share similarities; this is consistent with Tarda and Orgueil originating from the outer belt region. Applied to returned asteroidal samples, FTICR-MS may help unravelling the origin and evolution of organic compounds during the early stages of the solar system.","PeriodicalId":12613,"journal":{"name":"Geochemical Perspectives Letters","volume":" ","pages":""},"PeriodicalIF":4.9,"publicationDate":"2022-07-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"43424031","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
X.-N. Liu, R. Hin, C. Coath, M. van Soest, E. Melekhova, T. Elliott
We determined equilibrium Mg isotope fractionation between olivine and melt ( Δ 26/24 Mg Ol/melt ) in five, naturally quenched, olivine-glass pairs that were selected to show clear textural and chemical evidence of equilibration. We employed a high-precision, critical mixture double-spiking approach to obtain a weighted mean of Δ 26/24 Mg Ol/melt = − 0.071 ± 0.010 ‰ , for values corrected to a common olivine-glass temperature of 1438 K. As function of temperature, the fractionation can be expressed as Δ 26/24 Mg Ol/melt = ( − 1.46 ± 0.26) × 10 5 / T 2 . The samples analysed have variable H 2 O content from 0.1 to ∼ 1.2 wt. %, yet no discernible difference in Δ 26/24 Mg Ol/melt was evident. We have used this Δ 26/24 Mg Ol/melt to revisit the puzzling issue of elevated Mg isotope ratios in arc lavas. In new Mg isotope data on sample suites from the Lesser Antilles and Mariana arcs, we show that primitive samples have MORB-like Mg isotope ratios while the evolved samples tend to have isotopically heavier compositions. The magnitude of this variability is well explained by olivine fractionation during magmatic differentiation as calculated with our new equilibrium Δ 26/24 Mg Ol/melt .
{"title":"Equilibrium olivine-melt Mg isotopic fractionation explains high δ26Mg values in arc lavas","authors":"X.-N. Liu, R. Hin, C. Coath, M. van Soest, E. Melekhova, T. Elliott","doi":"10.7185/geochemlet.2226","DOIUrl":"https://doi.org/10.7185/geochemlet.2226","url":null,"abstract":"We determined equilibrium Mg isotope fractionation between olivine and melt ( Δ 26/24 Mg Ol/melt ) in five, naturally quenched, olivine-glass pairs that were selected to show clear textural and chemical evidence of equilibration. We employed a high-precision, critical mixture double-spiking approach to obtain a weighted mean of Δ 26/24 Mg Ol/melt = − 0.071 ± 0.010 ‰ , for values corrected to a common olivine-glass temperature of 1438 K. As function of temperature, the fractionation can be expressed as Δ 26/24 Mg Ol/melt = ( − 1.46 ± 0.26) × 10 5 / T 2 . The samples analysed have variable H 2 O content from 0.1 to ∼ 1.2 wt. %, yet no discernible difference in Δ 26/24 Mg Ol/melt was evident. We have used this Δ 26/24 Mg Ol/melt to revisit the puzzling issue of elevated Mg isotope ratios in arc lavas. In new Mg isotope data on sample suites from the Lesser Antilles and Mariana arcs, we show that primitive samples have MORB-like Mg isotope ratios while the evolved samples tend to have isotopically heavier compositions. The magnitude of this variability is well explained by olivine fractionation during magmatic differentiation as calculated with our new equilibrium Δ 26/24 Mg Ol/melt .","PeriodicalId":12613,"journal":{"name":"Geochemical Perspectives Letters","volume":" ","pages":""},"PeriodicalIF":4.9,"publicationDate":"2022-07-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"41644095","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
京公网安备 11010802042870号
京ICP备2023020795号-1
扫码关注我们
求助内容：
应助结果提醒方式：