Pilar Madrigal, Kaj Hoernle, Brian R. Jicha, Christian Timm, Dieter Garbe-Schönberg, William W. Sager, Folkmar Hauff, Maxim Portnyagin, Gene Yogodzinski
Our knowledge of the Cretaceous history of the northwestern Pacific plate relies on tectonic reconstructions that lack geochronologic and geochemical constraints due to the paucity of sampling in this area. We present new age and compositional data for samples from four Emperor seamounts: Meiji, Hanzei, Suizei, and Tenji. Tholeiites from Tenji (66 Ma) and Suizei (70 Ma) yield ages consistent with the expected age progression, whereas a trachytic sample from Hanzei (66 Ma, expected age of ca. 73 Ma) represents an alkalic post-shield event. The ridge-like morphology and depleted geochemistry of Meiji to Suizei seamounts and the age (78−75 Ma) and depleted composition of the volcanic elongated ridges (VERs) southeast of Detroit seamount (ca. 76 Ma) are consistent with plume-ridge interaction. The VERs account for the missing volume of volcanism expected from plume-ridge interaction for the oldest Emperor seamounts. A small seamount with mid-ocean ridge basalt−like geochemistry located east of northern Detroit seamount yielded an age of 100 Ma, representing a minimum age for the oceanic crustal sliver between the Emperor Trough and the Stalemate Fracture Zone. We propose ∼300 km of dextral offset along the Emperor Trough to explain the location of this older crustal sliver. Our new data provide important constraints on the poorly known early evolution of the Hawaiian-Emperor Seamount Chain and the Cretaceous Quiet Zone (Cretaceous Normal Superchron) geotectonic history of the northwestern Pacific plate.
{"title":"Early Emperor seamount evolution and geotectonics of the northwestern Pacific plate","authors":"Pilar Madrigal, Kaj Hoernle, Brian R. Jicha, Christian Timm, Dieter Garbe-Schönberg, William W. Sager, Folkmar Hauff, Maxim Portnyagin, Gene Yogodzinski","doi":"10.1130/g53477.1","DOIUrl":"https://doi.org/10.1130/g53477.1","url":null,"abstract":"Our knowledge of the Cretaceous history of the northwestern Pacific plate relies on tectonic reconstructions that lack geochronologic and geochemical constraints due to the paucity of sampling in this area. We present new age and compositional data for samples from four Emperor seamounts: Meiji, Hanzei, Suizei, and Tenji. Tholeiites from Tenji (66 Ma) and Suizei (70 Ma) yield ages consistent with the expected age progression, whereas a trachytic sample from Hanzei (66 Ma, expected age of ca. 73 Ma) represents an alkalic post-shield event. The ridge-like morphology and depleted geochemistry of Meiji to Suizei seamounts and the age (78−75 Ma) and depleted composition of the volcanic elongated ridges (VERs) southeast of Detroit seamount (ca. 76 Ma) are consistent with plume-ridge interaction. The VERs account for the missing volume of volcanism expected from plume-ridge interaction for the oldest Emperor seamounts. A small seamount with mid-ocean ridge basalt−like geochemistry located east of northern Detroit seamount yielded an age of 100 Ma, representing a minimum age for the oceanic crustal sliver between the Emperor Trough and the Stalemate Fracture Zone. We propose ∼300 km of dextral offset along the Emperor Trough to explain the location of this older crustal sliver. Our new data provide important constraints on the poorly known early evolution of the Hawaiian-Emperor Seamount Chain and the Cretaceous Quiet Zone (Cretaceous Normal Superchron) geotectonic history of the northwestern Pacific plate.","PeriodicalId":12642,"journal":{"name":"Geology","volume":"40 1","pages":""},"PeriodicalIF":5.8,"publicationDate":"2025-09-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145117007","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}
Laura Gnesko, Timothy Stahl, Joshu J. Mountjoy, Jonathan M. Carey
The impact of recurrent landslides on submarine canyon morphology, sediment dynamics, and tsunami hazard is poorly understood. This study presents the first detailed inventory of earthquake-induced submarine landslides, using high-resolution (2 m) pre- and postevent multibeam bathymetry of the upper Kaikōura Canyon, New Zealand, following the Mw 7.8, 2016 Kaikōura earthquake. Most failures initiated as small (∼1950 m2), shallow disaggregating slides (<10 m) in postglacial sediments draped over bedrock at the canyon headwall. Despite their size, ∼11.2 Mm3 of material failed from the upper canyon, nearly 100 times the volume loss per unit area observed on land, resulting in up to 210 m of headwall retreat and erasure of small gully systems. These shallow slides transitioned into flows, contributing to the 935 Mm3 gravity flow deeper in the canyon. Corrected digital elevation model (DEM) differencing shows submarine landslide volumes were 1.5−3 times larger than postevent estimates would predict. The sediment mobilized by shallow landsliding from the Kaikōura Canyon headwall provides valuable insights that could improve sediment gravity flow and submarine landslide hazard models. Despite the large sediment volume, no tsunami was generated, likely due to failure occurring as numerous small disaggregating slides. These findings indicate that landslide-driven tsunami hazard in active margin settings may be lower than expected.
{"title":"Transient evidence of shallow coseismic submarine landslides shaping canyon head geomorphology: Insights from the 2016 Kaikōura earthquake, New Zealand","authors":"Laura Gnesko, Timothy Stahl, Joshu J. Mountjoy, Jonathan M. Carey","doi":"10.1130/g53867.1","DOIUrl":"https://doi.org/10.1130/g53867.1","url":null,"abstract":"The impact of recurrent landslides on submarine canyon morphology, sediment dynamics, and tsunami hazard is poorly understood. This study presents the first detailed inventory of earthquake-induced submarine landslides, using high-resolution (2 m) pre- and postevent multibeam bathymetry of the upper Kaikōura Canyon, New Zealand, following the Mw 7.8, 2016 Kaikōura earthquake. Most failures initiated as small (∼1950 m2), shallow disaggregating slides (&lt;10 m) in postglacial sediments draped over bedrock at the canyon headwall. Despite their size, ∼11.2 Mm3 of material failed from the upper canyon, nearly 100 times the volume loss per unit area observed on land, resulting in up to 210 m of headwall retreat and erasure of small gully systems. These shallow slides transitioned into flows, contributing to the 935 Mm3 gravity flow deeper in the canyon. Corrected digital elevation model (DEM) differencing shows submarine landslide volumes were 1.5−3 times larger than postevent estimates would predict. The sediment mobilized by shallow landsliding from the Kaikōura Canyon headwall provides valuable insights that could improve sediment gravity flow and submarine landslide hazard models. Despite the large sediment volume, no tsunami was generated, likely due to failure occurring as numerous small disaggregating slides. These findings indicate that landslide-driven tsunami hazard in active margin settings may be lower than expected.","PeriodicalId":12642,"journal":{"name":"Geology","volume":"40 1","pages":""},"PeriodicalIF":5.8,"publicationDate":"2025-09-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145127702","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}
Xianqing Jing, Zhenyu Yang, Zheng Gong, Yabo Tong, Lemei Hu, Shu Yang
Tonian true polar wander (TPW) events, first reported from South China (SC), were later confirmed by a paleomagnetic study of Svalbard. However, recent studies have argued that the dispersion of the Tonian paleomagnetic poles in SC may instead have resulted from remagnetization, local rotation, or inclination shallowing. We conducted a detailed paleomagnetic study on the ca. 792 Ma Kaijianqiao Formation in SC. Demagnetization and rock magnetic experiments revealed a primary remanence carried by detrital hematite, which recorded seven geomagnetic polarity reversals. We reviewed the Tonian poles from SC and found that all have various positive field tests, which argue against remagnetization being the cause of their dispersion. Additionally, statistical tests suggest that inclination shallowing has had a minimal influence on these poles. The paleolatitudinal variation of SC during ca. 805−780 Ma demonstrates three stages of fast motion; although they exceed the speed of plate tectonics, they are consistent with the previously proposed TPW event in the late Tonian. Therefore, we explain the dispersion of the 810−750 Ma poles in SC by a combination of TPW and vertical-axis rotation. By comparing the paleolatitudinal variations of SC predicted by seven reconstruction models of Rodinia, we propose that SC was in the Southern Hemisphere during the late Tonian and located on the southern or western periphery of Rodinia.
{"title":"Tonian true polar wander events recorded by paleolatitudinal variations of South China and its Southern Hemispheric position in Rodinia","authors":"Xianqing Jing, Zhenyu Yang, Zheng Gong, Yabo Tong, Lemei Hu, Shu Yang","doi":"10.1130/g53710.1","DOIUrl":"https://doi.org/10.1130/g53710.1","url":null,"abstract":"Tonian true polar wander (TPW) events, first reported from South China (SC), were later confirmed by a paleomagnetic study of Svalbard. However, recent studies have argued that the dispersion of the Tonian paleomagnetic poles in SC may instead have resulted from remagnetization, local rotation, or inclination shallowing. We conducted a detailed paleomagnetic study on the ca. 792 Ma Kaijianqiao Formation in SC. Demagnetization and rock magnetic experiments revealed a primary remanence carried by detrital hematite, which recorded seven geomagnetic polarity reversals. We reviewed the Tonian poles from SC and found that all have various positive field tests, which argue against remagnetization being the cause of their dispersion. Additionally, statistical tests suggest that inclination shallowing has had a minimal influence on these poles. The paleolatitudinal variation of SC during ca. 805−780 Ma demonstrates three stages of fast motion; although they exceed the speed of plate tectonics, they are consistent with the previously proposed TPW event in the late Tonian. Therefore, we explain the dispersion of the 810−750 Ma poles in SC by a combination of TPW and vertical-axis rotation. By comparing the paleolatitudinal variations of SC predicted by seven reconstruction models of Rodinia, we propose that SC was in the Southern Hemisphere during the late Tonian and located on the southern or western periphery of Rodinia.","PeriodicalId":12642,"journal":{"name":"Geology","volume":"74 1","pages":""},"PeriodicalIF":5.8,"publicationDate":"2025-09-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145088917","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 thickness of the cratonic lithospheric mantle (CLM) influences the composition of primary mantle melts, the formation and distribution of ore deposits, and the stability of continents. However, it remains debated whether the thickness of the CLM has changed through time. Some studies suggest progressive thinning due to extension, convective removal, mantle plumes, or subduction-driven erosion, while others propose long-term stability due to the intrinsic buoyancy or strength of the CLM. To address this question, we provide new constraints on the evolution of the CLM through time by comparing two recently developed datasets: (1) a global dataset of paleo−lithosphere-asthenosphere boundary (LAB) depth estimates (dating back to 2.1 Ga) produced by fitting geotherms to xenolith- and xenocryst-derived pressure and temperature estimates; and (2) the present-day LAB depth derived from seismic tomography combined with a scaling between wavespeed and temperature. Our results show that the thickness of the CLM beneath most cratons has changed by <50 km since the Paleoproterozoic, that there are no systematic secular trends in CLM thickness changes through time, and that there is no evidence for the previously proposed existence of substantially thicker (>300 km) CLM in the past. These findings suggest that in the majority of places, the cratonic lithosphere has remained largely unchanged for billions of years, reinforcing the idea that cratonic roots represent long-lived, stable features of Earth’s lithosphere. Exceptions are regions with long histories in a supra-subduction setting, followed by the application of extensional stresses (e.g., North China).
{"title":"Long-term evolution, stability, and thickness of cratonic lithosphere","authors":"Z.J. Sudholz, K. Priestley, A. Copley","doi":"10.1130/g53481.1","DOIUrl":"https://doi.org/10.1130/g53481.1","url":null,"abstract":"The thickness of the cratonic lithospheric mantle (CLM) influences the composition of primary mantle melts, the formation and distribution of ore deposits, and the stability of continents. However, it remains debated whether the thickness of the CLM has changed through time. Some studies suggest progressive thinning due to extension, convective removal, mantle plumes, or subduction-driven erosion, while others propose long-term stability due to the intrinsic buoyancy or strength of the CLM. To address this question, we provide new constraints on the evolution of the CLM through time by comparing two recently developed datasets: (1) a global dataset of paleo−lithosphere-asthenosphere boundary (LAB) depth estimates (dating back to 2.1 Ga) produced by fitting geotherms to xenolith- and xenocryst-derived pressure and temperature estimates; and (2) the present-day LAB depth derived from seismic tomography combined with a scaling between wavespeed and temperature. Our results show that the thickness of the CLM beneath most cratons has changed by &lt;50 km since the Paleoproterozoic, that there are no systematic secular trends in CLM thickness changes through time, and that there is no evidence for the previously proposed existence of substantially thicker (&gt;300 km) CLM in the past. These findings suggest that in the majority of places, the cratonic lithosphere has remained largely unchanged for billions of years, reinforcing the idea that cratonic roots represent long-lived, stable features of Earth’s lithosphere. Exceptions are regions with long histories in a supra-subduction setting, followed by the application of extensional stresses (e.g., North China).","PeriodicalId":12642,"journal":{"name":"Geology","volume":"72 1","pages":""},"PeriodicalIF":5.8,"publicationDate":"2025-09-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145088922","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}
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 &gt;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}
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