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":null,"pages":null},"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":null,"pages":null},"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":null,"pages":null},"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":null,"pages":null},"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":null,"pages":null},"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}
Benjamin Eskesen, K. Fassmer, C. Münker, T. Ulrich, K. Szilas, Simon Wagner, J. Hoffmann, T. Nagel
We present petrological data and seven Lu-Hf garnet−amphibole−whole rock ages obtained from a single garnet-hornblende-mica schist sample from the Isua supracrustal belt (West Greenland). Garnets grew during prograde metamorphism toward regional amphibolite-facies peak conditions, and a mylonitic foliation formed during and after garnet growth. Garnet crystals show typical prograde zoning with no visible traces of a relict garnet generation. They do show various degrees of retrogression. While some crystals are perfectly euhedral with only minor chemical alteration along cracks, others are elongated in the foliation and either grew in this shape or were deformed. Six garnet splits were separated from crushed single crystals and one from a crushed bulk sample. Individual three-point garnet−hornblende−whole rock ages scatter between 2.603 ± 0.018 Ga and 2.432 ± 0.059 Ga for single garnets. The garnet split from the bulk sample defines an age of 2.463 ± 0.031 Ga, the data point farthest from the regression line for all data points (2.551 ± 0.074 Ga, mean square of weighted deviates = 25). We interpret these data to indicate partial retrogression of a Neoarchean garnet population not significantly older than the oldest obtained three-point age. Well-preserved garnet zoning, regional peak temperatures well below the closing temperature of the Lu-Hf system, and the small scatter of Lu-Hf ages preclude an interpretation of the observed metamorphism and deformation as being Eoarchean in age.
{"title":"Neoarchean synkinematic metamorphic peak in the Isua supracrustal belt (West Greenland)","authors":"Benjamin Eskesen, K. Fassmer, C. Münker, T. Ulrich, K. Szilas, Simon Wagner, J. Hoffmann, T. Nagel","doi":"10.1130/g51564.1","DOIUrl":"https://doi.org/10.1130/g51564.1","url":null,"abstract":"We present petrological data and seven Lu-Hf garnet−amphibole−whole rock ages obtained from a single garnet-hornblende-mica schist sample from the Isua supracrustal belt (West Greenland). Garnets grew during prograde metamorphism toward regional amphibolite-facies peak conditions, and a mylonitic foliation formed during and after garnet growth. Garnet crystals show typical prograde zoning with no visible traces of a relict garnet generation. They do show various degrees of retrogression. While some crystals are perfectly euhedral with only minor chemical alteration along cracks, others are elongated in the foliation and either grew in this shape or were deformed. Six garnet splits were separated from crushed single crystals and one from a crushed bulk sample. Individual three-point garnet−hornblende−whole rock ages scatter between 2.603 ± 0.018 Ga and 2.432 ± 0.059 Ga for single garnets. The garnet split from the bulk sample defines an age of 2.463 ± 0.031 Ga, the data point farthest from the regression line for all data points (2.551 ± 0.074 Ga, mean square of weighted deviates = 25). We interpret these data to indicate partial retrogression of a Neoarchean garnet population not significantly older than the oldest obtained three-point age. Well-preserved garnet zoning, regional peak temperatures well below the closing temperature of the Lu-Hf system, and the small scatter of Lu-Hf ages preclude an interpretation of the observed metamorphism and deformation as being Eoarchean in age.","PeriodicalId":12642,"journal":{"name":"Geology","volume":null,"pages":null},"PeriodicalIF":5.8,"publicationDate":"2023-08-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"47549075","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. Kelley, M. Yu, D. Lehrmann, D. Altıner, J. Payne
The tempo of biotic recovery following extinction reflects the time scales of evolutionary processes and the long-term consequences of degraded ecosystems, but recovery patterns are poorly resolved. In this study, we investigated the tempo of biotic recovery by evaluating metazoan-algal reef assembly following the end-Permian mass extinction. We combined satellite imagery analysis, field mapping, biostratigraphy, and quantitative petrography to assess recovery in the oldest-known and most stratigraphically extensive Lower to Middle Triassic platform-margin reef. The reef occurs in upper Spathian (upper Lower Triassic) to upper Anisian (lower Middle Triassic) strata of the Great Bank of Guizhou (GBG) isolated carbonate platform in south China. Previous work suggests that metazoan-algal reefs were absent for 8−10 m.y. following extinction but were biologically diverse from their Pelsonian (middle Anisian) initiation. This pattern implies that reefs can reassemble rapidly (<< 1 m.y.) when environmental conditions are favorable. In contrast, our analyses indicate that calcareous sponges, calcareous algae, and early scleractinian corals occurred progressively in the GBG reef and that biotic recovery metrics increased gradually. Unlike nonreef ecosystems, biodiverse metazoan-algal reefs were delayed until the late Pelsonian or early Illyrian, postdating broader marine ecosystem recovery and isotopic evidence for carbon-cycle stabilization by 2−4 m.y. Our findings suggest that reef and nonreef ecosystems differ in their recovery pattern and tempo. Reef recovery from severe environmental perturbation can require several million years, even after hospitable conditions return, highlighting the importance of modern reef conservation.
{"title":"Prolonged and gradual recovery of metazoan-algal reefs following the end-Permian mass extinction","authors":"B. Kelley, M. Yu, D. Lehrmann, D. Altıner, J. Payne","doi":"10.1130/g51058.1","DOIUrl":"https://doi.org/10.1130/g51058.1","url":null,"abstract":"The tempo of biotic recovery following extinction reflects the time scales of evolutionary processes and the long-term consequences of degraded ecosystems, but recovery patterns are poorly resolved. In this study, we investigated the tempo of biotic recovery by evaluating metazoan-algal reef assembly following the end-Permian mass extinction. We combined satellite imagery analysis, field mapping, biostratigraphy, and quantitative petrography to assess recovery in the oldest-known and most stratigraphically extensive Lower to Middle Triassic platform-margin reef. The reef occurs in upper Spathian (upper Lower Triassic) to upper Anisian (lower Middle Triassic) strata of the Great Bank of Guizhou (GBG) isolated carbonate platform in south China. Previous work suggests that metazoan-algal reefs were absent for 8−10 m.y. following extinction but were biologically diverse from their Pelsonian (middle Anisian) initiation. This pattern implies that reefs can reassemble rapidly (<< 1 m.y.) when environmental conditions are favorable. In contrast, our analyses indicate that calcareous sponges, calcareous algae, and early scleractinian corals occurred progressively in the GBG reef and that biotic recovery metrics increased gradually. Unlike nonreef ecosystems, biodiverse metazoan-algal reefs were delayed until the late Pelsonian or early Illyrian, postdating broader marine ecosystem recovery and isotopic evidence for carbon-cycle stabilization by 2−4 m.y. Our findings suggest that reef and nonreef ecosystems differ in their recovery pattern and tempo. Reef recovery from severe environmental perturbation can require several million years, even after hospitable conditions return, highlighting the importance of modern reef conservation.","PeriodicalId":12642,"journal":{"name":"Geology","volume":null,"pages":null},"PeriodicalIF":5.8,"publicationDate":"2023-08-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"42389912","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}
G. Volpe, G. Pozzi, M.E. Locchi, E. Tinti, M. Scuderi, C. Marone, C. Collettini
Although rheological heterogeneities are invoked to explain differences in fault-slip behavior, case studies where an interdisciplinary approach is adopted to capture their specific roles are still rare. In this work, we integrated geophysical, geological, and laboratory data to explain how rheological heterogeneities influence the earthquake activity at the roots of the seismogenic zone. During the 2016–2017 Central Italy sequence, following the major earthquakes, we observed a deepening of seismicity within the basement associated with a transient stress change. Part of this seismicity was organized in clusters of events, with similar sizes and waveforms. The structural study of exhumed basement rocks highlighted a heterogeneous fabric made of strong, quartz-rich lenses (up to 200 m) surrounded by a weak, interconnected phyllosilicate-rich matrix. Laboratory experiments simulating the main shock–induced increase in loading rate showed that the matrix lithology experienced an accelerating and self-decelerating aseismic creep, whereas the lens lithology showed dynamic instabilities. Our results suggest that the post–main shock loading rate increases favored accelerated creep within the matrix, which promoted, as a consequence, seismic instabilities within the lenses in the form of clustered seismicity. Our findings emphasize the strong connection between seismicity and the structural and frictional properties of the seismogenic zone.
{"title":"Rheological heterogeneities at the roots of the seismogenic zone","authors":"G. Volpe, G. Pozzi, M.E. Locchi, E. Tinti, M. Scuderi, C. Marone, C. Collettini","doi":"10.1130/g51432.1","DOIUrl":"https://doi.org/10.1130/g51432.1","url":null,"abstract":"Although rheological heterogeneities are invoked to explain differences in fault-slip behavior, case studies where an interdisciplinary approach is adopted to capture their specific roles are still rare. In this work, we integrated geophysical, geological, and laboratory data to explain how rheological heterogeneities influence the earthquake activity at the roots of the seismogenic zone. During the 2016–2017 Central Italy sequence, following the major earthquakes, we observed a deepening of seismicity within the basement associated with a transient stress change. Part of this seismicity was organized in clusters of events, with similar sizes and waveforms. The structural study of exhumed basement rocks highlighted a heterogeneous fabric made of strong, quartz-rich lenses (up to 200 m) surrounded by a weak, interconnected phyllosilicate-rich matrix. Laboratory experiments simulating the main shock–induced increase in loading rate showed that the matrix lithology experienced an accelerating and self-decelerating aseismic creep, whereas the lens lithology showed dynamic instabilities. Our results suggest that the post–main shock loading rate increases favored accelerated creep within the matrix, which promoted, as a consequence, seismic instabilities within the lenses in the form of clustered seismicity. Our findings emphasize the strong connection between seismicity and the structural and frictional properties of the seismogenic zone.","PeriodicalId":12642,"journal":{"name":"Geology","volume":null,"pages":null},"PeriodicalIF":5.8,"publicationDate":"2023-08-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"45909480","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}
Volcanoes exhibit a wide range of eruptive and geochemical behavior, which has significant implications for their associated risk. The suggested first-order drivers of intervolcanic diversity invoke a combination of crustal and mantle processes. To better constrain mantle-crustal-volcanic coupling, we used the well-studied Lesser Antilles island arc. Here, we show that melt flux from the mantle, identified by proxy in the form of boron isotopes in melt inclusions, correlates with the long-term volcanic productivity, the volcanic edifice height, and the geophysically defined along-arc crustal structure. These features are the consequence of a variable melt flux modulating the pressure-temperature-composition structure of the crust, which we inverted from xenolith mineral chemistry. Mafic to intermediate melts reside at relatively constant temperature (981 ± 52 °C; 2σ) in the middle crust (3.5−7.1 kbar), whereas chemically evolved (rhyolitic) melts are stored predominantly in the upper crust (<3.5 kbar) at maximum depths that vary geophysically along the arc (6−15 km). Our findings are applicable worldwide, where we see similar correlations among average magma geochemistry, eruptive magnitude, and rate of magma input.
{"title":"Eruptive dynamics reflect crustal structure and mantle productivity beneath volcanoes","authors":"O. Higgins, L. Caricchi","doi":"10.1130/g51355.1","DOIUrl":"https://doi.org/10.1130/g51355.1","url":null,"abstract":"Volcanoes exhibit a wide range of eruptive and geochemical behavior, which has significant implications for their associated risk. The suggested first-order drivers of intervolcanic diversity invoke a combination of crustal and mantle processes. To better constrain mantle-crustal-volcanic coupling, we used the well-studied Lesser Antilles island arc. Here, we show that melt flux from the mantle, identified by proxy in the form of boron isotopes in melt inclusions, correlates with the long-term volcanic productivity, the volcanic edifice height, and the geophysically defined along-arc crustal structure. These features are the consequence of a variable melt flux modulating the pressure-temperature-composition structure of the crust, which we inverted from xenolith mineral chemistry. Mafic to intermediate melts reside at relatively constant temperature (981 ± 52 °C; 2σ) in the middle crust (3.5−7.1 kbar), whereas chemically evolved (rhyolitic) melts are stored predominantly in the upper crust (<3.5 kbar) at maximum depths that vary geophysically along the arc (6−15 km). Our findings are applicable worldwide, where we see similar correlations among average magma geochemistry, eruptive magnitude, and rate of magma input.","PeriodicalId":12642,"journal":{"name":"Geology","volume":null,"pages":null},"PeriodicalIF":5.8,"publicationDate":"2023-08-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"46053031","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}
Megabeds are exceptionally large submarine deposits interpreted to originate from single catastrophic events. Megabeds are significant components of deep-water basins and are critical for understanding geohazards. We discovered a succession of four megabeds within the upper 70 m of the western Marsili Basin, Tyrrhenian Sea, deposited within the past 50 k.y. The megabeds were imaged as distinctive acoustically transparent units with ponded geometries, 10−25 m thick, separated by parallel-bedded strata. Cores from Site 650 of Ocean Drilling Program Leg 107 revealed that three of the four megabeds are made of alternating volcaniclastic sand and mud, and one is a volcaniclastic debris flow. Abundant shallow-water benthic foraminifera within the megabeds suggest that they were not sourced locally from the active Marsili Seamount, but most likely originated from the Campanian volcanic province to the north. The time interval during which the megabeds were deposited includes the 39.8 ka Campanian ignimbrite supereruption of the Campi Flegrei caldera, Italy, which is among the largest known eruptions on Earth, and the 14.9 ka Neapolitan Yellow Tuff supereruption. Volume (minimum) estimates range from 1.3 to 13.3 km3. However, similar megabeds observed in the neighboring Vavilov Basin to the west suggest that the megabeds in both basins may be correlative, and thus volumes could be much larger. The newly discovered megabeds of the Marsili Basin reveal significant geohazard events for the circum−Tyrrhenian Sea coastlines with a recurrence interval on the order of ∼10−15 k.y.
{"title":"50,000 yr of recurrent volcaniclastic megabed deposition in the Marsili Basin, Tyrrhenian Sea","authors":"D. Sawyer, R. Urgeles, C. Lo Iacono","doi":"10.1130/g51198.1","DOIUrl":"https://doi.org/10.1130/g51198.1","url":null,"abstract":"Megabeds are exceptionally large submarine deposits interpreted to originate from single catastrophic events. Megabeds are significant components of deep-water basins and are critical for understanding geohazards. We discovered a succession of four megabeds within the upper 70 m of the western Marsili Basin, Tyrrhenian Sea, deposited within the past 50 k.y. The megabeds were imaged as distinctive acoustically transparent units with ponded geometries, 10−25 m thick, separated by parallel-bedded strata. Cores from Site 650 of Ocean Drilling Program Leg 107 revealed that three of the four megabeds are made of alternating volcaniclastic sand and mud, and one is a volcaniclastic debris flow. Abundant shallow-water benthic foraminifera within the megabeds suggest that they were not sourced locally from the active Marsili Seamount, but most likely originated from the Campanian volcanic province to the north. The time interval during which the megabeds were deposited includes the 39.8 ka Campanian ignimbrite supereruption of the Campi Flegrei caldera, Italy, which is among the largest known eruptions on Earth, and the 14.9 ka Neapolitan Yellow Tuff supereruption. Volume (minimum) estimates range from 1.3 to 13.3 km3. However, similar megabeds observed in the neighboring Vavilov Basin to the west suggest that the megabeds in both basins may be correlative, and thus volumes could be much larger. The newly discovered megabeds of the Marsili Basin reveal significant geohazard events for the circum−Tyrrhenian Sea coastlines with a recurrence interval on the order of ∼10−15 k.y.","PeriodicalId":12642,"journal":{"name":"Geology","volume":null,"pages":null},"PeriodicalIF":5.8,"publicationDate":"2023-08-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"41743189","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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