Jonathan Obrist-Farner, Jeremy Maurer, Derek Gibson, Trenton McEnaney, Andreas Eckert, William F. Kenney, Jeffery Beeson, Nigel Wattrus, Quin Stangeland, Fatima Reyes
On 4 February 1976, a Mw 7.5 earthquake along the Motagua fault, Guatemala, ruptured ∼230 km of the North American and Caribbean plate boundary. Today, the plate boundary remains poorly monitored, and the 1976 earthquake is still not fully understood. Here, we present seismic reflection profiles and radiometrically dated sediment core data from six lakes around the Motagua fault, together with reports of destruction and a quasi-dynamic rupture model, which show that the 1976 earthquake experienced strong directivity that impacted the distribution of shaking. The earthquake left behind a detailed record of event deposits (EDs) in five of the six study lakes. Thicker EDs are present in Lake Atitlán, near the terminus of the earthquake rupture, whereas thinner EDs were found in lakes off-axis of the rupture direction. We argue that EDs can be utilized to constrain asymmetrical distribution of shaking during earthquakes and that paleoseismic studies should consider directivity as a factor controlling the thickness of EDs.
{"title":"Paleoseismic evidence of directivity for the 1976 Mw 7.5 Motagua earthquake, Guatemala","authors":"Jonathan Obrist-Farner, Jeremy Maurer, Derek Gibson, Trenton McEnaney, Andreas Eckert, William F. Kenney, Jeffery Beeson, Nigel Wattrus, Quin Stangeland, Fatima Reyes","doi":"10.1130/g53449.1","DOIUrl":"https://doi.org/10.1130/g53449.1","url":null,"abstract":"On 4 February 1976, a Mw 7.5 earthquake along the Motagua fault, Guatemala, ruptured ∼230 km of the North American and Caribbean plate boundary. Today, the plate boundary remains poorly monitored, and the 1976 earthquake is still not fully understood. Here, we present seismic reflection profiles and radiometrically dated sediment core data from six lakes around the Motagua fault, together with reports of destruction and a quasi-dynamic rupture model, which show that the 1976 earthquake experienced strong directivity that impacted the distribution of shaking. The earthquake left behind a detailed record of event deposits (EDs) in five of the six study lakes. Thicker EDs are present in Lake Atitlán, near the terminus of the earthquake rupture, whereas thinner EDs were found in lakes off-axis of the rupture direction. We argue that EDs can be utilized to constrain asymmetrical distribution of shaking during earthquakes and that paleoseismic studies should consider directivity as a factor controlling the thickness of EDs.","PeriodicalId":12642,"journal":{"name":"Geology","volume":"12 1","pages":""},"PeriodicalIF":5.8,"publicationDate":"2025-09-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145035560","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}
Oskar Schramm, Patrick J. Frings, Tommaso di Rocco, Andreas Pack, Michael Tatzel
Sedimentary cherts form from amorphous silica precursors that progressively crystallize into opal-CT and quartz during burial diagenesis. Recent studies have shown that the transformation kinetics of the silica polymorphs strongly depend on the prograde thermal history, suggesting a key role of basal heat flow in setting the 18O/16O and 17O/16O 18O/16O oxygen isotope ratios in chert (δ18Ochert, Δ′17Ochert). To investigate the relationship between paleo−heat flow and chert oxygen isotopes, we used Cretaceous to Neogene cherts that formed in the large igneous province Shatsky Rise in the western Pacific Ocean and a compilation of marine chert oxygen isotope ratios from previous studies. Using a reaction-advection-diffusion model, we demonstrate that the relationship between δ18Ochert, Δ′17Ochert, and the age of the underlying crust results from declining heat flow through sediment as the oceanic crust cools. Our reconstruction of heat flow at Shatsky Rise aligns with established geothermal background values. We propose that the Archean chert record indicates a diagenetic environment dominated by high heat flow that transitioned on billion-year time scales toward conditions resembling modern diagenesis.
{"title":"Oxygen isotopes in cherts record paleo−heat flow on Shatsky Rise (western Pacific Ocean)","authors":"Oskar Schramm, Patrick J. Frings, Tommaso di Rocco, Andreas Pack, Michael Tatzel","doi":"10.1130/g53296.1","DOIUrl":"https://doi.org/10.1130/g53296.1","url":null,"abstract":"Sedimentary cherts form from amorphous silica precursors that progressively crystallize into opal-CT and quartz during burial diagenesis. Recent studies have shown that the transformation kinetics of the silica polymorphs strongly depend on the prograde thermal history, suggesting a key role of basal heat flow in setting the 18O/16O and 17O/16O 18O/16O oxygen isotope ratios in chert (δ18Ochert, Δ′17Ochert). To investigate the relationship between paleo−heat flow and chert oxygen isotopes, we used Cretaceous to Neogene cherts that formed in the large igneous province Shatsky Rise in the western Pacific Ocean and a compilation of marine chert oxygen isotope ratios from previous studies. Using a reaction-advection-diffusion model, we demonstrate that the relationship between δ18Ochert, Δ′17Ochert, and the age of the underlying crust results from declining heat flow through sediment as the oceanic crust cools. Our reconstruction of heat flow at Shatsky Rise aligns with established geothermal background values. We propose that the Archean chert record indicates a diagenetic environment dominated by high heat flow that transitioned on billion-year time scales toward conditions resembling modern diagenesis.","PeriodicalId":12642,"journal":{"name":"Geology","volume":"35 1","pages":""},"PeriodicalIF":5.8,"publicationDate":"2025-09-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145017899","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}
Sheree E. Armistead, Bruce M. Eglington, Sally J. Pehrsson, David L. Huston
Understanding Earth’s early crustal architecture is critical to reconstructing the planet’s geodynamic evolution. We present a global analysis of ∼25,000 Pb isotope analyses from ore deposits, focusing on Archean cratons to investigate lithospheric evolution and continental configurations. Spatial patterns in model age and source µ (238U/204Pb) reveal isotopic domains that align with proposed Archean supercratons. Low µ values are characteristic of cratons interpreted to belong to the ca. 2.6 Ga Superia supercraton (e.g., Superior [Canada], Kaapvaal [southern Africa], and Hearne [Canada] cratons), whereas moderate to high µ values are typical of cratons associated with the contemporaneous Sclavia supercraton (e.g., Slave [Canada], Yilgarn [Australia], Dharwar [India], and Zimbabwe [southern Africa] cratons). These long-lived terrane-scale signatures suggest Pb isotopes can resolve lithospheric domains preserved across multiple cratons. Our results offer new geochemical constraints on Archean continental assembly and highlight the utility of ore-deposit Pb isotope data for testing early Earth plate configurations.
{"title":"Archean geodynamics and plate tectonics linked to Pb isotope variability","authors":"Sheree E. Armistead, Bruce M. Eglington, Sally J. Pehrsson, David L. Huston","doi":"10.1130/g53553.1","DOIUrl":"https://doi.org/10.1130/g53553.1","url":null,"abstract":"Understanding Earth’s early crustal architecture is critical to reconstructing the planet’s geodynamic evolution. We present a global analysis of ∼25,000 Pb isotope analyses from ore deposits, focusing on Archean cratons to investigate lithospheric evolution and continental configurations. Spatial patterns in model age and source µ (238U/204Pb) reveal isotopic domains that align with proposed Archean supercratons. Low µ values are characteristic of cratons interpreted to belong to the ca. 2.6 Ga Superia supercraton (e.g., Superior [Canada], Kaapvaal [southern Africa], and Hearne [Canada] cratons), whereas moderate to high µ values are typical of cratons associated with the contemporaneous Sclavia supercraton (e.g., Slave [Canada], Yilgarn [Australia], Dharwar [India], and Zimbabwe [southern Africa] cratons). These long-lived terrane-scale signatures suggest Pb isotopes can resolve lithospheric domains preserved across multiple cratons. Our results offer new geochemical constraints on Archean continental assembly and highlight the utility of ore-deposit Pb isotope data for testing early Earth plate configurations.","PeriodicalId":12642,"journal":{"name":"Geology","volume":"130 1","pages":""},"PeriodicalIF":5.8,"publicationDate":"2025-09-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145017900","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}
Zongqi Zou, Yi-Gang Xu, Zaicong Wang, Yu Wang, Ming Li, Meiling Wang, Yutian Lei
The low-velocity zone (LVZ) in shallow asthenosphere is crucial for Earth’s geodynamics and is widely linked to the presence of partial melts. Incipient melts from mantle peridotite melting are highly mobile and tend to quickly escape from their sources; however, it remains enigmatic how the LVZ can extend to the depths where partial melting initiates. Here, we identify a suite of primitive low-MgO basalts derived from an eclogitized oceanic crust at ∼200 km within the LVZ, providing a compelling scenario for the LVZ formation. These primitive basalts exhibit significantly heavier Fe isotopes and lighter Ca-Mo-O isotopes compared to mid-ocean-ridge basalts, indicating that they originated from eclogitized oceanic crust rather than peridotite. This highlights the fact that oceanic crust recycled into the mantle can melt to form primitive Mg-poor and Si-rich melts. Given their relatively high density and viscosity, these melts show low-mobility and accumulate at depths of ∼150−200 km, forming a low-velocity layer within the asthenosphere.
{"title":"Melting of eclogitic oceanic crust for the low-velocity zone within Earth’s upper asthenosphere","authors":"Zongqi Zou, Yi-Gang Xu, Zaicong Wang, Yu Wang, Ming Li, Meiling Wang, Yutian Lei","doi":"10.1130/g53540.1","DOIUrl":"https://doi.org/10.1130/g53540.1","url":null,"abstract":"The low-velocity zone (LVZ) in shallow asthenosphere is crucial for Earth’s geodynamics and is widely linked to the presence of partial melts. Incipient melts from mantle peridotite melting are highly mobile and tend to quickly escape from their sources; however, it remains enigmatic how the LVZ can extend to the depths where partial melting initiates. Here, we identify a suite of primitive low-MgO basalts derived from an eclogitized oceanic crust at ∼200 km within the LVZ, providing a compelling scenario for the LVZ formation. These primitive basalts exhibit significantly heavier Fe isotopes and lighter Ca-Mo-O isotopes compared to mid-ocean-ridge basalts, indicating that they originated from eclogitized oceanic crust rather than peridotite. This highlights the fact that oceanic crust recycled into the mantle can melt to form primitive Mg-poor and Si-rich melts. Given their relatively high density and viscosity, these melts show low-mobility and accumulate at depths of ∼150−200 km, forming a low-velocity layer within the asthenosphere.","PeriodicalId":12642,"journal":{"name":"Geology","volume":"24 1","pages":""},"PeriodicalIF":5.8,"publicationDate":"2025-09-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145003072","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}
Elizabeth J. Trower, Miquela Ingalls, James R. Gutoski, Virginia T. Wala
Although it is difficult to reconstruct Earth surface temperatures during Neoproterozoic time, sedimentological and paleomagnetic evidence demonstrate a dynamic climate, featuring two global “Snowball Earth” glaciations. The recent observation of petrographic fingerprints of ikaite, a mineral that typically forms in near-freezing sedimentary environments, in late Tonian strata was interpreted as evidence that low-latitude shallow marine environments were cold millions of years prior to the Cryogenian Period. Meanwhile, other recent work has demonstrated that elevated phosphate concentration ([DIP]) can inhibit calcite nucleation (perhaps enabling ikaite to form and persist at warmer temperatures) and that late Tonian carbonates formed in phosphate-rich seawater. So, was late Tonian seawater cold, or was it phosphate-rich? To address this question, we combined measurements of carbonate-associated phosphate and ooid-size-based pH constraints to reconstruct seawater [DIP] values for one snapshot of time in the late Tonian Period. Our seawater [DIP] estimates range from 3.8 µM to 7.8 µM, substantially elevated relative to modern shallow seawater and consistent with inferences from previous approaches. Our estimates are below values at which calcite nucleation inhibition has been observed, suggesting that elevated phosphate is an insufficient explanation for the ikaite forming in warm conditions and supporting the hypothesis that late Tonian climate was cool.
{"title":"New constraints on phosphate concentration and temperature in shallow late Tonian seawater","authors":"Elizabeth J. Trower, Miquela Ingalls, James R. Gutoski, Virginia T. Wala","doi":"10.1130/g53532.1","DOIUrl":"https://doi.org/10.1130/g53532.1","url":null,"abstract":"Although it is difficult to reconstruct Earth surface temperatures during Neoproterozoic time, sedimentological and paleomagnetic evidence demonstrate a dynamic climate, featuring two global “Snowball Earth” glaciations. The recent observation of petrographic fingerprints of ikaite, a mineral that typically forms in near-freezing sedimentary environments, in late Tonian strata was interpreted as evidence that low-latitude shallow marine environments were cold millions of years prior to the Cryogenian Period. Meanwhile, other recent work has demonstrated that elevated phosphate concentration ([DIP]) can inhibit calcite nucleation (perhaps enabling ikaite to form and persist at warmer temperatures) and that late Tonian carbonates formed in phosphate-rich seawater. So, was late Tonian seawater cold, or was it phosphate-rich? To address this question, we combined measurements of carbonate-associated phosphate and ooid-size-based pH constraints to reconstruct seawater [DIP] values for one snapshot of time in the late Tonian Period. Our seawater [DIP] estimates range from 3.8 µM to 7.8 µM, substantially elevated relative to modern shallow seawater and consistent with inferences from previous approaches. Our estimates are below values at which calcite nucleation inhibition has been observed, suggesting that elevated phosphate is an insufficient explanation for the ikaite forming in warm conditions and supporting the hypothesis that late Tonian climate was cool.","PeriodicalId":12642,"journal":{"name":"Geology","volume":"33 1","pages":""},"PeriodicalIF":5.8,"publicationDate":"2025-09-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145003073","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}
Trishit Ruj, Hanaya Okuda, Goro Komatsu, Hitoshi Hasegawa, James W. Head, Tomohiro Usui, Shun Mihira, Makito Kobayashi
Subsurface ice in the mid-latitudes of Mars represents one of the largest present-day water ice reservoirs. While atmospheric models predict Late Amazonian (during the past hundreds of millions of years) obliquity-driven ice accumulation, its long-term variations, and the factors influencing accumulation remain unclear. Using geomorphological evidence and numerical modeling, we reveal a southwestern depositional trend within northern mid-latitudinal crater walls and floors. Detailed crater-fill deposit analyses indicate multiple glaciation stages, including an earlier, high-intensity stage followed by a later, lower-intensity stage, both exhibiting this southwestern trend (ca. 640−98 Ma). We conclude that persistent multiple-stage Amazonian glaciations were governed by atmospheric water availability and obliquity-driven climate cycles.
{"title":"Long-term and multi-stage ice accumulation in the martian mid-latitudes during the Amazonian","authors":"Trishit Ruj, Hanaya Okuda, Goro Komatsu, Hitoshi Hasegawa, James W. Head, Tomohiro Usui, Shun Mihira, Makito Kobayashi","doi":"10.1130/g53418.1","DOIUrl":"https://doi.org/10.1130/g53418.1","url":null,"abstract":"Subsurface ice in the mid-latitudes of Mars represents one of the largest present-day water ice reservoirs. While atmospheric models predict Late Amazonian (during the past hundreds of millions of years) obliquity-driven ice accumulation, its long-term variations, and the factors influencing accumulation remain unclear. Using geomorphological evidence and numerical modeling, we reveal a southwestern depositional trend within northern mid-latitudinal crater walls and floors. Detailed crater-fill deposit analyses indicate multiple glaciation stages, including an earlier, high-intensity stage followed by a later, lower-intensity stage, both exhibiting this southwestern trend (ca. 640−98 Ma). We conclude that persistent multiple-stage Amazonian glaciations were governed by atmospheric water availability and obliquity-driven climate cycles.","PeriodicalId":12642,"journal":{"name":"Geology","volume":"63 1","pages":""},"PeriodicalIF":5.8,"publicationDate":"2025-09-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144931026","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}
Cody L. Colleps, Peter van der Beek, Julien Amalberti, Edward R. Sobel, Marissa M. Tremblay, Maxime Bernard
Apatite 4He/3He thermochronology has the potential to provide high-resolution low-temperature thermal histories that bring valuable insight into near-surface crustal processes. However, this system has yet to be directly evaluated using single-grain 4He/3He analyses from a natural sample with an established thermal history. We present apatite 4He/3He spectra from the widely used Fish Canyon Tuff (FCT) age standard (San Juan volcanic field, southern Colorado, USA), collected at two localities with contrasting thermal histories: (1) a distal locality (FCT-D) where the early Oligocene eruptive age of the FCT is preserved in the apatite (U-Th)/He (AHe) system and the thermal history is well established; and (2) the classic FCT sampling locality (FCT-C) with younger, Early Miocene AHe dates and an unconstrained posteruptive thermal history. FCT-D apatite shows 4He/3He spectra indicative of no diffusive loss, with relative edge depletion of 4He induced by alpha ejection only, corroborating rapid eruptive cooling. In contrast, FCT-C apatite revealed notably diffusive 4He/3He spectra. Thermal-history inversions highlight the resolving power of apatite 4He/3He thermochronology, demonstrating its ability to (1) independently resolve rapid eruptive cooling at the FCT-D site, and (2) improve the resolution of postemplacement reheating and Early Miocene cooling at the FCT-C site. Refined FCT-C thermal histories reveal a distinctive onset of moderate cooling at ca. 20−19 Ma, likely reflecting footwall topographic development coinciding with regional Rio Grande rifting. This collective assessment of 4He/3He systematics further verifies its ability to substantially improve thermal history resolution, which is crucial to elucidating mechanisms driving crustal cooling.
{"title":"Evaluating the resolving power of apatite 4He/3He thermochronology: Insights from the Fish Canyon Tuff","authors":"Cody L. Colleps, Peter van der Beek, Julien Amalberti, Edward R. Sobel, Marissa M. Tremblay, Maxime Bernard","doi":"10.1130/g53000.1","DOIUrl":"https://doi.org/10.1130/g53000.1","url":null,"abstract":"Apatite 4He/3He thermochronology has the potential to provide high-resolution low-temperature thermal histories that bring valuable insight into near-surface crustal processes. However, this system has yet to be directly evaluated using single-grain 4He/3He analyses from a natural sample with an established thermal history. We present apatite 4He/3He spectra from the widely used Fish Canyon Tuff (FCT) age standard (San Juan volcanic field, southern Colorado, USA), collected at two localities with contrasting thermal histories: (1) a distal locality (FCT-D) where the early Oligocene eruptive age of the FCT is preserved in the apatite (U-Th)/He (AHe) system and the thermal history is well established; and (2) the classic FCT sampling locality (FCT-C) with younger, Early Miocene AHe dates and an unconstrained posteruptive thermal history. FCT-D apatite shows 4He/3He spectra indicative of no diffusive loss, with relative edge depletion of 4He induced by alpha ejection only, corroborating rapid eruptive cooling. In contrast, FCT-C apatite revealed notably diffusive 4He/3He spectra. Thermal-history inversions highlight the resolving power of apatite 4He/3He thermochronology, demonstrating its ability to (1) independently resolve rapid eruptive cooling at the FCT-D site, and (2) improve the resolution of postemplacement reheating and Early Miocene cooling at the FCT-C site. Refined FCT-C thermal histories reveal a distinctive onset of moderate cooling at ca. 20−19 Ma, likely reflecting footwall topographic development coinciding with regional Rio Grande rifting. This collective assessment of 4He/3He systematics further verifies its ability to substantially improve thermal history resolution, which is crucial to elucidating mechanisms driving crustal cooling.","PeriodicalId":12642,"journal":{"name":"Geology","volume":"10 1","pages":""},"PeriodicalIF":5.8,"publicationDate":"2025-08-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144919587","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}
Yanzhe Fu, Chong Dong, Dolev Fabrikant, Chenyang Cai, Carolin Haug, Joachim T. Haug, Diying Huang
Animals have evolved diverse defensive strategies under selective pressures, with mimicry being a crucial survival strategy for insects. Leaf mimicry is widespread in modern ecosystems, yet its fossil record remains sparse, often lacking direct evidence of target plant or clear morphological adaptations. We report three novel cases of leaf mimicry in Jurassic orthopterans (grasshoppers and crickets, including katydids) (Prophalangopsidae) from the Daohugou biota (ca. 163.5 Ma, northeastern China), in which the forewings exhibit highly specialized contrasting color patterns that closely resemble the abundantly co-occurring bennettitalean (extinct seed-bearing, cycad-like group) leaves. These cases provide the first unambiguous evidence in which both the mimicking insects and their plant models are preserved in the same bedding plane. It represents the first known instance of orthopteran mimicry in the Jurassic, fills a gap in the fossil record, and suggests that leaf mimicry has been a long-standing adaptive strategy in Orthoptera, independently evolving across different lineages throughout geological history. This finding highlights the dynamic interplay between plant community succession, predation pressures, and insect defensive strategies, expanding our understanding of the ecological significance and evolution of leaf mimicry in orthopterans.
{"title":"Unique leaf mimicry in Jurassic insects","authors":"Yanzhe Fu, Chong Dong, Dolev Fabrikant, Chenyang Cai, Carolin Haug, Joachim T. Haug, Diying Huang","doi":"10.1130/g53399.1","DOIUrl":"https://doi.org/10.1130/g53399.1","url":null,"abstract":"Animals have evolved diverse defensive strategies under selective pressures, with mimicry being a crucial survival strategy for insects. Leaf mimicry is widespread in modern ecosystems, yet its fossil record remains sparse, often lacking direct evidence of target plant or clear morphological adaptations. We report three novel cases of leaf mimicry in Jurassic orthopterans (grasshoppers and crickets, including katydids) (Prophalangopsidae) from the Daohugou biota (ca. 163.5 Ma, northeastern China), in which the forewings exhibit highly specialized contrasting color patterns that closely resemble the abundantly co-occurring bennettitalean (extinct seed-bearing, cycad-like group) leaves. These cases provide the first unambiguous evidence in which both the mimicking insects and their plant models are preserved in the same bedding plane. It represents the first known instance of orthopteran mimicry in the Jurassic, fills a gap in the fossil record, and suggests that leaf mimicry has been a long-standing adaptive strategy in Orthoptera, independently evolving across different lineages throughout geological history. This finding highlights the dynamic interplay between plant community succession, predation pressures, and insect defensive strategies, expanding our understanding of the ecological significance and evolution of leaf mimicry in orthopterans.","PeriodicalId":12642,"journal":{"name":"Geology","volume":"11 1","pages":""},"PeriodicalIF":5.8,"publicationDate":"2025-08-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144916093","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}
Ana Anzulović, Anne H. Davis, Carmen Gaina, Razvan Caracas
Kimberlite melts are primary carriers of mantle-derived carbon and hydrogen, playing an important role in Earth’s deep carbon cycle and diamond transport. Their low densities, viscosities, and vapor exsolution enable fast ascent rates. Ascending from the upper mantle, kimberlite melts incorporate xenoliths and xenocrysts and exsolve volatiles. These processes alter their initial composition, increasing the discrepancy between the proto-kimberlite magma and the magma that reaches the surface. To explain kimberlite volcanism, we examine atomic diffusivities and densities of kimberlite melts with varying volatile contents. We show that water makes the melts more diffusive, which should also lower their viscosity. All our kimberlite melts are positively buoyant below the lower continental crust (the MOHO discontinuity). They require ∼8.2 wt% CO2 to cross and rise through the MOHO. Above the MOHO, the most volatile-rich kimberlite melts can carry up to ∼44% xenolithic fragments of depleted peridotite type.
{"title":"Buoyancy of volatile-rich kimberlite melts, magma ascent, and xenolith transport","authors":"Ana Anzulović, Anne H. Davis, Carmen Gaina, Razvan Caracas","doi":"10.1130/g53387.1","DOIUrl":"https://doi.org/10.1130/g53387.1","url":null,"abstract":"Kimberlite melts are primary carriers of mantle-derived carbon and hydrogen, playing an important role in Earth’s deep carbon cycle and diamond transport. Their low densities, viscosities, and vapor exsolution enable fast ascent rates. Ascending from the upper mantle, kimberlite melts incorporate xenoliths and xenocrysts and exsolve volatiles. These processes alter their initial composition, increasing the discrepancy between the proto-kimberlite magma and the magma that reaches the surface. To explain kimberlite volcanism, we examine atomic diffusivities and densities of kimberlite melts with varying volatile contents. We show that water makes the melts more diffusive, which should also lower their viscosity. All our kimberlite melts are positively buoyant below the lower continental crust (the MOHO discontinuity). They require ∼8.2 wt% CO2 to cross and rise through the MOHO. Above the MOHO, the most volatile-rich kimberlite melts can carry up to ∼44% xenolithic fragments of depleted peridotite type.","PeriodicalId":12642,"journal":{"name":"Geology","volume":"31 1","pages":""},"PeriodicalIF":5.8,"publicationDate":"2025-08-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144900812","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}
Fluid-present melting and fluid-absent melting are two primary mechanisms for the chemical differentiation of continental crust. However, it is still challenging to decode these processes with conventional geochemical methods. In this study, we present systematic Fe isotope data of anatectic migmatites and gneisses from the Dabie orogen, China, which were formed by different mechanisms of crustal anatexis. Fluid-present melting of biotite generates migmatites with restricted Fe3+/ΣFe (0.31−0.44) and homogeneous δ56Fe values (0.06‰−0.17‰). In contrast, fluid-absent melting of phengite produces migmatites and migmatitic gneisses with dramatic Fe3+/ΣFe (0.26−0.94) and δ56Fe (0.04‰−0.61‰) variations. Quantitative modeling of Fe distribution during partial melting reveals that Fe isotope fractionation is governed by source mineral assemblages under varying melting regimes. During fluid-absent melting, the reactant phengite has much higher Fe3+/ΣFe and δ56Fe values than the peritectic biotite, resulting in high and heterogeneous δ56Fe values in the complementary melt. In contrast, during fluid-present melting, the reactant biotite and peritectic amphibole have similarly low Fe3+/ΣFe and δ56Fe values, leading to low and homogeneous δ56Fe values in the complementary melt. This establishes Fe isotopes as a novel tracer for crustal anatexis, critical for understanding continental reworking and intracrustal differentiation.
{"title":"Fe isotope decoding of fluid-absent versus fluid-present melting of deeply subducted continental crust","authors":"Er-Lin Zhu, Qiong-Xia Xia, Yi-Xiang Chen, Ren-Xu Chen, Hao-Hong Shu, Zhao-Ya Li, Yong-Fei Zheng","doi":"10.1130/g52997.1","DOIUrl":"https://doi.org/10.1130/g52997.1","url":null,"abstract":"Fluid-present melting and fluid-absent melting are two primary mechanisms for the chemical differentiation of continental crust. However, it is still challenging to decode these processes with conventional geochemical methods. In this study, we present systematic Fe isotope data of anatectic migmatites and gneisses from the Dabie orogen, China, which were formed by different mechanisms of crustal anatexis. Fluid-present melting of biotite generates migmatites with restricted Fe3+/ΣFe (0.31−0.44) and homogeneous δ56Fe values (0.06‰−0.17‰). In contrast, fluid-absent melting of phengite produces migmatites and migmatitic gneisses with dramatic Fe3+/ΣFe (0.26−0.94) and δ56Fe (0.04‰−0.61‰) variations. Quantitative modeling of Fe distribution during partial melting reveals that Fe isotope fractionation is governed by source mineral assemblages under varying melting regimes. During fluid-absent melting, the reactant phengite has much higher Fe3+/ΣFe and δ56Fe values than the peritectic biotite, resulting in high and heterogeneous δ56Fe values in the complementary melt. In contrast, during fluid-present melting, the reactant biotite and peritectic amphibole have similarly low Fe3+/ΣFe and δ56Fe values, leading to low and homogeneous δ56Fe values in the complementary melt. This establishes Fe isotopes as a novel tracer for crustal anatexis, critical for understanding continental reworking and intracrustal differentiation.","PeriodicalId":12642,"journal":{"name":"Geology","volume":"27 1","pages":""},"PeriodicalIF":5.8,"publicationDate":"2025-08-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144900811","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}
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