Thomas Poulet, Heather A. Sheldon, Valentin Zuchuat, Susanne Schmid
Density-driven flow caused by fluid density contrasts in saturated porous rocks plays a critical role in many geological applications, including mineral exploration, hydrogen or carbon storage, and the migration of brines or hydrocarbons. Yet, the influence of anisotropic permeability on density-driven flow, as is common in sedimentary basins, is generally overlooked. By expressing the gravitational force acting on fluids with contrasting densities in anisotropic saturated porous media, we analytically estimate the velocity and angle of a propagating plume as functions of the dip angle of the permeability tensor and the ratio of longitudinal to transverse permeability anisotropy (r). The sensitivity of the plume angle to the bedding angle is greatest in the common case of near-horizontal layers. We demonstrate how, for large permeability anisotropy (e.g., r >100), a dip of only 1° dramatically affects plume migration compared to the perfectly horizontal case. This highlights the need for accurate representation of strata orientation and associated anisotropy in fluid-flow simulations. These results could affect mineral exploration strategies in sedimentary basins, where the slope and anisotropy of sedimentary strata could result in dense mineralizing brines migrating closer or farther from their source than previously expected. Overall, these findings are pertinent to the propagation of both lighter and denser plumes, e.g., supercritical CO2 or brines, revealing where and how fast these plumes can migrate through the dipping, anisotropic strata in sedimentary basins.
{"title":"Small dip, big impact: How 1° strata inclination affects density-driven flow in anisotropic rocks","authors":"Thomas Poulet, Heather A. Sheldon, Valentin Zuchuat, Susanne Schmid","doi":"10.1130/g53888.1","DOIUrl":"https://doi.org/10.1130/g53888.1","url":null,"abstract":"Density-driven flow caused by fluid density contrasts in saturated porous rocks plays a critical role in many geological applications, including mineral exploration, hydrogen or carbon storage, and the migration of brines or hydrocarbons. Yet, the influence of anisotropic permeability on density-driven flow, as is common in sedimentary basins, is generally overlooked. By expressing the gravitational force acting on fluids with contrasting densities in anisotropic saturated porous media, we analytically estimate the velocity and angle of a propagating plume as functions of the dip angle of the permeability tensor and the ratio of longitudinal to transverse permeability anisotropy (r). The sensitivity of the plume angle to the bedding angle is greatest in the common case of near-horizontal layers. We demonstrate how, for large permeability anisotropy (e.g., r >100), a dip of only 1° dramatically affects plume migration compared to the perfectly horizontal case. This highlights the need for accurate representation of strata orientation and associated anisotropy in fluid-flow simulations. These results could affect mineral exploration strategies in sedimentary basins, where the slope and anisotropy of sedimentary strata could result in dense mineralizing brines migrating closer or farther from their source than previously expected. Overall, these findings are pertinent to the propagation of both lighter and denser plumes, e.g., supercritical CO2 or brines, revealing where and how fast these plumes can migrate through the dipping, anisotropic strata in sedimentary basins.","PeriodicalId":12642,"journal":{"name":"Geology","volume":"193 1","pages":""},"PeriodicalIF":5.8,"publicationDate":"2025-09-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145077253","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}
Xin-Meng Liu, Li Liu, Di-Cheng Zhu, Peter A. Cawood, Michael D. Blum, Liang-Liang Zhang, Yao Wang, Yao Lu, Qing Wang, Yu-Xin Chang, Daniel F. Stockli
The physio-chemical resilience of zircons has been key in their increasing application to deciphering geological processes through Earth history. However, zircons are not immune to mechanical abrasion and chemical alteration. This study quantifies the loss of zircon rims from the Brahmaputra source-to-sink (S2S) system, which drains the Himalayan-Tibetan orogen and transports sediment to the deep Bay of Bengal over a total vertical relief of some 7000 m. During sediment transport from this S2S system, median zircon rim thickness decreases by ∼50%, suggesting that information contained in the rim would be lost after reworking of grains through two orogenic and associated sedimentary cycles. To validate this discovery at a global scale, we apply Monte Carlo weighted bootstrap resampling of a global detrital zircon core and rim age data set. After the impacts from changing tectonic regime (increasing metamorphic rim since the late Neoproterozoic and rim formation during continental collision events) were decoded, proportions of rim versus core increase over time and clearly show that old rims have been erased after several rounds of sediment recycling in response to multiple orogenic cycles. Our work suggests that crustal information archived in zircons can be lost during surficial sediment transport in addition to deep crustal-recycling processes such as lithospheric delamination, subduction erosion, and sediment subduction.
{"title":"Erasure of zircon rims by sediment transport after two orogenic cycles","authors":"Xin-Meng Liu, Li Liu, Di-Cheng Zhu, Peter A. Cawood, Michael D. Blum, Liang-Liang Zhang, Yao Wang, Yao Lu, Qing Wang, Yu-Xin Chang, Daniel F. Stockli","doi":"10.1130/g53821.1","DOIUrl":"https://doi.org/10.1130/g53821.1","url":null,"abstract":"The physio-chemical resilience of zircons has been key in their increasing application to deciphering geological processes through Earth history. However, zircons are not immune to mechanical abrasion and chemical alteration. This study quantifies the loss of zircon rims from the Brahmaputra source-to-sink (S2S) system, which drains the Himalayan-Tibetan orogen and transports sediment to the deep Bay of Bengal over a total vertical relief of some 7000 m. During sediment transport from this S2S system, median zircon rim thickness decreases by ∼50%, suggesting that information contained in the rim would be lost after reworking of grains through two orogenic and associated sedimentary cycles. To validate this discovery at a global scale, we apply Monte Carlo weighted bootstrap resampling of a global detrital zircon core and rim age data set. After the impacts from changing tectonic regime (increasing metamorphic rim since the late Neoproterozoic and rim formation during continental collision events) were decoded, proportions of rim versus core increase over time and clearly show that old rims have been erased after several rounds of sediment recycling in response to multiple orogenic cycles. Our work suggests that crustal information archived in zircons can be lost during surficial sediment transport in addition to deep crustal-recycling processes such as lithospheric delamination, subduction erosion, and sediment subduction.","PeriodicalId":12642,"journal":{"name":"Geology","volume":"49 1","pages":""},"PeriodicalIF":5.8,"publicationDate":"2025-09-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145077252","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}
Sarah E. Mazza, Jan Render, Caroline Ruppert, Steven B. Shirey, Josh Wimpenny, Gregory A. Brennecka
Volatile recycling and storage in the mantle transition zone (MTZ) is important for the refertilization of the upper mantle and is associated with the generation of high-µ (HIMU, where µ is 238U/204Pb) mantle. One way to probe the MTZ and the processes associated with mantle convection is to sample lavas that originate from the shallow mantle and were contaminated by upwelling from the MTZ, such as at the previously proposed shallow plume of Bermuda. Here we present the first δ66Zn isotopic compositions of Bermuda silica-undersaturated and silica-saturated lavas to explore the origin of the carbon-rich lithologies and the genesis of the large seamount found in the western North Atlantic Ocean. Contrasting with global δ66Zn data sets, our results (δ66Zn between 0.24 ± 0.04 and 0.41 ± 0.04) do not support direct sampling of recycled marine carbonates in the Bermuda HIMU mantle. Instead, we show that δ66Zn fractionation toward higher values is associated with magmatic processes and incorporation of carbon sourced from deep fluids associated with the formation of carbonatites. These carbon-rich fluids are likely sourced from the metasomatic reactions between the subducted cold slab of the Iapetus oceanic lithosphere ca. 500 Ma and the thickened continental lithospheric mantle of Pangea. Melting of this metasomatized mantle was triggered by the arrival of the Farallon slab to the eastern North American margin in the late Cenozoic via shallow convection.
{"title":"Zinc isotope constraints on the cycling of carbon in the Bermuda mantle source","authors":"Sarah E. Mazza, Jan Render, Caroline Ruppert, Steven B. Shirey, Josh Wimpenny, Gregory A. Brennecka","doi":"10.1130/g53656.1","DOIUrl":"https://doi.org/10.1130/g53656.1","url":null,"abstract":"Volatile recycling and storage in the mantle transition zone (MTZ) is important for the refertilization of the upper mantle and is associated with the generation of high-µ (HIMU, where µ is 238U/204Pb) mantle. One way to probe the MTZ and the processes associated with mantle convection is to sample lavas that originate from the shallow mantle and were contaminated by upwelling from the MTZ, such as at the previously proposed shallow plume of Bermuda. Here we present the first δ66Zn isotopic compositions of Bermuda silica-undersaturated and silica-saturated lavas to explore the origin of the carbon-rich lithologies and the genesis of the large seamount found in the western North Atlantic Ocean. Contrasting with global δ66Zn data sets, our results (δ66Zn between 0.24 ± 0.04 and 0.41 ± 0.04) do not support direct sampling of recycled marine carbonates in the Bermuda HIMU mantle. Instead, we show that δ66Zn fractionation toward higher values is associated with magmatic processes and incorporation of carbon sourced from deep fluids associated with the formation of carbonatites. These carbon-rich fluids are likely sourced from the metasomatic reactions between the subducted cold slab of the Iapetus oceanic lithosphere ca. 500 Ma and the thickened continental lithospheric mantle of Pangea. Melting of this metasomatized mantle was triggered by the arrival of the Farallon slab to the eastern North American margin in the late Cenozoic via shallow convection.","PeriodicalId":12642,"journal":{"name":"Geology","volume":"124 1","pages":""},"PeriodicalIF":5.8,"publicationDate":"2025-09-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145071973","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}
Annia K. Fayon, Lars N. Hansen, Sandra Piazolo, Amanda Dillman, William O. Nachlas
The distribution of Pb in minerals provides a key window into deciphering the time scales of geologic processes. However, the role of deformation-induced dislocations on Pb mobility and redistribution remains largely unconstrained. We conducted a series of experiments to constrain the processes controlling Pb mobility during deformation of apatite. Torsion experiments on single crystals of Durango apatite at 300 MPa confining pressure and 1100 °C resulted in gradual lattice distortion and a network of subgrain boundaries in response to dislocation nucleation, movement, and recovery. Results from a static diffusion experiment at the same pressure-temperature conditions with a Pb source are consistent with known rates of volume diffusion. In contrast, torsion of an apatite single crystal coated in a Pb source revealed substantial mobility of Pb during deformation. This sample developed similar deformation-related microstructures, containing increased concentrations of Pb in and near subgrain boundaries. Our results demonstrate that during crystal-plastic deformation of apatite at these experimental conditions, Pb is transported orders of magnitude farther than predicted by published diffusivities, highlighting the importance of active crystal-plastic deformation in enhancing Pb mobility in apatite. We suggest that this enhanced mobility results from the capture and drag of Pb in Cottrell atmospheres associated with mobile dislocations during crystal-plastic deformation. Our results have important implications for geothermochronological analyses relying on Pb concentrations in apatite, which will be affected by deformation below the Pb diffusion closure temperatures. Similar effects are likely to extend to trace elements in other accessory phases.
{"title":"Dislocation motion enhances Pb mobility in experimentally deformed apatite","authors":"Annia K. Fayon, Lars N. Hansen, Sandra Piazolo, Amanda Dillman, William O. Nachlas","doi":"10.1130/g53841.1","DOIUrl":"https://doi.org/10.1130/g53841.1","url":null,"abstract":"The distribution of Pb in minerals provides a key window into deciphering the time scales of geologic processes. However, the role of deformation-induced dislocations on Pb mobility and redistribution remains largely unconstrained. We conducted a series of experiments to constrain the processes controlling Pb mobility during deformation of apatite. Torsion experiments on single crystals of Durango apatite at 300 MPa confining pressure and 1100 °C resulted in gradual lattice distortion and a network of subgrain boundaries in response to dislocation nucleation, movement, and recovery. Results from a static diffusion experiment at the same pressure-temperature conditions with a Pb source are consistent with known rates of volume diffusion. In contrast, torsion of an apatite single crystal coated in a Pb source revealed substantial mobility of Pb during deformation. This sample developed similar deformation-related microstructures, containing increased concentrations of Pb in and near subgrain boundaries. Our results demonstrate that during crystal-plastic deformation of apatite at these experimental conditions, Pb is transported orders of magnitude farther than predicted by published diffusivities, highlighting the importance of active crystal-plastic deformation in enhancing Pb mobility in apatite. We suggest that this enhanced mobility results from the capture and drag of Pb in Cottrell atmospheres associated with mobile dislocations during crystal-plastic deformation. Our results have important implications for geothermochronological analyses relying on Pb concentrations in apatite, which will be affected by deformation below the Pb diffusion closure temperatures. Similar effects are likely to extend to trace elements in other accessory phases.","PeriodicalId":12642,"journal":{"name":"Geology","volume":"72 1","pages":""},"PeriodicalIF":5.8,"publicationDate":"2025-09-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145035557","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 widespread presence of Mesoproterozoic detrital zircon in western Laurentia has long been interpreted as evidence for transcontinental river systems transporting sediment from the Grenville orogen. This model asserts that Grenville-age zircon were carried across Laurentia during the Neoproterozoic and Paleozoic, but recent isotopic and provenance data challenge this interpretation. Here, we show that detrital zircon age distributions and Hf isotopic compositions east and west of the Transcontinental Arch remained distinct until the late Paleozoic, inconsistent with repeated sediment mixing by a long-lived transcontinental river system. Instead, multiple Stenian magmatic sources in western Laurentia, including the Llano Uplift, Pikes Peak batholith, and the Southwestern Laurentia Large Igneous Province, provide plausible proximal sources of zircon. Additionally, the Pearya terrane, the northern Yukon, and formerly adjacent Antarctic crust may have contributed detrital zircon to western Laurentia’s sedimentary record. Post-Devonian sediment redistribution may have been accomplished by a combination of fluvial, shallow marine, and eolian processes, or indirect sediment routing. These findings suggest that late Paleozoic processes, rather than a Proterozoic transcontinental river(s), were responsible for distributing Grenville-age zircon across Laurentia. This revised model fundamentally alters the prevailing understanding of sediment routing in deep time and highlights the importance of reevaluating long-assumed geodynamic and provenance frameworks.
{"title":"Rethinking the “Grenville Flood” of Laurentian detrital zircon: Proximal sources, not continental rivers","authors":"Christopher J. Spencer, Mark E. Holland","doi":"10.1130/g53720.1","DOIUrl":"https://doi.org/10.1130/g53720.1","url":null,"abstract":"The widespread presence of Mesoproterozoic detrital zircon in western Laurentia has long been interpreted as evidence for transcontinental river systems transporting sediment from the Grenville orogen. This model asserts that Grenville-age zircon were carried across Laurentia during the Neoproterozoic and Paleozoic, but recent isotopic and provenance data challenge this interpretation. Here, we show that detrital zircon age distributions and Hf isotopic compositions east and west of the Transcontinental Arch remained distinct until the late Paleozoic, inconsistent with repeated sediment mixing by a long-lived transcontinental river system. Instead, multiple Stenian magmatic sources in western Laurentia, including the Llano Uplift, Pikes Peak batholith, and the Southwestern Laurentia Large Igneous Province, provide plausible proximal sources of zircon. Additionally, the Pearya terrane, the northern Yukon, and formerly adjacent Antarctic crust may have contributed detrital zircon to western Laurentia’s sedimentary record. Post-Devonian sediment redistribution may have been accomplished by a combination of fluvial, shallow marine, and eolian processes, or indirect sediment routing. These findings suggest that late Paleozoic processes, rather than a Proterozoic transcontinental river(s), were responsible for distributing Grenville-age zircon across Laurentia. This revised model fundamentally alters the prevailing understanding of sediment routing in deep time and highlights the importance of reevaluating long-assumed geodynamic and provenance frameworks.","PeriodicalId":12642,"journal":{"name":"Geology","volume":"714 1","pages":""},"PeriodicalIF":5.8,"publicationDate":"2025-09-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145035558","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}
Zsuzsanna P. Allerton, Liam Courtney-Davies, Martin Danišík, George J. Hudak, Christian Teyssier, Jennifer T. Mitchell, Phillip Larson
The age and origin of hematite deposits in the Vermilion District of Minnesota (USA), Lake Superior region, has been debated for over a century and inferred to be Neoarchean or Mesoproterozoic. Using a new geochronological approach combining U-Pb and (U-Th)/He double-dating of hematite, we present the first direct dates for hematite deposits at the Soudan iron mine, revealing a previously unknown Paleoproterozoic mineralization event and a thermal history recording the emplacement of the proximal Mesoproterozoic Midcontinent Rift System. Hematite phases yield U-Pb crystallization dates ranging between 1.8 Ga and 1.6 Ga and (U-Th)/He dates in the range of 1.63−0.53 Ga, with a distinct cluster at ca. 1.1 Ga. We propose that replacement-style hematite mineralization was generated during Paleoproterozoic orogenic events, including the Yavapai (1.71−1.68 Ga) and/or Mazatzal (1.65−1.60 Ga) accretionary orogenies and associated magmatism related to the assembly of Laurentia that reactivated shear zones and facilitated hydrothermal alteration deep into the Archean craton. (U-Th)/He data suggest that hematite ore experienced a thermal overprint that did not reset the U-Pb system, with the most consistent dates coinciding with the establishment of the Midcontinent Rift System at ca. 1.1 Ga. Double-dating of hematite is demonstrated to directly link iron mineralization to thermal and tectonic events in Precambrian cratons and to place constraints on genesis not available from coexisting accessory minerals.
{"title":"Hematite double-dating defines Proterozoic mineralization and thermal history of Archean banded iron formations in northeastern Minnesota, USA","authors":"Zsuzsanna P. Allerton, Liam Courtney-Davies, Martin Danišík, George J. Hudak, Christian Teyssier, Jennifer T. Mitchell, Phillip Larson","doi":"10.1130/g53517.1","DOIUrl":"https://doi.org/10.1130/g53517.1","url":null,"abstract":"The age and origin of hematite deposits in the Vermilion District of Minnesota (USA), Lake Superior region, has been debated for over a century and inferred to be Neoarchean or Mesoproterozoic. Using a new geochronological approach combining U-Pb and (U-Th)/He double-dating of hematite, we present the first direct dates for hematite deposits at the Soudan iron mine, revealing a previously unknown Paleoproterozoic mineralization event and a thermal history recording the emplacement of the proximal Mesoproterozoic Midcontinent Rift System. Hematite phases yield U-Pb crystallization dates ranging between 1.8 Ga and 1.6 Ga and (U-Th)/He dates in the range of 1.63−0.53 Ga, with a distinct cluster at ca. 1.1 Ga. We propose that replacement-style hematite mineralization was generated during Paleoproterozoic orogenic events, including the Yavapai (1.71−1.68 Ga) and/or Mazatzal (1.65−1.60 Ga) accretionary orogenies and associated magmatism related to the assembly of Laurentia that reactivated shear zones and facilitated hydrothermal alteration deep into the Archean craton. (U-Th)/He data suggest that hematite ore experienced a thermal overprint that did not reset the U-Pb system, with the most consistent dates coinciding with the establishment of the Midcontinent Rift System at ca. 1.1 Ga. Double-dating of hematite is demonstrated to directly link iron mineralization to thermal and tectonic events in Precambrian cratons and to place constraints on genesis not available from coexisting accessory minerals.","PeriodicalId":12642,"journal":{"name":"Geology","volume":"54 1","pages":""},"PeriodicalIF":5.8,"publicationDate":"2025-09-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145035561","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}
We use phase-equilibrium and trace-element modeling to address the effects of magmatic H2O, oxygen fugacity (fO2), and differentiation depth of mantle-derived magmas on the generation of porphyry copper deposit (PCD)−forming magmas. We explore how these factors control first-order compositional trends indicative of high PCD-forming potential [Sr/Y and (Eu/Eu*)/Yb versus SiO2 and fO2] and test different models for the ideal amount of H2O and fO2 of PCD-forming magmas. Our findings suggest that initial oxidized conditions (i.e., magmas derived from an oxidized source) are necessary for the generation of PCD-forming magmas. We show that wet to super-wet magmatism (H2O >4−8 wt%) combined with an initially oxidized state better matches the required conditions for PCD generation. Importantly, we find that garnet is not necessary for PCD formation; amphibole-bearing but garnet-free assemblages can also produce PCD-forming magmas.
我们利用相平衡和微量元素模型研究了岩浆H2O、氧逸度（fO2）和幔源岩浆分异深度对斑岩型铜矿床（PCD）形成岩浆的影响。我们探讨了这些因素如何控制指示高形成潜力的一级成分趋势[Sr/Y和(Eu/Eu*)/Yb vs . SiO2和fO2]，并测试了形成pcd岩浆的理想H2O和fO2量的不同模型。我们的研究结果表明，初始氧化条件（即来自氧化源的岩浆）是形成pcd的岩浆的必要条件。研究表明，湿至超湿岩浆作用（H2O >4 - 8 wt%）与初始氧化态相结合，更符合PCD生成所需的条件。重要的是，我们发现石榴石不是形成PCD所必需的；含角闪石但不含石榴石的组合也可产生形成pdc的岩浆。
{"title":"Source-oxidized and (super-)wet magmas explain porphyry copper fertility vectors: A thermodynamic modeling approach","authors":"David Hernández-Uribe, Santiago Tassara","doi":"10.1130/g53405.1","DOIUrl":"https://doi.org/10.1130/g53405.1","url":null,"abstract":"We use phase-equilibrium and trace-element modeling to address the effects of magmatic H2O, oxygen fugacity (fO2), and differentiation depth of mantle-derived magmas on the generation of porphyry copper deposit (PCD)−forming magmas. We explore how these factors control first-order compositional trends indicative of high PCD-forming potential [Sr/Y and (Eu/Eu*)/Yb versus SiO2 and fO2] and test different models for the ideal amount of H2O and fO2 of PCD-forming magmas. Our findings suggest that initial oxidized conditions (i.e., magmas derived from an oxidized source) are necessary for the generation of PCD-forming magmas. We show that wet to super-wet magmatism (H2O >4−8 wt%) combined with an initially oxidized state better matches the required conditions for PCD generation. Importantly, we find that garnet is not necessary for PCD formation; amphibole-bearing but garnet-free assemblages can also produce PCD-forming magmas.","PeriodicalId":12642,"journal":{"name":"Geology","volume":"21 1","pages":""},"PeriodicalIF":5.8,"publicationDate":"2025-09-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145035674","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}
Jonathan Obrist-Farner, Jeremy Maurer, Derek Gibson, Trenton McEnaney, Andreas Eckert, William F. Kenney, Jeffery Beeson, Nigel Wattrus, Quin Stangeland, Fatima Reyes
On 4 February 1976, a Mw 7.5 earthquake along the Motagua fault, Guatemala, ruptured ∼230 km of the North American and Caribbean plate boundary. Today, the plate boundary remains poorly monitored, and the 1976 earthquake is still not fully understood. Here, we present seismic reflection profiles and radiometrically dated sediment core data from six lakes around the Motagua fault, together with reports of destruction and a quasi-dynamic rupture model, which show that the 1976 earthquake experienced strong directivity that impacted the distribution of shaking. The earthquake left behind a detailed record of event deposits (EDs) in five of the six study lakes. Thicker EDs are present in Lake Atitlán, near the terminus of the earthquake rupture, whereas thinner EDs were found in lakes off-axis of the rupture direction. We argue that EDs can be utilized to constrain asymmetrical distribution of shaking during earthquakes and that paleoseismic studies should consider directivity as a factor controlling the thickness of EDs.
{"title":"Paleoseismic evidence of directivity for the 1976 Mw 7.5 Motagua earthquake, Guatemala","authors":"Jonathan Obrist-Farner, Jeremy Maurer, Derek Gibson, Trenton McEnaney, Andreas Eckert, William F. Kenney, Jeffery Beeson, Nigel Wattrus, Quin Stangeland, Fatima Reyes","doi":"10.1130/g53449.1","DOIUrl":"https://doi.org/10.1130/g53449.1","url":null,"abstract":"On 4 February 1976, a Mw 7.5 earthquake along the Motagua fault, Guatemala, ruptured ∼230 km of the North American and Caribbean plate boundary. Today, the plate boundary remains poorly monitored, and the 1976 earthquake is still not fully understood. Here, we present seismic reflection profiles and radiometrically dated sediment core data from six lakes around the Motagua fault, together with reports of destruction and a quasi-dynamic rupture model, which show that the 1976 earthquake experienced strong directivity that impacted the distribution of shaking. The earthquake left behind a detailed record of event deposits (EDs) in five of the six study lakes. Thicker EDs are present in Lake Atitlán, near the terminus of the earthquake rupture, whereas thinner EDs were found in lakes off-axis of the rupture direction. We argue that EDs can be utilized to constrain asymmetrical distribution of shaking during earthquakes and that paleoseismic studies should consider directivity as a factor controlling the thickness of EDs.","PeriodicalId":12642,"journal":{"name":"Geology","volume":"12 1","pages":""},"PeriodicalIF":5.8,"publicationDate":"2025-09-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145035560","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}
Oskar Schramm, Patrick J. Frings, Tommaso di Rocco, Andreas Pack, Michael Tatzel
Sedimentary cherts form from amorphous silica precursors that progressively crystallize into opal-CT and quartz during burial diagenesis. Recent studies have shown that the transformation kinetics of the silica polymorphs strongly depend on the prograde thermal history, suggesting a key role of basal heat flow in setting the 18O/16O and 17O/16O 18O/16O oxygen isotope ratios in chert (δ18Ochert, Δ′17Ochert). To investigate the relationship between paleo−heat flow and chert oxygen isotopes, we used Cretaceous to Neogene cherts that formed in the large igneous province Shatsky Rise in the western Pacific Ocean and a compilation of marine chert oxygen isotope ratios from previous studies. Using a reaction-advection-diffusion model, we demonstrate that the relationship between δ18Ochert, Δ′17Ochert, and the age of the underlying crust results from declining heat flow through sediment as the oceanic crust cools. Our reconstruction of heat flow at Shatsky Rise aligns with established geothermal background values. We propose that the Archean chert record indicates a diagenetic environment dominated by high heat flow that transitioned on billion-year time scales toward conditions resembling modern diagenesis.
{"title":"Oxygen isotopes in cherts record paleo−heat flow on Shatsky Rise (western Pacific Ocean)","authors":"Oskar Schramm, Patrick J. Frings, Tommaso di Rocco, Andreas Pack, Michael Tatzel","doi":"10.1130/g53296.1","DOIUrl":"https://doi.org/10.1130/g53296.1","url":null,"abstract":"Sedimentary cherts form from amorphous silica precursors that progressively crystallize into opal-CT and quartz during burial diagenesis. Recent studies have shown that the transformation kinetics of the silica polymorphs strongly depend on the prograde thermal history, suggesting a key role of basal heat flow in setting the 18O/16O and 17O/16O 18O/16O oxygen isotope ratios in chert (δ18Ochert, Δ′17Ochert). To investigate the relationship between paleo−heat flow and chert oxygen isotopes, we used Cretaceous to Neogene cherts that formed in the large igneous province Shatsky Rise in the western Pacific Ocean and a compilation of marine chert oxygen isotope ratios from previous studies. Using a reaction-advection-diffusion model, we demonstrate that the relationship between δ18Ochert, Δ′17Ochert, and the age of the underlying crust results from declining heat flow through sediment as the oceanic crust cools. Our reconstruction of heat flow at Shatsky Rise aligns with established geothermal background values. We propose that the Archean chert record indicates a diagenetic environment dominated by high heat flow that transitioned on billion-year time scales toward conditions resembling modern diagenesis.","PeriodicalId":12642,"journal":{"name":"Geology","volume":"35 1","pages":""},"PeriodicalIF":5.8,"publicationDate":"2025-09-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145017899","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}
Sheree E. Armistead, Bruce M. Eglington, Sally J. Pehrsson, David L. Huston
Understanding Earth’s early crustal architecture is critical to reconstructing the planet’s geodynamic evolution. We present a global analysis of ∼25,000 Pb isotope analyses from ore deposits, focusing on Archean cratons to investigate lithospheric evolution and continental configurations. Spatial patterns in model age and source µ (238U/204Pb) reveal isotopic domains that align with proposed Archean supercratons. Low µ values are characteristic of cratons interpreted to belong to the ca. 2.6 Ga Superia supercraton (e.g., Superior [Canada], Kaapvaal [southern Africa], and Hearne [Canada] cratons), whereas moderate to high µ values are typical of cratons associated with the contemporaneous Sclavia supercraton (e.g., Slave [Canada], Yilgarn [Australia], Dharwar [India], and Zimbabwe [southern Africa] cratons). These long-lived terrane-scale signatures suggest Pb isotopes can resolve lithospheric domains preserved across multiple cratons. Our results offer new geochemical constraints on Archean continental assembly and highlight the utility of ore-deposit Pb isotope data for testing early Earth plate configurations.
{"title":"Archean geodynamics and plate tectonics linked to Pb isotope variability","authors":"Sheree E. Armistead, Bruce M. Eglington, Sally J. Pehrsson, David L. Huston","doi":"10.1130/g53553.1","DOIUrl":"https://doi.org/10.1130/g53553.1","url":null,"abstract":"Understanding Earth’s early crustal architecture is critical to reconstructing the planet’s geodynamic evolution. We present a global analysis of ∼25,000 Pb isotope analyses from ore deposits, focusing on Archean cratons to investigate lithospheric evolution and continental configurations. Spatial patterns in model age and source µ (238U/204Pb) reveal isotopic domains that align with proposed Archean supercratons. Low µ values are characteristic of cratons interpreted to belong to the ca. 2.6 Ga Superia supercraton (e.g., Superior [Canada], Kaapvaal [southern Africa], and Hearne [Canada] cratons), whereas moderate to high µ values are typical of cratons associated with the contemporaneous Sclavia supercraton (e.g., Slave [Canada], Yilgarn [Australia], Dharwar [India], and Zimbabwe [southern Africa] cratons). These long-lived terrane-scale signatures suggest Pb isotopes can resolve lithospheric domains preserved across multiple cratons. Our results offer new geochemical constraints on Archean continental assembly and highlight the utility of ore-deposit Pb isotope data for testing early Earth plate configurations.","PeriodicalId":12642,"journal":{"name":"Geology","volume":"130 1","pages":""},"PeriodicalIF":5.8,"publicationDate":"2025-09-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145017900","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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