Geochemistry Geophysics Geosystems最新文献

{"title":"Elasticity of Nacrite: Implications for Subduction Zone Dynamics","authors":"Ishita Das,&nbsp;Gaurav Shukla","doi":"10.1029/2024GC011786","DOIUrl":"https://doi.org/10.1029/2024GC011786","url":null,"abstract":"<p>Subduction zones exhibit heterogeneities in composition due to different mineral assemblages transported into the mantle by the descending slabs, thus affecting the seismic properties of the region. These minerals are typically rich in alumina and silica and often contain hydrous phases. Nacrite, Al₂Si₂O₅(OH)₄, a mineral consisting of these components, forms in basaltic crust through hydrothermal alteration and is frequently overlooked due to its structural alikeness with its polytypes, making it hard to distinguish by traditional methods. Its occurrence in oceanic sediments and altered basaltic crust significantly impacts the subduction process by facilitating the transport of water into deeper mantle regions. In this study, we investigate the equation of state and elasticity of nacrite using first-principles calculations based on density functional theory corrected for dispersive forces over its pressure stability range. Anomalous behavior of elastic coefficients are suggestive of a polytypic transformation, evidenced by anomalous softening in the shear modulus and a decrease of approximately 3% in shear wave velocity observed at low pressures (<span></span><math>\u0000 <semantics>\u0000 <mrow>\u0000 <mo>∼</mo>\u0000 </mrow>\u0000 <annotation> ${sim} $</annotation>\u0000 </semantics></math> 2 GPa). Our studies indicate that nacrite exhibits a significantly lower shear wave velocity compared to the surrounding mantle, resulting in very high V_P/V_S ratios. These findings emphasize the role of nacrite in the subduction zones of Japan and Alaska, particularly in the formation of low-velocity layers. We propose that nacrite's presence is a significant factor explaining these observations, alongside other hydrous minerals like lawsonite, glaucophane, etc., contributing to the low-velocity layers in these regions.</p>","PeriodicalId":50422,"journal":{"name":"Geochemistry Geophysics Geosystems","volume":"25 12","pages":""},"PeriodicalIF":2.9,"publicationDate":"2024-12-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1029/2024GC011786","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142851342","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}

{"title":"Seventeen Million Years of Episodic Volcanism Recorded Within the Geologist Seamounts: Implications for Tectonic Drivers of Intraplate Volcanism","authors":"Brandon Scott,&nbsp;Kevin Konrad","doi":"10.1029/2024GC011806","DOIUrl":"https://doi.org/10.1029/2024GC011806","url":null,"abstract":"<p>Upwelling and decompression of mantle plumes is the primary mechanism for large volumes of intraplate volcanism; however, many seamounts do not correlate spatially, temporally, or geochemically with plumes. One region of enigmatic volcanism in the ocean basins that is not clearly attributable to plume-derived magmatism is the Geologist Seamounts and the wider South Hawaiian Seamount Province (∼19°N, 157°W). Here we present new bathymetric maps as well as ⁴⁰Ar/³⁹Ar age determinations and major and trace element geochemistry for six remote-operated vehicle recovered igneous rock samples (NOAA-OER EX1504L3) and two dredged samples (KK840824-02) from the Geologist Seamounts. The new ages indicate that volcanism was active from 90 to 87 Ma and 74 to 73 Ma, inferring that in conjunction with previous ages of ∼84 Ma, seamount emplacement initiated near the paleo Pacific-Farallon spreading ridge and volcanism spanned at least ∼17 m.y. Geochemical analyses indicate that Geologist Seamount lava flows are highly alkalic and represent low-degree partial mantle melts primarily formed from a mixture of melting within the garnet and spinel stability field. The ages and morphology inferred that the seamounts were likely not related to an extinct plume. Instead, we build upon previous models that local microblock formation corresponded to regional lithospheric extension. We propose that the microblock was bounded by the Molokai and short-lived Kana Keoki fracture zones. Regional deformation and corresponding volcanism among the Geologist Seamounts associated with the microblock potentially occurred in pulses contemporaneous to independently constrained changes in Pacific Plate motion—indicating that major changes in plate vectors can generate intraplate volcanism.</p>","PeriodicalId":50422,"journal":{"name":"Geochemistry Geophysics Geosystems","volume":"25 12","pages":""},"PeriodicalIF":2.9,"publicationDate":"2024-12-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1029/2024GC011806","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142851351","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}

{"title":"The Jurassic–Cretaceous Transition in the Slovenian Basin (Alpine Atlantic): Further Evidence for Palaeoenvironmental Record in Pelagic Sediments","authors":"D. G. Lodowski,&nbsp;J. Grabowski,&nbsp;B. Rožič,&nbsp;P. Žvab-Rožič,&nbsp;D. Reháková,&nbsp;L. Slapnik,&nbsp;J. Iwańczuk,&nbsp;A. Chmielewski,&nbsp;A. Teodorski","doi":"10.1029/2024GC011728","DOIUrl":"https://doi.org/10.1029/2024GC011728","url":null,"abstract":"<p>Over the vast area of present-day Europe, the Tithonian–Berriasian transition was a time of climate aridization, which was supposedly related to the more general trend of the latest Jurassic–earliest Cretaceous cooling and restrictions in atmospheric circulation. Recent studies suggest that such conditions affected also some other paleoenvironmental processes such as monsoonal upwellings, seafloor ventilation and circulation of nutrients within the water column. In order to test this model, the uppermost Jurassic–lowermost Cretaceous sedimentary succession of the Slovenian Basin was correlated with a reference data from the Bakony Basin (Transdanubian Range, Hungary). Stratigraphic calibration was ensured by integrated stratigraphy, utilizing bio- (calpionellids, calcareous dinocysts) and chemostratigraphic tools (δ¹³C stratigraphy) as well as regional correlations of magnetic susceptibility and terrigenous input. Paleoclimate, paleoredox and paleoproductivity conditions were evaluated based on various geochemical proxies. Both the Slovenian and the Bakony basin sections were found to document late Tithonian–early Berriasian climate aridization as well as related signals of seafloor hypoxia and elevated accumulations of micronutrients. Significant geochemical contrast between the basal (lower Tithonian) radiolarites and overlying upper Tithonian–Berriasian carbonates evidences the inverse relation between the surface productivity and the amount of nutrient-type trace metals buried in sediments. The rhythm of paleoclimatically controlled environmental changes, with relatively humid early Tithonian, arid late Tithonian–early Berriasian, and again humid late Berriasian, correlates with those estimated for Vocontian Basin (SE France) and the Sub-Boreal domain of Western and Central Europe. This indicates that climatic stratigraphy is a useful tool for global correlation of the Jurassic/Cretaceous boundary interval.</p>","PeriodicalId":50422,"journal":{"name":"Geochemistry Geophysics Geosystems","volume":"25 12","pages":""},"PeriodicalIF":2.9,"publicationDate":"2024-12-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1029/2024GC011728","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142860911","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}

{"title":"Kinetic Isotopic Degassing of CO2 During the 2021 Fagradalsfjall Eruption and the δ13C Signature of the Icelandic Mantle","authors":"Yves Moussallam,&nbsp;Estelle F. Rose-Koga,&nbsp;Tobias P. Fischer,&nbsp;Guillaume Georgeais,&nbsp;Hyun Joo Lee,&nbsp;Janine Birnbaum,&nbsp;Melissa A. Pfeffer,&nbsp;Talfan Barnie,&nbsp;Edouard Regis","doi":"10.1029/2024GC011997","DOIUrl":"https://doi.org/10.1029/2024GC011997","url":null,"abstract":"<p>CO₂ is the first volatile to exsolve in magmatic systems and plays a crucial role in driving magma ascent and volcanic eruptions. Carbon stable isotopes serve as valuable tracers for understanding the transfer of CO₂ from the melt to the gas phase during passive degassing or active eruptions. In this study, we present δ¹³C measurements from the 2021 Fagradalsfjall eruption, obtained from (a) volcanic gases emitted during the eruption and collected via unmanned aerial systems (UAS), and (b) a series of mineral-hosted melt inclusions from the corresponding tephra deposits. These data sets jointly track the carbon isotopic evolution of the melt and gas phases during the last 10 km of magma ascent. The isotopic evolution of both phases indicates that kinetic degassing, a process previously only identified in mid-ocean ridge basalts, took place in the 10 to 1 km depth range, followed by equilibrium degassing at near-surface conditions in the last kilometer. Postulating that the melt was first saturated with CO₂ at 27 km depth and that degassing from then to 10 km depth took place via equilibrium isotopic fractionation, the melt inclusion data constrain the initial δ¹³C signature of the Icelandic mantle to −6.5 ± 2.5‰ but also show indications of possible isotopic heterogeneity in the mantle source.</p>","PeriodicalId":50422,"journal":{"name":"Geochemistry Geophysics Geosystems","volume":"25 12","pages":""},"PeriodicalIF":2.9,"publicationDate":"2024-12-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1029/2024GC011997","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142860362","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}

{"title":"Microseismicity Around Loki's Castle Hydrothermal Vent Field Reveals the Early Stages of Detachment Faulting at the Mohns-Knipovich Ridge Intersection","authors":"Matthias Pilot,&nbsp;Marie Jakobsen Lien,&nbsp;Vera Schlindwein,&nbsp;Lars Ottemöller,&nbsp;Thibaut Barreyre","doi":"10.1029/2024GC011732","DOIUrl":"https://doi.org/10.1029/2024GC011732","url":null,"abstract":"<p>At slow to ultraslow spreading ridges, the limited melt supply results in tectonic accretion and the exhumation of mantle rocks. Melt supply is focused toward volcanic centers where magmatic accretion dominates. In areas where the ridges reorientate, both types of accretion can occur across the ridge axis with detachment faults developing on the inside corners and hydrothermal vent fields located in close proximity. Microseismicity studies improve the understanding of the tectonic processes at detachment faults and their interplay with hydrothermal vent systems, but are mostly limited to mature detachment faults or short deployment times. This study presents results from a ∼11 months ocean bottom seismometer deployment around the Loki's Castle hydrothermal vent field at the intersection of the slow to ultraslow spreading Mohns and Knipovich Ridge. We observe seismicity to be highly asymmetric with the majority of the plate divergence being accommodated by an emerging detachment fault at the inside corner of the intersection west of Loki's Castle. Seismic activity related to the detachment fault displays a distinct contrast, with continuous low-magnitude events occurring at depth and episodic large-magnitude events concentrated in clusters within the footwall. The detachment fault shows no significant roll-over at shallow depths and the locus of spreading is located east of the detachment. These results suggest that the detachment fault west of Loki’s Castle is at an early development stage.</p>","PeriodicalId":50422,"journal":{"name":"Geochemistry Geophysics Geosystems","volume":"25 12","pages":""},"PeriodicalIF":2.9,"publicationDate":"2024-12-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1029/2024GC011732","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142762476","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}

{"title":"Auriferous Fluid Evolution and the Role of Carbonaceous Matter in a Saddle-Reef Gold Deposit: Dufferin Deposit, Meguma Terrane, Nova Scotia, Canada","authors":"Mitchell J. Kerr,&nbsp;Jacob J. Hanley,&nbsp;Daniel J. Kontak,&nbsp;Preetysha Ramlochund,&nbsp;Zoltán Zajacz","doi":"10.1029/2024GC011861","DOIUrl":"https://doi.org/10.1029/2024GC011861","url":null,"abstract":"<p>The metaturbidite-hosted, ∼380 Ma Dufferin gold deposit, Meguma terrane, northeastern Appalachian Orogen (Nova Scotia, Canada) is an orogenic gold deposit with mineralized saddle reef-type quartz veins hosted by metasandstones and black slates in a tightly folded anticline. Together with native gold inclusions, genetically related hydrothermal carbonaceous material (CM) in veins occurs as pyrobitumen in cavities and along fractures/grain boundaries proximal to vein contacts and wallrock fragments. Integrating several microanalytical methods we document the precipitation of gold via coupled fluid-<i>f</i>O₂ reduction (via interaction with CM) and pH increase. These changes in fluid chemistry destabilized gold bisulfide complexes, leading to efficient Au precipitation from a gold-undersaturated (0.045 ± 0.024 ppm Au; 1σ; <i>n</i> = 58 fluid inclusions) aqueous-carbonic fluid (H₂O-NaCl-CO₂ ± N₂ ± CH₄). The proposed mineralization mechanism is supported by: (a) a complementary decrease in Au and redox-sensitive semimetals (As, Sb), and increase in wall rock-derived elements (i.e., Mg, K, Ca, Sr, Fe) concentrations in fluid inclusions with time; (b) a corresponding decrease in the X_CO2, consistent with CO₂ removal via reduction/respeciation and late carbonate precipitation; and (c) gold embedding in, or on, the surface of CM inside mineralized cavities and fractures. Despite mineralizing fluids transporting low concentrations of Au far from saturation, precipitation of gold was locally evidently high where such fluids interacted with CM, contributing to the overall gold endowment of Meguma deposits. This work re-emphasizes CM as a potential prerequisite for efficient gold precipitation within the overall genetic model for similar orogenic metasedimentary settings globally where the presence and/or role of CM has been documented.</p>","PeriodicalId":50422,"journal":{"name":"Geochemistry Geophysics Geosystems","volume":"25 12","pages":""},"PeriodicalIF":2.9,"publicationDate":"2024-11-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1029/2024GC011861","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142749262","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}

{"title":"Magma Chamber Response to Ice Unloading: Applications to Volcanism in the West Antarctic Rift System","authors":"A. N. Coonin,&nbsp;C. Huber,&nbsp;J. Troch,&nbsp;M. Townsend,&nbsp;K. Scholz,&nbsp;B. S. Singer","doi":"10.1029/2024GC011743","DOIUrl":"https://doi.org/10.1029/2024GC011743","url":null,"abstract":"<p>Volcanic activity has been shown to affect Earth's climate in a myriad of ways. One such example is that eruptions proximate to surface ice will promote ice melting. In turn, the crustal unloading associated with melting an ice sheet affects the internal dynamics of the underlying magma plumbing system. Geochronologic data from the Andes over the last two glacial cycles suggest that glaciation and volcanism may interact via a positive feedback loop. At present, accurate sea-level predictions hinge on our ability to forecast the stability of the West Antarctic Ice Sheet, and thus require consideration of two-way subglacial volcano-deglaciation processes. The West Antarctic Ice Sheet is particularly vulnerable to collapse, yet its position atop an active volcanic rift is seldom considered. Ice unloading deepens the zone of melting and alters the crustal stress field, impacting conditions for dike initiation, propagation, and arrest. However, the consequences for internal magma chamber dynamics and long-term eruption behavior remain elusive. Given that unloading-triggered volcanism in West Antarctica may contribute to the uncertainty of ice loss projections, we adapt a previously published thermomechanical magma chamber model and simulate a shrinking ice load through a prescribed lithostatic pressure decrease. We investigate the impacts of varying unloading scenarios on magma volatile partitioning and eruptive trajectory. Considering the removal of km-thick ice sheets, we demonstrate that the rate of unloading influences the cumulative mass erupted and consequently the heat released into the ice. These findings provide fundamental insights into the complex volcano-ice interactions in West Antarctica and other subglacial volcanic settings.</p>","PeriodicalId":50422,"journal":{"name":"Geochemistry Geophysics Geosystems","volume":"25 12","pages":""},"PeriodicalIF":2.9,"publicationDate":"2024-11-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1029/2024GC011743","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142748945","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}

{"title":"Slab-Plume Interactions Beneath Australia and New Zealand: New Insight From Whole-Mantle Tomography","authors":"Genti Toyokuni,&nbsp;Dapeng Zhao","doi":"10.1029/2024GC011739","DOIUrl":"https://doi.org/10.1029/2024GC011739","url":null,"abstract":"&lt;p&gt;Australia, New Zealand, and the surrounding regions have experienced complex plate interactions with significant seismic and volcanic activities. The Taupo volcano on the North Island of New Zealand has experienced multiple catastrophic eruptions. Although Australia is known as a stable landmass with low seismic and volcanic activity, intraplate volcanoes along its eastern coast are considered to be caused by hot mantle plumes. To better understand the seismic and volcanic activities in the region, it is necessary to study the detailed 3-D structure of the crust and mantle. Here we apply a well-established global tomography method to reveal the 3-D &lt;i&gt;P&lt;/i&gt;-wave velocity (&lt;span&gt;&lt;/span&gt;&lt;math&gt;\u0000 &lt;semantics&gt;\u0000 &lt;mrow&gt;\u0000 &lt;msub&gt;\u0000 &lt;mi&gt;V&lt;/mi&gt;\u0000 &lt;mi&gt;P&lt;/mi&gt;\u0000 &lt;/msub&gt;\u0000 &lt;/mrow&gt;\u0000 &lt;annotation&gt; ${V}_{P}$&lt;/annotation&gt;\u0000 &lt;/semantics&gt;&lt;/math&gt;) structure of the whole mantle beneath this region. We used ∼7 million &lt;i&gt;P&lt;/i&gt;, &lt;i&gt;pP&lt;/i&gt;, &lt;i&gt;PP&lt;/i&gt;, &lt;i&gt;PcP&lt;/i&gt;, and &lt;i&gt;Pdiff&lt;/i&gt; wave arrival times of 23,666 earthquakes recorded at 14,181 seismograph stations worldwide. The resulting &lt;span&gt;&lt;/span&gt;&lt;math&gt;\u0000 &lt;semantics&gt;\u0000 &lt;mrow&gt;\u0000 &lt;msub&gt;\u0000 &lt;mi&gt;V&lt;/mi&gt;\u0000 &lt;mi&gt;P&lt;/mi&gt;\u0000 &lt;/msub&gt;\u0000 &lt;/mrow&gt;\u0000 &lt;annotation&gt; ${V}_{P}$&lt;/annotation&gt;\u0000 &lt;/semantics&gt;&lt;/math&gt; tomography clearly shows high-&lt;span&gt;&lt;/span&gt;&lt;math&gt;\u0000 &lt;semantics&gt;\u0000 &lt;mrow&gt;\u0000 &lt;msub&gt;\u0000 &lt;mi&gt;V&lt;/mi&gt;\u0000 &lt;mi&gt;P&lt;/mi&gt;\u0000 &lt;/msub&gt;\u0000 &lt;/mrow&gt;\u0000 &lt;annotation&gt; ${V}_{P}$&lt;/annotation&gt;\u0000 &lt;/semantics&gt;&lt;/math&gt; subducted slabs, and low-&lt;span&gt;&lt;/span&gt;&lt;math&gt;\u0000 &lt;semantics&gt;\u0000 &lt;mrow&gt;\u0000 &lt;msub&gt;\u0000 &lt;mi&gt;V&lt;/mi&gt;\u0000 &lt;mi&gt;P&lt;/mi&gt;\u0000 &lt;/msub&gt;\u0000 &lt;/mrow&gt;\u0000 &lt;annotation&gt; ${V}_{P}$&lt;/annotation&gt;\u0000 &lt;/semantics&gt;&lt;/math&gt; anomalies above and below the slabs, which may reflect corner flow in the mantle wedge and subslab hot mantle upwelling (SHMU), respectively. A slab window is revealed beneath the North Island of New Zealand. Given the development of SHMU beneath this region, the catastrophic eruptions of the Taupo volcano might be powered by a mixture of island arc magma and SHMU through the slab window. Beneath the intraplate volcanoes along the eastern coast of Australia and the Tasman Sea, a thin low-&lt;span&gt;&lt;/span&gt;&lt;math&gt;\u0000 &lt;semantics&gt;\u0000 &lt;mrow&gt;\u0000 &lt;msub&gt;\u0000 &lt;mi&gt;V&lt;/mi&gt;\u0000 &lt;mi&gt;P&lt;/mi&gt;\u0000 &lt;/msub&gt;\u0000 &lt;/mrow&gt;\u0000 &lt;annotation&gt; ${V}_{P}$&lt;/annotat","PeriodicalId":50422,"journal":{"name":"Geochemistry Geophysics Geosystems","volume":"25 11","pages":""},"PeriodicalIF":2.9,"publicationDate":"2024-11-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1029/2024GC011739","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142737598","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}

{"title":"Slip History, Tectonic Evolution, and Fault Zone Structure Along the Southern Alpine Fault, New Zealand","authors":"A. M. Mere,&nbsp;N. C. Barth,&nbsp;J. J. Schwartz,&nbsp;A. Kylander-Clark","doi":"10.1029/2024GC011839","DOIUrl":"https://doi.org/10.1029/2024GC011839","url":null,"abstract":"<p>The study of active fault zones is fundamental to understanding both long-term tectonics and short-term earthquake behavior. Here, we integrate lidar-enabled geomorphic-geologic mapping and petrochronological analysis to reveal the slip-history, tectonic evolution, and structure of the southern Alpine Fault in New Zealand. New petrographic, zircon U-Pb and zircon trace-element data from fault-displaced basement units provides constraint on ∼70–90 km of right-lateral displacement on the presently active strand of the southern Alpine Fault, which we infer is of Plio-Quaternary age. This incremental displacement has accumulated while the offshore part of the fault has evolved within a distributed zone of plate boundary deformation. We hypothesize that pre-existing faults in the continental crust of the Pacific Plate have been exploited as components of this distributed plate boundary system. Along the onshore southern Alpine Fault, detailed mapping of active fault traces reveals complexity in geomorphic fault expression. Our analysis suggests that the major geomorphic features of the southern Alpine Fault correspond to penetrative fault zone structures. We emphasize the region immediately south of the central-southern section boundary, where a major extensional stepover and restraining bend are located along-strike of each other. We infer that this geometry may reflect segmentation of the Alpine Fault between two distinct fault segments. The ends of these proposed segments meet near where several Holocene earthquake ruptures have terminated. Our new constraints on the evolution and structure of the southern Alpine Fault help contribute to improved characterization of the greatest onshore source of earthquake hazard in New Zealand.</p>","PeriodicalId":50422,"journal":{"name":"Geochemistry Geophysics Geosystems","volume":"25 11","pages":""},"PeriodicalIF":2.9,"publicationDate":"2024-11-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1029/2024GC011839","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142707890","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}

{"title":"The Enigmatic Pockmarks of the Sandy Southeastern North Sea","authors":"Christoph Böttner,&nbsp;Jasper J. L. Hoffmann,&nbsp;Daniel Unverricht,&nbsp;Mark Schmidt,&nbsp;Timo Spiegel,&nbsp;Jacob Geersen,&nbsp;Thomas Harald Müller,&nbsp;Jens Karstens,&nbsp;Katrine Juul Andresen,&nbsp;Lasse Sander,&nbsp;Jens Schneider von Deimling,&nbsp;Christopher Schmidt","doi":"10.1029/2024GC011837","DOIUrl":"https://doi.org/10.1029/2024GC011837","url":null,"abstract":"<p>Natural seafloor depressions, known as pockmarks, are common subaqueous geomorphological features found from the deep ocean trenches to shallow lakes. Pockmarks can form rapidly or over millions of years and have a large variety of shapes created and maintained by a large variety of mechanisms. In the sandy sediments of the southeastern North Sea, abundant shallow pockmarks are ubiquitous and occur at shallow water depths (&lt;50 m). Their formation has previously been linked to methane seepage from the seafloor. Here, we characterize over 50,000 pockmarks based on their morphology, geochemical signature, and the subsurface pre-conditions using a new integrated geoscientific data set, combining geophysical and sedimentological data with geochemical porewater and oceanographic analysis. We test whether the methane seepage is indeed responsible for pockmark formation. However, our data suggest that neither the seepage of light hydrocarbons nor groundwater is driving pockmark formation. Because of this lack of evidence for fluid seepage, we favor the previously suggested biotic formation but also discuss positive feedback mechanisms in ocean bottom currents as a formation process. Based on a comparison of pockmarks to the central and southeastern North Sea, we find that local lithology significantly affects pockmark morphology. Muddy lithologies favor the formation of larger, long-lived structures, while sandy lithologies lead to short-lived, small-scale structures that are large in area but with shallow incision depth. We conclude that pockmarks in sandy environments might have been overlooked globally due to their shallow incision depth and recommend reevaluating the role of hydrocarbon ebullition in pockmark formation.</p>","PeriodicalId":50422,"journal":{"name":"Geochemistry Geophysics Geosystems","volume":"25 11","pages":""},"PeriodicalIF":2.9,"publicationDate":"2024-11-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1029/2024GC011837","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142707858","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}