Geology Pub Date : 2024-02-28 DOI: 10.1130/g51875.1

Wei Jian, Jingwen Mao, Bernd Lehmann, Nigel J. Cook, Jiankang Li, Shiwei Song, Lei Zhu

{"title":"Hyper-enrichment of gold via quartz fracturing and growth of polymetallic melt droplets","authors":"Wei Jian, Jingwen Mao, Bernd Lehmann, Nigel J. Cook, Jiankang Li, Shiwei Song, Lei Zhu","doi":"10.1130/g51875.1","DOIUrl":"https://doi.org/10.1130/g51875.1","url":null,"abstract":"Gold precipitation in hydrothermal systems is traditionally attributed to supersaturation of gold due to decreasing gold complex stability triggered by changes in physicochemical conditions of the ore fluid. However, ultrahigh-grade gold veins in orogenic (shear zone related) gold deposits can contain kilograms per tonne of gold or more, in marked contrast to the typically very low gold concentrations (tens of parts per billion) in fluid. The gold mineral assemblage is commonly restricted to native gold and/or Au-(Ag)-tellurides and occurs in micro-fractures of sheared quartz veins. Textural and compositional characterization of such assemblages, coupled with hydrothermal diamond anvil cell experiments and heating-freezing experiments, provides evidence for an alternative ultrahigh-grade gold enrichment mechanism via growth of polymetallic melt droplets induced by quartz fracturing. We propose that polymetallic melt droplets of Au-Ag-Te-Bi−rich composition form through adsorption-reduction of metal complexes on fractured quartz surfaces, where surface silanol groups and hydrogen serve as reductants. The melt droplets subsequently grow by catalyzing reduction of metal complexes and absorbing metals from fluids percolating in the fractured quartz network. The mobile and reactive polymetallic melt droplets can repeatedly react with the fluid on protracted quartz fracturing and efficiently continue to scavenge gold from multiple pulses of gold-undersaturated ore fluids.","PeriodicalId":503125,"journal":{"name":"Geology","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2024-02-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140422003","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

Subduction erosion revealed by exhumed lower arc crustal rocks in an accretionary complex, northeastern China 中国东北部一增生复合体中出露的下弧地壳岩石揭示的俯冲侵蚀作用

Geology Pub Date : 2024-02-28 DOI: 10.1130/g51803.1

Mengyu Xu, W. Xiao, Kai Liu, B. Wan, Ross N. Mitchell, G. Rosenbaum, Hao Wang

{"title":"Subduction erosion revealed by exhumed lower arc crustal rocks in an accretionary complex, northeastern China","authors":"Mengyu Xu, W. Xiao, Kai Liu, B. Wan, Ross N. Mitchell, G. Rosenbaum, Hao Wang","doi":"10.1130/g51803.1","DOIUrl":"https://doi.org/10.1130/g51803.1","url":null,"abstract":"Subduction erosion at convergent margins is a leading mechanism for the destruction (recycling and reworking) of continental crust. But because of the lack of direct evidence, it is not straightforward to identify erosive events and their intensities in fossil subduction zones. The Heilongjiang accretionary complex in northeastern China was formed during the early Mesozoic subduction of the Paleo-Pacific Ocean. We investigated amphibolites from this accretionary complex, whose protoliths (based on whole-rock trace elements and Sr-Nd-Hf isotopes) were mafic continental arc magmatic rocks (255−249 Ma; zircon core U-Pb ages) from the upper plate. Phase equilibria modeling constrained by mineral geochemistry indicates that the amphibolites and their wall rocks were first heated to low granulite facies (750−800 °C, ∼7 kbar) at 251−244 Ma (zircon rim U-Pb ages) and then cooled to ∼700 °C with increasing pressure (8−9 kbar) before 213−187 Ma (titanite and apatite U-Pb ages). To explain the occurrence of the lower arc crustal lithologies in the accretionary complex and their metamorphic history, we propose that the subducting plate strongly eroded the forearc crust, allowing the plate interface to advance landward and scrape the amphibolites and wall rocks formed under the old arc, which finally were exhumed along the subduction channel and became components of the complex. The case study exemplifies direct petrological evidence of strong subduction erosion occurring in an ancient orogen, thus implying that consumption of the entire forearc crust could occur within only ∼50 m.y.","PeriodicalId":503125,"journal":{"name":"Geology","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2024-02-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140418126","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

Fluid environment controls along-strike variation in slip style: Midcrustal geological signatures from the Red River fault, China 流体环境控制着沿走向的滑动方式变化：中国红河断层的地壳中层地质特征

Geology Pub Date : 2024-02-28 DOI: 10.1130/g51865.1

Qingbao Duan, Å. Fagereng, Jianye Chen, Thomas Blenkinsop

{"title":"Fluid environment controls along-strike variation in slip style: Midcrustal geological signatures from the Red River fault, China","authors":"Qingbao Duan, Å. Fagereng, Jianye Chen, Thomas Blenkinsop","doi":"10.1130/g51865.1","DOIUrl":"https://doi.org/10.1130/g51865.1","url":null,"abstract":"The slip style of continental midcrustal shear zones plays a crucial role in determining the seismogenic potential of faults, but it remains poorly understood because geological observations that can be directly tied to seismic behavior are scarce. We describe frictional-viscous shear zones in the Red River fault, China, which consists of two segments with distinct seismic behaviors and fluid availabilities. The northern segment hosts moderate to large earthquakes, and midcrustal fault slip is localized into mylonitized pseudotachylyte-bearing layers where dynamically recrystallized quartz records flow stresses exceeding 100 MPa and accelerated viscous creep. The southern segment is dominantly aseismic but active microseimically. Fault slip is accommodated in several mylonitized cataclasite layers, comprising interconnected biotite and intervening fractured clasts, with evidence for pervasive dissolution-precipitation creep. Microstructures, paleopiezometry, and microphysical modeling suggest transient aseismic slip in response to increased strain rates during viscous creep at <50 MPa. We interpret that along-strike variations in fluid environment control fault slip styles and seismic behaviors. The dry and strong northern segment is capable of nucleating large earthquakes, while greater fluid availability in the southern segment activates dissolution-precipitation creep at low driving stresses, which limits interseismic elastic strain accumulation at frictional-viscous transition depths. In this model, compaction-driven fluid pressurization and dilatant hardening are invoked to explain the aseismic slip transients in the southern segment.","PeriodicalId":503125,"journal":{"name":"Geology","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2024-02-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140418865","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

Large-scale submarine landslides in the Barberton Greenstone Belt, southern Africa—Evidence for subduction and great earthquakes in the Paleoarchean 非洲南部巴伯顿绿岩带的大规模海底滑坡--古近纪俯冲和大地震的证据

Geology Pub Date : 2024-02-27 DOI: 10.1130/g51997.1

Simon Lamb, C. D. de Ronde

引用次数: 0

Summer warming during Heinrich Stadial 1 in Northeast China 中国东北地区海因里希 1 号极昼期间的夏季升温

Geology Pub Date : 2024-02-26 DOI: 10.1130/g51881.1

Zeyang Zhu, Jing Wu, G. Chu, P. Rioual, Jiaxin Lu, Luo Wang, Jiaqi Liu

{"title":"Summer warming during Heinrich Stadial 1 in Northeast China","authors":"Zeyang Zhu, Jing Wu, G. Chu, P. Rioual, Jiaxin Lu, Luo Wang, Jiaqi Liu","doi":"10.1130/g51881.1","DOIUrl":"https://doi.org/10.1130/g51881.1","url":null,"abstract":"The last deglaciation is considered a key period for exploring the underlying dynamics of temperature changes because it was characterized by multiple millennial-scale abrupt climatic events. However, the limited number of quantitative temperature records in Northeast (NE) China covering the last deglaciation hampers a complete understanding of the mechanisms and processes behind the temperature changes that occurred in that region. Here, we present a quantitative reconstruction of summer temperature over the last deglaciation based on bacterial branched glycerol dialkyl glycerol tetraethers (brGDGTs) analyzed from the sediment sequence of Lake Kielguo, a small volcanic lake in NE China. The results show that summer temperature was lowest during the interval ca. 20−18.2 calibrated (cal.) k.y. B.P. with a value of ∼11.1 °C and increased by ∼1.9 °C during Heinrich Stadial 1 (HS1) and by ∼2.7 °C during the transition to the Bølling-Allerød (B-A). The summer temperatures during the B-A warm interval and Younger Dryas cold interval were ∼14.1 °C and ∼12.0 °C, respectively. The summer temperature record from the Lake Kielguo sediment sequence indicates that summer warming dominated the climate change state during HS1 in East Asia, which is different from the cooling pattern controlled by winter temperatures in the North Atlantic and Greenland realms. This distinction can be explained by weakened winter cooling signals triggered by the collapse of Atlantic Meridional Overturning Circulation when these signals propagated to East Asia, and increased summer temperature warming controlled by orbital and greenhouse gases during HS1 in East Asia.","PeriodicalId":503125,"journal":{"name":"Geology","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2024-02-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140429803","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

Reconciling plate motion and faulting at a rift-rift-rift triple junction 在断裂-断裂-断裂三重交界处调和板块运动和断层作用

Geology Pub Date : 2024-02-23 DOI: 10.1130/g51909.1

D. Maestrelli, Federico Sani, Derek Keir, C. Pagli, Alessandro La Rosa, A. Muluneh, Sascha Brune, G. Corti

{"title":"Reconciling plate motion and faulting at a rift-rift-rift triple junction","authors":"D. Maestrelli, Federico Sani, Derek Keir, C. Pagli, Alessandro La Rosa, A. Muluneh, Sascha Brune, G. Corti","doi":"10.1130/g51909.1","DOIUrl":"https://doi.org/10.1130/g51909.1","url":null,"abstract":"Rift-Rift-Rift triple junctions are regions where three plates interact, generating complex networks of variably oriented faults. While the geometry of the fault networks is easily constrained from their surface expression, what remains unclear is how the kinematics of faults and their interactions vary spatially, and how these relate to the unusual crustal motions that result from three plates diverging from each other. The Afar depression lies at the triple junction between the African, Arabian, and Somalian plates (in the Horn of Africa), where the unique combination of observational data from structural mapping, seismicity, and Global Navigation Satellite System (GNSS) allows us to understand the link between fault kinematics and plate motions. We complement these observations with an analog model to gain insights into how the patterns and directions of faults relate to overall plate motions. A key finding in both the model and nature is that some adjacent normal faults form at high angles and generate T-shaped structures. These purely normal faults are synchronously active, which means that the extension direction varies ∼90° locally. These kinematic contrasts in our model and in nature occur despite the relatively smooth pattern of overall surface motions. The results indicate that normal faults interacting at high angles to form the T-shaped structures can evolve synchronously within a stress field that varies gently in magnitude but dramatically in orientation over a few kilometers.","PeriodicalId":503125,"journal":{"name":"Geology","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2024-02-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140435571","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

Long-lived Northern Hemisphere convergence systems driven by upper-mantle thermal inhomogeneity 上地幔热不均匀性驱动的北半球长寿命辐合系统

Geology Pub Date : 2024-02-21 DOI: 10.1130/g51948.1

Liang Liu, Zebin Cao, J.P. Morgan, Hongyan Li, Fan Yang, Yi-Gang Xu

引用次数: 0

Tracking cycles of Phanerozoic opening and closing of ocean basins using detrital rutile and zircon geochronology and geochemistry 利用碎屑金红石和锆石地质年代学和地球化学追踪新生代海洋盆地开闭周期

Geology Pub Date : 2024-02-21 DOI: 10.1130/g51826.1

M. Odlum, T. Capaldi, Kelly D. Thomson, D. Stockli

{"title":"Tracking cycles of Phanerozoic opening and closing of ocean basins using detrital rutile and zircon geochronology and geochemistry","authors":"M. Odlum, T. Capaldi, Kelly D. Thomson, D. Stockli","doi":"10.1130/g51826.1","DOIUrl":"https://doi.org/10.1130/g51826.1","url":null,"abstract":"Sedimentary basins provide a deep time archive of tectonic and Earth-surface processes that can be leveraged by detrital mineral U-Pb dating and geochemistry to track paleogeography, magmatism, and crustal evolution. Zircon preserves the long-term (billions of years) record of supercontinent cycles; however, it is biased toward preserving felsic crustal records. Detrital rutile complements the detrital zircon record by providing constraints on the time and temperature of rifting and mafic magmatism, metamorphism, exhumation of the middle and lower crust, subduction, and amagmatic orogenesis. We use detrital zircon U-Pb and detrital rutile U-Pb geochronology and trace element analysis of Permian to Eocene siliciclastic rocks in the southern Pyrenees to capture supercontinent cycles of ocean basins opening and closing. Detrital rutile age spectra show peaks at ca. 100 Ma associated with rifting and hyperextension in the Pyrenean realm, 200 Ma associated with the Central Atlantic Magmatic Province, and 330 Ma, 375 Ma, and 400 Ma associated with subduction and Rheic Ocean crust formation. Zr-in-rutile thermometry and rutile Cr-Nb systematics provide further insight into metamorphic facies (peak metamorphic temperatures) and source rock lithology (mafic versus felsic affinity). Detrital zircon age spectra have peaks at ca. 300 Ma, 450 Ma, and 600 Ma associated with major orogenic events and felsic magmatism, and Th/U ratios provide information on relative zircon formation temperatures. Comparison of these independent records shows that detrital rutile reflects rifting, magma-poor orogenesis, and oceanic lithospheric processes, while detrital zircon detects continental lithospheric processes. Integrated detrital zircon and rutile data sets archive past geological events across multiple Wilson cycles.","PeriodicalId":503125,"journal":{"name":"Geology","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2024-02-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140443146","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

Discovery of modern living intertidal stromatolites on Sheybarah Island, Red Sea, Saudi Arabia 在沙特阿拉伯红海 Sheybarah 岛发现现代潮间带生物叠层石

Geology Pub Date : 2024-02-15 DOI: 10.1130/g51793.1

Volker Vahrenkamp, V. Chandra, E. Garuglieri, R. Marasco, Kai Hachmann, Pankaj Khanna, Daniele Daffonchio, Alexander Petrovic

{"title":"Discovery of modern living intertidal stromatolites on Sheybarah Island, Red Sea, Saudi Arabia","authors":"Volker Vahrenkamp, V. Chandra, E. Garuglieri, R. Marasco, Kai Hachmann, Pankaj Khanna, Daniele Daffonchio, Alexander Petrovic","doi":"10.1130/g51793.1","DOIUrl":"https://doi.org/10.1130/g51793.1","url":null,"abstract":"Microbial carbonates, and stromatolites in particular, represent the earliest geological record of life on Earth, which dominated the planet as the sole biotic carbonate factory for almost 3 b.y., from the Archean to the late Proterozoic. Rare and sparsely scattered across the globe in the present day, modern “living” stromatolites are typically relegated to extreme environmental niches, remaining as vestiges of a prodigious microbial past. Here, we report the first discovery of living shallow-marine stromatolites in the Middle East, on Sheybarah Island, Al Wajh carbonate platform, on the NE Red Sea shelf (Saudi Arabia). We detail their regional distribution and describe their environmental conditions, internal structures, and microbial diversity. We also report the first discovery of reticulated filaments in a photic setting, associated with these stromatolites. The Sheybarah stromatolites occur in the intertidal to shallow subtidal zones along the seaward-facing beach in three depth-dependent growth forms. Their inner layers were formed by microbially mediated accretion and differential lithification of sediment grains. Compositional microbial analysis revealed the presence of a wide range of microbial life forms.","PeriodicalId":503125,"journal":{"name":"Geology","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2024-02-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139774633","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

Discovery of modern living intertidal stromatolites on Sheybarah Island, Red Sea, Saudi Arabia 在沙特阿拉伯红海 Sheybarah 岛发现现代潮间带生物叠层石

Geology Pub Date : 2024-02-15 DOI: 10.1130/g51793.1

Volker Vahrenkamp, V. Chandra, E. Garuglieri, R. Marasco, Kai Hachmann, Pankaj Khanna, Daniele Daffonchio, Alexander Petrovic

{"title":"Discovery of modern living intertidal stromatolites on Sheybarah Island, Red Sea, Saudi Arabia","authors":"Volker Vahrenkamp, V. Chandra, E. Garuglieri, R. Marasco, Kai Hachmann, Pankaj Khanna, Daniele Daffonchio, Alexander Petrovic","doi":"10.1130/g51793.1","DOIUrl":"https://doi.org/10.1130/g51793.1","url":null,"abstract":"Microbial carbonates, and stromatolites in particular, represent the earliest geological record of life on Earth, which dominated the planet as the sole biotic carbonate factory for almost 3 b.y., from the Archean to the late Proterozoic. Rare and sparsely scattered across the globe in the present day, modern “living” stromatolites are typically relegated to extreme environmental niches, remaining as vestiges of a prodigious microbial past. Here, we report the first discovery of living shallow-marine stromatolites in the Middle East, on Sheybarah Island, Al Wajh carbonate platform, on the NE Red Sea shelf (Saudi Arabia). We detail their regional distribution and describe their environmental conditions, internal structures, and microbial diversity. We also report the first discovery of reticulated filaments in a photic setting, associated with these stromatolites. The Sheybarah stromatolites occur in the intertidal to shallow subtidal zones along the seaward-facing beach in three depth-dependent growth forms. Their inner layers were formed by microbially mediated accretion and differential lithification of sediment grains. Compositional microbial analysis revealed the presence of a wide range of microbial life forms.","PeriodicalId":503125,"journal":{"name":"Geology","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2024-02-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139834394","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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