Geology最新文献

{"title":"The dynamic nature of aTiO2: Implications for Ti-based thermometers in magmatic systems","authors":"L.M. Fonseca Teixeira, J. Troch, O. Bachmann","doi":"10.1130/g51587.1","DOIUrl":"https://doi.org/10.1130/g51587.1","url":null,"abstract":"In recent decades, new Ti-based thermometers have found widespread use in geosciences, providing a convenient and powerful tool for investigating the crystallization temperatures of quartz and zircons in magmatic systems. However, a commonly overlooked aspect is the constraint of TiO2 activity (aTiO2liquid–rutile). Many studies assume aTiO2 to be constant or equate the presence of Ti-rich phases, such as ilmenite, with fixed activity levels. Using solubility models and data from natural systems, we demonstrate that aTiO2 is a dynamic parameter, influenced by temperature, mineral assemblage, and TiO2 content in the melt. Focusing on examples from several volcanic fields (Bishop Tuff, Fish Canyon Tuff, Yellowstone, and Shiveluch), we discuss the impact of these factors on aTiO2 and highlight how inadequate constraint of aTiO2 can lead to erroneous interpretations of magma storage conditions.","PeriodicalId":12642,"journal":{"name":"Geology","volume":"6 1","pages":""},"PeriodicalIF":5.8,"publicationDate":"2024-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"138840383","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":"Mid-Proterozoic geomagnetic field was more consistent with a dipole than a quadrupole: REPLY","authors":"Zheng Gong, David A.D. Evans, Zhongtian Zhang, Chi Yan","doi":"10.1130/g51903y.1","DOIUrl":"https://doi.org/10.1130/g51903y.1","url":null,"abstract":"Abstract not available","PeriodicalId":12642,"journal":{"name":"Geology","volume":"177 1","pages":""},"PeriodicalIF":5.8,"publicationDate":"2024-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"138840080","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":"Origin of Archean Pb isotope variability through open-system Paleoarchean crustal anatexis","authors":"M.I.H. Hartnady, C.L. Kirkand, S.P. Johnson, R.H. Smithies, L.S. Doucet, D.R. Mole","doi":"10.1130/g51507.1","DOIUrl":"https://doi.org/10.1130/g51507.1","url":null,"abstract":"Lead isotopic data imply that thorium and uranium were fractionated from one another in Earth’s early history; however, the origin of this fractionation is poorly understood. We report new in situ Pb isotope data from orthoclase in 144 granites sampled across the Archean Yilgarn craton (Western Australia) to characterize its Pb isotope variability and evolution. Granite Pb isotope compositions reveal three Pb sources, a mantle-derived Pb reservoir and two crustal Pb reservoirs, distinguished by their implied source 232Th/238U (κPb). High-κPb granites reflect sources with high 232Th/238U (~4.7) and are largely co-located with Eoarchean–Paleoarchean crust. The Pb isotope compositions of most granites, and those of volcanic-hosted massive sulfide (VHMS) and gold ores, define a mixing array between a mantle Pb source and a Th-rich Eoarchean–Paleoarchean source. Pb isotope modeling indicates that the high-κPb source rocks experienced Th/U fractionation at ca. 3.3 Ga. As Th/U fractionation in the Yilgarn craton must have occurred before Earth’s atmosphere was oxygenated, subaerial weathering cannot explain the apparent differences in their geochemical behavior. Instead, the high Th/U source reflects Eoarchean–Paleoarchean rocks that experienced prior high-temperature metamorphism, partial melting, and melt loss in the presence of a Th-sequestering mineral like monazite. Archean Pb isotope variability thus has its origins in open-system high-temperature metamorphic processes responsible for the differentiation and stabilization of Earth’s continental crust.Thorium and uranium are highly incompatible trace elements that are partitioned into Earth’s crust over geological time (Galer and O’nions, 1985; Allègre et al., 1986). Being two of the main heat-producing elements in the silicate Earth, understanding their partitioning between different geochemical reservoirs is important for tracking our planet’s thermal evolution and internal differentiation.Thorium has a single valence state (4+) whereas U exists in two valence states (4+ and 6+), with the highly water-soluble hexavalent species dominant under oxidized surface conditions (Zartman and Haines, 1988). Since the Great Oxidation Event (2.5–2.4 Ga), U has preferentially been recycled into the mantle, causing a progressive lowering of the Th/U ratio in the mantle and in rocks derived from it (McCulloch, 1993; Collerson and Kamber, 1999; Elliott et al., 1999; Zartman and Richardson, 2005). However, in the Archean, when Earth’s atmosphere was largely devoid of oxygen, neither mantle melting, fractional crystallization, nor weathering and recycling processes could have fractionated U and Th. Hence, it is thought the geochemical behavior of these elements was identical from the surface down to the upper mantle (Liu et al., 2019). Nevertheless, some lines of evidence show that Th and U were fractionated from one another early in Earth’s history. For example, variability in the 208Pb/204Pb ratios of some Arche","PeriodicalId":12642,"journal":{"name":"Geology","volume":"32 1","pages":""},"PeriodicalIF":5.8,"publicationDate":"2024-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"138840104","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":"Strongly peraluminous granites provide independent evidence for an increase in biomass burial across the Precambrian–Phanerozoic boundary","authors":"Sami Mikhail, Eva E. Stüeken, Toby J. Boocock, Megan Athey, Nick Mappin, Adrian J. Boyce, Janne Liebmann, Christopher J. Spencer, Claire E. Bucholz","doi":"10.1130/g51800.1","DOIUrl":"https://doi.org/10.1130/g51800.1","url":null,"abstract":"Strongly peraluminous granites (SPGs) are generated by the partial melting of sedimentary rocks and can thus provide a novel archive to reveal secular trends in Earth’s environmental history that integrate siliciclastic sedimentary lithologies. The nitrogen (N) content of Archean, Proterozoic, and Phanerozoic SPGs reveals a systematic increase across the Precambrian–Phanerozoic boundary. This rise is supported by a coeval increase in the phosphorus (P) contents of SPGs. Collectively, these data are most parsimoniously explained by an absolute increase in biomass burial in the late Proterozoic or early Phanerozoic by a factor of ~5 and as much as 8. The Precambrian–Phanerozoic transition was a time of progressive oxygenation of surface environments paired with major biological innovations, including the rise of eukaryotic algae to ecological dominance. Because oxygenation suppresses biomass preservation in sediments, the increase in net biomass burial preserved in SPGs reveals an expansion of the biosphere and an increase in primary production across this interval.","PeriodicalId":12642,"journal":{"name":"Geology","volume":"116 1","pages":""},"PeriodicalIF":5.8,"publicationDate":"2024-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"138840335","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":"Mid-Proterozoic geomagnetic field was more consistent with a dipole than a quadrupole: COMMENT","authors":"James W. Sears","doi":"10.1130/g51799c.1","DOIUrl":"https://doi.org/10.1130/g51799c.1","url":null,"abstract":"Abstract not available","PeriodicalId":12642,"journal":{"name":"Geology","volume":"27 1","pages":""},"PeriodicalIF":5.8,"publicationDate":"2024-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"138840362","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":"Elastic stresses can form metamorphic fabrics","authors":"J. Gilgannon, Damien Freitas, R. E. Rizzo, John Wheeler, Ian B. Butler, Sohan Seth, Federica Marone, C. Schlepütz, Gina McGill, Ian Watt, Oliver Plümper, Lisa Eberhard, Hamed Amiri, A. Chogani, F. Fusseis","doi":"10.1130/g51612.1","DOIUrl":"https://doi.org/10.1130/g51612.1","url":null,"abstract":"Detailing the relationship between stress and reactions in metamorphic rocks has been controversial, and much of the debate has centered on theory. Here, we add to this discussion and make a major advance by showing in time-resolved synchrotron microtomography experiments that a reacting and deforming sample experiencing an elastic differential stress produces a fabric orthogonal to the largest principal stress. This fabric forms very early in the reaction and can be shown to be unrelated to strain. The consequences of this are significant because a non-hydrostatic stress state is a very common geological occurrence. Our data provide the basis for new interpretations of the classical, and enigmatic, serpentine fabrics of Val Malenco, Italy, and Cerro del Almirez, Spain, where we relate the reported fabrics to transient, and cyclical, differential stresses from magma intrusion and the earthquake cycle.","PeriodicalId":12642,"journal":{"name":"Geology","volume":"119 12","pages":""},"PeriodicalIF":5.8,"publicationDate":"2023-12-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"138959733","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":"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}