Geology最新文献

{"title":"Constraints of boron and oxygen stable isotopes on dehydration fluids, sediment-derived melts, and crustal assimilation of the Toba volcanic system (Indonesia)","authors":"Ping-Ping Liu, Dian-Bing Wang, Mei-Fu Zhou, Xian-Hua Li, Qiuli Li, G. Gaetani, B. Monteleone, Vadim Kamenetsky","doi":"10.1130/g51690.1","DOIUrl":"https://doi.org/10.1130/g51690.1","url":null,"abstract":"Arc magmas are produced from the mantle wedge, with possible addition of fluids and melts derived from serpentinites and sediments in the subducting slab. Identification of various sources and their relevant contributions to such magmas is challenging; in particular, at continental arcs where crustal assimilation may overprint initial geochemical signatures. This study presents oxygen isotopic compositions of zoned olivine grains from post-caldera basalts and boron contents and isotopes of these basalts and glassy melt inclusions hosted in quartz and clinopyroxene of silicic tuffs in the Toba volcanic system, Indonesia. High-magnesian (≥87 mol% Fo [forsterite]) cores of olivine in the basalts have δ18O values ranging from 5.12‰ to 6.14‰, indicating that the mantle source underneath Toba is variably enriched in 18O. Olivine with <87 mol% Fo has highly variable (4.8−7.2‰), but overall increased, δ18O values, interpreted to reflect assimilation of high δ18O crustal materials during fractional crystallization. Mass balance calculations constrain the overall volume of crustal assimilation for the basalts as ≤13%. The processes responsible for the 18O-enriched basaltic melts are further constrained by boron data that indicate the addition of <0.1 wt% fluids to the mantle, >40% of the fluids being derived from serpentinites and others from altered oceanic crust and sediments. This amount of fluids can increase δ18O of the magma by only ∼0.02‰. Approximately 6−9% sediment-derived melt hybridization in the mantle wedge is further needed to yield basaltic melts with δ18O values in equilibrium with those of the high-Fo olivine cores. The cogenetic silicic tuffs, on the other hand, seem to record a higher proportion of fluid addition dominated by sediment-derived fluids to the mantle source, in addition to crustal assimilation. Our reconnaissance study therefore demonstrates the application of combined B and O isotopes to differentiate between melts and fluids derived from serpentinites and sediments in the subducted slab—an application that can be applied to arc magmas worldwide.","PeriodicalId":12642,"journal":{"name":"Geology","volume":"225 2","pages":""},"PeriodicalIF":5.8,"publicationDate":"2023-12-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"138997287","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}

{"title":"Early Cambrian Cambroclavus is a scleritomous eumetazoan unrelated to bryozoan or dasyclad algae","authors":"Kai Xiang, Zongjun Yin, Wei Liu, Fangchen Zhao, Maoyan Zhu","doi":"10.1130/g51663.1","DOIUrl":"https://doi.org/10.1130/g51663.1","url":null,"abstract":"The origin of Bryozoa has long been an intriguing mystery, largely due to the dearth of unambiguous bryozoan fossils within Cambrian strata. The earliest bryozoan thus far identified, Protomelission, an early Cambrian microfossil from Australia and China, was recently contested and proposed to be dasyclad algae. Our reanalysis of micro-computed tomography data from Protomelission specimens, however, unveils previously unrevealed structures, indicating Protomelission to be neither bryozoan nor alga, but a scleritome of Cambroclavus, an early Cambrian microfossil typically found as disarticulated sclerites. The long-sought scleritomes suggest that enigmatic cambroclaves likely represent an extinct group of epitheliozoan-grade eumetazoan, with spiny sclerites covering their epidermis for defense. The prevalence of bizarre animals like cambroclaves, lacking modern analogues, implies a greater disparity of animal body plans during the Cambrian explosion than previously recognized. Our findings underscore the absence of definitive early Cambrian bryozoan fossils, further highlighting the dilemma of the origin of Bryozoa.","PeriodicalId":12642,"journal":{"name":"Geology","volume":"10 7","pages":""},"PeriodicalIF":5.8,"publicationDate":"2023-12-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139008739","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}

{"title":"Controls on topography and erosion of the north-central Andes","authors":"Joel S. Leonard, K. Whipple, Arjun M. Heimsath","doi":"10.1130/g51618.1","DOIUrl":"https://doi.org/10.1130/g51618.1","url":null,"abstract":"We present 17 new 10Be erosion rates from southern Peru sampled across an extreme orographic rainfall gradient. Using a rainfall-weighted variant of the normalized channel steepness index, ksnQ, we show that channel steepness values, and thus topography, are adjusted to spatially varying rainfall. Rocks with similar physical characteristics define distinct relationships between ksnQ and erosion rate (E), suggesting ksnQ is also resolving lithologic variations in erodibility. However, substantial uncertainty exists in parameters describing these relationships. By combining our new data with 38 published erosion rates from Peru and Bolivia, we collapse the range of compatible parameter values and resolve robust, nonlinear ksnQ−E relationships suggestive of important influences of erosional thresholds, rock properties, sediment characteristics, and temporal runoff variability. In contrast, neither climatic nor lithologic effects are clear using the traditional channel steepness metric, ksn. Our results highlight that accounting for spatial rainfall variations is essential for disentangling the multiple influences of climate, lithology, and tectonics common in mountain landscapes, which is a necessary first step toward greater understanding of how these landscapes evolve.","PeriodicalId":12642,"journal":{"name":"Geology","volume":"2 5","pages":""},"PeriodicalIF":5.8,"publicationDate":"2023-12-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139009842","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}

{"title":"Holocene gigascale rock avalanches in Vaigat strait, West Greenland—Implications for geohazard","authors":"K. Svennevig, Matthew J. Owen, Michele Citterio, Tove Nielsen, Salik Rosing, Jan Harff, Rudolf Endler, Mathieu Morlighem, E. Rignot","doi":"10.1130/g51234.1","DOIUrl":"https://doi.org/10.1130/g51234.1","url":null,"abstract":"Rock avalanche−triggered displacement waves (also termed tsunamis) have recently occurred in Greenland and Alaska, and they illustrate the presence of such hazards in polar regions. To improve understanding of the magnitude of this hazard for these areas, we investigated gigascale subaerial rock avalanches impacting a partially confined water body within the Vaigat strait (western Greenland). We present a new combined subaerial to subaqueous digital elevation model, alongside a new compilation of seismic data, which revealed nine deglacial to Holocene rock avalanche complexes that are between one and two orders of magnitude larger than nearby historical rock avalanches. The three largest complexes have deposit thicknesses up to 300 m, runout distances reaching 19 km, and best-estimate volumes from 1.7 to 8.4 km3. Based on the morphology and the volume−angle of reach relations, it is likely that each complex represents a single or few events, thus making them among the largest displacement wave−generating subaerial to submarine rock avalanches on Earth. We estimated displacement wave magnitude up to 280 m on the opposite shore. The ages of the deposits are poorly constrained but the main rock avalanche activity is referable to early Holocene times. With significant climatic changes predicted in the Arctic, we recommend that hazard assessments account for events not only from the historical record but also those from the recent geological past.","PeriodicalId":12642,"journal":{"name":"Geology","volume":"5 5","pages":""},"PeriodicalIF":5.8,"publicationDate":"2023-12-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"138980319","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}

{"title":"Geochemical mapping of lithospheric architecture disproves Archean terrane accretion in the Yilgarn craton","authors":"R. H. Smithies, K. Gessner, Y. Lu, C. Kirkland, T. Ivanic, J. Lowrey, D.C. Champion, J. Sapkota, Q. Masurel, N. Thébaud, R. Quentin de Gromard","doi":"10.1130/g51707.1","DOIUrl":"https://doi.org/10.1130/g51707.1","url":null,"abstract":"The basement of Mesoarchean to Neoarchean greenstone basins in the Yilgarn craton is composed of fragments of evolved crust up to 3.7 Ga old. New cratonwide geochemical and isotopic data with unparalleled spatial resolution image a NE- to ENE-trending architecture in pre−2.73 Ga crust. These trends cannot be reconciled with plate-tectonic models, as they persist across younger NNW-striking structural fabrics, including a proposed suture previously interpreted to result from exotic terrane accretion. Our results suggest that, in spite of their substantial strike length, the NNW-trending structures have limited horizontal displacement and, although important for understanding regional geology, may be a geodynamically insignificant overprint of the primary ENE-trending architecture. We propose that these greenstone provinces or belts include individual basins formed in rifts with location, size, and orientation influenced by the interaction between basement fragments and regional crustal extension.","PeriodicalId":12642,"journal":{"name":"Geology","volume":"12 11","pages":""},"PeriodicalIF":5.8,"publicationDate":"2023-12-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"138590064","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}

{"title":"Magma-carbonate interactions drive CO2 production and metal enrichment in shallow dikes and sills at volcanic arcs","authors":"R.A. Morris, D. Canil, J. Spence","doi":"10.1130/g51439.1","DOIUrl":"https://doi.org/10.1130/g51439.1","url":null,"abstract":"The contribution of CO2 from crustal carbonates into arc magmas is debated, as is its role in the long-term C cycle. To better understand the contributions and mechanisms that drive CO2 production in arc magmas, we examined in detail basaltic dike and sill contacts with carbonate in the Jurassic Bonanza arc on Vancouver Island, Canada. We discovered discrete boundary melts that formed along dike and sill margins in contact with limestone, which display unique Ca, U, and Sr enrichments, Si depletion, and 87Sr/86Sr that approaches host limestone values (∼0.708). Binary mixing modeling indicates ∼20%−25% limestone assimilation into basalt formed the boundary melts. Contrasting viscosities between boundary and interior melts hinder mixing and chemical homogenization but appear to promote uphill diffusion and metal enrichment within systems that cool in minutes to days. While shallow dikes and sills may be volumetrically minor in an arc magma system, the open flow of magma and large surface area in channels greatly enhances magma-carbonate interactions, and ultimately CO2 production, likely over that of more common and voluminous plutons.","PeriodicalId":12642,"journal":{"name":"Geology","volume":"5 8","pages":""},"PeriodicalIF":5.8,"publicationDate":"2023-12-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"138591298","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}

{"title":"ERRATUM: Microbial sulfate reduction plays an important role at the initial stage of subseafloor sulfide mineralization","authors":"Tatsuo Nozaki, Toshiro Nagase, Takayuki Ushikubo, Kenji Shimizu, Jun-ichiro Ishibashi, the D/V Chikyu Expedition 909 Scientists","doi":"10.1130/g47943e.1","DOIUrl":"https://doi.org/10.1130/g47943e.1","url":null,"abstract":"ORIGINAL ARTICLE: 2021, v. 49, no. 6, p. 222–227, https://doi.org/10.1130/G47943.1. First published 7 October 2020.","PeriodicalId":12642,"journal":{"name":"Geology","volume":" 36","pages":""},"PeriodicalIF":5.8,"publicationDate":"2023-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"138481024","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}

{"title":"Hearing Assessment After Total Annular Excision Tympanoplasty- Our Institutional Experience.","authors":"Devisha Agarwal, Manish Chandra","doi":"10.1007/s12070-023-04083-8","DOIUrl":"10.1007/s12070-023-04083-8","url":null,"abstract":"<p><strong>Objective: </strong>The objectives of this study were to record graft uptake, hearing status and any complication(s) after total annular excision (TAE) tympanoplasty and to compare them with previously operated underlay tympanoplasty patients.</p><p><strong>Design: </strong>Prospective study.</p><p><strong>Methods: </strong>Patients with chronic otitis media mucosal type aged between 15-45 years attending our outpatient department were assessed and eligible patients who gave consent for the study were included.</p><p><strong>Result: </strong>Patients of chronic otitis media mucosal type who underwent TAE tympanoplasty had 80% graft uptake. Post TAE tympanoplasty patients had good hearing assessed by tuning fork test and pure tone audiometry. Maximum improvement in hearing was seen at 500Hz frequency by pure tone audiometry in TAE tympanoplasty group. Histopathological examination of remnant tympanic membrane showed mucosalization.</p><p><strong>Conclusion: </strong>TAE tympanoplasty can effectively prevent development of granular myringitis.</p><p><strong>Supplementary information: </strong>The online version contains supplementary material available at 10.1007/s12070-023-04083-8.</p>","PeriodicalId":12642,"journal":{"name":"Geology","volume":"24 1","pages":"3711-3717"},"PeriodicalIF":4.8,"publicationDate":"2023-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.ncbi.nlm.nih.gov/pmc/articles/PMC10645727/pdf/","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"85839389","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"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":"Delayed Onset of a Contralateral \"White-Eyed Shunt\" Posterior Draining Carotid-Cavernous Fistula Following Ipsilateral \"Red-Eyed Shunt\".","authors":"Molly P Aldred, Subahari Raviskanthan, Peter W Mortensen, Richard P Klucznik, Andrew G Lee","doi":"10.1097/WNO.0000000000001546","DOIUrl":"10.1097/WNO.0000000000001546","url":null,"abstract":"","PeriodicalId":12642,"journal":{"name":"Geology","volume":"44 1","pages":"e201-e203"},"PeriodicalIF":2.9,"publicationDate":"2023-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"85780585","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}

{"title":"The application of dual clumped isotope thermometer (Δ47 and Δ48) to the understanding of dolomite formation","authors":"Chaojin Lu, Peter K. Swart","doi":"10.1130/g51576.1","DOIUrl":"https://doi.org/10.1130/g51576.1","url":null,"abstract":"Although several studies have shown the possibility of kinetic isotopic effects during the precipitation of carbonates using the dual clumped isotope proxy (Δ47 and Δ48), this approach has not yet been applied to the study of dolomite. We present Δ47 and Δ48 values of two types of Cenozoic Bahamian dolomites formed by distinctly different mechanisms. One dolomite, present in a core drilled on the island of San Salvador, is believed to have formed from normal seawater in the open system, while the other, taken from the Clino core drilled on the margin of the Great Bahama Bank, was precipitated associated with microbial sulfate reduction in the closed system. The Δ48-derived temperatures of San Salvador dolomites are consistent with their Δ47-temperatures, which are in turn close to the expected value of normal seawater. In contrast, dolomites from Clino show slightly elevated Δ47-derived temperatures (∼15 °C higher than the expected) and significantly increased Δ48-temperatures (∼145 °C) that are positively correlated with the sulfur isotopes of carbonate associated sulfate, in excess of +30‰. Such an association suggests a non-equilibrium process driven by microbial sulfate reduction, which elevates the alkalinity and depresses the pH of dolomitizing fluids. Notably, the greater amplitude of disequilibrium in Δ48 relative to Δ47 values demonstrates the sensitivity of the Δ48 proxy to kinetic isotope effects in dolomite. Conclusively, this study shows the potential of the dual clumped isotope proxy to identify microbial-mediated dolomitization in modern and ancient records.","PeriodicalId":12642,"journal":{"name":"Geology","volume":"63 11","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-11-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"136283291","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}