Recycling of oxidized sulfur from subducting slabs to the mantle wedge provides simultaneous explanations for the elevated oxygen fugacity (fO2) in subduction zones, their high hydrothermal and magmatic sulfur outputs, and the enriched sulfur isotopic signatures (i.e., δ34S > 0‰) of these outputs. However, a quantitative understanding of the abundance and speciation of sulfur in slab fluids consistent with high pressure experiments is lacking. Here we analyze published experimental data for anhydrite solubility in H2O-NaCl solutions to calibrate a high-pressure aqueous speciation model of sulfur within the framework of the deep earth water model. We characterize aqueous complexes, required to account for the high experimental anhydrite solubilities. We then use this framework to predict the speciation and solubility of sulfur in chemically complex fluids in equilibrium with model subducting mafic and ultramafic lithologies, from 2 to 3 GPa and 400 to 800°C at log fO2 from FMQ-2 to FMQ+4. We show that sulfate complexes of calcium and sodium markedly enhance the stability of sulfate in moderately oxidized fluids in equilibrium with pyrite at fO2 conditions of FMQ+1 to +2, causing large sulfur isotope fractionations up to 10‰ in the fluid relative to the slab. Such fluids could impart oxidized, sulfur-rich and high δ34S signatures to the mantle wedge that are ultimately transferred to arc magmas, without the need to invoke 34S-rich subducted lithologies.
{"title":"Oxidized Sulfur Species in Slab Fluids as a Source of Enriched Sulfur Isotope Signatures in Arcs","authors":"Patrick Beaudry, Dimitri A. Sverjensky","doi":"10.1029/2024GC011542","DOIUrl":"https://doi.org/10.1029/2024GC011542","url":null,"abstract":"<p>Recycling of oxidized sulfur from subducting slabs to the mantle wedge provides simultaneous explanations for the elevated oxygen fugacity (<i>f</i>O<sub>2</sub>) in subduction zones, their high hydrothermal and magmatic sulfur outputs, and the enriched sulfur isotopic signatures (i.e., δ<sup>34</sup>S > 0‰) of these outputs. However, a quantitative understanding of the abundance and speciation of sulfur in slab fluids consistent with high pressure experiments is lacking. Here we analyze published experimental data for anhydrite solubility in H<sub>2</sub>O-NaCl solutions to calibrate a high-pressure aqueous speciation model of sulfur within the framework of the deep earth water model. We characterize aqueous complexes, required to account for the high experimental anhydrite solubilities. We then use this framework to predict the speciation and solubility of sulfur in chemically complex fluids in equilibrium with model subducting mafic and ultramafic lithologies, from 2 to 3 GPa and 400 to 800°C at log <i>f</i>O<sub>2</sub> from FMQ-2 to FMQ+4. We show that sulfate complexes of calcium and sodium markedly enhance the stability of sulfate in moderately oxidized fluids in equilibrium with pyrite at <i>f</i>O<sub>2</sub> conditions of FMQ+1 to +2, causing large sulfur isotope fractionations up to 10‰ in the fluid relative to the slab. Such fluids could impart oxidized, sulfur-rich and high δ<sup>34</sup>S signatures to the mantle wedge that are ultimately transferred to arc magmas, without the need to invoke <sup>34</sup>S-rich subducted lithologies.</p>","PeriodicalId":50422,"journal":{"name":"Geochemistry Geophysics Geosystems","volume":null,"pages":null},"PeriodicalIF":2.9,"publicationDate":"2024-06-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1029/2024GC011542","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141488967","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
X. Guan, C. Wu, Y. Xu, J. Saylor, C. Lin, W. Zhang
Source-to-sink systems respond to and therefore potentially record topographic and tectonic changes. North of the Tian Shan Belt, the Sikeshu subbasin of the SW Junggar Basin transitioned from active extension in the Triassic to post-extensional subsidence in the Jurassic-Cretaceous. Sediment in the Sikeshu subbasin has been shown to be derived from the Tianshan. However, the details of the source-to-sink system remain unclear and discrepancies exist between proxy records. The heavy minerals in the Middle Triassic in the Sikeshu subbasin are dominated by garnets. To investigate the garnet sources and decipher the Mesozoic source-to-sink evolution, we conducted petrological and sedimentary analysis and detrital garnet and tourmaline geochemistry. We found that the geochemistry of garnets in the Middle Triassic sandstone is most consistent with that of the skarns in the Yili Block (YB) in Tianshan, while the geochemistry of 55%–84% of garnets in other Mesozoic sandstones is consistent with that of garnets in amphibolites in the YB. The geochemistry of the tourmalines since the Upper Triassic is consistent with that of the meta-sedimentary rocks in the YB and Central Tianshan Block. The dominance of garnets sourced from skarns in the Middle Triassic probably indicates a near-source point provenance and the broader range of garnet compositions from the Upper Triassic–Lower Cretaceous suggests multiple sources. We infer that the point source changed to multiple sources, which is consistent with the zircon spectra changing from unimodal to multimodal. This change reflects the expansion of the drainage that accompanies a change from active rifting to a post-rift stage.
{"title":"Source-To-Sink Analysis in the Mesozoic SW Junggar Basin, Central Asia: Evidence From Detrital Garnet and Tourmaline Geochemistry","authors":"X. Guan, C. Wu, Y. Xu, J. Saylor, C. Lin, W. Zhang","doi":"10.1029/2024GC011455","DOIUrl":"https://doi.org/10.1029/2024GC011455","url":null,"abstract":"<p>Source-to-sink systems respond to and therefore potentially record topographic and tectonic changes. North of the Tian Shan Belt, the Sikeshu subbasin of the SW Junggar Basin transitioned from active extension in the Triassic to post-extensional subsidence in the Jurassic-Cretaceous. Sediment in the Sikeshu subbasin has been shown to be derived from the Tianshan. However, the details of the source-to-sink system remain unclear and discrepancies exist between proxy records. The heavy minerals in the Middle Triassic in the Sikeshu subbasin are dominated by garnets. To investigate the garnet sources and decipher the Mesozoic source-to-sink evolution, we conducted petrological and sedimentary analysis and detrital garnet and tourmaline geochemistry. We found that the geochemistry of garnets in the Middle Triassic sandstone is most consistent with that of the skarns in the Yili Block (YB) in Tianshan, while the geochemistry of 55%–84% of garnets in other Mesozoic sandstones is consistent with that of garnets in amphibolites in the YB. The geochemistry of the tourmalines since the Upper Triassic is consistent with that of the meta-sedimentary rocks in the YB and Central Tianshan Block. The dominance of garnets sourced from skarns in the Middle Triassic probably indicates a near-source point provenance and the broader range of garnet compositions from the Upper Triassic–Lower Cretaceous suggests multiple sources. We infer that the point source changed to multiple sources, which is consistent with the zircon spectra changing from unimodal to multimodal. This change reflects the expansion of the drainage that accompanies a change from active rifting to a post-rift stage.</p>","PeriodicalId":50422,"journal":{"name":"Geochemistry Geophysics Geosystems","volume":null,"pages":null},"PeriodicalIF":2.9,"publicationDate":"2024-06-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1029/2024GC011455","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141488984","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
An animated 100,000-year-interval tectonic reconstruction of the Woodlark Basin in the southwest Pacific illustrates how, at intermediate initial spreading rates, orogenic continents break up (dyke model), spreading segments nucleate, transform faults initiate and ocean basins evolve. We refine the location/timing of initial seafloor spreading and Euler poles of rotation back to 6.2 Ma. In the easternmost basin, where spreading younger than 2.6 Ma is not co-polar with that to the west, we recognize the formation of a Ghizo microplate and Ranongga Transform Fault at ∼2.6 Ma and a 3-degree rotational opening of the Itina Trough from 2.6 to 1.0 Ma. Allowing for that motion, we show that the 5.2–2.6 Ma seafloor in the easternmost basin formed co-polar with that to the west. We also identify a ridge jump reorientation at ∼1.0 Ma that formed the NE-trending Simbo Spreading Segment, whose neovolcanic zone includes Simbo Island and a submarine edifice to its south. Proposed deterministic models of ridge propagation (due to topographic gradients, mantle flow away from hotspots and/or changing plate motion) are not consistent with those observed; mantle chemical heterogeneities and melting anomalies are a potential cause that remains to be tested. We reconstruct the northern conjugate of the oldest extant oceanic crust and estimate the initiation of its subduction at ∼2.6 Ma, concomitant with observed changes in plate motion and segmentation. Where subducted, the young oceanic lithosphere between the conjugate rifted margins appears to be resorbed into the mantle, leaving a slab window where the Pacific subducted slab remains attached.
西南太平洋伍德拉克盆地 10 万年间隔的构造重建动画展示了在中等初始扩张速率下,造山大陆如何断裂(堤坝模型)、扩张段如何成核、转换断层如何启动以及海洋盆地如何演化。我们将初始海底扩张的位置/时间和欧拉旋转极点细化到 6.2 Ma。在最东部的海盆中,小于 2.6 Ma 的扩张与西部的扩张不是同极的,我们认识到在 ∼ 2.6 Ma 形成了 Ghizo 微板块和 Ranongga 转换断层,从 2.6 Ma 到 1.0 Ma 伊蒂纳海槽旋转了 3 度。考虑到这一运动,我们表明最东部海盆的 5.2-2.6 Ma 海底与西部海盆的海底形成了同极性。我们还确定了在 1.0 Ma ∼ 1.0 Ma 海脊跃升重新定向,形成了东北走向的辛博扩张段,其新火山带包括辛博岛及其南面的海底大厦。所提出的海脊传播的确定性模型(由于地形梯度、地幔流离开热点和/或板块运动的变化)与所观察到的不一致;地幔化学异质性和熔融异常是一个有待检验的潜在原因。我们重建了现存最古老大洋地壳的北共轭,并估计其俯冲开始于 ∼ 2.6 Ma,与观测到的板块运动和分段变化同步。在俯冲的地方,共轭断裂边缘之间年轻的大洋岩石圈似乎被重新吸收到地幔中,留下一个板块窗口,太平洋俯冲板块仍然附着在那里。
{"title":"A Detailed Reconstruction of the Woodlark Basin","authors":"E. K. Benyshek, B. Taylor, A. M. Goodliffe","doi":"10.1029/2023GC011410","DOIUrl":"https://doi.org/10.1029/2023GC011410","url":null,"abstract":"<p>An animated 100,000-year-interval tectonic reconstruction of the Woodlark Basin in the southwest Pacific illustrates how, at intermediate initial spreading rates, orogenic continents break up (dyke model), spreading segments nucleate, transform faults initiate and ocean basins evolve. We refine the location/timing of initial seafloor spreading and Euler poles of rotation back to 6.2 Ma. In the easternmost basin, where spreading younger than 2.6 Ma is not co-polar with that to the west, we recognize the formation of a Ghizo microplate and Ranongga Transform Fault at ∼2.6 Ma and a 3-degree rotational opening of the Itina Trough from 2.6 to 1.0 Ma. Allowing for that motion, we show that the 5.2–2.6 Ma seafloor in the easternmost basin formed co-polar with that to the west. We also identify a ridge jump reorientation at ∼1.0 Ma that formed the NE-trending Simbo Spreading Segment, whose neovolcanic zone includes Simbo Island and a submarine edifice to its south. Proposed deterministic models of ridge propagation (due to topographic gradients, mantle flow away from hotspots and/or changing plate motion) are not consistent with those observed; mantle chemical heterogeneities and melting anomalies are a potential cause that remains to be tested. We reconstruct the northern conjugate of the oldest extant oceanic crust and estimate the initiation of its subduction at ∼2.6 Ma, concomitant with observed changes in plate motion and segmentation. Where subducted, the young oceanic lithosphere between the conjugate rifted margins appears to be resorbed into the mantle, leaving a slab window where the Pacific subducted slab remains attached.</p>","PeriodicalId":50422,"journal":{"name":"Geochemistry Geophysics Geosystems","volume":null,"pages":null},"PeriodicalIF":2.9,"publicationDate":"2024-06-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1029/2023GC011410","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141488966","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
J. P. Lever, K. E. Sundell, D. M. Pearson, D.T. Brennan
Sedimentary basins are valuable archives of tectonic processes involved in continental rifting. The northern Rocky Mountains preserve the Belt Supergroup, one of the most complete records of Mesoproterozoic strata on Earth; however, debate remains about its tectonic origin. We investigated a recently identified package of Mesoproterozoic strata at Leaton Gulch near Challis, Idaho, using a combination of traditional and newer sedimentological tools. Results suggest that the Leaton Gulch stratigraphic section was deposited in a fluvial setting ca. 1,380–1,317 Ma, spanning the poorly documented interval between late Belt Supergroup deposition at ∼1,370 Ma and recently characterized Deer Trail Group strata that are less than 1,300 Ma. Detrital zircon age distributions from Leaton Gulch demonstrate a similar provenance signature to Missoula Group rocks of the upper Belt Supergroup; however, Leaton Gulch strata are up to ∼70 Ma younger than most prior age constraints on Belt Supergroup rocks. Regional metabentonites (interpreted as metamorphosed reworked tuffs) found within Leaton Gulch and Missoula Group strata show dominantly radiogenic εHf(t), with a range of −8 to +15, interpreted as a mix of primary mantle and remelted metasedimentary sources. Zircon trace element data of the metabentonite from Leaton Gulch suggest a 1,450–1,300 Ma geochemically consistent and moderate–high silica melt source. Collectively, the strata of Leaton Gulch record basin sedimentation during a critical window of Mesoproterozoic time. We speculate that sedimentation during late-stage Belt Supergroup deposition thickened and stepped westward, abandoning the main Belt basin, culminating with breakup of the Nuna Supercontinent.
沉积盆地是大陆断裂构造过程的宝贵档案。落基山脉北部保留了贝尔特超群,这是地球上中新生代地层最完整的记录之一;然而,关于它的构造起源仍存在争议。我们结合使用传统和较新的沉积学工具,对爱达荷州查利斯附近利顿沟最近发现的一套中新生代地层进行了研究。研究结果表明,Leaton Gulch 地层剖面是在大约 1,380-1,317 Ma 的河流环境中沉积的,跨越了文献记载较少的从 1,370 Ma ∼ 1,370 Ma 的晚期带超群沉积到最近特征为小于 1,300 Ma 的鹿径组地层之间的区间。利顿沟的锆英石年龄分布显示出与上贝尔特超群的米苏拉群岩石相似的产状特征;然而,利顿沟地层比大多数先前对贝尔特超群岩石的年龄限制要年轻 70 Ma。在利顿沟地层和米苏拉群地层中发现的区域性变质凝灰岩(解释为变质再加工凝灰岩)显示出主要的放射性εHf(t),范围为-8至+15,解释为原生地幔和重熔变质岩的混合来源。来自利顿沟的偏闪长岩的锆石痕量元素数据表明,其地质化学成分在 1450-1300 Ma 之间保持一致,并具有中等偏高的二氧化硅熔体来源。总体而言,利顿沟的地层记录了中新生代一个关键时间窗口的盆地沉积。我们推测,在带状超群沉积晚期,沉积增厚并向西阶梯式发展,放弃了带状主盆地,最终导致努纳超洲断裂。
{"title":"Recently Identified Mesoproterozoic Strata in South-Central Idaho Document Late-Stage Rifting of the Nuna Supercontinent in Western Laurentia","authors":"J. P. Lever, K. E. Sundell, D. M. Pearson, D.T. Brennan","doi":"10.1029/2024GC011503","DOIUrl":"https://doi.org/10.1029/2024GC011503","url":null,"abstract":"<p>Sedimentary basins are valuable archives of tectonic processes involved in continental rifting. The northern Rocky Mountains preserve the Belt Supergroup, one of the most complete records of Mesoproterozoic strata on Earth; however, debate remains about its tectonic origin. We investigated a recently identified package of Mesoproterozoic strata at Leaton Gulch near Challis, Idaho, using a combination of traditional and newer sedimentological tools. Results suggest that the Leaton Gulch stratigraphic section was deposited in a fluvial setting ca. 1,380–1,317 Ma, spanning the poorly documented interval between late Belt Supergroup deposition at ∼1,370 Ma and recently characterized Deer Trail Group strata that are less than 1,300 Ma. Detrital zircon age distributions from Leaton Gulch demonstrate a similar provenance signature to Missoula Group rocks of the upper Belt Supergroup; however, Leaton Gulch strata are up to ∼70 Ma younger than most prior age constraints on Belt Supergroup rocks. Regional metabentonites (interpreted as metamorphosed reworked tuffs) found within Leaton Gulch and Missoula Group strata show dominantly radiogenic εHf<sub>(t)</sub>, with a range of −8 to +15, interpreted as a mix of primary mantle and remelted metasedimentary sources. Zircon trace element data of the metabentonite from Leaton Gulch suggest a 1,450–1,300 Ma geochemically consistent and moderate–high silica melt source. Collectively, the strata of Leaton Gulch record basin sedimentation during a critical window of Mesoproterozoic time. We speculate that sedimentation during late-stage Belt Supergroup deposition thickened and stepped westward, abandoning the main Belt basin, culminating with breakup of the Nuna Supercontinent.</p>","PeriodicalId":50422,"journal":{"name":"Geochemistry Geophysics Geosystems","volume":null,"pages":null},"PeriodicalIF":2.9,"publicationDate":"2024-06-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1029/2024GC011503","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141488848","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Riddhi Dave, Fiona Darbyshire, Juan Carlos Afonso, I. Fomin
The Archean Superior craton was formed by the assemblage of continental and oceanic terranes at ∼2.6 Ga. The craton is surrounded by multiple Proterozoic mobile belts, including the Paleoproterozoic Trans-Hudson Orogen which brought together the Superior and Rae/Hearne cratons at ∼1.9–1.8 Ga. Despite numerous studies on Precambrian lithospheric formation and evolution, the deep thermochemical structure of the Superior craton and its surroundings remains poorly understood. Here we investigate the upper mantle beneath the region from the surface to 400 km depth by jointly inverting Rayleigh wave phase velocity dispersion data, elevation, geoid height and surface heat flow, using a probabilistic inversion to obtain a (pseudo-)3D model of composition, density and temperature. The lithospheric structure is dominated by thick cratonic roots (>300 km) beneath the eastern and western arms of the Superior craton, with a chemically depleted signature (Mg# > 92.5), consistent with independent results from mantle xenoliths. Beneath the surrounding Proterozoic and Phanerozoic orogens, the Mid-continent Rift and Hudson Strait, we observe a relatively thinner lithosphere and more fertile composition, indicating that these regions have undergone lithospheric modification and erosion. Our model supports the hypothesis that the core of the Superior craton is well-preserved and has evaded lithospheric destruction and refertilization. We propose three factors playing a critical role in the craton's stability: (a) the presence of a mid-lithospheric discontinuity, (b) the correct isopycnic conditions to sustain a strength contrast between the craton and the surrounding mantle, and (c) the presence of weaker mobile belts around the craton.
{"title":"Thermochemical Structure of the Superior Craton and Environs: Implications for the Evolution and Preservation of Cratonic Lithosphere","authors":"Riddhi Dave, Fiona Darbyshire, Juan Carlos Afonso, I. Fomin","doi":"10.1029/2024GC011454","DOIUrl":"https://doi.org/10.1029/2024GC011454","url":null,"abstract":"<p>The Archean Superior craton was formed by the assemblage of continental and oceanic terranes at ∼2.6 Ga. The craton is surrounded by multiple Proterozoic mobile belts, including the Paleoproterozoic Trans-Hudson Orogen which brought together the Superior and Rae/Hearne cratons at ∼1.9–1.8 Ga. Despite numerous studies on Precambrian lithospheric formation and evolution, the deep thermochemical structure of the Superior craton and its surroundings remains poorly understood. Here we investigate the upper mantle beneath the region from the surface to 400 km depth by jointly inverting Rayleigh wave phase velocity dispersion data, elevation, geoid height and surface heat flow, using a probabilistic inversion to obtain a (pseudo-)3D model of composition, density and temperature. The lithospheric structure is dominated by thick cratonic roots (>300 km) beneath the eastern and western arms of the Superior craton, with a chemically depleted signature (Mg# > 92.5), consistent with independent results from mantle xenoliths. Beneath the surrounding Proterozoic and Phanerozoic orogens, the Mid-continent Rift and Hudson Strait, we observe a relatively thinner lithosphere and more fertile composition, indicating that these regions have undergone lithospheric modification and erosion. Our model supports the hypothesis that the core of the Superior craton is well-preserved and has evaded lithospheric destruction and refertilization. We propose three factors playing a critical role in the craton's stability: (a) the presence of a mid-lithospheric discontinuity, (b) the correct isopycnic conditions to sustain a strength contrast between the craton and the surrounding mantle, and (c) the presence of weaker mobile belts around the craton.</p>","PeriodicalId":50422,"journal":{"name":"Geochemistry Geophysics Geosystems","volume":null,"pages":null},"PeriodicalIF":2.9,"publicationDate":"2024-06-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1029/2024GC011454","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141488847","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Sarah Z. Rosengard, Jose Mauro S. Moura, Robert G. M. Spencer, Carl Johnson, Ann McNichol, Andrew D. Steen, Valier Galy
The Amazon River mobilizes organic carbon across one of the world's largest terrestrial carbon reservoirs. Quantifying the sources of particulate organic carbon (POC) to this flux is typically challenging in large systems such as the Amazon River due to hydrodynamic sorting of sediments. Here, we analyze the composition of POC collected from multiple total suspended sediment (TSS) profiles in the mainstem at Óbidos, and surface samples from the Madeira, Solimões and Tapajós Rivers. As hypothesized, TSS and POC concentrations in the mainstem increased with depth and fit well to Rouse models for sediment sorting by grain size. Coupling these profiles with Acoustic Doppler Current Profiler discharge data, we estimate a large decrease in POC flux (from 540 to 370 kg per second) between the rising and falling stages of the Amazon River mainstem. The C/N ratio and stable and radiocarbon signatures of bulk POC are less variable within the cross-section at Óbidos and suggest that riverine POC in the Amazon River is predominantly soil-derived. However, smaller shifts in these compositional metrics with depth, including leaf wax n-alkanes and fatty acids, are consistent with the perspective that deeper and larger particles carry fresher, less degraded organic matter sources (i.e., vegetation debris) through the mainstem. Overall, our cross-sectional surveys at Óbidos highlight the importance of depth-specific sampling for estimating riverine export fluxes. At the same time, they imply that this approach to sampling is perhaps less essential with respect to characterizing the composition of POC sources exported by the river.
{"title":"Depth-Partitioning of Particulate Organic Carbon Composition in the Rising and Falling Stages of the Amazon River","authors":"Sarah Z. Rosengard, Jose Mauro S. Moura, Robert G. M. Spencer, Carl Johnson, Ann McNichol, Andrew D. Steen, Valier Galy","doi":"10.1029/2023GC011273","DOIUrl":"https://doi.org/10.1029/2023GC011273","url":null,"abstract":"<p>The Amazon River mobilizes organic carbon across one of the world's largest terrestrial carbon reservoirs. Quantifying the sources of particulate organic carbon (POC) to this flux is typically challenging in large systems such as the Amazon River due to hydrodynamic sorting of sediments. Here, we analyze the composition of POC collected from multiple total suspended sediment (TSS) profiles in the mainstem at Óbidos, and surface samples from the Madeira, Solimões and Tapajós Rivers. As hypothesized, TSS and POC concentrations in the mainstem increased with depth and fit well to Rouse models for sediment sorting by grain size. Coupling these profiles with Acoustic Doppler Current Profiler discharge data, we estimate a large decrease in POC flux (from 540 to 370 kg per second) between the rising and falling stages of the Amazon River mainstem. The C/N ratio and stable and radiocarbon signatures of bulk POC are less variable within the cross-section at Óbidos and suggest that riverine POC in the Amazon River is predominantly soil-derived. However, smaller shifts in these compositional metrics with depth, including leaf wax <i>n</i>-alkanes and fatty acids, are consistent with the perspective that deeper and larger particles carry fresher, less degraded organic matter sources (i.e., vegetation debris) through the mainstem. Overall, our cross-sectional surveys at Óbidos highlight the importance of depth-specific sampling for estimating riverine export fluxes. At the same time, they imply that this approach to sampling is perhaps less essential with respect to characterizing the composition of POC sources exported by the river.</p>","PeriodicalId":50422,"journal":{"name":"Geochemistry Geophysics Geosystems","volume":null,"pages":null},"PeriodicalIF":2.9,"publicationDate":"2024-06-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1029/2023GC011273","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141488823","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Michel Kühn, Christian Berndt, Sebastian F. L. Watt, Matthew J. Hornbach, Sebastian Krastel, Kristina Sass, Steffen Kutterolf, Tim Freudenthal, Katrin Huhn, Jens Karstens, Bettina Schramm, Judith Elger, Christoph Böttner, Dirk Klaeschen
Volcanic flank collapses, especially those in island settings, have generated some of the most voluminous mass transport deposits on Earth and can trigger devastating tsunamis. Reliable tsunami hazard assessments for flank collapse-driven tsunamis require an understanding of the complex emplacement processes involved. The seafloor sequence southeast of Montserrat (Lesser Antilles) is a key site for the study of volcanic flank collapse emplacement processes that span subaerial to submarine environments. Here, we present new 2D and 3D seismic data as well as MeBo drill core data from one of the most extensive mass transport deposits offshore Montserrat, which exemplifies multi-phase landslide deposition from volcanic islands. The deposits reveal emplacement in multiple stages including two blocky volcanic debris avalanches, secondary seafloor failure and a late-stage erosive density current that carved channel-like incisions into the hummocky surface of the deposit about 15 km from the source region. The highly erosive density current potentially originated from downslope-acceleration of fine-grained material that was suspended in the water column earlier during the slide. Late-stage erosive turbidity currents may be a more common process following volcanic sector collapse than has been previously recognized, exerting a potentially important control on the observed deposit morphology as well as on the runout and the overall shape of the deposit.
{"title":"Volcanic Flank Collapse, Secondary Sediment Failure and Flow-Transition: Multi-Stage Landslide Emplacement Offshore Montserrat, Lesser Antilles","authors":"Michel Kühn, Christian Berndt, Sebastian F. L. Watt, Matthew J. Hornbach, Sebastian Krastel, Kristina Sass, Steffen Kutterolf, Tim Freudenthal, Katrin Huhn, Jens Karstens, Bettina Schramm, Judith Elger, Christoph Böttner, Dirk Klaeschen","doi":"10.1029/2024GC011564","DOIUrl":"https://doi.org/10.1029/2024GC011564","url":null,"abstract":"<p>Volcanic flank collapses, especially those in island settings, have generated some of the most voluminous mass transport deposits on Earth and can trigger devastating tsunamis. Reliable tsunami hazard assessments for flank collapse-driven tsunamis require an understanding of the complex emplacement processes involved. The seafloor sequence southeast of Montserrat (Lesser Antilles) is a key site for the study of volcanic flank collapse emplacement processes that span subaerial to submarine environments. Here, we present new 2D and 3D seismic data as well as MeBo drill core data from one of the most extensive mass transport deposits offshore Montserrat, which exemplifies multi-phase landslide deposition from volcanic islands. The deposits reveal emplacement in multiple stages including two blocky volcanic debris avalanches, secondary seafloor failure and a late-stage erosive density current that carved channel-like incisions into the hummocky surface of the deposit about 15 km from the source region. The highly erosive density current potentially originated from downslope-acceleration of fine-grained material that was suspended in the water column earlier during the slide. Late-stage erosive turbidity currents may be a more common process following volcanic sector collapse than has been previously recognized, exerting a potentially important control on the observed deposit morphology as well as on the runout and the overall shape of the deposit.</p>","PeriodicalId":50422,"journal":{"name":"Geochemistry Geophysics Geosystems","volume":null,"pages":null},"PeriodicalIF":2.9,"publicationDate":"2024-06-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1029/2024GC011564","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141488228","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Aaron Wolfgang Ashley, Suraj Bajgain, Mainak Mookherjee
The continental crust is produced by the solidification of aluminosilicate-rich magmas which are sourced from deep below the surface. Migration of the magma depends on the density (ρ) contrast to source rocks and the melt viscosity (η). At the surface, these silica-rich melts are typically sluggish due to high η > 1,000 Pa s. Yet at their source regions, the melt properties are complexly influenced by pressure (P), temperature (T), and water contents (