Geology最新文献

{"title":"Warming, acidification, and calcification feedback during the first hyperthermal of the Cenozoic—The Latest Danian Event","authors":"Margareta Harbich, James S.K. Barnet, James W.B. Rae, Dick Kroon","doi":"10.1130/g51330.1","DOIUrl":"https://doi.org/10.1130/g51330.1","url":null,"abstract":"The Latest Danian Event (LDE; ca. 62.15 Ma) is a major double-spiked eccentricity-driven transient warming event and carbon cycle perturbation (hyperthermal) in the early Paleocene, which has received significantly less attention compared to the larger events of the late Paleocene−early Eocene. A better understanding of the nature of the LDE may broaden our understanding of hyperthermals more generally and improve our knowledge of Earth system responses to extreme climate states. We present planktic and benthic foraminiferal Mg/Ca and B/Ca records that shed new light on changes in South Atlantic temperature and carbonate chemistry during the LDE. Our planktic Mg/Ca record reveals a pulsed increase in sea-surface temperature of at least ∼1.5 °C during the older carbon isotope excursion, and ∼0.5 °C during the younger isotope excursion. We observe drops in planktic and benthic B/Ca, synchronous with pronounced negative excursions in benthic δ13C, which suggest a shift in the carbonate system toward more acidic, dissolved inorganic carbon−rich conditions, in both the surface and deep ocean. Conditions remained more acidic following the LDE, which we suggest may be linked to an enhanced ocean alkalinity sink due to changes in the makeup of planktic calcifiers, hinting at a novel feedback between calcifier ecology and ocean-atmosphere CO2.","PeriodicalId":12642,"journal":{"name":"Geology","volume":"349 11","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-11-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135475548","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":"Age variability and decadal time-averaging in oyster reef death assemblages","authors":"Stephen R. Durham, Gregory P. Dietl, Quan Hua, John C. Handley, Darrell Kaufman, Cheryl P. Clark","doi":"10.1130/g50778.1","DOIUrl":"https://doi.org/10.1130/g50778.1","url":null,"abstract":"Using paleoecological data to inform resource management decisions is challenging without an understanding of the ages and degrees of time-averaging in molluscan death assemblage (DA) samples. We illustrate this challenge by documenting the spatial and stratigraphic variability in age and time-averaging of oyster reef DAs. By radiocarbon dating a total of 630 oyster shells from samples at two burial depths on 31 oyster reefs around Florida, southeastern United States, we found that (1) spatial and stratigraphic variability in DA sample ages and time-averaging is of similar magnitude, and (2) the shallow oyster reef DAs are among the youngest and highest-resolution molluscan DAs documented to date, with most having decadal-scale time-averaging estimates, and sometimes less. This information increases the potential utility of the DAs for habitat management because DA data can be placed in a more specific temporal context relative to real-time monitoring data. More broadly, the results highlight the potential to obtain decadal-scale resolution from oyster bioherms in the fossil record.Decades of work on molluscan death assemblages (DAs) have successfully documented temporal changes in community composition or species attributes from direct assessments of the remains themselves (e.g., Kowalewski et al., 2000; Kidwell, 2007; Dietl and Durham, 2016; Albano et al., 2021) or from proxy information derived from them (e.g., Gillikin et al., 2019). Despite the promise of such geohistorical records for conservation paleobiology, examples of their use by resource managers are still uncommon (Groff et al., 2023). One reason is the difficulty of putting DA data in temporal context. Geochronological analyses (e.g., radiocarbon dating) are expensive and difficult to interpret, leading many conservation paleobiological studies to work around age-related uncertainties by citing general assumptions and/or studies from similar depositional settings (e.g., Dietl and Durham, 2016).However, assemblage- or specimen-level chronological control is often required to meaningfully compare DA data with the annual or subannual real-time monitoring data typically used for resource management. This was the case for the Historical Oyster Body Size (HOBS) project in Florida, southeastern United States—codeveloped by the Florida Department of Environmental Protection (FDEP) Office of Resilience and Coastal Protection (ORCP) and the Paleontological Research Institution (PRI; Dietl et al., 2023)—which aimed to use oyster reef DA samples to supplement real-time monitoring data on oyster body sizes for ORCP’s Statewide Ecosystem Assessment of Coastal and Aquatic Resources (SEACAR) project (www.floridadep.gov/SEACAR).The aquatic preserves managed by ORCP were established between 1966 and 2020 to be maintained “in an essentially natural or existing condition” (Florida Administrative Code R.18-20.001[2]; Florida Department of State, 1997). Thus, management of each preserve is often focused","PeriodicalId":12642,"journal":{"name":"Geology","volume":"57 46","pages":""},"PeriodicalIF":5.8,"publicationDate":"2023-11-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"71512732","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":"High-resolution chronostratigraphy of late Mesozoic sequences in northern North China: Implications for the linkages among intracontinental orogeny, volcanism, Jehol Biota, and Pacific plate subduction","authors":"Qiang Ma, Yuting Zhong, Qingzhu Yin, Magdalena H. Huyskens, Liang Ma, Xiaoping Xia, Qing-Ren Meng, Zhong-He Zhou, Yi-Gang Xu","doi":"10.1130/g51535.1","DOIUrl":"https://doi.org/10.1130/g51535.1","url":null,"abstract":"Subduction of the paleo-Pacific plate during the late Mesozoic is thought to have been responsible for the destruction of the North China craton, manifested by intense volcanism, lithospheric deformation, and dramatic changes in surface morphology and terrestrial ecosystems. However, the timing and correlations of these consequential events remain obscure. This issue was addressed here by carrying out a high-resolution geochronologic study on the Upper Jurassic−Lower Cretaceous sequences of the Luanping basin, northern Hebei Province, China. Secondary ion mass spectrometry (SIMS) and chemical abrasion−isotope dilution−isotope ratio mass spectrometry (CA-ID-IRMS) zircon U-Pb ages from samples near the boundaries of the stratigraphic units help to redefine the chronostratigraphic framework of this basin and more importantly reveal that the second phase of the Yanshanian orogeny, representing a tectonic transition from flat to steep subduction of the paleo-Pacific plate, occurred within 0.87 ± 0.10 m.y. between 134.162 ± 0.091 Ma and 133.295 ± 0.043 Ma. Crustal extension then followed and resulted in development of rift basins and vigorous volcanism. The Jehol Biota came into being in Lower Cretaceous successions formed after ca. 130 Ma. The late Mesozoic Luanping basin therefore records how the subduction of the paleo-Pacific plate drove intracontinental orogeny, volcanism, basin development, and ecosystem evolution.","PeriodicalId":12642,"journal":{"name":"Geology","volume":"29 6","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-11-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135221878","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":"A unique record of prokaryote cell pyritization","authors":"Nathan Barling, Farid Saleh, Xiaoya Ma","doi":"10.1130/g51352.1","DOIUrl":"https://doi.org/10.1130/g51352.1","url":null,"abstract":"Prokaryotes, including bacteria, are a major component of both modern and ancient ecosystems. Although fossilized prokaryotes are commonly discovered in sedimentary rocks, it is rare to find them preserved in situ alongside macrofossils, particularly as pyritized cells in sites of exceptional fossil preservation. We examined prokaryotes preserved in the Lower Cretaceous Crato Formation of Brazil and demonstrate the widespread presence of spherical microorganisms preserved on the surface of Crato invertebrate fossils. These microorganisms were pyritized, covering decaying carcasses, 1.14 ± 0.01 μm in size, hollow with smooth surfaces, and can be found as aggregates resembling modern prokaryotes, particularly, coccoid bacterial colonies. It is likely that the observed microorganisms covered the carcasses before permissive conditions were established for pyritization, which must have been so rapid as to inhibit the autolysis of their delicate membranes. This is a new record of prokaryote fossils preserved in pyrite in association with macrofossils, which highlights the unique diagenetic and paleoenvironmental conditions of the Crato Formation that facilitated this mode of fossilization.Prokaryotes, including bacteria, play a major role in ecosystems and provide some of the earliest evidence of life on Earth (e.g., Homann, 2019; Javaux 2019). Bacteria in the fossil record can be preserved in stromatolites, thrombolites, and simple microbial mats (e.g., Noffke et al., 2003; Peters et al., 2017; Gueriau et al., 2020). They can also be phosphatized (Cosmidis et al., 2013) in association with decaying macrofossils, replicating the anatomy of the degrading tissue (e.g., Wilby and Briggs, 1997). In some cases, bacteria can be preserved as carbonaceous material or in pyrite, but this type of preservation is biased toward cyanobacteria that have relatively resistant cell walls (Wilson and Taylor, 2017; Demoulin et al., 2019). Outside of these narrow windows of preservation (see also Toporski et al., 2002), bacterial occurrences in the fossil record become rarer and highly debated (e.g., Nims et al., 2021). Numerous spherical and elongated microstructures associated with macrofossils have been reported globally and were interpreted as the remains of microorganisms that contribute to the decomposition of organic material (e.g., Lindgren et al., 2015; Schweitzer et al., 2015). However, these microstructures were interpreted as melanosomes by other researchers (e.g., Vinther, 2015, 2016, and references therein). Interestingly, although pyritization is a main pathway for macrofossil preservation in the fossil record and is mediated by sulfate-reducing bacteria, there is little evidence of prokaryote pyritization alongside macrofossils. This is because preservation by pyrite in Lagerstätten is commonly believed to be too coarse to preserve minute organisms such as prokaryotes. Our study aims to investigate microorganism preservation in the Lower Cretaceous Crato F","PeriodicalId":12642,"journal":{"name":"Geology","volume":"40 48","pages":""},"PeriodicalIF":5.8,"publicationDate":"2023-11-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"71491854","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":"Linking source and sink: The timing of deposition of Paleogene syntectonic strata in Central Asia","authors":"Feng Cheng, Andrew V. Zuza, Marc Jolivet, Andreas Mulch, Niels Meijer, Zhaojie Guo","doi":"10.1130/g51382.1","DOIUrl":"https://doi.org/10.1130/g51382.1","url":null,"abstract":"Determining the age of siliciclastic continental sequences in the absence of comprehensive biostratigraphy or radiometric dating of geological markers (e.g., volcanic layers) is inherently challenging. This issue is well exemplified in the current debate on the age of Cenozoic terrestrial strata in Central Asia, where competing age models constrained by non-unique paleomagnetic correlations are interpreted to reflect the growth of the Tibetan Plateau and its impact on Central Asian climate change. Here we present a new approach to evaluate competing age models by comparing the onset of rapid basement exhumation constrained by low-temperature thermochronology in the sediment source region with the initiation of growth strata in the adjacent sedimentary sink. We first validate this method in regions with well-constrained age models and subsequently apply this approach to the Tarim and Qaidam Basins in the northern Tibetan Plateau. The results of this analysis show that syntectonic sedimentation had already initiated during the Paleocene–Eocene and was followed by intensified Oligocene–Miocene mountain building along the northern margin of the plateau. Based on this refined Paleogene tectonic history, we further arrive at a temporal correlation between Paleogene tectonism in Northern Tibet and the retreat of the Proto-Paratethys Sea, a major water body that extended across Eurasia and was closely associated with climatic and biodiversity changes. We thus highlight the previously underestimated role tectonics in Northern Tibet had in the evolution and demise of the Proto-Paratethys Sea during the Paleogene.Because correlation of paleomagnetic data from continental basins to the Geomagnetic Polarity Time Scale (Ogg, 2020) is commonly non-unique, magnetostratigraphy alone can lead to dramatically different age models for continental siliciclastic sequences in the absence of fossils or radiometrically datable volcanic ash layers (Lowe, 2011). This inevitably leads to contrasting models for the timing, rates, and duration of tectonic and paleoclimatic processes. This fundamental challenge is well exemplified in Cenozoic terrestrial strata in Central Asia (Figs. 1A–1E), where competing age models have strongly diverging implications for the growth of the Tibetan Plateau (Ji et al., 2017; Staisch et al., 2020; Wang et al., 2022) and its association with Asia paleo-environments including the retreat of the Proto-Paratethys Sea, a major water body that covered large surfaces of Eurasia during the Paleogene (Bosboom et al., 2017; Sun and Liu, 2006; Zheng et al., 2015).The two largest terrestrial basins in the Cenozoic Tibetan orogen are the Tarim and Qaidam Basins, which contain critical archives of mountain building and paleoclimate (Fig. 1B). The growth strata and thick-bedded conglomerates in the Lulehe Formation, the basal stratigraphic unit of Cenozoic strata in the Qaidam Basin (Fig. 1D), are interpreted as synorogenic sediments that record the initiati","PeriodicalId":12642,"journal":{"name":"Geology","volume":"40 51","pages":""},"PeriodicalIF":5.8,"publicationDate":"2023-11-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"71491852","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":"Asymmetry and evolution of craton-influenced rifted margins","authors":"G. Raghuram, M. Pérez-Gussinyé, M. Andrés-Martínez, J. García-Pintado, M. Neto Araujo, J.P. Morgan","doi":"10.1130/g51370.1","DOIUrl":"https://doi.org/10.1130/g51370.1","url":null,"abstract":"Rifting can result in asymmetric conjugate margins. In numerical models with laterally homogeneous lithosphere, the polarity of the asymmetry is random and results from spontaneous strain localization on a dominant fault/shear zone. However, along the central South Atlantic, margin width is well correlated to the proximity of the rift to a craton during rifting. To understand the evolution of rifting close to a craton, we used numerical experiments that included a thick craton lithosphere adjacent to a thinner, mobile-belt lithosphere. When rifting starts close to the craton, i.e., ≤ 100 km, deformation focuses along a fault/shear zone dipping toward the craton, leading to cratonward asymmetric asthenospheric uplift and rift migration. This results in a narrow margin on the craton side and a wide margin on the mobile-belt side. Craton-related asymmetry results in the wide margin subsiding more than the narrow one, inducing the formation of large synrift sag basins in the wide conjugate, as in the South Atlantic. This differential subsidence is preserved for ~100 m.y. after breakup and may partly explain the present-day higher dynamic topography close to cratons in the central South Atlantic. Mantle flow during asymmetric rifting leads to weakening of the craton lithosphere, partial intermixing, and recycling into the convective mantle, as interpreted for this sector of the South Atlantic ridge. Thus, rifting adjacent to a craton may have wide-ranging tectonic, stratigraphic, and compositional consequences that affect not only margin architecture, but also the development of subsequent dynamic topography and the spreading system.","PeriodicalId":12642,"journal":{"name":"Geology","volume":"40 50","pages":""},"PeriodicalIF":5.8,"publicationDate":"2023-11-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"71491853","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":"Effect of short-term, climate-driven sediment deposition on tectonically controlled alluvial channel incision","authors":"Xueliang Wang, John J. Clague, Paolo Frattini, Shengwen Qi, Hengxing Lan, Wen Zhang, Lihui Li, Juanjuan Sun, Giovanni Battista Crosta","doi":"10.1130/g51671.1","DOIUrl":"https://doi.org/10.1130/g51671.1","url":null,"abstract":"Debate about relations between rates of fluvial incision and time (the “Sadler effect”) continues, impeding the use of incision rates to infer tectonic and climatic processes. There is a dearth of detailed field evidence that can be used to explore the coupling between tectonics and climate in controlling alluvial channel geometry and incision rates over time scales of 102−105 yr. We present field data from the Rumei watershed of southeast Tibet, which we obtained by mapping and dating late Pleistocene (ca. 135 ka) fluvial terraces and related channels, measuring channel hydraulic geometry, and calculating channel steepness indexes and incision rates. The evidence indicates that climate forcing is the main driver of sediment production and delivery to streams in the watershed. New aggradation events altered alluvial valley and channel geometry and, coupled with tectonic uplift, affected the rate of channel incision in the catchment. We propose a conceptual model (see pdf for equation) that links uplift-driven incision (see pdf for equation) induced by climate change, which is valid in catchments and other areas. We conclude that the reduction in incision depth caused by climate-driven channel aggradation is significant on short time scales (102−105 yr), and its cumulative effect contributes to the “Sadler effect” on long time scales (>106 yr).","PeriodicalId":12642,"journal":{"name":"Geology","volume":"32 5","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-10-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"136019462","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":"No evidence for a volcanic trigger for late Cambrian carbon-cycle perturbations","authors":"J. Frieling, T.A. Mather, I.M. Fendley, H.C. Jenkyns, Z. Zhao, T.W. Dahl, B.A. Bergquist, K. Cheng, A.T. Nielsen, A.J. Dickson","doi":"10.1130/g51570.1","DOIUrl":"https://doi.org/10.1130/g51570.1","url":null,"abstract":"The early Paleozoic was marked by several carbon-cycle perturbations and associated carbon-isotope excursions (CIEs). Whether these CIEs are connected to significant (external) triggers, as is commonly considered to be the case for CIEs in the Mesozoic and Cenozoic, or result from small carbon-cycle imbalances that became amplified through lack of efficient silicate weathering or other feedbacks remains unclear. We present concentration and isotope data for sedimentary mercury (Hg) and osmium (Os) to assess the impact of subaerial and submarine volcanism and weathering during the late Cambrian and early Ordovician. Data from the Alum Shale Formation (Sweden) cover the Steptoean positive carbon-isotope excursion (SPICE; ca. 497–494 Ma), a period marked by marine anoxia and biotic overturning, and several smaller CIEs extending into the early Ordovician. Our Hg and Os data offer no strong evidence that the CIEs present in our record were driven by (globally) elevated volcanism or continental weathering. Organic-carbon and Hg concentrations covary cyclically, providing further evidence of an unperturbed Hg cycle. Mesozoic and Cenozoic CIEs are commonly linked to enhanced volcanic activity and weathering, but similar late Cambrian–early Ordovician events cannot easily be connected to such external triggers. Our results are more consistent with reduced early Paleozoic carbon-cycle resilience that allowed small imbalances to develop into large CIEs.","PeriodicalId":12642,"journal":{"name":"Geology","volume":"154 12","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-10-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"134910267","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":"Clumped isotope evidence for microbial alteration of thermogenic methane in terrestrial mud volcanoes","authors":"Jiarui Liu, Tina Treude, Orhan R. Abbasov, Elnur E. Baloglanov, Adil A. Aliyev, Carolynn M. Harris, William D. Leavitt, Edward D. Young","doi":"10.1130/g51667.1","DOIUrl":"https://doi.org/10.1130/g51667.1","url":null,"abstract":"Methane in oil reservoirs originates mostly from thermogenic sources, yet secondary microbial methane production from petroleum biodegradation is known to be pervasive. The conventional approach for identifying this secondary microbial methane commonly relies on geochemical characteristics of other gas molecules such as the carbon isotopic composition of carbon dioxide and propane. This information is sometimes obscured by isotopic variations in source material and may not be available in certain geological reservoirs. To better constrain the presence of secondary microbial methane, we studied the clumped isotopologue compositions of methane in terrestrial Azerbaijanian mud volcanoes, which support the occurrence of secondary microbial gas. Here, a deficit in Δ12CH2D2 of thermogenic methane occurs due to different δD of hydrogen sources that contribute to the formation of methane molecules (i.e., combinatorial effect). The Δ12CH2D2 is expected to move toward equilibrium as thermal maturity increases. More importantly, both Δ13CH3D and Δ12CH2D2 values of methane approach low-temperature thermodynamic equilibrium in most gases, suggesting that the original thermogenic methane has been altered by newly formed microbial methane in addition to isotope exchange among methane molecules catalyzed by the methyl-coenzyme M reductase enzyme. We conclude that methane clumped isotopes provide a unique proxy for identifying secondary microbial methane and understanding the exact evolution stages for natural gases.","PeriodicalId":12642,"journal":{"name":"Geology","volume":"59 2","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-10-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"134909836","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 formation of lithium-rich pegmatites through multi-stage melting","authors":"Lot Koopmans, Tania Martins, Robert Linnen, Nicholas J. Gardiner, Catriona M. Breasley, Richard M. Palin, Lee A. Groat, David Silva, Laurence J. Robb","doi":"10.1130/g51633.1","DOIUrl":"https://doi.org/10.1130/g51633.1","url":null,"abstract":"Lithium-cesium-tantalum−type pegmatites (the primary source of lithium) crystallize from highly evolved, volatile felsic melts that incorporated crustal material in their source. Pegmatites are classically thought to form either from extreme fractionation of a parental granite body or via low-degree partial melting of a metamorphic rock (anatectic origin). However, the processes that lead to the formation of economic lithium pegmatite deposits remain enigmatic, because precipitation of lithium ore minerals requires melt lithium concentrations in excess of 5000 ppm—∼500 times upper crustal abundances. We use petrological modeling to quantify lithium enrichment in an anatectic-origin scenario and show that it is primarily driven by the relative stability of residual biotite and muscovite at medium to high pressures (∼8 kbar), and biotite and cordierite at low pressures (∼3 kbar). We show anatexis of an average lithium-enriched metasedimentary source cannot sufficiently elevate the lithium content of the ensuing melt to form economic deposits; however, if this first-generation melt—now crystallized as granitic crust—is re-melted, the second-generation melt will be sufficiently concentrated in lithium to crystallize lithium ore minerals. We propose a petrogenetic model for anatectic-origin lithium pegmatites, in which a region experiences at least two stages of partial melting, ultimately generating lithium-rich melts without invoking extensive fractional crystallization. This mechanism can both account for the occurrence of unzoned lithium pegmatites and explain why economic pegmatites in many terranes are younger than their inferred source granites.","PeriodicalId":12642,"journal":{"name":"Geology","volume":"56 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-10-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"136032879","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}