Lingtong Meng, Y. Chu, Wei Lin, Ross N. Mitchell, Liang Zhao
Establishing the mechanisms for craton modification is critical for understanding cratonic stability and architecture. It is well known that oceanic subduction and mantle plumes can destroy and destabilize the overriding cratonic lithosphere, but the role of continental subduction in craton modification remains unclear. In the North China craton (NCC), which experienced deep continental subduction of the Yangtze block (YB) during the early Mesozoic, we report the presence of the YB crust embedded in the overriding craton. Combining our new results with previous observations, we argue that during 250–220 Ma, a 200-km-long tract of the NCC lithosphere was bulldozed by the subducted YB, resulting in a lithospheric suture far from the suture zone at the surface. This lithospheric removal occurred at middle-lower crustal levels (16–20 km depth)—much shallower than previously thought possible. The bulldozed NCC lithosphere was replenished by the subducted YB continental lithosphere rather than the asthenosphere, thus terminating the lithosphere modification. With essentially no net loss of lithosphere during deep continental subduction, the NCC maintained its stability until Early Cretaceous paleo-Pacific oceanic subduction. This “bulldoze and rebuild” model can thus account for how a craton maintains stability during a collision with another continental plate.
{"title":"Bulldoze and rebuild: Modifying cratonic lithosphere via removal and replacement induced by continental subduction","authors":"Lingtong Meng, Y. Chu, Wei Lin, Ross N. Mitchell, Liang Zhao","doi":"10.1130/g51766.1","DOIUrl":"https://doi.org/10.1130/g51766.1","url":null,"abstract":"Establishing the mechanisms for craton modification is critical for understanding cratonic stability and architecture. It is well known that oceanic subduction and mantle plumes can destroy and destabilize the overriding cratonic lithosphere, but the role of continental subduction in craton modification remains unclear. In the North China craton (NCC), which experienced deep continental subduction of the Yangtze block (YB) during the early Mesozoic, we report the presence of the YB crust embedded in the overriding craton. Combining our new results with previous observations, we argue that during 250–220 Ma, a 200-km-long tract of the NCC lithosphere was bulldozed by the subducted YB, resulting in a lithospheric suture far from the suture zone at the surface. This lithospheric removal occurred at middle-lower crustal levels (16–20 km depth)—much shallower than previously thought possible. The bulldozed NCC lithosphere was replenished by the subducted YB continental lithosphere rather than the asthenosphere, thus terminating the lithosphere modification. With essentially no net loss of lithosphere during deep continental subduction, the NCC maintained its stability until Early Cretaceous paleo-Pacific oceanic subduction. This “bulldoze and rebuild” model can thus account for how a craton maintains stability during a collision with another continental plate.","PeriodicalId":503125,"journal":{"name":"Geology","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2024-02-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139825535","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}
Lingtong Meng, Y. Chu, Wei Lin, Ross N. Mitchell, Liang Zhao
Establishing the mechanisms for craton modification is critical for understanding cratonic stability and architecture. It is well known that oceanic subduction and mantle plumes can destroy and destabilize the overriding cratonic lithosphere, but the role of continental subduction in craton modification remains unclear. In the North China craton (NCC), which experienced deep continental subduction of the Yangtze block (YB) during the early Mesozoic, we report the presence of the YB crust embedded in the overriding craton. Combining our new results with previous observations, we argue that during 250–220 Ma, a 200-km-long tract of the NCC lithosphere was bulldozed by the subducted YB, resulting in a lithospheric suture far from the suture zone at the surface. This lithospheric removal occurred at middle-lower crustal levels (16–20 km depth)—much shallower than previously thought possible. The bulldozed NCC lithosphere was replenished by the subducted YB continental lithosphere rather than the asthenosphere, thus terminating the lithosphere modification. With essentially no net loss of lithosphere during deep continental subduction, the NCC maintained its stability until Early Cretaceous paleo-Pacific oceanic subduction. This “bulldoze and rebuild” model can thus account for how a craton maintains stability during a collision with another continental plate.
{"title":"Bulldoze and rebuild: Modifying cratonic lithosphere via removal and replacement induced by continental subduction","authors":"Lingtong Meng, Y. Chu, Wei Lin, Ross N. Mitchell, Liang Zhao","doi":"10.1130/g51766.1","DOIUrl":"https://doi.org/10.1130/g51766.1","url":null,"abstract":"Establishing the mechanisms for craton modification is critical for understanding cratonic stability and architecture. It is well known that oceanic subduction and mantle plumes can destroy and destabilize the overriding cratonic lithosphere, but the role of continental subduction in craton modification remains unclear. In the North China craton (NCC), which experienced deep continental subduction of the Yangtze block (YB) during the early Mesozoic, we report the presence of the YB crust embedded in the overriding craton. Combining our new results with previous observations, we argue that during 250–220 Ma, a 200-km-long tract of the NCC lithosphere was bulldozed by the subducted YB, resulting in a lithospheric suture far from the suture zone at the surface. This lithospheric removal occurred at middle-lower crustal levels (16–20 km depth)—much shallower than previously thought possible. The bulldozed NCC lithosphere was replenished by the subducted YB continental lithosphere rather than the asthenosphere, thus terminating the lithosphere modification. With essentially no net loss of lithosphere during deep continental subduction, the NCC maintained its stability until Early Cretaceous paleo-Pacific oceanic subduction. This “bulldoze and rebuild” model can thus account for how a craton maintains stability during a collision with another continental plate.","PeriodicalId":503125,"journal":{"name":"Geology","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2024-02-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139885673","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}
Suzanne Autrey-Mulligan, Chloe Bonamici, Michael L. Williams, K.E. Karlstrom, C. Condit
Burial pressures (depths) within mountain belts place fundamental constraints on the growth and stabilization of continental crust. We report precise metamorphic pressures for ca. 1.7 Ga rocks from the Upper Granite Gorge (UGG) of the Grand Canyon (southwestern United States) and, for the first time, resolve pressure variations across this continuous exposure of mid-crustal rocks. We applied quartz-in-garnet (QuiG) barometry and pseudosection modeling to determine pressures in domains (“blocks”) with evidence of higher and lower peak metamorphic grades. New pressure-temperature (P-T) paths constructed using this integrated approach show that a hot block sample reached 7 kbar and a cold block sample never surpassed 5 kbar, revealing an ∼2 kbar P difference between hot and cold blocks and delineating distinct P-T paths for these domains in the UGG. Our findings suggest that hot and cold blocks were likely metamorphosed at different crustal levels within a pre-Yavapai, Paleoproterozoic orogen and were subsequently juxtaposed during and/or after the Yavapai Orogeny at mid-crustal levels. The deformation that produced differential vertical displacement of crustal blocks post-dated peak metamorphism and could reflect extensional collapse of a large orogen and/or renewed folding and thrusting at the Paleoproterozoic Laurentian plate margin.
山带内的埋藏压力（深度）对大陆地壳的生长和稳定具有根本性的制约作用。我们报告了大峡谷上花岗岩峡谷（UGG）约 1.7 Ga 岩石的精确变质压力。我们报告了大峡谷（美国西南部）上花岗岩峡谷（UGG）约 1.7 Ga 岩石的精确变质压力，并首次解析了这一连续出露的地壳中层岩石的压力变化。我们应用石英石榴石（QuiG）气压测量法和假吸力模型来确定具有较高和较低变质峰值的区域（"区块"）的压力。利用这种综合方法构建的新的压力-温度（P-T）路径显示，热块样本的压力达到了7千巴，而冷块样本的压力从未超过5千巴，这揭示了热块和冷块之间的压力差∼2千巴，并为UGG中的这些域划分了不同的P-T路径。我们的研究结果表明，热块和冷块很可能是在前亚瓦派世、古新生代造山运动中的不同地壳层位变质的，随后在亚瓦派造山运动期间和/或之后并置在中地壳层位。造成地壳块体不同垂直位移的变形发生在变质作用高峰期之后，可能反映了大型造山带的延伸塌陷和/或新生代劳伦伦板块边缘的褶皱与推移。
{"title":"Resolving pressure differences within the Grand Canyon Precambrian basement: Implications for Proterozoic tectonics","authors":"Suzanne Autrey-Mulligan, Chloe Bonamici, Michael L. Williams, K.E. Karlstrom, C. Condit","doi":"10.1130/g51706.1","DOIUrl":"https://doi.org/10.1130/g51706.1","url":null,"abstract":"Burial pressures (depths) within mountain belts place fundamental constraints on the growth and stabilization of continental crust. We report precise metamorphic pressures for ca. 1.7 Ga rocks from the Upper Granite Gorge (UGG) of the Grand Canyon (southwestern United States) and, for the first time, resolve pressure variations across this continuous exposure of mid-crustal rocks. We applied quartz-in-garnet (QuiG) barometry and pseudosection modeling to determine pressures in domains (“blocks”) with evidence of higher and lower peak metamorphic grades. New pressure-temperature (P-T) paths constructed using this integrated approach show that a hot block sample reached 7 kbar and a cold block sample never surpassed 5 kbar, revealing an ∼2 kbar P difference between hot and cold blocks and delineating distinct P-T paths for these domains in the UGG. Our findings suggest that hot and cold blocks were likely metamorphosed at different crustal levels within a pre-Yavapai, Paleoproterozoic orogen and were subsequently juxtaposed during and/or after the Yavapai Orogeny at mid-crustal levels. The deformation that produced differential vertical displacement of crustal blocks post-dated peak metamorphism and could reflect extensional collapse of a large orogen and/or renewed folding and thrusting at the Paleoproterozoic Laurentian plate margin.","PeriodicalId":503125,"journal":{"name":"Geology","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2024-01-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139598085","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}
Burgess Shale−type (BST) Lagerstätten record an exceptional variety of Cambrian soft-bodied fauna, yet these deposits are typically restricted to outboard depositional settings >1000 km from the paleocoastline. For shallow, well-oxygenated shelf environments, our knowledge of non-mineralized animals (the majority of diversity) is severely limited, giving rise to substantial bias in our perception of Cambrian biotas. An alternate means of detecting soft-bodied Cambrian fauna, independent of paleobathymetry, is to use acid maceration to extract microscopic organic remains of non-mineralized animals, known as “small carbonaceous fossils” (SCFs). Here, a hitherto unknown diversity of Cambrian arthropod and mollusk remains are reported from shallow-marine sediments (Cambrian Stage 3 Mickwitzia Sandstone, Sweden). These microfossils comprise a variety of arthropod cuticles preserving sub-micron-scale anatomy alongside abundant radular mouthparts from mollusks—among the oldest known arthropod and molluscan SCFs on record. Significantly, at least three distinct types of fossil radula are identifiable (uniseriate, distichous, and polystichous forms), revealing that substantial diversification of the basic molluscan radula had already taken place by the early Cambrian. These cryptic elements of the biota—otherwise undetectable in such deposits—offer novel insights into Cambrian primary consumers as well as aspects of the fauna that are absent from deeper-water BST deposits.
{"title":"Life in the Cambrian shallows: Exceptionally preserved arthropod and mollusk microfossils from the early Cambrian of Sweden","authors":"Ben J. Slater","doi":"10.1130/g51829.1","DOIUrl":"https://doi.org/10.1130/g51829.1","url":null,"abstract":"Burgess Shale−type (BST) Lagerstätten record an exceptional variety of Cambrian soft-bodied fauna, yet these deposits are typically restricted to outboard depositional settings >1000 km from the paleocoastline. For shallow, well-oxygenated shelf environments, our knowledge of non-mineralized animals (the majority of diversity) is severely limited, giving rise to substantial bias in our perception of Cambrian biotas. An alternate means of detecting soft-bodied Cambrian fauna, independent of paleobathymetry, is to use acid maceration to extract microscopic organic remains of non-mineralized animals, known as “small carbonaceous fossils” (SCFs). Here, a hitherto unknown diversity of Cambrian arthropod and mollusk remains are reported from shallow-marine sediments (Cambrian Stage 3 Mickwitzia Sandstone, Sweden). These microfossils comprise a variety of arthropod cuticles preserving sub-micron-scale anatomy alongside abundant radular mouthparts from mollusks—among the oldest known arthropod and molluscan SCFs on record. Significantly, at least three distinct types of fossil radula are identifiable (uniseriate, distichous, and polystichous forms), revealing that substantial diversification of the basic molluscan radula had already taken place by the early Cambrian. These cryptic elements of the biota—otherwise undetectable in such deposits—offer novel insights into Cambrian primary consumers as well as aspects of the fauna that are absent from deeper-water BST deposits.","PeriodicalId":503125,"journal":{"name":"Geology","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2024-01-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139596768","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}
Thomas P. Farrell, Domingo Aerden, E. Baxter, Paul G. Starr, Michael L. Williams
Multiple studies have applied zoned garnet geochronology to place temporal constraints on the rates of metamorphism and deformation during orogenesis. We report new high-resolution isotope dilution−thermal ionization mass spectrometry Sm-Nd isochron ages on concentric growth zones from microstructurally and thermodynamically characterized garnets from the Betic Cordillera, southern Spain. Our ages for the garnet core (13.64 ± 0.31 Ma), mantle (13.41 ± 0.37 Ma), and rim (13.34 ± 0.45 Ma) indicate rapid garnet growth and are consistent with published garnet ages interpreted to reflect high-pressure metamorphism in the region. Thermodynamic analysis indicates garnets grew during subduction at ∼1.5−2.0 GPa and 570−600 °C. The core to rim duration of spiral garnet growth was just a few hundred thousand years. While other zoned garnet studies have shown similar rapid growth in subduction zone settings, this is the first documentation of such rapid growth of a spiral garnet. Combining this garnet growth duration with the magnitude of spiral inclusion trail curvature, we compute a strain rate of ∼10−13 s−1, an order of magnitude faster than all previous spiral garnet studies. We interpret that these spiral garnets recorded a rapid pulse of deformation and strain during the final stages of subduction and incipient exhumation.
{"title":"Rapid development of spiral garnets during subduction zone metamorphism revealed from high-resolution Sm-Nd garnet geochronology","authors":"Thomas P. Farrell, Domingo Aerden, E. Baxter, Paul G. Starr, Michael L. Williams","doi":"10.1130/g51882.1","DOIUrl":"https://doi.org/10.1130/g51882.1","url":null,"abstract":"Multiple studies have applied zoned garnet geochronology to place temporal constraints on the rates of metamorphism and deformation during orogenesis. We report new high-resolution isotope dilution−thermal ionization mass spectrometry Sm-Nd isochron ages on concentric growth zones from microstructurally and thermodynamically characterized garnets from the Betic Cordillera, southern Spain. Our ages for the garnet core (13.64 ± 0.31 Ma), mantle (13.41 ± 0.37 Ma), and rim (13.34 ± 0.45 Ma) indicate rapid garnet growth and are consistent with published garnet ages interpreted to reflect high-pressure metamorphism in the region. Thermodynamic analysis indicates garnets grew during subduction at ∼1.5−2.0 GPa and 570−600 °C. The core to rim duration of spiral garnet growth was just a few hundred thousand years. While other zoned garnet studies have shown similar rapid growth in subduction zone settings, this is the first documentation of such rapid growth of a spiral garnet. Combining this garnet growth duration with the magnitude of spiral inclusion trail curvature, we compute a strain rate of ∼10−13 s−1, an order of magnitude faster than all previous spiral garnet studies. We interpret that these spiral garnets recorded a rapid pulse of deformation and strain during the final stages of subduction and incipient exhumation.","PeriodicalId":503125,"journal":{"name":"Geology","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2024-01-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139598442","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}
Vann Smith, Angela Hessler, Lorena Moscardelli, David Bord, Iulia Olariu, Maria Antonieta Lorente, Evan Sivil, Xiuju Liu
We report a new ecological refugium for the Cheirolepidiaceae family (pollen form genus Classopollis) in the Paleocene Lower Wilcox Group in the Gulf Coast of southeastern Texas based on palynological analysis of four wells. The Cheirolepidiaceae were once thought to have gone extinct at the Cretaceous−Paleogene (K/Pg) boundary or earlier in North America; however, similar ecological refugia for this family in the Paleocene have previously been reported in China, Argentina, and potentially the Rocky Mountains of the United States. The highest relative abundances of Classopollis pollen were found in delta front, lagoon, and shoreface depositional paleoenvironments marked by high mud-fraction Sr/Ba (a geochemical proxy for salinity), and abundances generally increased down section in older Paleocene strata. The high relative abundance of Classopollis pollen in the well samples, the rarity of reworked Mesozoic palynomorphs, the generally good preservation of Classopollis pollen, and the similarity of Classopollis fluorescence spectra to other in situ Paleocene pollen all provide strong evidence for the survival of the Cheirolepidiaceae family in the coastal salt marshes of Texas through at least the late Paleocene.
{"title":"A late refugium for Classopollis in the Paleocene Lower Wilcox Group along the Texas Gulf Coast","authors":"Vann Smith, Angela Hessler, Lorena Moscardelli, David Bord, Iulia Olariu, Maria Antonieta Lorente, Evan Sivil, Xiuju Liu","doi":"10.1130/g51772.1","DOIUrl":"https://doi.org/10.1130/g51772.1","url":null,"abstract":"We report a new ecological refugium for the Cheirolepidiaceae family (pollen form genus Classopollis) in the Paleocene Lower Wilcox Group in the Gulf Coast of southeastern Texas based on palynological analysis of four wells. The Cheirolepidiaceae were once thought to have gone extinct at the Cretaceous−Paleogene (K/Pg) boundary or earlier in North America; however, similar ecological refugia for this family in the Paleocene have previously been reported in China, Argentina, and potentially the Rocky Mountains of the United States. The highest relative abundances of Classopollis pollen were found in delta front, lagoon, and shoreface depositional paleoenvironments marked by high mud-fraction Sr/Ba (a geochemical proxy for salinity), and abundances generally increased down section in older Paleocene strata. The high relative abundance of Classopollis pollen in the well samples, the rarity of reworked Mesozoic palynomorphs, the generally good preservation of Classopollis pollen, and the similarity of Classopollis fluorescence spectra to other in situ Paleocene pollen all provide strong evidence for the survival of the Cheirolepidiaceae family in the coastal salt marshes of Texas through at least the late Paleocene.","PeriodicalId":503125,"journal":{"name":"Geology","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2024-01-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139608811","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}
Rare earth elements are critical constituents for modern technologies, and some of their largest natural resource deposits are related to carbonatite systems. However, the mechanisms leading to rare earth element mineralization and the role of magmatic fluids in carbonatite systems remain poorly understood. Here, we present the first in situ characterization of fluids and their trace-element compositions in natural carbonatite systems by studying secondary quartz-hosted fluid inclusions from Oldoinyo Lengai volcano. By comparing our data to other fluids and melts from various carbonatite systems, we constructed a model for fluid-mediated rare earth element transport and mineralization. We show that carbonatite-related fluids are rich in alkali-carbonate + sulfate + chloride and CO2, but poor in H2O, and they can be significant carriers of rare earth elements (>1600 ppm). We argue that fluid CO2 contents are essential to preclude or slow down the interaction with wall rock during migration and that fluid-mediated rare earth element mineralization occurs when partial pressure of CO2 decreases in the fluid (i.e., during degassing).
{"title":"Rare earth element transport and mineralization linked to fluids from carbonatite systems","authors":"Emanuel Mororó, M. Berkesi, Z. Zajacz, T. Guzmics","doi":"10.1130/g51531.1","DOIUrl":"https://doi.org/10.1130/g51531.1","url":null,"abstract":"Rare earth elements are critical constituents for modern technologies, and some of their largest natural resource deposits are related to carbonatite systems. However, the mechanisms leading to rare earth element mineralization and the role of magmatic fluids in carbonatite systems remain poorly understood. Here, we present the first in situ characterization of fluids and their trace-element compositions in natural carbonatite systems by studying secondary quartz-hosted fluid inclusions from Oldoinyo Lengai volcano. By comparing our data to other fluids and melts from various carbonatite systems, we constructed a model for fluid-mediated rare earth element transport and mineralization. We show that carbonatite-related fluids are rich in alkali-carbonate + sulfate + chloride and CO2, but poor in H2O, and they can be significant carriers of rare earth elements (>1600 ppm). We argue that fluid CO2 contents are essential to preclude or slow down the interaction with wall rock during migration and that fluid-mediated rare earth element mineralization occurs when partial pressure of CO2 decreases in the fluid (i.e., during degassing).","PeriodicalId":503125,"journal":{"name":"Geology","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2024-01-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139613459","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}
Constraining the magma supply to a subvolcanic reservoir is crucial to characterizing unrest and evaluating the potential for a forthcoming eruption. With the advent of GPS, tiltmeters, and satellite interferometry, it has been possible to infer changes in the supply rate of magma to shallow reservoirs over time scales of as much as decades. While these methods have impacted our ability to characterize volcanic unrest, they only probe magmatic activity over short time scales. Here, we constrain changes in magma supply rate at Sakurajima volcano (Kyushu, Japan) over the past five centuries. The combination of thermo-mechanical modeling, documented eruption history, and textural analyses of pumices allows us to tightly constrain the long-term rate of magma supply to the subvolcanic chamber through time. Specifically, we find that magma supply rate has increased by roughly an order of magnitude over the past 500 years and that the bubble content in the magma chamber has increased over time, explaining the changes in eruption volume between the Bunmei (ca. A.D. 1470), An-ei (ca. A.D. 1780), and Taisho (A.D. 1914) eruptions.
{"title":"Increase in magma supply to Sakurajima volcano’s (Japan) shallow magma chamber over the past 500 years","authors":"Christian Huber, Atsushi Toramaru","doi":"10.1130/g51763.1","DOIUrl":"https://doi.org/10.1130/g51763.1","url":null,"abstract":"Constraining the magma supply to a subvolcanic reservoir is crucial to characterizing unrest and evaluating the potential for a forthcoming eruption. With the advent of GPS, tiltmeters, and satellite interferometry, it has been possible to infer changes in the supply rate of magma to shallow reservoirs over time scales of as much as decades. While these methods have impacted our ability to characterize volcanic unrest, they only probe magmatic activity over short time scales. Here, we constrain changes in magma supply rate at Sakurajima volcano (Kyushu, Japan) over the past five centuries. The combination of thermo-mechanical modeling, documented eruption history, and textural analyses of pumices allows us to tightly constrain the long-term rate of magma supply to the subvolcanic chamber through time. Specifically, we find that magma supply rate has increased by roughly an order of magnitude over the past 500 years and that the bubble content in the magma chamber has increased over time, explaining the changes in eruption volume between the Bunmei (ca. A.D. 1470), An-ei (ca. A.D. 1780), and Taisho (A.D. 1914) eruptions.","PeriodicalId":503125,"journal":{"name":"Geology","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2024-01-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139615517","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}
Youseph Ibrahim, Patrice F. Rey, D. Whitney, C. Teyssier, Françoise Roger, Valérie Bosse, Bénédicte Cenki
In central Australia, an apparently coeval gneiss dome (Entia Dome) developed adjacent to a thrust belt (Arltunga Nappe Complex) within an intracratonic setting. Here we employ a combination of fieldwork, geochronology, and numerical modeling to investigate the structure and tectonic evolution of these features. We present a structural model linking an extensional domain comprising the Entia Dome, across a transitional zone containing the Bruna décollement zone and the Illogwa shear zone, into a contractional zone comprising thrusts and duplexes of the Arltunga Nappe Complex. Supported by numerical modeling, we propose a tectonic model in which the dome and nappe complex formed synchronously because of the convergent gravitational collapse of the 30−40-km-deep Paleozoic Harts Range rift.
{"title":"From dome to duplex: Convergent gravitational collapse explains coeval intracratonic doming and nappe tectonics, central Australia","authors":"Youseph Ibrahim, Patrice F. Rey, D. Whitney, C. Teyssier, Françoise Roger, Valérie Bosse, Bénédicte Cenki","doi":"10.1130/g51721.1","DOIUrl":"https://doi.org/10.1130/g51721.1","url":null,"abstract":"In central Australia, an apparently coeval gneiss dome (Entia Dome) developed adjacent to a thrust belt (Arltunga Nappe Complex) within an intracratonic setting. Here we employ a combination of fieldwork, geochronology, and numerical modeling to investigate the structure and tectonic evolution of these features. We present a structural model linking an extensional domain comprising the Entia Dome, across a transitional zone containing the Bruna décollement zone and the Illogwa shear zone, into a contractional zone comprising thrusts and duplexes of the Arltunga Nappe Complex. Supported by numerical modeling, we propose a tectonic model in which the dome and nappe complex formed synchronously because of the convergent gravitational collapse of the 30−40-km-deep Paleozoic Harts Range rift.","PeriodicalId":503125,"journal":{"name":"Geology","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2024-01-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139620206","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}
Liang Qi, Mingcai Hou, Jacob A. Mulder, Peter A. Cawood, Yao Guo, Shitou Wu, Liangxuan Jiao, Xiaolin Zhang, Ouyang Hui
Direct dating of vertebrate fossils is difficult due to complex postburial diagenetic processes and the often low and heterogeneous concentration of radioisotopes (e.g., U) in fossilized bone material. Here, we demonstrate a novel approach to dating vertebrate fossils via laser ablation−inductively coupled plasma−mass spectrometry U-Pb dating of early diagenetic calcite cements precipitated within bone cavities of a Jurassic sauropod from the Sichuan Basin, South China. Early diagenetic calcite yielded a U-Pb age of 165.3 ± 3.6/5.6 Ma, in agreement with a maximum depositional age of 165.8 ± 1.0 Ma from detrital zircon ages of the surrounding rocks, suggesting that diagenesis occurred shortly after the death of the sauropod. This new age demonstrates that the best-known Jurassic large sauropod faunas in South China are much older than those in North America and Africa, suggesting the geographical isolation of South China. Authigenic apatite U-Pb dating on the fibrolamellar bones from the same sauropod gave a distinctly younger age, indicating more complex U-Pb system behavior, possibly due to U uptake by residual organic matter and recrystallization of apatite after early diagenesis. Our findings demonstrate that U-Pb dating of calcite cements within bone cavities has significant potential for constraining the burial age of vertebrate fossils, which could aid in constructing a more robust temporal framework for the radiation and evolution of vertebrates.
{"title":"In situ U-Pb dating of Jurassic dinosaur bones from Sichuan Basin, South China","authors":"Liang Qi, Mingcai Hou, Jacob A. Mulder, Peter A. Cawood, Yao Guo, Shitou Wu, Liangxuan Jiao, Xiaolin Zhang, Ouyang Hui","doi":"10.1130/g51872.1","DOIUrl":"https://doi.org/10.1130/g51872.1","url":null,"abstract":"Direct dating of vertebrate fossils is difficult due to complex postburial diagenetic processes and the often low and heterogeneous concentration of radioisotopes (e.g., U) in fossilized bone material. Here, we demonstrate a novel approach to dating vertebrate fossils via laser ablation−inductively coupled plasma−mass spectrometry U-Pb dating of early diagenetic calcite cements precipitated within bone cavities of a Jurassic sauropod from the Sichuan Basin, South China. Early diagenetic calcite yielded a U-Pb age of 165.3 ± 3.6/5.6 Ma, in agreement with a maximum depositional age of 165.8 ± 1.0 Ma from detrital zircon ages of the surrounding rocks, suggesting that diagenesis occurred shortly after the death of the sauropod. This new age demonstrates that the best-known Jurassic large sauropod faunas in South China are much older than those in North America and Africa, suggesting the geographical isolation of South China. Authigenic apatite U-Pb dating on the fibrolamellar bones from the same sauropod gave a distinctly younger age, indicating more complex U-Pb system behavior, possibly due to U uptake by residual organic matter and recrystallization of apatite after early diagenesis. Our findings demonstrate that U-Pb dating of calcite cements within bone cavities has significant potential for constraining the burial age of vertebrate fossils, which could aid in constructing a more robust temporal framework for the radiation and evolution of vertebrates.","PeriodicalId":503125,"journal":{"name":"Geology","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2024-01-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139619434","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}
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