Sneha Suresh, Simon J. Barker, Paul W. Williams, Colin J.N. Wilson, Trevor H. Worthy, Jeffrey Lang, John Hellstrom, Travis Cross, Shane J. Cronin, Joel A. Baker
Limestone caves are commonly located close to volcanic regions and can preserve signals of past eruptions, providing crucial chronostratigraphic constraints within and beyond U-Th dating limits for karst development and cave evolution. Here we document five caves in the Waitomo karst region of New Zealand that contain volcanic ash (tephra) from the Taupō Volcanic Zone, a highly active region of silicic volcanism. The cave-hosted deposits are glassy due to their protection from weathering, with one example being poorly sorted and locally indurated where pyroclastic flows filled the cave. Other deposits are bedded and inferred to have been water remobilized into the caves from surficial ash deposits. Glass compositions indicate that tephras located in cave floors and roof cavities and on cave walls were sourced from four caldera-forming eruptions, the 1.55 Ma Ngaroma, 1 Ma Kidnappers, 349 ka Whakamaru, and ca. 50 ka Rotoiti events, plus a smaller-volume event from Taupō volcano at ca. 40 ka, highlighting the repeated impact of explosive eruptions on this region. Tephra studies in caves thus provide crucial information that can be used to constrain cave sediment and volcanic histories, vertebrate fossil chronologies, and cave system and landscape evolution.
石灰岩洞穴通常位于火山区域附近，可以保存过去火山喷发的信号，为岩溶发育和洞穴演化提供了重要的年代地层限制。在这里，我们记录了新西兰怀托莫喀斯特地区的五个洞穴，这些洞穴含有来自陶普火山带的火山灰（tephra），陶普火山带是一个高度活跃的硅火山活动区域。岩洞型矿床由于不受风化作用而呈玻璃状，其中一个例子是分选不良，在火山碎屑流充满洞穴的地方局部硬化。其他沉积物是层状的，据推测是水从地表火山灰沉积物中重新注入洞穴。玻璃成分表明，洞底、洞顶洞洞和洞壁上的有机质来自四次火山口形成的喷发，分别是1.55 Ma Ngaroma、1 Ma Kidnappers、349 ka Whakamaru和约50 ka Rotoiti事件，以及约40 ka tauphi火山的一次较小体积的喷发，突出了爆炸喷发对该地区的反复影响。因此，洞穴中的洞穴研究提供了重要的信息，可以用来限制洞穴沉积物和火山历史，脊椎动物化石年代学，洞穴系统和景观演化。
{"title":"Nowhere to hide: Volcanic ash invasion of limestone caves in New Zealand","authors":"Sneha Suresh, Simon J. Barker, Paul W. Williams, Colin J.N. Wilson, Trevor H. Worthy, Jeffrey Lang, John Hellstrom, Travis Cross, Shane J. Cronin, Joel A. Baker","doi":"10.1130/g53695.1","DOIUrl":"https://doi.org/10.1130/g53695.1","url":null,"abstract":"Limestone caves are commonly located close to volcanic regions and can preserve signals of past eruptions, providing crucial chronostratigraphic constraints within and beyond U-Th dating limits for karst development and cave evolution. Here we document five caves in the Waitomo karst region of New Zealand that contain volcanic ash (tephra) from the Taupō Volcanic Zone, a highly active region of silicic volcanism. The cave-hosted deposits are glassy due to their protection from weathering, with one example being poorly sorted and locally indurated where pyroclastic flows filled the cave. Other deposits are bedded and inferred to have been water remobilized into the caves from surficial ash deposits. Glass compositions indicate that tephras located in cave floors and roof cavities and on cave walls were sourced from four caldera-forming eruptions, the 1.55 Ma Ngaroma, 1 Ma Kidnappers, 349 ka Whakamaru, and ca. 50 ka Rotoiti events, plus a smaller-volume event from Taupō volcano at ca. 40 ka, highlighting the repeated impact of explosive eruptions on this region. Tephra studies in caves thus provide crucial information that can be used to constrain cave sediment and volcanic histories, vertebrate fossil chronologies, and cave system and landscape evolution.","PeriodicalId":12642,"journal":{"name":"Geology","volume":"9 1","pages":""},"PeriodicalIF":5.8,"publicationDate":"2025-08-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144900634","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}
Xiaocong Luan, Colin D. Sproat, Jisuo Jin, Peir K. Pufahl, Rongchang Wu, Renbin Zhan
Cool-water settings characterize Ordovician occurrences of Phanerozoic ooidal ironstones (POIs), contrasting sharply with the warm and humid climate typical of other POIs. This geological puzzle was deciphered in this study based on a complex suite of Middle−Late Ordovician POIs in South China hosted in tropical sediments of a warm-water origin, and coeval ferruginous ooid-bearing sediments and ferruginous microbialites that accumulated in a relatively cool-water setting. Here, we demonstrate that, despite their different depositional settings, all Ordovician ferruginous deposits of South China share similar petrographic ultrastructures and δ56Fe isotopic signatures. This suggests that the formation of POIs was not likely controlled by water temperature but instead is attributable to a microbial iron factory, associated with active upwelling generated from frequent cool-water incursions from Gondwana. This model also explains the predominant occurrence of Ordovician ferruginous deposits in cool-water realms in peri-Gondwana. The Darriwilian peak of their abundance corresponds to the onset of an icehouse episode and a paleotropical cold-water tongue that created complex depositional environments across the South China plate.
{"title":"Upwelling-related ferruginous ooids, microbialites, and the Darriwilian tipping point of Ordovician climate","authors":"Xiaocong Luan, Colin D. Sproat, Jisuo Jin, Peir K. Pufahl, Rongchang Wu, Renbin Zhan","doi":"10.1130/g53374.1","DOIUrl":"https://doi.org/10.1130/g53374.1","url":null,"abstract":"Cool-water settings characterize Ordovician occurrences of Phanerozoic ooidal ironstones (POIs), contrasting sharply with the warm and humid climate typical of other POIs. This geological puzzle was deciphered in this study based on a complex suite of Middle−Late Ordovician POIs in South China hosted in tropical sediments of a warm-water origin, and coeval ferruginous ooid-bearing sediments and ferruginous microbialites that accumulated in a relatively cool-water setting. Here, we demonstrate that, despite their different depositional settings, all Ordovician ferruginous deposits of South China share similar petrographic ultrastructures and δ56Fe isotopic signatures. This suggests that the formation of POIs was not likely controlled by water temperature but instead is attributable to a microbial iron factory, associated with active upwelling generated from frequent cool-water incursions from Gondwana. This model also explains the predominant occurrence of Ordovician ferruginous deposits in cool-water realms in peri-Gondwana. The Darriwilian peak of their abundance corresponds to the onset of an icehouse episode and a paleotropical cold-water tongue that created complex depositional environments across the South China plate.","PeriodicalId":12642,"journal":{"name":"Geology","volume":"183 1","pages":""},"PeriodicalIF":5.8,"publicationDate":"2025-08-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144850889","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}
Slab break-off and polarity reversal are tectonic events that often occur in relation to the subduction process. For example, the Western Alps and Ontong Java are high profile cases of slab break-off and polarity reversal. A sufficient number of high-quality geological examples indicate a very short time frame (an average of <6 m.y.) for slab break-off and polarity reversal after a collisional event. On the other hand, previous numerical modeling studies propose the timing of these collision break-off events to be on an average time scale between 7.5 and 23.2 m.y. This study reconciles the geological observations from 17 ancient and contemporary subduction zones with a suite of numerical experiments. By synthesizing geological evidence and our geodynamic models, we propose that the majority of slab break-off and polarity reversal processes can be geologically fast (average <6 m.y.), contrary to current thinking.
{"title":"Slab break-off and subduction polarity reversal after collision can be very fast","authors":"Erkan Gün, Philip J. Heron, Russell N. Pysklywec","doi":"10.1130/g52507.1","DOIUrl":"https://doi.org/10.1130/g52507.1","url":null,"abstract":"Slab break-off and polarity reversal are tectonic events that often occur in relation to the subduction process. For example, the Western Alps and Ontong Java are high profile cases of slab break-off and polarity reversal. A sufficient number of high-quality geological examples indicate a very short time frame (an average of &lt;6 m.y.) for slab break-off and polarity reversal after a collisional event. On the other hand, previous numerical modeling studies propose the timing of these collision break-off events to be on an average time scale between 7.5 and 23.2 m.y. This study reconciles the geological observations from 17 ancient and contemporary subduction zones with a suite of numerical experiments. By synthesizing geological evidence and our geodynamic models, we propose that the majority of slab break-off and polarity reversal processes can be geologically fast (average &lt;6 m.y.), contrary to current thinking.","PeriodicalId":12642,"journal":{"name":"Geology","volume":"79 1","pages":""},"PeriodicalIF":5.8,"publicationDate":"2025-08-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144850893","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}
Juliana Olsen-Valdez, Cedric J. Hagen, Sarah J. Widlansky, Elizabeth J. Trower, Kathryn E. Snell, William C. Clyde
Thrombolites—clotted organo-sedimentary deposits—forming today preserve carbonate carbon isotope (δ13Ccarb) values that suggest that photosynthesis shifts the δ13C value of the local dissolved inorganic carbon pool, resulting in carbonate minerals with δ13Ccarb values 1‰−6‰ higher than that expected for carbonate minerals precipitated in equilibrium with ambient lake water. To test whether these signals are preserved in the geologic record, we analyzed the δ13Ccarb values of thrombolites from the Cretaceous to Eocene Sheep Pass Formation (Nevada, USA). We performed fabric-specific analyses of both the clot component (interpreted to reflect photosynthetically influenced precipitation) and adjacent matrix carbonate (interpreted to reflect abiotic precipitation) and find that the δ13Ccarb values of clot components are consistently offset to higher values than adjacent matrix. The mean offset (Δ13C) between the clots and matrix was +2.77‰ (±0.94, 2 s.e.). These Δ13C values are consistent with predictions by a model of diurnal carbon cycling driven by photosynthesis. Modeled Δ13C values also match the documented Δ13C values in modern lakes with thrombolites. We interpret that Sheep Pass Formation Δ13C values preserve signals related to both local and external influences on the dissolved inorganic carbon pool. Fabric-informed sampling can disentangle these two signals, allowing for more robust chemostratigraphy from microbialite archives in addition to identification of a biosignature of photosynthesis.
{"title":"Photosynthetic carbon cycling signal preserved in carbonate δ13C values of ancient thrombolites","authors":"Juliana Olsen-Valdez, Cedric J. Hagen, Sarah J. Widlansky, Elizabeth J. Trower, Kathryn E. Snell, William C. Clyde","doi":"10.1130/g53716.1","DOIUrl":"https://doi.org/10.1130/g53716.1","url":null,"abstract":"Thrombolites—clotted organo-sedimentary deposits—forming today preserve carbonate carbon isotope (δ13Ccarb) values that suggest that photosynthesis shifts the δ13C value of the local dissolved inorganic carbon pool, resulting in carbonate minerals with δ13Ccarb values 1‰−6‰ higher than that expected for carbonate minerals precipitated in equilibrium with ambient lake water. To test whether these signals are preserved in the geologic record, we analyzed the δ13Ccarb values of thrombolites from the Cretaceous to Eocene Sheep Pass Formation (Nevada, USA). We performed fabric-specific analyses of both the clot component (interpreted to reflect photosynthetically influenced precipitation) and adjacent matrix carbonate (interpreted to reflect abiotic precipitation) and find that the δ13Ccarb values of clot components are consistently offset to higher values than adjacent matrix. The mean offset (Δ13C) between the clots and matrix was +2.77‰ (±0.94, 2 s.e.). These Δ13C values are consistent with predictions by a model of diurnal carbon cycling driven by photosynthesis. Modeled Δ13C values also match the documented Δ13C values in modern lakes with thrombolites. We interpret that Sheep Pass Formation Δ13C values preserve signals related to both local and external influences on the dissolved inorganic carbon pool. Fabric-informed sampling can disentangle these two signals, allowing for more robust chemostratigraphy from microbialite archives in addition to identification of a biosignature of photosynthesis.","PeriodicalId":12642,"journal":{"name":"Geology","volume":"15 1","pages":""},"PeriodicalIF":5.8,"publicationDate":"2025-08-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144792717","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}
Paleoelevation data from continental arcs provide a record of tectonic processes and reveal feedbacks between surface uplift and paleoclimate. Here we reconstruct the Oligocene–Miocene paleoelevation of the central Cascade arc (northwestern USA) using δD values of paleoprecipitation preserved within hydrated volcanic glass. From the early Oligocene to early Miocene (ca. 33–17 Ma), we observe a 30‰ decrease in δD values of samples collected east of the range. Interpreted using a Rayleigh distillation model, these data indicate arc elevations increased by 1.1 ± 0.4 km during this interval, coeval with geochemical evidence for a 12 km increase in Moho depth. In the context of existing geochemical, thermochronologic, and structural data, Oligocene to early Miocene surface uplift was predominantly driven by magmatic additions to the crust during a period of high magmatic production rates. Surface uplift was synchronous with leeward drying, suggesting that an orographic rain shadow was established by the early Miocene. These results highlight the role of crustal thickness and paleoelevation changes in controlling regional climate in magmatic arcs.
{"title":"Surface uplift of the central Cascade Range, northwestern USA, via Oligocene to early Miocene crustal thickening","authors":"Luke C. Basler, Elizabeth J. Cassel","doi":"10.1130/g53421.1","DOIUrl":"https://doi.org/10.1130/g53421.1","url":null,"abstract":"Paleoelevation data from continental arcs provide a record of tectonic processes and reveal feedbacks between surface uplift and paleoclimate. Here we reconstruct the Oligocene–Miocene paleoelevation of the central Cascade arc (northwestern USA) using δD values of paleoprecipitation preserved within hydrated volcanic glass. From the early Oligocene to early Miocene (ca. 33–17 Ma), we observe a 30‰ decrease in δD values of samples collected east of the range. Interpreted using a Rayleigh distillation model, these data indicate arc elevations increased by 1.1 ± 0.4 km during this interval, coeval with geochemical evidence for a 12 km increase in Moho depth. In the context of existing geochemical, thermochronologic, and structural data, Oligocene to early Miocene surface uplift was predominantly driven by magmatic additions to the crust during a period of high magmatic production rates. Surface uplift was synchronous with leeward drying, suggesting that an orographic rain shadow was established by the early Miocene. These results highlight the role of crustal thickness and paleoelevation changes in controlling regional climate in magmatic arcs.","PeriodicalId":12642,"journal":{"name":"Geology","volume":"15 1","pages":""},"PeriodicalIF":5.8,"publicationDate":"2025-08-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144786517","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}
Yuhan Li, Ingo Grevemeyer, Adam H. Robinson, Timothy J. Henstock, Milena Marjanović, Anke Dannowski, Norbert Kaul, Ingo Klaucke, Paola Vannucchi, Helene-Sophie Hilbert, Damon A.H. Teagle, Jason Phipps Morgan
The subduction of seamounts greatly affects arc volcanism, earthquakes, and tectonic deformation of the overriding plate, but the role of seamounts during bending and hydration of the incoming plate at subduction zones is poorly understood. We present seismic tomographic results along three profiles from the Middle America Trench offshore northern Costa Rica. The crustal and upper mantle P-wave velocities decrease toward the trench, with the onset of velocity reduction at ∼70 km from the trench axis, indicating bend-faulting, alteration, and hydration of the incoming plate. The most prominent low-velocity anomaly of 7.6−7.8 km/s in the upper mantle occurs beneath a seamount at the outer rise, indicating enhanced hydration with ∼2.4 wt% water content, compared to ∼1.1−1.2 wt% in the subducting plate away from the seamount. Near the seamount, extremely low heat flow (<10 mW/m2) supports vigorous hydrothermal recharge of seawater. Our results reveal that subducting seamounts efficiently increase the permeability of the oceanic crust prior to subduction, facilitate the transport of seawater into the mantle, exert control on widespread serpentinization, and potentially promote water recycling back into Earth’s interior.
{"title":"Impact of seamounts on the hydration of subducting plates","authors":"Yuhan Li, Ingo Grevemeyer, Adam H. Robinson, Timothy J. Henstock, Milena Marjanović, Anke Dannowski, Norbert Kaul, Ingo Klaucke, Paola Vannucchi, Helene-Sophie Hilbert, Damon A.H. Teagle, Jason Phipps Morgan","doi":"10.1130/g53355.1","DOIUrl":"https://doi.org/10.1130/g53355.1","url":null,"abstract":"The subduction of seamounts greatly affects arc volcanism, earthquakes, and tectonic deformation of the overriding plate, but the role of seamounts during bending and hydration of the incoming plate at subduction zones is poorly understood. We present seismic tomographic results along three profiles from the Middle America Trench offshore northern Costa Rica. The crustal and upper mantle P-wave velocities decrease toward the trench, with the onset of velocity reduction at ∼70 km from the trench axis, indicating bend-faulting, alteration, and hydration of the incoming plate. The most prominent low-velocity anomaly of 7.6−7.8 km/s in the upper mantle occurs beneath a seamount at the outer rise, indicating enhanced hydration with ∼2.4 wt% water content, compared to ∼1.1−1.2 wt% in the subducting plate away from the seamount. Near the seamount, extremely low heat flow (&lt;10 mW/m2) supports vigorous hydrothermal recharge of seawater. Our results reveal that subducting seamounts efficiently increase the permeability of the oceanic crust prior to subduction, facilitate the transport of seawater into the mantle, exert control on widespread serpentinization, and potentially promote water recycling back into Earth’s interior.","PeriodicalId":12642,"journal":{"name":"Geology","volume":"5 1","pages":""},"PeriodicalIF":5.8,"publicationDate":"2025-08-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144763515","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}
Cailey B. Condit, Eirini M. Poulaki, Peter C. Lindquist, Claire I.O. Nichols, Megan E. Ferrell, Margo L. Odlum, William F. Hoover, Victor E. Guevara
Mélange (or block-in-matrix structures) exerts a first-order control on both the mechanical and chemical evolution of subduction megathrusts. However, the timing and mechanisms that form mélanges are variable and debated. Field observations and (micro-) structural analyses from a metasedimentary mélange in the lawsonite blueschist unit of the Catalina Schist (Santa Catalina Island, California, USA) reveal that syn-subduction deformation and fluid-mediated processes led to mélange formation at the plate interface. Deposited as turbidites, early shear occurred parallel to bedding planes (S1 foliation). At near peak subduction conditions, at the base of the subduction seismogenic zone (∼1.0 GPa, 320 °C), the rocks were intensely deformed in recumbent open to tight folds (F2) with axial planar cleavages (S2). Fracturing, fluid flow, and quartz precipitation are preserved as extensional vein mesh networks in fold noses. Continued shearing led to boudinage of these strengthened noses and transformation into strong blocks within the weaker less-veined matrix composed of high-strain fold limbs (S1−2). Microstructures reveal viscous deformation in the high-strain fold limbs occurred by pressure-solution creep of fine-grained quartz ± albite. In contrast, the fold noses and/or blocks contain coarse-grained quartz veins with little evidence of deformation. These rocks record the development of syn-subduction block-in-matrix mélange structures through the interaction of deformation and mineral precipitation; pressure solution weakened fold limbs-turned-matrix and veining strengthened fold noses-turned-blocks. Although mélange structure is often invoked to explain tremor and slow slip, rheological analysis indicates that these metasedimentary rocks can host tectonic creeping but cannot accommodate slow-slip strain rates by the deformation mechanisms preserved in their microstructures.
{"title":"Fluid-mediated deformation leads to weakening, strengthening, and block-in-matrix structures during prograde subduction mélange formation","authors":"Cailey B. Condit, Eirini M. Poulaki, Peter C. Lindquist, Claire I.O. Nichols, Megan E. Ferrell, Margo L. Odlum, William F. Hoover, Victor E. Guevara","doi":"10.1130/g53323.1","DOIUrl":"https://doi.org/10.1130/g53323.1","url":null,"abstract":"Mélange (or block-in-matrix structures) exerts a first-order control on both the mechanical and chemical evolution of subduction megathrusts. However, the timing and mechanisms that form mélanges are variable and debated. Field observations and (micro-) structural analyses from a metasedimentary mélange in the lawsonite blueschist unit of the Catalina Schist (Santa Catalina Island, California, USA) reveal that syn-subduction deformation and fluid-mediated processes led to mélange formation at the plate interface. Deposited as turbidites, early shear occurred parallel to bedding planes (S1 foliation). At near peak subduction conditions, at the base of the subduction seismogenic zone (∼1.0 GPa, 320 °C), the rocks were intensely deformed in recumbent open to tight folds (F2) with axial planar cleavages (S2). Fracturing, fluid flow, and quartz precipitation are preserved as extensional vein mesh networks in fold noses. Continued shearing led to boudinage of these strengthened noses and transformation into strong blocks within the weaker less-veined matrix composed of high-strain fold limbs (S1−2). Microstructures reveal viscous deformation in the high-strain fold limbs occurred by pressure-solution creep of fine-grained quartz ± albite. In contrast, the fold noses and/or blocks contain coarse-grained quartz veins with little evidence of deformation. These rocks record the development of syn-subduction block-in-matrix mélange structures through the interaction of deformation and mineral precipitation; pressure solution weakened fold limbs-turned-matrix and veining strengthened fold noses-turned-blocks. Although mélange structure is often invoked to explain tremor and slow slip, rheological analysis indicates that these metasedimentary rocks can host tectonic creeping but cannot accommodate slow-slip strain rates by the deformation mechanisms preserved in their microstructures.","PeriodicalId":12642,"journal":{"name":"Geology","volume":"10 1","pages":""},"PeriodicalIF":5.8,"publicationDate":"2025-08-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144763398","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 M. Gernon, Sascha Brune, Thea K. Hincks, Derek Keir
The Northern Appalachian Anomaly (NAA) is a prominent low-seismic-velocity zone, ∼400 km in diameter, in the asthenosphere beneath New England (northeastern USA). Previous studies interpreted this shallow feature, occurring at a depth of ∼200 km, as a thermal anomaly tied to edge-driven convection along the North American continental margins. Those studies recognized, however, that upwelling here is highly unusual given that the passive margin has been tectonically quiescent for ∼180 m.y. We propose an alternative model, based on geologic observations, geotectonic reconstructions, and geodynamic simulations, that the anomaly instead represents a Rayleigh-Taylor instability linked to the breakup of the distant Labrador Sea continental margin. A Labrador Sea origin at breakup, ca. 85−80 Ma, would imply the migration of a chain of Rayleigh-Taylor instabilities at a rate of ∼22 km/m.y., close to expected rates from geodynamic models. A migrating-instability origin for the anomaly can reconcile its spatial characteristics, depth profile, and position near a long-inactive continental margin. A corollary is that the north-central Greenland anomaly, a mirror-image of the NAA, also potentially originated at the time of breakup. Further, The Central Appalachian Anomaly may fit this model if it represents an early-stage instability linked to rifting onset in the Labrador Sea. The NAA and other associated anomalies viably represent a legacy of continental rifting and breakup along the distant Labrador Sea margins.
{"title":"A viable Labrador Sea rifting origin of the Northern Appalachian and related seismic anomalies","authors":"Thomas M. Gernon, Sascha Brune, Thea K. Hincks, Derek Keir","doi":"10.1130/g53588.1","DOIUrl":"https://doi.org/10.1130/g53588.1","url":null,"abstract":"The Northern Appalachian Anomaly (NAA) is a prominent low-seismic-velocity zone, ∼400 km in diameter, in the asthenosphere beneath New England (northeastern USA). Previous studies interpreted this shallow feature, occurring at a depth of ∼200 km, as a thermal anomaly tied to edge-driven convection along the North American continental margins. Those studies recognized, however, that upwelling here is highly unusual given that the passive margin has been tectonically quiescent for ∼180 m.y. We propose an alternative model, based on geologic observations, geotectonic reconstructions, and geodynamic simulations, that the anomaly instead represents a Rayleigh-Taylor instability linked to the breakup of the distant Labrador Sea continental margin. A Labrador Sea origin at breakup, ca. 85−80 Ma, would imply the migration of a chain of Rayleigh-Taylor instabilities at a rate of ∼22 km/m.y., close to expected rates from geodynamic models. A migrating-instability origin for the anomaly can reconcile its spatial characteristics, depth profile, and position near a long-inactive continental margin. A corollary is that the north-central Greenland anomaly, a mirror-image of the NAA, also potentially originated at the time of breakup. Further, The Central Appalachian Anomaly may fit this model if it represents an early-stage instability linked to rifting onset in the Labrador Sea. The NAA and other associated anomalies viably represent a legacy of continental rifting and breakup along the distant Labrador Sea margins.","PeriodicalId":12642,"journal":{"name":"Geology","volume":"718 1","pages":""},"PeriodicalIF":5.8,"publicationDate":"2025-07-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144747397","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}
John W.F. Waldron, S. Andrew DuFrane, David I. Schofield, Sandra M. Barr
The Appalachian−Caledonide orogen records protracted Paleozoic convergence during Iapetus Ocean closure. Grampian−Taconian arc-continent collision at the Laurentian margin and subduction polarity reversal were followed by Ordovician to Silurian subduction-accretion beneath the Laurentian margin, culminating in continental collision in the Scandinavian Caledonides, and soft collision along the Solway−Navan−Silvermines line in Britain and Ireland. Laurentia-derived detrital zircon crossed this boundary, commonly regarded as the main Iapetus suture, upon collision at ca. 430 Ma. Calc-alkaline magmatism continued into the Devonian on both sides of the supposed suture, producing the “trans-suture suite” of magmatic rocks that extend south as far as a boundary, here termed the Ynys Môn line, separating the Lakesman terrane from the Monian belt of North Wales. South of this line, Laurentia-derived detritus is absent from Silurian samples, but appears in Emsian Old Red Sandstone. Laurentia-derived detritus was held up at the Ynys Môn line for at least 12 Myr. This boundary is interpreted as a previously unrecognized suture, recording obliquely sinistral north-dipping subduction of a remaining tract of Iapetus, leading to magmatism north of the boundary and eventual Acadian collision.
{"title":"Is Britain divided by an Acadian suture?","authors":"John W.F. Waldron, S. Andrew DuFrane, David I. Schofield, Sandra M. Barr","doi":"10.1130/g53431.1","DOIUrl":"https://doi.org/10.1130/g53431.1","url":null,"abstract":"The Appalachian−Caledonide orogen records protracted Paleozoic convergence during Iapetus Ocean closure. Grampian−Taconian arc-continent collision at the Laurentian margin and subduction polarity reversal were followed by Ordovician to Silurian subduction-accretion beneath the Laurentian margin, culminating in continental collision in the Scandinavian Caledonides, and soft collision along the Solway−Navan−Silvermines line in Britain and Ireland. Laurentia-derived detrital zircon crossed this boundary, commonly regarded as the main Iapetus suture, upon collision at ca. 430 Ma. Calc-alkaline magmatism continued into the Devonian on both sides of the supposed suture, producing the “trans-suture suite” of magmatic rocks that extend south as far as a boundary, here termed the Ynys Môn line, separating the Lakesman terrane from the Monian belt of North Wales. South of this line, Laurentia-derived detritus is absent from Silurian samples, but appears in Emsian Old Red Sandstone. Laurentia-derived detritus was held up at the Ynys Môn line for at least 12 Myr. This boundary is interpreted as a previously unrecognized suture, recording obliquely sinistral north-dipping subduction of a remaining tract of Iapetus, leading to magmatism north of the boundary and eventual Acadian collision.","PeriodicalId":12642,"journal":{"name":"Geology","volume":"15 1","pages":""},"PeriodicalIF":5.8,"publicationDate":"2025-07-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144737039","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}
Earth’s landscapes, geochemical cycles, and sedimentary record are shaped by the source-to-sink transport of sediment. Sediment is sourced in erosional landscapes under the influence of climate and tectonics, transported through net bypass zones that can obscure forcing signals, and deposited in sinks to build the sedimentary record. Despite the importance of source-to-sink sediment transport in Earth science, the relative abundance of these domains remains unquantified, and the extent to which Earth’s surface resembles classic conceptual models has not been tested. Here we produce a global database of Earth’s source-to-sink systems. Results show that Earth’s land area is mostly erosional (59%), with bypass (22%) and sink (19%) domains less common (18%, 6%, and 76%, respectively, including oceans and Antarctica). Higher elevations are likelier to be erosional, with the world’s lowlands and large rivers disproportionately depositional. Large parts of the world are not described by the source-to-sink model; these areas are mostly deserts or shields without substantial rivers or sediment transport. Even in areas that do resemble the classic textbook progression, systems show exceptional source-to-sink domain variability between catchments and down the world’s major rivers. While the source-to-sink paradigm remains useful, it cannot describe the sedimentologically inactive areas that make up much of the world.
{"title":"The unexpected global distribution of Earth’s sediment sources and sinks","authors":"Harrison K. Martin, Michael P. Lamb","doi":"10.1130/g53289.1","DOIUrl":"https://doi.org/10.1130/g53289.1","url":null,"abstract":"Earth’s landscapes, geochemical cycles, and sedimentary record are shaped by the source-to-sink transport of sediment. Sediment is sourced in erosional landscapes under the influence of climate and tectonics, transported through net bypass zones that can obscure forcing signals, and deposited in sinks to build the sedimentary record. Despite the importance of source-to-sink sediment transport in Earth science, the relative abundance of these domains remains unquantified, and the extent to which Earth’s surface resembles classic conceptual models has not been tested. Here we produce a global database of Earth’s source-to-sink systems. Results show that Earth’s land area is mostly erosional (59%), with bypass (22%) and sink (19%) domains less common (18%, 6%, and 76%, respectively, including oceans and Antarctica). Higher elevations are likelier to be erosional, with the world’s lowlands and large rivers disproportionately depositional. Large parts of the world are not described by the source-to-sink model; these areas are mostly deserts or shields without substantial rivers or sediment transport. Even in areas that do resemble the classic textbook progression, systems show exceptional source-to-sink domain variability between catchments and down the world’s major rivers. While the source-to-sink paradigm remains useful, it cannot describe the sedimentologically inactive areas that make up much of the world.","PeriodicalId":12642,"journal":{"name":"Geology","volume":"25 1","pages":""},"PeriodicalIF":5.8,"publicationDate":"2025-07-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144701438","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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