Geology最新文献

{"title":"Post-salt carbonates control salt-tectonic minibasin formation","authors":"Leonardo M. Pichel, Ritske S. Huismans, Robert Gawthorpe, Jan Inge Faleide","doi":"10.1130/g51717.1","DOIUrl":"https://doi.org/10.1130/g51717.1","url":null,"abstract":"Salt tectonics on passive margins are driven by sediment loading and gliding with minimal influence from basement-involved tectonics and is associated with variable and complex salt structures, such as minibasins and diapirs. A major enigma in salt tectonics is the origin of load-driven diapir-flanked minibasins, synclinal depocenters formed by localized subsidence of synkinematic sediments into salt. How can less-dense clastic sediments sink into the denser salt, promoting diapirism at their flanks? We use two-dimensional numerical modeling of lithospheric extension including syn- and post-rift sedimentation to understand the evolution of salt-tectonic minibasins along rifted passive margins. Our results show that these minibasins are driven by deposition of dense early post-salt carbonates and then amplified during progradation of less-dense and compacting clastics. In contrast, basin-scale salt flow driven by clastic progradation alone, without deposition of early post-salt carbonates, does not produce minibasins as observed on salt-bearing passive margins.","PeriodicalId":12642,"journal":{"name":"Geology","volume":"22 1","pages":""},"PeriodicalIF":5.8,"publicationDate":"2024-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"138839995","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":"Sustained deformation across the Sub-Himalayas since 200 ka","authors":"Chloé Bouscary, Georgina E. King, Djordje Grujic, Jérôme Lavé, Rafael Almeida, György Hetényi, Frédéric Herman","doi":"10.1130/g51656.1","DOIUrl":"https://doi.org/10.1130/g51656.1","url":null,"abstract":"The Himalayan Main Frontal Thrust (MFT) currently accommodates approximately half, i.e., 12–23 mm/yr, of the convergence between the Indian and Eurasian tectonic plates by uplift and deformation of the Sub-Himalayas. While deformation is well documented at modern and million-year time scales, almost no quantitative data are available that constrain Quaternary time scale deformation rates along and within this key tectonic unit. Filling this knowledge gap is crucial to better understanding tectonics and the seismic cycle in this densely populated Himalayan region. We quantify exhumation rates in the Sub-Himalayas using the recently established luminescence thermochronometry technique over time scales of 105 yr, which documents exhumation over the final few kilometers of Earth’s crust. The ultra-low closure temperature of luminescence thermochronometry enables us to resolve thermal histories from the Siwalik Group (Nepal) rocks, which have experienced maximum burial temperatures of ~120 °C. An extensive set of 33 samples was collected from western Nepal to eastern Bhutan, from which 22 yield exhumation rates of ~3–11 mm/yr over the past ~200 k.y. We converted these values to minimum cumulative thrust slip rates of ~6–22 mm/yr, assuming a thrust dip angle of 30°. Our luminescence thermochronometry results show that the Sub-Himalayan fold-and-thrust belt, particularly the MFT, accommodates at least 62% of Himalayan convergence since at least 200 ka. Our data also show activity of some intra-Siwalik thrusts throughout this period, implying that internal deformation of the orogenic wedge and strain partitioning may have occurred.","PeriodicalId":12642,"journal":{"name":"Geology","volume":"1996 1","pages":""},"PeriodicalIF":5.8,"publicationDate":"2024-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"138886869","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":"Timing of India-Asia collision and significant coupling between them around 51 Ma: Insights from the activation history of the Zhongba-Gyangze thrust in southern Tibet","authors":"Qi Zhao, Yi Yan, Satoshi Tonai, Yildirim Dilek, Zuofei Zhu","doi":"10.1130/g51615.1","DOIUrl":"https://doi.org/10.1130/g51615.1","url":null,"abstract":"Constraining the timing of tectonic coupling between converging plates is crucial for understanding the transition from continental subduction to continental collision. In the case of the India-Asia collision, thrusting of an accretionary complex onto the Indian continental margin provides the most direct temporal constraint on the early stages of continental collision, as it represents the most immediate upper-crustal fault system corresponding to plate coupling. Here, we used structural analysis combined with K-Ar dating and hydrogen isotopes of authigenic illite and muscovite to unravel the time-progressive development of the Zhongba-Gyangze thrust (ZGT), which represents a tectonic boundary fault in southern Tibet. Our results suggest that the ZGT evolved from its initiation as a single fault zone infiltrated by metamorphic fluids with high δD values (–47‰ to –55‰) at ca. 80 Ma to multiple deformation localization zones starting around 51 Ma. This latter phase is represented by the development of different generations of authigenic 1 M/1Md illite and significant input of meteoric fluids with δD values ranging from –71‰ to –98‰ through multiple episodes of brittle fault reactivation. A Late Cretaceous tectono-thermal event related to the subduction of a Neotethyan oceanic ridge may have been responsible for the formation of 2M1 illite/muscovite at ca. 80 Ma. The oldest (ca. 51 Ma) 1 M/1Md illite age coincides with the first major pulse of shortening in the upper plate after the initial India-Asia contact. Given the synchronous deceleration of India-Asia convergence, the ca. 51 Ma deformation pulse across the Yarlung-Zangbo suture zone demarcates strong coupling (i.e., the onset of continental collision) between India and Asia at this time.","PeriodicalId":12642,"journal":{"name":"Geology","volume":"22 1","pages":""},"PeriodicalIF":5.8,"publicationDate":"2024-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"138840006","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":"Expanding the metamorphic devolatilization model: Komatiites as a source for orogenic gold deposits in high-grade metamorphic rocks","authors":"Chang Yu, Richen Zhong, Andrew G. Tomkins, Hao Cui, Yanjing Chen","doi":"10.1130/g51446.1","DOIUrl":"https://doi.org/10.1130/g51446.1","url":null,"abstract":"Orogenic gold deposits contribute the largest proportion of the world’s gold reserves, and the source of their ore-forming components has been recognized as the metamorphic devolatilization of metapelites or metabasites across the greenschist- to amphibolite-facies transition. However, hypozonal orogenic gold deposits represent an enigma in this context. Some of these apparently formed in higher-grade metamorphic rocks when temperatures were beyond the wet solidus of quartz-feldspar–bearing rocks; it is therefore puzzling how these fluids were generated in the source and migrated through the crust without causing partial melting. Here, we show that devolatilization of hydrated komatiites, a volumetrically significant lithological unit in Precambrian greenstone belts, is a viable model that can plausibly lead to gold mineralization at amphibolite-facies conditions. Our thermodynamic simulations indicate that subsolidus metamorphic devolatilization of komatiites at ~700 °C (upper amphibolite facies) can unlock significant amounts of gold via dehydration of talc and chlorite. This genetic model is supported by the geochemical characteristics of, and estimated pressure-temperature (P-T) formation conditions of, hypozonal gold deposits and the intimate spatiotemporal association between hypozonal deposits and komatiites in greenstone belts. This work expands the P-T range of the metamorphic devolatilization model and enhances its robustness in explaining gold mineralization in metamorphic terranes.Orogenic gold deposits are widely studied because they contribute over a quarter of the world’s gold supply (Goldfarb et al., 2005); however, the source(s) of their ore-forming components (fluid, sulfur, gold, and other metals) has(have) long been debated (Goldfarb and Groves, 2015; Groves et al., 2020; Kolb et al., 2015; Phillips and Powell, 2010; Selvaraja et al., 2017; Tomkins, 2010; Wang et al., 2022; Zhao et al., 2019). The widely accepted metamorphic devolatilization model (Phillips and Powell, 2010) emphasizes that gold-bearing fluids are produced by metamorphic dehydration of hydrous crustal rocks, particularly at the greenschist to amphibolite transition, largely through breakdown of chlorite (~12% H2O) to minerals like biotite (~4% H2O), hornblende (~2% H2O), and garnet (anhydrous) (Goldfarb et al., 2005; Phillips and Powell, 2010; Pitcairn et al., 2006; Tomkins, 2010; Zhong et al., 2015). At temperatures higher than the greenschist-amphibolite transition, there is minimal opportunity for fluid liberation from the metamorphosed mafic and sedimentary rocks. As a result, gold and sulfur are thought to be inaccessible in the sources under these conditions (Tomkins, 2013). Since fluids generated at the greenschist-amphibolite transition tend to migrate upward into rocks of lower metamorphic grades, this model satisfactorily explains the formation of orogenic gold in lower-amphibolite- to greenschist-facies terranes.Deposits are also found in higher-gra","PeriodicalId":12642,"journal":{"name":"Geology","volume":"59 1","pages":""},"PeriodicalIF":5.8,"publicationDate":"2024-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"138840039","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 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}