Geology最新文献

{"title":"Discovery of Permian–Triassic eclogite in northern Tibet establishes coeval subduction erosion along an ~3000-km-long arc: COMMENT","authors":"Shuguang Song, Hafiz U. Rehman","doi":"10.1130/g51860c.1","DOIUrl":"https://doi.org/10.1130/g51860c.1","url":null,"abstract":"Abstract not available","PeriodicalId":12642,"journal":{"name":"Geology","volume":"23 1","pages":""},"PeriodicalIF":5.8,"publicationDate":"2024-03-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140015420","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-precision U-Pb geochronology links magmatism in the Southwestern Laurentia large igneous province and Midcontinent Rift","authors":"M. Mohr, M. Schmitz, N. Swanson‐Hysell, K.E. Karlstrom, F.A. Macdonald, M. E. Holland, Y. Zhang, N.S. Anderson","doi":"10.1130/g51786.1","DOIUrl":"https://doi.org/10.1130/g51786.1","url":null,"abstract":"The Southwestern Laurentia large igneous province (SWLLIP) comprises voluminous, widespread ca 1.1 Ga magmatism in the southwestern United States and northern Mexico. The timing and tempo of SWLLIP magmatism and its relationship to other late Mesoproterozoic igneous provinces have been unclear due to difficulties in dating mafic rocks at high precision. New precise U-Pb zircon dates for comagmatic felsic segregations within mafic rocks reveal distinct magmatic episodes at ca. 1098 Ma (represented by massive sills in Death Valley, California, the Grand Canyon, and central Arizona) and ca. 1083 Ma (represented by the Cardenas Basalts in the Grand Canyon and a sill in the Dead Mountains, California). The ca. 1098 Ma magmatic pulse was short-lived, lasting 0.25 –0.24 +0.67 m.y., and voluminous and widespread, evidenced by the ≥100 m sills in Death Valley, the Grand Canyon, and central Arizona, consistent with decompression melting of an upwelling mantle plume. The ca. 1083 Ma magmatism may have been generated by a secondary plume pulse or post-plume lithosphere extension.\u0000 The ca. 1098 Ma pulse of magmatism in southwestern Laurentia occurred ∼2 m.y. prior to an anomalous renewal of voluminous melt generation in the Midcontinent Rift of central Laurentia that is recorded by the ca. 1096 Ma Duluth Complex layered mafic intrusions. Rates of lateral plume spread predicted by mantle plume lubrication theory support a model where a plume derived from the deep mantle impinged near southwestern Laurentia, then spread to thinned Midcontinent Rift lithosphere over ∼2 m.y. to elevate mantle temperatures and generate melt. This geodynamic hypothesis reconciles the close temporal relationships between voluminous magmatism across Laurentia and provides an explanation for that anomalous renewal of high magmatic flux within the protracted magmatic history of the Midcontinent Rift.","PeriodicalId":12642,"journal":{"name":"Geology","volume":"49 11","pages":""},"PeriodicalIF":5.8,"publicationDate":"2024-01-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139442155","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 Bayesian astrochronology for the Cambrian first occurrence of trilobites in West Gondwana (Morocco)","authors":"Matthias Sinnesael, Andrew R. Millard, Martin R. Smith","doi":"10.1130/g51718.1","DOIUrl":"https://doi.org/10.1130/g51718.1","url":null,"abstract":"The first occurrence of trilobites at ca. 520 Ma is an iconic feature of the Cambrian Explosion. Developing a robust evolutionary view on early Cambrian life is generally hindered by large uncertainties in the ages of fossil finds and their global stratigraphic correlation. We developed an astrochronological interpretation for the Tiout section in Morocco that features some of the oldest trilobite fossils. Our novel approach to incorporating individual astronomical cycle durations in an integrated radioisotopic and astrochronological Bayesian age-depth model results in an age estimate of 519.62 Ma (519.70−519.54 Ma 95% highest posterior distribution) for the first occurrence of trilobites in West Gondwana. This level of precise age estimation is exceptional for biological events in deep time and demonstrates the power of our novel approach.","PeriodicalId":12642,"journal":{"name":"Geology","volume":"20 11","pages":""},"PeriodicalIF":5.8,"publicationDate":"2024-01-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139445658","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":"Methane-carbon budget of a ferruginous meromictic lake and implications for marine methane dynamics on early Earth","authors":"Sajjad Akam, Pei-Chuan Chuang, Sergei Katsev, C. Wittkop, Michelle Chamberlain, Andrew W. Dale, Klaus Wallmann, Adam J. Heathcote, E. Swanner","doi":"10.1130/g51713.1","DOIUrl":"https://doi.org/10.1130/g51713.1","url":null,"abstract":"The greenhouse gas methane (CH4) contributed to a warm climate that maintained liquid water and sustained Earth’s habitability in the Precambrian despite the faint young sun. The viability of methanogenesis (ME) in ferruginous environments, however, is debated, as iron reduction can potentially outcompete ME as a pathway of organic carbon remineralization (OCR). Here, we document that ME is a dominant OCR process in Brownie Lake, Minnesota (midwestern United States), which is a ferruginous (iron-rich, sulfate-poor) and meromictic (stratified with permanent anoxic bottom waters) system. We report ME accounting for ≥90% and >9% ± 7% of the anaerobic OCR in the water column and sediments, respectively, and an overall particulate organic carbon loading to CH4 conversion efficiency of ≥18% ± 7% in the anoxic zone of Brownie Lake. Our results, along with previous reports from ferruginous systems, suggest that even under low primary productivity in Precambrian oceans, the efficient conversion of organic carbon would have enabled marine CH4 to play a major role in early Earth’s biogeochemical evolution.","PeriodicalId":12642,"journal":{"name":"Geology","volume":"59 3","pages":""},"PeriodicalIF":5.8,"publicationDate":"2024-01-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139383523","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":"Toroidal flow around the Tonga slab moved the Samoan plume during the Pliocene","authors":"K. Konrad, Matthew G. Jackson, Bernhard Steinberger, A. Koppers, Andrea Marie Balbas, Valerie Finlayson, J. Konter, Allison Price","doi":"10.1130/g51588.1","DOIUrl":"https://doi.org/10.1130/g51588.1","url":null,"abstract":"Age-progressive seamount tracks generated by lithospheric motion over a stationary mantle plume have long been used to reconstruct absolute plate motion (APM) models. However, the basis of these models requires the plumes to move significantly slower than the overriding lithosphere. When a plume interacts with a convergent or divergent plate boundary, it is often deflected within the strong local mantle flow fields associated with such regimes. Here, we examined the age progression and geometry of the Samoa hotspot track, focusing on lava flow samples dredged from the deep flanks of seamounts in order to best reconstruct when a given seamount was overlying the mantle plume (i.e., during the shield-building stage). The Samoan seamounts display an apparent local plate velocity of 7.8 cm/yr from 0 to 9 Ma, 11.1 cm/yr from 9 to 14 Ma, and 5.6 cm/yr from 14 to 24 Ma. Current fixed and mobile hotspot Pacific APM models cannot reproduce the geometry of the Samoa seamount track if a long-term fixed hotspot location, currently beneath the active Vailulu’u Seamount, is assumed. Rather, reconstruction of the eruptive locations of the Samoan seamounts using APM models indicates that the surface expression of the plume migrated ∼2° northward in the Pliocene. Large-scale mantle flow beneath the Pacific Ocean Basin cannot explain this plume migration. Instead, the best explanation is that toroidal flow fields—generated by westward migration of the Tonga Trench and associated slab rollback—have deflected the conduit northward over the past 2−3 m.y. These observations provide novel constraints on the ways in which plume-trench interactions can alter hotspot track geometries.","PeriodicalId":12642,"journal":{"name":"Geology","volume":"3 4","pages":""},"PeriodicalIF":5.8,"publicationDate":"2024-01-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139389517","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":"Mechanisms of nitrogen isotope fractionation at an ancient black smoker in the 2.7 Ga Abitibi greenstone belt, Canada","authors":"A.N. Martin, E. Stüeken, J.A.-S. Michaud, C. Münker, S. Weyer, E.H.P. van Hees, M.M. Gehringer","doi":"10.1130/g51689.1","DOIUrl":"https://doi.org/10.1130/g51689.1","url":null,"abstract":"The biological nitrogen (N) cycle on early Earth is enigmatic because of limited data from Archean (meta-)sediments and the potential alteration of primary biotic signatures. Here we further investigate unusual 15N enrichments reported in 2.7 Ga meta-sediments from the Abitibi greenstone belt, Canada, purportedly related to a 15N-enriched Archean atmosphere. Given that sediments from this region are contemporaneous with large-scale volcanogenic massive sulfide deposits, we utilize Cu and Zn contents to trace the effects of hydrothermal circulation on N isotope fractionation. We show that high δ15Nbulk values as high as +23‰ are associated with Cu-Zn mineralization, whereas unmineralized organic-rich shales exhibit much lower δ15Nbulk and δ15Nkerogen values. Moreover, we find a large offset between δ15Nbulk and δ15Nkerogen of as much as 17‰ and relate this to the addition of organic-bound N during the late-stage emplacement of organic-rich veins. We conclude that the previously reported high δ15N values are most parsimoniously explained by biotic and abiotic mechanisms rather than a 15N-enriched atmosphere. Crucially, both mechanisms require the presence of NH4+ in hydrothermal fluids, supporting the hypothesis that hydrothermal discharge was an important nutrient source for Neoarchean marine life.","PeriodicalId":12642,"journal":{"name":"Geology","volume":"13 24","pages":""},"PeriodicalIF":5.8,"publicationDate":"2024-01-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139389571","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":"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}