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Correlating mantle cooling with tectonic transitions on early Earth 地幔冷却与早期地球构造转变的相关性
Geology Pub Date : 2024-01-12 DOI: 10.1130/g51874.1
P. Gunawardana, P. Chowdhury, Gabriele Morra, Peter A. Cawood
{"title":"Correlating mantle cooling with tectonic transitions on early Earth","authors":"P. Gunawardana, P. Chowdhury, Gabriele Morra, Peter A. Cawood","doi":"10.1130/g51874.1","DOIUrl":"https://doi.org/10.1130/g51874.1","url":null,"abstract":"The dominant tectonic mode operating on early Earth (before ca. 2.5 Ga) remains elusive, with an increasing body of evidence suggesting that non-plate tectonic modes were likely more prevalent at that time. Thus, how plate tectonics evolved after that remains contentious. We performed two-dimensional numerical modeling of mantle convection at temperatures appropriate for the Hadean−Archean eons and show that subduction and rift systems may have spontaneously emerged on Earth from an earlier drip-and-rift−dominated tectonic mode in response to the secular cooling of the mantle. This cooling of the mantle was mediated by repeated events of rifting and dripping that likely occurred over a few hundred million years. As the mantle cooled, its effective viscosity and the thickness and strength of the lithosphere increased, which helped establish rigid plates and initiate plate tectonics on Earth.","PeriodicalId":503125,"journal":{"name":"Geology","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2024-01-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139624366","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
引用次数: 0
Mantle flow and olivine fabric transition in the Myanmar continental subduction zone 缅甸大陆俯冲带的岩浆流动和橄榄石结构转变
Geology Pub Date : 2024-01-11 DOI: 10.1130/g51698.1
Enbo Fan, Y. Ai, Stephen S. Gao, Yumei He, Kelly H. Liu, M. Jiang, Guangbing Hou, Shun Yang, Chit Thet Mon, Myo Thant, K. Sein
{"title":"Mantle flow and olivine fabric transition in the Myanmar continental subduction zone","authors":"Enbo Fan, Y. Ai, Stephen S. Gao, Yumei He, Kelly H. Liu, M. Jiang, Guangbing Hou, Shun Yang, Chit Thet Mon, Myo Thant, K. Sein","doi":"10.1130/g51698.1","DOIUrl":"https://doi.org/10.1130/g51698.1","url":null,"abstract":"One of the major advances in mineral physics and seismology is the realization that different olivine fabric types are functions of temperature, shear stress, and water content in oceanic subducting systems. The distribution of different olivine fabric types and geodynamic processes in the mantle wedge above a subducting continental slab remain poorly understood. Here, based on splitting analysis of shear waves recorded by 46 stations recently deployed in central Myanmar, we reveal trench-perpendicular fast orientations between the 80 and 100 km slab contours sandwiched between trench-parallel fast orientations from the mantle wedge tip to the backarc. The dramatic change in fast orientations indicates the transition of olivine fabric types in the mantle wedge combined with corner flow. Cold continental subduction and shear stress reduction caused by partial melting favor B-type and C- or E-type olivine fabrics, respectively.","PeriodicalId":503125,"journal":{"name":"Geology","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2024-01-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139626595","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
引用次数: 0
An Eoarchean continental nucleus for the Fennoscandian Shield and a link to the North Atlantic craton 芬诺斯坎地盾的新元古代大陆核以及与北大西洋克拉通的联系
Geology Pub Date : 2023-12-28 DOI: 10.1130/g51658.1
Andreas Petersson, T. Waight, A. Kemp, M. Whitehouse, J. Valley
{"title":"An Eoarchean continental nucleus for the Fennoscandian Shield and a link to the North Atlantic craton","authors":"Andreas Petersson, T. Waight, A. Kemp, M. Whitehouse, J. Valley","doi":"10.1130/g51658.1","DOIUrl":"https://doi.org/10.1130/g51658.1","url":null,"abstract":"Enabling the build-up of continental crust is a vital step in the stabilization of cratonic lithosphere. However, these initial crustal nuclei are commonly either destroyed by recycling or buried by younger rocks. In the Fennoscandian Shield, the oldest rocks are ca. 3.5 Ga, but ca. 3.7 Ga inherited and detrital zircons suggest the presence of an older, unexposed crustal substrate. We present U-Pb, O, and Hf isotope data from detrital zircons of three major Finnish rivers as well as zircon O and Hf isotope data from previously dated rocks of the Archean Suomujärvi and Pudasjärvi complexes, central Finland. Combined, these data indicate a previously unidentified ca. 3.75 Ga crustal nucleus in the Fennoscandian Shield. This adds to the growing number of Eoarchean nuclei recognized in Archean terranes around the globe, highlighting the importance of such nuclei in enabling the growth of continental crust. The isotope signatures of the Fennoscandian nucleus correlate with equivalent-aged rocks in Greenland, consistent with a common Eoarchean evolution for Fennoscandia and the North Atlantic craton.","PeriodicalId":503125,"journal":{"name":"Geology","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2023-12-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139152258","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
引用次数: 0
Garnet versus amphibole: Implications for magmatic differentiation and slab melting 石榴石与闪石：对岩浆分异和板块熔融的影响
Geology Pub Date : 2023-11-30 DOI: 10.1130/g51637.1
Yajie Gao, Hugh St. C. O’Neill, J. Mavrogenes
{"title":"Garnet versus amphibole: Implications for magmatic differentiation and slab melting","authors":"Yajie Gao, Hugh St. C. O’Neill, J. Mavrogenes","doi":"10.1130/g51637.1","DOIUrl":"https://doi.org/10.1130/g51637.1","url":null,"abstract":"The garnet signature in the rare earth element (REE) abundances in adakites has been considered a key genetic indicator of these controversial rocks, whose proposed origins include direct melting of subducted oceanic crust (“slab melts”). We show that the garnet signature may be quantified using the shape coefficients of chondrite-normalized REE patterns. We applied this method to a global data set of Cenozoic and Quaternary volcanic samples described as “adakites.” The results indicate that many, but not all, suites of rocks labeled as adakites have undergone fractional crystallization of garnet, starting from parental melts attributable to partial melts of garnet-bearing sources. The extreme garnet signatures seen in many examples require hybrid sources, consisting of subducted sediment as well as igneous oceanic crust; however, extensive deep-crustal differentiation obscures the major and trace-element characteristics of these sources, casting doubt on their identification as primitive slab melts.","PeriodicalId":503125,"journal":{"name":"Geology","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2023-11-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139201000","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
引用次数: 0
Metasomatized mantle sources for orogenic gold deposits hosted in high-grade metamorphic rocks: Evidence from Hg isotopes 高品位变质岩中蕴藏的成因金矿床的变质地幔源：来自汞同位素的证据
Geology Pub Date : 2023-11-29 DOI: 10.1130/g51593.1
Qingfei Wang, Xuefei Liu, Runsheng Yin, Weijun Weng, Hesen Zhao, Lin Yang, D. Zhai, Dapeng Li, Yao Ma, D. Groves, Jun Deng
{"title":"Metasomatized mantle sources for orogenic gold deposits hosted in high-grade metamorphic rocks: Evidence from Hg isotopes","authors":"Qingfei Wang, Xuefei Liu, Runsheng Yin, Weijun Weng, Hesen Zhao, Lin Yang, D. Zhai, Dapeng Li, Yao Ma, D. Groves, Jun Deng","doi":"10.1130/g51593.1","DOIUrl":"https://doi.org/10.1130/g51593.1","url":null,"abstract":"Investigation of Hg isotope ratios of gold-related sulfides and penecontemporaneous mafic dikes from four orogenic gold provinces on the margins of the North China Craton and Yangtze Craton identifies three orogenic gold deposit (OGD) groups from different tectonic regimes. Ore-related sulfides of group 1 OGDs and mafic dikes from the craton margin reworked via oceanic subduction mostly have positive Δ199Hg values. The group 2 OGDs and mafic dikes from the margin that witnessed complex oceanic and continental subductions have mixed positive to negative Δ199Hg values. The group 3 OGDs on the margin that experienced continental subduction have dominantly negative Δ199Hg values. These isotopic differences indicate subduction histories have a first-order control on the distinct sources for the OGDs. It indicates that OGDs were derived from fluids from the mantle lithosphere metasomatized by contrasting subduction components, not from metamorphic fluids as is widely accepted. Group 1 OGDs and dikes were sourced from metasomatized mantle, which inherited the positive Δ199Hg of both recycled marine sediments and seawater during oceanic subduction, whereas group 3 with negative Δ199Hg was derived from mantle lithosphere metasomatized by subduction of mainly continental components. This genetic model identifies regions with high-grade metamorphic rocks above metasomatized mantle lithosphere as promising new OGD exploration targets.","PeriodicalId":503125,"journal":{"name":"Geology","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2023-11-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139209741","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
引用次数: 0
Marine snowstorm during the Permian−Triassic mass extinction 二叠纪-三叠纪大灭绝期间的海洋雪暴
Geology Pub Date : 2023-11-29 DOI: 10.1130/g51497.1
S. Grasby, O. Ardakani, Xiaojun Liu, D. P. Bond, P. Wignall, Lorna J. Strachan
{"title":"Marine snowstorm during the Permian−Triassic mass extinction","authors":"S. Grasby, O. Ardakani, Xiaojun Liu, D. P. Bond, P. Wignall, Lorna J. Strachan","doi":"10.1130/g51497.1","DOIUrl":"https://doi.org/10.1130/g51497.1","url":null,"abstract":"The Permian−Triassic mass extinction (PTME) interval is marked by major excursions in both inorganic and organic carbon (C) isotopes. Carbon cycle models predict that these trends were driven by large increases in productivity, yet organic C−rich rocks are not recorded in most PTME shelf sedimentary successions. Anomalous C-rich facies have been reported from rare abyssal plains records now exposed in Japan and New Zealand, where black shales at the PTME are extraordinarily organic-rich units. We examined organic matter at the Waiheke, New Zealand, section, and results show that these deposits are dominated by lamalginites composed of unicellar solitary or colonial phytoplankton produced during algal blooms that falls as “marine snow.” We modeled the impact of ash fall from eruptions in the Siberian Traps large igneous province and argue that they fertilized the Panthalassa Ocean with P and Fe, leading to a marine “snowstorm” and significant C drawdown marking this major biobloom during the PTME.","PeriodicalId":503125,"journal":{"name":"Geology","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2023-11-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139213449","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
引用次数: 0
Intrusion tip velocity controls the emplacement mechanism of sheet intrusions 侵入体顶端速度控制着片状侵入体的成岩机制
Geology Pub Date : 2023-11-28 DOI: 10.1130/g51509.1
Jonas Köpping, A. Cruden, Samuel T. Thiele, Craig Magee, Andrew Bunger
{"title":"Intrusion tip velocity controls the emplacement mechanism of sheet intrusions","authors":"Jonas Köpping, A. Cruden, Samuel T. Thiele, Craig Magee, Andrew Bunger","doi":"10.1130/g51509.1","DOIUrl":"https://doi.org/10.1130/g51509.1","url":null,"abstract":"Space for intruding magma is created by elastic, viscous, and/or plastic deformation of host rocks. Such deformation impacts the geometries of igneous intrusions, particularly sills and dikes. For example, tapered intrusion tips indicate linear-elastic fracturing during emplacement, whereas fluidization of host rocks has been linked to development of elongate magma fingers with rounded tips. Although host rock fluidization has only been observed at the lateral tips of magma fingers, it is assumed to occur at their leading edges (frontal tips) and thereby control their propagation and geometry. Here, we present macro- and microstructural evidence of fluidized sedimentary host rock at the lateral tips of magma fingers emanating from the Shonkin Sag laccolith (Montana, western United States), and we explore whether fluidization could have occurred at their frontal tips. Specifically, we combine heat diffusion modeling and fracture tip velocity estimates to show that: (1) low intrusion tip velocities (≤10−5 m s−1) allow pore fluids ahead of the intrusion to reach temperatures sufficient to cause fluidization, but (2) when tip velocities are high (∼0.01−1 m s−1), which is typical for many sheet intrusions, fluidization ahead of propagating tips is inhibited. Our results suggest that intrusion tip velocity (i.e., strain rate) is a first-order control on how rocks accommodate magma. Spatially and temporally varying velocities of lateral and frontal tips suggest that deformation mechanisms at these sites may be decoupled, meaning magma finger formation may not require host rock fluidization. It is thus critical to consider strain rate and three-dimensional intrusion geometry when inferring dominant magma emplacement mechanisms.","PeriodicalId":503125,"journal":{"name":"Geology","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2023-11-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139221806","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
引用次数: 0
Massive rare earth element storage in sub-continental lithospheric mantle initiated by diapirism, not by melting 大陆下岩石圈地幔中大量稀土元素的储存是由断裂作用而非熔融作用引发的
Geology Pub Date : 2023-11-28 DOI: 10.1130/g51102.1
XinXiang Zhu, Yan Liu, Zengqian Hou
{"title":"Massive rare earth element storage in sub-continental lithospheric mantle initiated by diapirism, not by melting","authors":"XinXiang Zhu, Yan Liu, Zengqian Hou","doi":"10.1130/g51102.1","DOIUrl":"https://doi.org/10.1130/g51102.1","url":null,"abstract":"Rare earth elements (REEs) are essential metals for modern technologies. Recent studies suggest that subcontinental lithospheric mantle (SCLM) remelting, previously fertilized by subducted marine sediments, leads to formation of REE-bearing rocks. However, the transfer mechanism of REE-rich sediments from the subducted slab to the overlying mantle wedge is unclear. We present high-pressure experiments on natural REE-rich marine sediments at 3–4 GPa and 800–1000 °C to constrain the phase relations, sediment melting behavior, and REE migration during subduction. Our results show recrystallization into an eclogite-like assemblage, with melting only occurring at 4 GPa, 1000 °C, experiments. Regardless of melting behavior, REE are refractory and mostly hosted by apatite. Buoyancy calculations suggest that most of the eclogite-like residues would form solid-state diapirs, ascending to the SCLM, resulting in the REE-fertilized source. Such flux may be required for substantial REE transport during subduction, as a foundation for economic-grade mineralization.","PeriodicalId":503125,"journal":{"name":"Geology","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2023-11-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139223858","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
引用次数: 0
Pleistocene Colorado River terraces in the canyonlands region (Utah, USA) record unsteady, transient incision and growth of the Cataract Canyon knickzone by salt tectonics 峡谷地带（美国犹他州）更新世科罗拉多河阶地记录了盐构造对卡特拉克峡谷节理带不稳定、短暂的侵蚀和增长
Geology Pub Date : 2023-11-20 DOI: 10.1130/g51599.1
Natalie Tanski, J. Pederson, T. Rittenour, A. Hidy
{"title":"Pleistocene Colorado River terraces in the canyonlands region (Utah, USA) record unsteady, transient incision and growth of the Cataract Canyon knickzone by salt tectonics","authors":"Natalie Tanski, J. Pederson, T. Rittenour, A. Hidy","doi":"10.1130/g51599.1","DOIUrl":"https://doi.org/10.1130/g51599.1","url":null,"abstract":"Colorado River terraces in the canyonlands region of southeastern Utah can be dated and analyzed to address the controls of incision and nature of the Colorado Plateau's largest channel-steepness anomaly, Cataract Canyon. Field correlations supported by luminescence and cosmogenic-nuclide ages on strath terraces along Meander Canyon, upstream of Cataract Canyon, reveal a complex record of unsteady incision over the past ∼340 k.y. at an average rate of ∼0.4 mm/yr. Both an upstream progression of rapid incision and a unique sigmoidal long-profile pattern of terraces indicate incision in response to episodic baselevel fall. Also, terraces converge downstream with the anomalously low-gradient modern channel above Cataract Canyon. We interpret these results as indicating that growth of the Cataract Canyon knickzone is due to an erosion-salt tectonics feedback since at least the Mid Pleistocene, which has imparted unsteady, and currently elevated, local baselevel. More broadly, the canyonlands region is marked by rapid and unsteady incision that is complicated by local geologic controls even while being absent of any regional or mantle-driven uplift.","PeriodicalId":503125,"journal":{"name":"Geology","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2023-11-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139258333","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
引用次数: 0
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