Stephen Howcutt, M. Spagnolo, B. Rea, Jan Jaszewski, I. Barr, D. Coppola, L. de Siena, T. Girona, Andie Gomez-Patron, D. Mullan, M. Pritchard
We present a continentwide study of 600 glaciers located on and near 37 ice-clad volcanoes in South America. Results demonstrate glacier sensitivity to volcanic heat. We distinguished between “volcanic glaciers” (≤1 km from volcanic centers; n = 74), and “proximal glaciers” (1−15 km; n = 526) and calculated their equilibrium line altitudes (ELAs). For each ice-clad volcano, we compared the ELAs of its volcanic glaciers to those of its proximal glaciers, which showed that the ELAs of the former are higher than the ELAs of the latter. ∆ELAmean, defined as the offset between the mean ELA of the volcanic glaciers compared with that of the proximal glaciers, was calculated for each ice-clad volcano. ∆ELAmean was positive for 92% of the 37 volcanoes, and a quantitative relationship between ΔELAmean and volcanic thermal anomaly was established. Results highlight the impact of volcanic heat on glacier elevation; emphasize the need to exclude glaciers on, or near, volcanoes from glacier-climate investigations; and demonstrate the first-order potential for glaciers as “volcanic thermometers.” Volcanic-glacier monitoring could contribute to our understanding of magmatic and thermal activity, with changes in glacier geometries potentially reflecting long-term fluctuations in volcanic heat and unrest.
{"title":"Icy thermometers: Quantifying the impact of volcanic heat on glacier elevation","authors":"Stephen Howcutt, M. Spagnolo, B. Rea, Jan Jaszewski, I. Barr, D. Coppola, L. de Siena, T. Girona, Andie Gomez-Patron, D. Mullan, M. Pritchard","doi":"10.1130/g51411.1","DOIUrl":"https://doi.org/10.1130/g51411.1","url":null,"abstract":"We present a continentwide study of 600 glaciers located on and near 37 ice-clad volcanoes in South America. Results demonstrate glacier sensitivity to volcanic heat. We distinguished between “volcanic glaciers” (≤1 km from volcanic centers; n = 74), and “proximal glaciers” (1−15 km; n = 526) and calculated their equilibrium line altitudes (ELAs). For each ice-clad volcano, we compared the ELAs of its volcanic glaciers to those of its proximal glaciers, which showed that the ELAs of the former are higher than the ELAs of the latter. ∆ELAmean, defined as the offset between the mean ELA of the volcanic glaciers compared with that of the proximal glaciers, was calculated for each ice-clad volcano. ∆ELAmean was positive for 92% of the 37 volcanoes, and a quantitative relationship between ΔELAmean and volcanic thermal anomaly was established. Results highlight the impact of volcanic heat on glacier elevation; emphasize the need to exclude glaciers on, or near, volcanoes from glacier-climate investigations; and demonstrate the first-order potential for glaciers as “volcanic thermometers.” Volcanic-glacier monitoring could contribute to our understanding of magmatic and thermal activity, with changes in glacier geometries potentially reflecting long-term fluctuations in volcanic heat and unrest.","PeriodicalId":12642,"journal":{"name":"Geology","volume":" ","pages":""},"PeriodicalIF":5.8,"publicationDate":"2023-08-31","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"48503925","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}
A new chronology for graphite formation related to subduction-zone metamorphism in Laytonville Quarry (California, USA) of the Franciscan Complex using the Re-Os decay system yields a precise graphite-pyrite Re-Os age of 161.39 ± 2.08 Ma (MSWD = 0.15; n = 5). Combined with Raman thermometry estimates (461−506 °C), this age links graphitization to the early stages of Franciscan subduction, synchronous with deep (blueschist-eclogite) rather than shallow subduction processes. Initial 187Os/188Os (0.195) of Laytonville graphite suggests that radiogenic 187Os/188Os signatures (0.130−0.158) preserved in some Franciscan forearc mantle peridotites (ca. 160−150 Ma) were plausibly sourced from graphitic carbon in the subducted slab, with graphitization being the primary mechanism for Os release. This conclusion implies that graphitic carbon is an important mineralogical host for Os recycling in subduction settings.
{"title":"Did subducted graphite fertilize the Franciscan mantle wedge with radiogenic Os?","authors":"J. Toma, R. Creaser","doi":"10.1130/g51331.1","DOIUrl":"https://doi.org/10.1130/g51331.1","url":null,"abstract":"A new chronology for graphite formation related to subduction-zone metamorphism in Laytonville Quarry (California, USA) of the Franciscan Complex using the Re-Os decay system yields a precise graphite-pyrite Re-Os age of 161.39 ± 2.08 Ma (MSWD = 0.15; n = 5). Combined with Raman thermometry estimates (461−506 °C), this age links graphitization to the early stages of Franciscan subduction, synchronous with deep (blueschist-eclogite) rather than shallow subduction processes. Initial 187Os/188Os (0.195) of Laytonville graphite suggests that radiogenic 187Os/188Os signatures (0.130−0.158) preserved in some Franciscan forearc mantle peridotites (ca. 160−150 Ma) were plausibly sourced from graphitic carbon in the subducted slab, with graphitization being the primary mechanism for Os release. This conclusion implies that graphitic carbon is an important mineralogical host for Os recycling in subduction settings.","PeriodicalId":12642,"journal":{"name":"Geology","volume":" ","pages":""},"PeriodicalIF":5.8,"publicationDate":"2023-08-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"41948248","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}
Nikolaos N. Zegkinoglou, R. Mathur, S. Kilias, L. Godfrey, Vasilios Pletsas, P. Nomikou, N. Zaronikola
We analyzed the first Cu isotopes in primary cupreous pyrite and orpiment, from modern CO2-degassing, seafloor massive sulfide diffuser vents (“ΚCO2Ds”), from the Kolumbo submarine volcano, Hellenic volcanic arc. Samples came from six ΚCO2Ds that are actively boiling. Pyrite comprises colloform pyrite-I and euhedral pyrite-II, which occur erratically distributed within the ΚCO2Ds and are contemporaneous with barite and spatially concurrent with the chalcopyrite that is lining narrow internal conduits, respectively. Orpiment occurs on the outer walls of the KCO2Ds with barite and stibnite. The δ65Cupyrite-I values show high variability, ranging from +2.93‰ to +6.38‰, whereas the δ65Cupyrite-II and δ65Cuchalcopyrite values vary from −0.94‰ to +0.25‰ and −0.45‰ to −0.09‰, respectively. The range of δ65Cuorpiment between +1.90‰ and +25.73‰ is the most extreme ever reported from any geological setting. Pyrite-I is concentrically layered, with a core comprising random crystallites, whereas the mantle crystallites have grain-size, shape, and orientation variability between layers. Pyrite-II forms aggregates of uniform euhedral pyrite crystals. Pyrite-I has higher concentrations of Cu (≤21,960 ppm) compared to pyrite-II (≤4963 ppm), and both have incompatible and volatile metal(loid)-rich composition and low Sb/Pb (<0.5) and Tl/Pb (<0.03) ratios. When combined with evidence for significant magmatic contributions at Kolumbo and geochemical and micro-textural evidence for recurrent intense boiling and/or flashing or gentle and/or non-boiling, the measured extreme δ65Cu values are consistent with transport of Cu by vapor that is preferentially enriched by heavy 65Cu and controlled by continuous Rayleigh distillation−type Cu fractionation. Boiling-induced Cu vapor transport can generate extreme Cu isotope fractionation.
{"title":"Boiling-induced extreme Cu isotope fractionation in sulfide minerals forming by active hydrothermal diffusers at the Aegean Kolumbo volcano: Evidence from in situ isotope analysis","authors":"Nikolaos N. Zegkinoglou, R. Mathur, S. Kilias, L. Godfrey, Vasilios Pletsas, P. Nomikou, N. Zaronikola","doi":"10.1130/g51404.1","DOIUrl":"https://doi.org/10.1130/g51404.1","url":null,"abstract":"We analyzed the first Cu isotopes in primary cupreous pyrite and orpiment, from modern CO2-degassing, seafloor massive sulfide diffuser vents (“ΚCO2Ds”), from the Kolumbo submarine volcano, Hellenic volcanic arc. Samples came from six ΚCO2Ds that are actively boiling. Pyrite comprises colloform pyrite-I and euhedral pyrite-II, which occur erratically distributed within the ΚCO2Ds and are contemporaneous with barite and spatially concurrent with the chalcopyrite that is lining narrow internal conduits, respectively. Orpiment occurs on the outer walls of the KCO2Ds with barite and stibnite. The δ65Cupyrite-I values show high variability, ranging from +2.93‰ to +6.38‰, whereas the δ65Cupyrite-II and δ65Cuchalcopyrite values vary from −0.94‰ to +0.25‰ and −0.45‰ to −0.09‰, respectively. The range of δ65Cuorpiment between +1.90‰ and +25.73‰ is the most extreme ever reported from any geological setting. Pyrite-I is concentrically layered, with a core comprising random crystallites, whereas the mantle crystallites have grain-size, shape, and orientation variability between layers. Pyrite-II forms aggregates of uniform euhedral pyrite crystals. Pyrite-I has higher concentrations of Cu (≤21,960 ppm) compared to pyrite-II (≤4963 ppm), and both have incompatible and volatile metal(loid)-rich composition and low Sb/Pb (<0.5) and Tl/Pb (<0.03) ratios. When combined with evidence for significant magmatic contributions at Kolumbo and geochemical and micro-textural evidence for recurrent intense boiling and/or flashing or gentle and/or non-boiling, the measured extreme δ65Cu values are consistent with transport of Cu by vapor that is preferentially enriched by heavy 65Cu and controlled by continuous Rayleigh distillation−type Cu fractionation. Boiling-induced Cu vapor transport can generate extreme Cu isotope fractionation.","PeriodicalId":12642,"journal":{"name":"Geology","volume":" ","pages":""},"PeriodicalIF":5.8,"publicationDate":"2023-08-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"43557342","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}
Recent research has found that the subsiding Sunda Shelf (Southeast Asia) was permanently exposed prior to ca. 400 ka with initial submersion-exposure cyclicity, associated with interglacial-glacial sea-level cycles, beginning between 400 and 240 ka. We analyzed the impact submersion-exposure cycles on regional environment and climate through a 640 k.y. leaf-wax carbon isotope (δ13Cwax) reconstruction at Andaman Sea Site U1448, representing relative changes in C3/C4 plant abundances. Prior to ca. 250 ka, the Sunda region was inhabited by a stable C3 (forest) biome, after which submersion-exposure cycles initiated with the deglacial sea-level rise at ca. 250 ka. During subsequent glacial-age sea-level drops, the newly exposed shelf was rapidly colonized by C4 grasses, followed by slow transitions back to C3 forests, representing a tenfold increase in the variability of C3/C4 vegetation in the Sunda region. The C3/C4 regime shift since 250 ka is coherent across the Southeast (SE) Asia peninsula and Sunda Shelf and is coincident with a shift in the east-west sea-surface temperature gradient in the equatorial Pacific Ocean. We hypothesize that the expansion of C4 grasslands promoted and sustained drier glacial-age climates over SE Asia via a feedback mechanism that contributed to weakening the ascending branch of the east-west atmospheric circulation in the equatorial Pacific region known as the Walker Circulation. Our results indicate that the Sunda Shelf region has a larger influence on Walker Circulation than is seen in current paleoclimate simulations.
{"title":"Pleistocene Sunda Shelf submersion-exposure cycles initiate vegetation Walker Circulation feedback","authors":"S. McGrath, S. Clemens, Yongsong Huang","doi":"10.1130/g51412.1","DOIUrl":"https://doi.org/10.1130/g51412.1","url":null,"abstract":"Recent research has found that the subsiding Sunda Shelf (Southeast Asia) was permanently exposed prior to ca. 400 ka with initial submersion-exposure cyclicity, associated with interglacial-glacial sea-level cycles, beginning between 400 and 240 ka. We analyzed the impact submersion-exposure cycles on regional environment and climate through a 640 k.y. leaf-wax carbon isotope (δ13Cwax) reconstruction at Andaman Sea Site U1448, representing relative changes in C3/C4 plant abundances. Prior to ca. 250 ka, the Sunda region was inhabited by a stable C3 (forest) biome, after which submersion-exposure cycles initiated with the deglacial sea-level rise at ca. 250 ka. During subsequent glacial-age sea-level drops, the newly exposed shelf was rapidly colonized by C4 grasses, followed by slow transitions back to C3 forests, representing a tenfold increase in the variability of C3/C4 vegetation in the Sunda region. The C3/C4 regime shift since 250 ka is coherent across the Southeast (SE) Asia peninsula and Sunda Shelf and is coincident with a shift in the east-west sea-surface temperature gradient in the equatorial Pacific Ocean. We hypothesize that the expansion of C4 grasslands promoted and sustained drier glacial-age climates over SE Asia via a feedback mechanism that contributed to weakening the ascending branch of the east-west atmospheric circulation in the equatorial Pacific region known as the Walker Circulation. Our results indicate that the Sunda Shelf region has a larger influence on Walker Circulation than is seen in current paleoclimate simulations.","PeriodicalId":12642,"journal":{"name":"Geology","volume":" ","pages":""},"PeriodicalIF":5.8,"publicationDate":"2023-08-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"49406977","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}
V. Polyak, Brionna H. Curry, Daniel J. Lavery, Z. Strasberg, S. Cutler, Wenkai Song, L. Crossey, K. Karlstrom, Y. Asmerom
We report exceptionally negative δ238U values for spring water (−2.5‰ to −0.8‰) and travertine calcite (−3.2‰ to −1.1‰) from an area where the Jemez lineament intersects the western margins of the Rio Grande rift, west-central New Mexico (southwestern United States). The highest anomalies come from the southern margins of the Valles Caldera and are related to upwelling CO2-charged spring water forming travertine mounds along joints and faults. The anomaly likely occurs due to CO2 lixiviation of uranium in a deep-seated reduced environment where 235U is preferentially leached along a long flow path through Precambrian granitic basement, resulting in spring water with exceptionally low δ238U values inherited by the calcite that precipitated near or at the surface at relatively low temperatures, i.e., ∼40 °C (modern temperatures). The lowest δ238U values are preserved in settings where upwelling waters are least diluted by oxidized aquifer groundwaters. Given these low δ238U values in travertine are associated with and possibly indicators of upwelling CO2 related to tectonic and magmatic activity, studies such as ours may be used to identify this association far back in time.
{"title":"Large negative δ238U anomalies in endogenic-type travertine systems","authors":"V. Polyak, Brionna H. Curry, Daniel J. Lavery, Z. Strasberg, S. Cutler, Wenkai Song, L. Crossey, K. Karlstrom, Y. Asmerom","doi":"10.1130/g51333.1","DOIUrl":"https://doi.org/10.1130/g51333.1","url":null,"abstract":"We report exceptionally negative δ238U values for spring water (−2.5‰ to −0.8‰) and travertine calcite (−3.2‰ to −1.1‰) from an area where the Jemez lineament intersects the western margins of the Rio Grande rift, west-central New Mexico (southwestern United States). The highest anomalies come from the southern margins of the Valles Caldera and are related to upwelling CO2-charged spring water forming travertine mounds along joints and faults. The anomaly likely occurs due to CO2 lixiviation of uranium in a deep-seated reduced environment where 235U is preferentially leached along a long flow path through Precambrian granitic basement, resulting in spring water with exceptionally low δ238U values inherited by the calcite that precipitated near or at the surface at relatively low temperatures, i.e., ∼40 °C (modern temperatures). The lowest δ238U values are preserved in settings where upwelling waters are least diluted by oxidized aquifer groundwaters. Given these low δ238U values in travertine are associated with and possibly indicators of upwelling CO2 related to tectonic and magmatic activity, studies such as ours may be used to identify this association far back in time.","PeriodicalId":12642,"journal":{"name":"Geology","volume":" ","pages":""},"PeriodicalIF":5.8,"publicationDate":"2023-08-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"48033998","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}
The relative proportions of carbon, nitrogen, and phosphorus, commonly referred to as the Redfield ratio (106:16:1), have likely varied dramatically through Earth’s history in response to changes in oceanic redox state and nutrient availability. However, there have been few attempts to track long-term secular patterns in the elemental stoichiometry of marine life. We use a sediment reactive-transport (diagenetic) modeling approach to provide new constraints on the elemental stoichiometry of marine ecosystems during Earth’s early history, by simulating environmental conditions associated with the formation and deposition of suites of Archean sedimentary iron and phosphorus-bearing minerals. Our results suggest that siderite formation in porewaters linked to dissimilatory iron reduction but limited formation of authigenic P phases can only be reproduced when C to P ratios in marine biomass are at least 500 (mol/mol), approximately five times higher than the values that characterize the modern ocean. This constraint indicates that Archean oceans were strongly nutrient-limited.
{"title":"Constraining the elemental stoichiometry of early marine life","authors":"M. Fakhraee, L. Tarhan, C. Reinhard, N. Planavsky","doi":"10.1130/g51416.1","DOIUrl":"https://doi.org/10.1130/g51416.1","url":null,"abstract":"The relative proportions of carbon, nitrogen, and phosphorus, commonly referred to as the Redfield ratio (106:16:1), have likely varied dramatically through Earth’s history in response to changes in oceanic redox state and nutrient availability. However, there have been few attempts to track long-term secular patterns in the elemental stoichiometry of marine life. We use a sediment reactive-transport (diagenetic) modeling approach to provide new constraints on the elemental stoichiometry of marine ecosystems during Earth’s early history, by simulating environmental conditions associated with the formation and deposition of suites of Archean sedimentary iron and phosphorus-bearing minerals. Our results suggest that siderite formation in porewaters linked to dissimilatory iron reduction but limited formation of authigenic P phases can only be reproduced when C to P ratios in marine biomass are at least 500 (mol/mol), approximately five times higher than the values that characterize the modern ocean. This constraint indicates that Archean oceans were strongly nutrient-limited.","PeriodicalId":12642,"journal":{"name":"Geology","volume":" ","pages":""},"PeriodicalIF":5.8,"publicationDate":"2023-08-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"46712050","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}
K. Nichols, D. Rood, R. Venturelli, G. Balco, Jonathan R. Adams, Louise Guillaume, S. Campbell, B. Goehring, B. Hall, K. Wilcken, J. Woodward, Joanne S. Johnson
Pine Island Glacier, West Antarctica, is the largest Antarctic contributor to global sea-level rise and is vulnerable to rapid retreat, yet our knowledge of its deglacial history since the Last Glacial Maximum is based largely on marine sediments that record a retreat history ending in the early Holocene. Using a suite of 10Be exposure ages from onshore glacial deposits directly adjacent to Pine Island Glacier, we show that this major glacier thinned rapidly in the early to mid-Holocene. Our results indicate that Pine Island Glacier was at least 690 m thicker than present prior to ca. 8 ka. We infer that the rapid thinning detected at the site furthest downstream records the arrival and stabilization of the retreating grounding line at that site by 8−6 ka. By combining our exposure ages and the marine record, we extend knowledge of Pine Island Glacier retreat both spatially and temporally: to 50 km from the modern grounding line and to the mid-Holocene, providing a data set that is important for future numerical ice-sheet model validation.
{"title":"Offshore-onshore record of Last Glacial Maximum−to−present grounding line retreat at Pine Island Glacier, Antarctica","authors":"K. Nichols, D. Rood, R. Venturelli, G. Balco, Jonathan R. Adams, Louise Guillaume, S. Campbell, B. Goehring, B. Hall, K. Wilcken, J. Woodward, Joanne S. Johnson","doi":"10.1130/g51326.1","DOIUrl":"https://doi.org/10.1130/g51326.1","url":null,"abstract":"Pine Island Glacier, West Antarctica, is the largest Antarctic contributor to global sea-level rise and is vulnerable to rapid retreat, yet our knowledge of its deglacial history since the Last Glacial Maximum is based largely on marine sediments that record a retreat history ending in the early Holocene. Using a suite of 10Be exposure ages from onshore glacial deposits directly adjacent to Pine Island Glacier, we show that this major glacier thinned rapidly in the early to mid-Holocene. Our results indicate that Pine Island Glacier was at least 690 m thicker than present prior to ca. 8 ka. We infer that the rapid thinning detected at the site furthest downstream records the arrival and stabilization of the retreating grounding line at that site by 8−6 ka. By combining our exposure ages and the marine record, we extend knowledge of Pine Island Glacier retreat both spatially and temporally: to 50 km from the modern grounding line and to the mid-Holocene, providing a data set that is important for future numerical ice-sheet model validation.","PeriodicalId":12642,"journal":{"name":"Geology","volume":" ","pages":""},"PeriodicalIF":5.8,"publicationDate":"2023-08-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"49043703","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}
S. Barnes, M. Yudovskaya, G. Iacono-Marziano, Margaux Le Vaillant, L. Schoneveld, A. Cruden
The Norilsk-Talnakh orebodies in Siberia are some of the largest examples on Earth of magmatic Ni−Cu−platinum group element (PGE) deposits, formed by segregation of immiscible sulfide melts from silicate magmas. They show distinctive features attributable to degassing of a magmatic vapor phase during ore formation, including: vesiculation of the host intrusions, widespread intrusion breccias, and extensive hydrofracturing, skarns, and metasomatic replacement in the country rocks. Much of the magmatic sulfide was generated by assimilation of anhydrite and carbonaceous material, leading to injection of a suspension of fine sulfide droplets attached to gas bubbles into propagating tube-like host sills ("chonoliths"). Catastrophic vapor phase exsolution associated with a drop in magma overpressure at the transition from vertical to horizontal magma flow enabled explosive propagation of chonoliths, rapid "harvesting" and gravity deposition of the characteristic coarse sulfide globules that form much of the ore, and extensive magmatic fluid interaction with country rocks.
西伯利亚的Norilsk-Talnakh矿体是地球上最大的岩浆Ni - Cu -铂族元素(PGE)矿床，由硅酸盐岩浆中不混溶的硫化物熔体分离形成。它们具有成矿过程中岩浆气相脱气的独特特征，包括:寄主侵入体的囊化作用，侵入角砾岩的广泛分布，以及围岩中广泛存在的水力压裂、矽卡岩和交代置换。大部分岩浆硫化物是由硬石膏和碳质物质的同化作用产生的，导致附着在气泡上的细硫化物液滴悬浮液注入到传播的管状宿主层(“球粒岩”)中。从垂直岩浆流到水平岩浆流的转变过程中，岩浆超压的下降带来了灾难性的气相析出，这使得球粒岩的爆炸性传播、形成大部分矿石的特征粗硫粒的快速“收获”和重力沉积，以及岩浆流体与乡村岩石的广泛相互作用成为可能。
{"title":"Role of volatiles in intrusion emplacement and sulfide deposition in the supergiant Norilsk-Talnakh Ni-Cu-PGE ore deposits","authors":"S. Barnes, M. Yudovskaya, G. Iacono-Marziano, Margaux Le Vaillant, L. Schoneveld, A. Cruden","doi":"10.1130/g51359.1","DOIUrl":"https://doi.org/10.1130/g51359.1","url":null,"abstract":"The Norilsk-Talnakh orebodies in Siberia are some of the largest examples on Earth of magmatic Ni−Cu−platinum group element (PGE) deposits, formed by segregation of immiscible sulfide melts from silicate magmas. They show distinctive features attributable to degassing of a magmatic vapor phase during ore formation, including: vesiculation of the host intrusions, widespread intrusion breccias, and extensive hydrofracturing, skarns, and metasomatic replacement in the country rocks. Much of the magmatic sulfide was generated by assimilation of anhydrite and carbonaceous material, leading to injection of a suspension of fine sulfide droplets attached to gas bubbles into propagating tube-like host sills (\"chonoliths\"). Catastrophic vapor phase exsolution associated with a drop in magma overpressure at the transition from vertical to horizontal magma flow enabled explosive propagation of chonoliths, rapid \"harvesting\" and gravity deposition of the characteristic coarse sulfide globules that form much of the ore, and extensive magmatic fluid interaction with country rocks.","PeriodicalId":12642,"journal":{"name":"Geology","volume":" ","pages":""},"PeriodicalIF":5.8,"publicationDate":"2023-08-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"45882966","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}
Yong-Shu Huang, Qi Liu, Fei-Xiang Liu, Xiaochun Li, Yu Liu, G. Tang, H. Fan, Xian‐Hua Li, Qiu-Li Li
Carbonatites, the most silica-poor igneous rocks, have a close relationship with rare earth element (REE) ore deposits, where low SiO2 activity is considered to contribute to economic REE mineralization. However, a paradox is raised by quartz, commonly regarded as a Si-saturation proxy, which occurs in some giant carbonatites or carbonatite-related REE deposits such as those at Bayan Obo, China, and Mountain Pass, California, USA. A unique perception for the origin of quartz in carbonatites is provided here using Si isotope analysis. Quartz grains from the Bayan Obo carbonatite and REE ores commonly occur as inclusions in fluorite, or they coexist with fluorite, thus implicating the importance of fluorine in their hydrothermal origin. The quartz grains have remarkably large variations in δ30Si values, ranging from −4.55‰ to 1.71‰ in secondary ion mass spectrometry analyses, which have not been documented elsewhere in high- to medium-temperature magmatic-hydrothermal processes. Theoretical calculations demonstrate that such large Si isotopic fractionation can be generated during the formation and breakdown of Si-O and Si-F bonds due to their difference in bond strength. These results imply the presence of silicon fluoride species in the fluid and highlight the role of fluorine in quartz formation in silicon-poor carbonatite. The exsolved fluids from carbonatite magmas containing silicon fluoride species may decrease silica activity, which has the potential to impede incorporation of REEs into magmatic apatite, and thus facilitate late-stage hydrothermal REE enrichment and formation of REE orebodies.
{"title":"Large Si isotope fractionation reveals formation mechanism of quartz in silicon-poor carbonatite","authors":"Yong-Shu Huang, Qi Liu, Fei-Xiang Liu, Xiaochun Li, Yu Liu, G. Tang, H. Fan, Xian‐Hua Li, Qiu-Li Li","doi":"10.1130/g51314.1","DOIUrl":"https://doi.org/10.1130/g51314.1","url":null,"abstract":"Carbonatites, the most silica-poor igneous rocks, have a close relationship with rare earth element (REE) ore deposits, where low SiO2 activity is considered to contribute to economic REE mineralization. However, a paradox is raised by quartz, commonly regarded as a Si-saturation proxy, which occurs in some giant carbonatites or carbonatite-related REE deposits such as those at Bayan Obo, China, and Mountain Pass, California, USA. A unique perception for the origin of quartz in carbonatites is provided here using Si isotope analysis. Quartz grains from the Bayan Obo carbonatite and REE ores commonly occur as inclusions in fluorite, or they coexist with fluorite, thus implicating the importance of fluorine in their hydrothermal origin. The quartz grains have remarkably large variations in δ30Si values, ranging from −4.55‰ to 1.71‰ in secondary ion mass spectrometry analyses, which have not been documented elsewhere in high- to medium-temperature magmatic-hydrothermal processes. Theoretical calculations demonstrate that such large Si isotopic fractionation can be generated during the formation and breakdown of Si-O and Si-F bonds due to their difference in bond strength. These results imply the presence of silicon fluoride species in the fluid and highlight the role of fluorine in quartz formation in silicon-poor carbonatite. The exsolved fluids from carbonatite magmas containing silicon fluoride species may decrease silica activity, which has the potential to impede incorporation of REEs into magmatic apatite, and thus facilitate late-stage hydrothermal REE enrichment and formation of REE orebodies.","PeriodicalId":12642,"journal":{"name":"Geology","volume":" ","pages":""},"PeriodicalIF":5.8,"publicationDate":"2023-08-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"48479402","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}
R. Bryant, J. Richardson, T. Kalia, O. Gros, J. Lópéz-Garriga, C. Blättler
Bivalves that host sulfur-oxidizing bacterial gill-hosted endosymbionts can inhabit low-diversity, sulfidic environmental niches. However, understanding the history of this life strategy is limited by the lack of a robust method that can be applied to fossils. Measurements of carbonate-associated sulfate S isotope ratios (CAS-δ34S) in carbonate fossils could fill this void by fingerprinting symbiont-driven oxidation of environmental sulfide. We begin to evaluate this prediction using modern lucinid bivalves, a useful test case because: (1) all modern genera host symbionts and live in sulfidic sediments, and (2) morphological evidence suggests that this has been true since the earliest ancestral lucinids. We measured S speciation, abundance, and CAS-δ34S values in the shells of a suite of modern infaunal lucinids, in addition to epifaunal bivalves with and without S-oxidizing symbionts as controls. For infaunal lucinids, CAS concentrations were at most one-third of those of non-symbiotic epifaunal bivalves, and CAS-δ34S values were lower (9.2‰−18.5‰) than in modern seawater (21‰) or epifaunal bivalves (20.8‰−21‰). These observations indicate that lucinids with symbionts incorporate sulfide-derived sulfate into their shells as a direct consequence of their chemosymbiosis. We argue that both the concentration and the magnitude of 34S depletion in infaunal lucinid CAS reflect environmental sulfide concentrations and could viably reveal chemosymbiosis in fossils.
{"title":"Inorganic sulfate−based signatures of chemosymbiosis in modern infaunal lucinids","authors":"R. Bryant, J. Richardson, T. Kalia, O. Gros, J. Lópéz-Garriga, C. Blättler","doi":"10.1130/g51353.1","DOIUrl":"https://doi.org/10.1130/g51353.1","url":null,"abstract":"Bivalves that host sulfur-oxidizing bacterial gill-hosted endosymbionts can inhabit low-diversity, sulfidic environmental niches. However, understanding the history of this life strategy is limited by the lack of a robust method that can be applied to fossils. Measurements of carbonate-associated sulfate S isotope ratios (CAS-δ34S) in carbonate fossils could fill this void by fingerprinting symbiont-driven oxidation of environmental sulfide. We begin to evaluate this prediction using modern lucinid bivalves, a useful test case because: (1) all modern genera host symbionts and live in sulfidic sediments, and (2) morphological evidence suggests that this has been true since the earliest ancestral lucinids. We measured S speciation, abundance, and CAS-δ34S values in the shells of a suite of modern infaunal lucinids, in addition to epifaunal bivalves with and without S-oxidizing symbionts as controls. For infaunal lucinids, CAS concentrations were at most one-third of those of non-symbiotic epifaunal bivalves, and CAS-δ34S values were lower (9.2‰−18.5‰) than in modern seawater (21‰) or epifaunal bivalves (20.8‰−21‰). These observations indicate that lucinids with symbionts incorporate sulfide-derived sulfate into their shells as a direct consequence of their chemosymbiosis. We argue that both the concentration and the magnitude of 34S depletion in infaunal lucinid CAS reflect environmental sulfide concentrations and could viably reveal chemosymbiosis in fossils.","PeriodicalId":12642,"journal":{"name":"Geology","volume":" ","pages":""},"PeriodicalIF":5.8,"publicationDate":"2023-08-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"48123383","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}
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