Alvaro P. Crósta, Gabriel G. Silva, Ludovic Ferrière, Philippe Nonnotte, Eugen Libowitzky, Fred Jourdan
Tektites, a rare type of impact glass, are known to occur only in five distinct strewn fields on Earth. We report on the discovery of a new tektite strewn field in northeastern Brazil. This recent finding resulted in the collection of ∼500 specimens found within a strewn field at least 90 km long. Mostly black in color, the masses, hereby named “geraisites” after the Brazilian state of Minas Gerais, range from <1 g up to 85.4 g and exhibit various shapes, rarely showing lechatelierite inclusions. In terms of chemical composition, they fall in the dacite and rhyolite fields of the total alkali versus silica diagram, with similar SiO2 and slightly higher Na2O + K2O content in comparison with other known tektites. Some variations in trace elements from sample to sample, such as for Cr and Ni, are observed. Water contents of the glass are extremely low, ranging between 70 and 110 ppm. The best estimate for their age of formation measured by the 40Ar/39Ar method is currently ca. 6.3 Ma, although the possible presence of inherited 40Ar* will require more analyses to fully establish their age. Strontium, Nd, and Hf isotopic compositions as well as Nd and Hf model ages provide insights into the age and composition of the source rocks, having a continental crustal composition, most likely Mesoarchean felsic rocks.
陨石是一种罕见的撞击玻璃，已知只存在于地球上五个不同的散布区域。我们报道在巴西东北部发现了一个新的布满陨石的地区。最近的发现是在至少90公里长的散布区域内收集到约500个标本的结果。这些群众大多是黑人，因此以巴西米纳斯吉拉斯州的名字命名为“吉拉斯人”，他们的范围从&；1 g ~ 85.4 g，形态各异，很少有卵黄铜矿包裹体。在化学成分上，它们落在总碱-硅图的英安岩和流纹岩场，与其他已知的晶岩相比，SiO2含量相似，Na2O + K2O含量略高。观察到不同样品中微量元素的变化，如Cr和Ni。玻璃的含水量极低，在70到110 ppm之间。目前，用40Ar/39Ar方法对它们形成年龄的最佳估计约为6.3 Ma，尽管可能存在遗传的40Ar*需要更多的分析来完全确定它们的年龄。锶、Nd和Hf同位素组成以及Nd和Hf模式年龄提供了对烃源岩年龄和组成的见解，具有大陆地壳组成，最有可能是中太古宙长英质岩石。
{"title":"Geraisite: The first tektite occurrence in Brazil","authors":"Alvaro P. Crósta, Gabriel G. Silva, Ludovic Ferrière, Philippe Nonnotte, Eugen Libowitzky, Fred Jourdan","doi":"10.1130/g53805.1","DOIUrl":"https://doi.org/10.1130/g53805.1","url":null,"abstract":"Tektites, a rare type of impact glass, are known to occur only in five distinct strewn fields on Earth. We report on the discovery of a new tektite strewn field in northeastern Brazil. This recent finding resulted in the collection of ∼500 specimens found within a strewn field at least 90 km long. Mostly black in color, the masses, hereby named “geraisites” after the Brazilian state of Minas Gerais, range from &lt;1 g up to 85.4 g and exhibit various shapes, rarely showing lechatelierite inclusions. In terms of chemical composition, they fall in the dacite and rhyolite fields of the total alkali versus silica diagram, with similar SiO2 and slightly higher Na2O + K2O content in comparison with other known tektites. Some variations in trace elements from sample to sample, such as for Cr and Ni, are observed. Water contents of the glass are extremely low, ranging between 70 and 110 ppm. The best estimate for their age of formation measured by the 40Ar/39Ar method is currently ca. 6.3 Ma, although the possible presence of inherited 40Ar* will require more analyses to fully establish their age. Strontium, Nd, and Hf isotopic compositions as well as Nd and Hf model ages provide insights into the age and composition of the source rocks, having a continental crustal composition, most likely Mesoarchean felsic rocks.","PeriodicalId":12642,"journal":{"name":"Geology","volume":"131 1","pages":""},"PeriodicalIF":5.8,"publicationDate":"2025-12-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145664839","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}
Trent B. Thomas, Francis A. Macdonald, David C. Catling
The Cryogenian Period (720−635 Ma) witnessed two Snowball Earth glaciations: the largest known perturbations to the geologic carbon cycle in Earth history. These two runaway ice-albedo catastrophes naturally test planetary climate stability and habitability. Geochronological data show that the Sturtian glaciation lasted 56 m.y., and the Marinoan was as short as 4 m.y., which is an unexplained difference previously attributed to changing volcanic outgassing rates and dust or ice albedo. Here, we propose that this difference in duration is instead due to changes in the extent of seafloor weathering, which was elevated during both glaciations by an acidic ocean under relatively high CO2. By assuming modern volcanic outgassing rates and a conservative range of ice albedos, we find that seafloor weathering rates 25−53 times higher than modern are required to suppress atmospheric CO2 and maintain glaciation for a 56 m.y. Sturtian glaciation, whereas <15 times higher than modern are required for a 4 m.y. Marinoan glaciation. Rates were plausibly enhanced further by reduced deep-sea sedimentation and low marine sulfate, which would have prevented hydrothermal anhydrite production and created more porous, weatherable oceanic crust. Geochemical data indicate low marine sulfate (<2 mM) during the Sturtian, which rebounded for the Marinoan (up to ∼30 mM), and can account for the different seafloor weathering rates required by our model. Thus, our results suggest seafloor weathering and evolving ocean redox chemistry are critical for determining the duration of Snowball Earth glaciations.
{"title":"Seafloor weathering can explain the disparate durations of Snowball glaciations","authors":"Trent B. Thomas, Francis A. Macdonald, David C. Catling","doi":"10.1130/g53722.1","DOIUrl":"https://doi.org/10.1130/g53722.1","url":null,"abstract":"The Cryogenian Period (720−635 Ma) witnessed two Snowball Earth glaciations: the largest known perturbations to the geologic carbon cycle in Earth history. These two runaway ice-albedo catastrophes naturally test planetary climate stability and habitability. Geochronological data show that the Sturtian glaciation lasted 56 m.y., and the Marinoan was as short as 4 m.y., which is an unexplained difference previously attributed to changing volcanic outgassing rates and dust or ice albedo. Here, we propose that this difference in duration is instead due to changes in the extent of seafloor weathering, which was elevated during both glaciations by an acidic ocean under relatively high CO2. By assuming modern volcanic outgassing rates and a conservative range of ice albedos, we find that seafloor weathering rates 25−53 times higher than modern are required to suppress atmospheric CO2 and maintain glaciation for a 56 m.y. Sturtian glaciation, whereas &lt;15 times higher than modern are required for a 4 m.y. Marinoan glaciation. Rates were plausibly enhanced further by reduced deep-sea sedimentation and low marine sulfate, which would have prevented hydrothermal anhydrite production and created more porous, weatherable oceanic crust. Geochemical data indicate low marine sulfate (&lt;2 mM) during the Sturtian, which rebounded for the Marinoan (up to ∼30 mM), and can account for the different seafloor weathering rates required by our model. Thus, our results suggest seafloor weathering and evolving ocean redox chemistry are critical for determining the duration of Snowball Earth glaciations.","PeriodicalId":12642,"journal":{"name":"Geology","volume":"169 1","pages":""},"PeriodicalIF":5.8,"publicationDate":"2025-12-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145664841","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}
Victoria M. Fernandes, Andreas Ruby, Fergus McNab, Hella Wittmann, Andrew D. Wickert, Lennart Grimm, Taylor Schildgen
We explore the relative importance of tectonic, geodynamic, and surface processes in driving landscape evolution in Argentine Patagonia using 64 new 10Be exposure ages of fluvial terraces preserved over >250 km along the Shehuén and Santa Cruz rivers (50°S). Terrace ages range from 33 ka to 1.5 Ma and coincide with Patagonian glaciations. We demonstrate that landscapes can respond directly to changes in climate forcing driven by the Mid-Pleistocene Transition: our results reveal a transition to 100-k.y. terrace periodicity, and a transient phase of accelerated incision starting at ca. 1 Ma. A regionally uniform incision rate of 130−180 m m.y.−1 since 1 Ma suggests uplift linked to asthenospheric heating in the Patagonian slab window, while transient accelerated incision suggests convective instabilities in a low-viscosity mantle. We establish a temporal link between climate oscillations, fluvial incision, and mantle-driven epeirogenic uplift.
{"title":"Mantle-driven, climatically modulated landscape evolution in Southern Patagonia","authors":"Victoria M. Fernandes, Andreas Ruby, Fergus McNab, Hella Wittmann, Andrew D. Wickert, Lennart Grimm, Taylor Schildgen","doi":"10.1130/g53764.1","DOIUrl":"https://doi.org/10.1130/g53764.1","url":null,"abstract":"We explore the relative importance of tectonic, geodynamic, and surface processes in driving landscape evolution in Argentine Patagonia using 64 new 10Be exposure ages of fluvial terraces preserved over &gt;250 km along the Shehuén and Santa Cruz rivers (50°S). Terrace ages range from 33 ka to 1.5 Ma and coincide with Patagonian glaciations. We demonstrate that landscapes can respond directly to changes in climate forcing driven by the Mid-Pleistocene Transition: our results reveal a transition to 100-k.y. terrace periodicity, and a transient phase of accelerated incision starting at ca. 1 Ma. A regionally uniform incision rate of 130−180 m m.y.−1 since 1 Ma suggests uplift linked to asthenospheric heating in the Patagonian slab window, while transient accelerated incision suggests convective instabilities in a low-viscosity mantle. We establish a temporal link between climate oscillations, fluvial incision, and mantle-driven epeirogenic uplift.","PeriodicalId":12642,"journal":{"name":"Geology","volume":"115 1","pages":""},"PeriodicalIF":5.8,"publicationDate":"2025-12-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145664840","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}
Shelby D. Litton, Dennis L. Newell, Kevin Mahan, Benoit Gasnier, Philippe Goncalves
Dehydrating slabs release aqueous fluids that can cause widespread metasomatism of the overlying lithosphere. Studies of mantle and crustal xenoliths provide critical mineralogical and geochemical constraints on these processes. The Colorado Plateau is a natural laboratory for documenting how chemical modification to the lithosphere impacted tectono-magmatic and geodynamic phenomena in the western United States since the latest Cretaceous. Diatremes of the Oligocene Navajo volcanic field host lower crustal xenoliths with evidence of pre- (M1) and post-hydration (M2) metamorphic textures and mineral assemblages. New hydrogen stable isotope results from hydrous minerals in felsic and mafic lower crustal xenoliths hosted in serpentinized ultramafic microbreccia diatremes show deuterium enrichment during M2. M1 minerals have δD values (Vienna standard mean ocean water, VSMOW) from −103‰ to −69‰ (−82‰ ± 12‰; mean ± 1σ), compared to M2 hydrous phases with values from −81‰ to −23‰ (−50‰ ± 14‰). Using available thermobarometry-based temperature constraints of ∼500 °C for M2, we estimate the δD values of the hydrous fluids as ∼−17‰ ± 15‰. We suggest that Laramide-age, slab-derived aqueous fluids permeated into the lower crust of the Colorado Plateau and that shallow subduction transports and releases water far inboard from subduction zones. Results suggest that this part of the global subduction cycle facilitates hydrous metasomatism of large swaths of continental lithosphere with implications for de-densification and uplift of continental plateaus, subsequent magmatism, and transport of volatiles and metals in modern and ancient flat slab systems.
{"title":"Xenolith hydrogen isotope evidence for lower crustal hydration during cycles of flat slab subduction","authors":"Shelby D. Litton, Dennis L. Newell, Kevin Mahan, Benoit Gasnier, Philippe Goncalves","doi":"10.1130/g53815.1","DOIUrl":"https://doi.org/10.1130/g53815.1","url":null,"abstract":"Dehydrating slabs release aqueous fluids that can cause widespread metasomatism of the overlying lithosphere. Studies of mantle and crustal xenoliths provide critical mineralogical and geochemical constraints on these processes. The Colorado Plateau is a natural laboratory for documenting how chemical modification to the lithosphere impacted tectono-magmatic and geodynamic phenomena in the western United States since the latest Cretaceous. Diatremes of the Oligocene Navajo volcanic field host lower crustal xenoliths with evidence of pre- (M1) and post-hydration (M2) metamorphic textures and mineral assemblages. New hydrogen stable isotope results from hydrous minerals in felsic and mafic lower crustal xenoliths hosted in serpentinized ultramafic microbreccia diatremes show deuterium enrichment during M2. M1 minerals have δD values (Vienna standard mean ocean water, VSMOW) from −103‰ to −69‰ (−82‰ ± 12‰; mean ± 1σ), compared to M2 hydrous phases with values from −81‰ to −23‰ (−50‰ ± 14‰). Using available thermobarometry-based temperature constraints of ∼500 °C for M2, we estimate the δD values of the hydrous fluids as ∼−17‰ ± 15‰. We suggest that Laramide-age, slab-derived aqueous fluids permeated into the lower crust of the Colorado Plateau and that shallow subduction transports and releases water far inboard from subduction zones. Results suggest that this part of the global subduction cycle facilitates hydrous metasomatism of large swaths of continental lithosphere with implications for de-densification and uplift of continental plateaus, subsequent magmatism, and transport of volatiles and metals in modern and ancient flat slab systems.","PeriodicalId":12642,"journal":{"name":"Geology","volume":"131 1","pages":""},"PeriodicalIF":5.8,"publicationDate":"2025-12-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145664937","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}
Sinan Özaydın, Patrice F. Rey, Vasileios Chatzaras
Magnetotellurics (MT) utilize measurements of electromagnetic fields at Earth’s surface to image the electrical conductivity distribution at depths from a few meters to ∼200 km. MT is especially powerful for mapping mineralized fluid pathways, as it is sensitive to interconnected minor conductive phases such as fluids, melts, or sulfides. However, conductivity anomalies documented by lithosphere-scale MT surveys do not necessarily capture the geometry of conductivity structures at depth and are often hard to interpret. To address this limitation, we developed a new approach that integrates laboratory-based conductivity with 3-D thermomechanical modeling. Our aim was to test the relationship between strain and conductivity in the case of a pull-apart basin. We show that networks of high-strain zones, which largely govern fluid transfer across the lithosphere, exert a first-order control on spatial distribution of conductivity anomalies. When compared to real MT data from the Marmara pull-apart basin along the North Anatolian fault (northwestern Türkiye), our synthetic survey shows good agreement with observed conductivity anomalies. This relationship suggests that strain plays a key role in controlling electrical conductivity distribution in the lithosphere by facilitating the interconnectivity of conductive phases.
{"title":"Strain controls the electrical conductivity distribution in the lithosphere","authors":"Sinan Özaydın, Patrice F. Rey, Vasileios Chatzaras","doi":"10.1130/g53957.1","DOIUrl":"https://doi.org/10.1130/g53957.1","url":null,"abstract":"Magnetotellurics (MT) utilize measurements of electromagnetic fields at Earth’s surface to image the electrical conductivity distribution at depths from a few meters to ∼200 km. MT is especially powerful for mapping mineralized fluid pathways, as it is sensitive to interconnected minor conductive phases such as fluids, melts, or sulfides. However, conductivity anomalies documented by lithosphere-scale MT surveys do not necessarily capture the geometry of conductivity structures at depth and are often hard to interpret. To address this limitation, we developed a new approach that integrates laboratory-based conductivity with 3-D thermomechanical modeling. Our aim was to test the relationship between strain and conductivity in the case of a pull-apart basin. We show that networks of high-strain zones, which largely govern fluid transfer across the lithosphere, exert a first-order control on spatial distribution of conductivity anomalies. When compared to real MT data from the Marmara pull-apart basin along the North Anatolian fault (northwestern Türkiye), our synthetic survey shows good agreement with observed conductivity anomalies. This relationship suggests that strain plays a key role in controlling electrical conductivity distribution in the lithosphere by facilitating the interconnectivity of conductive phases.","PeriodicalId":12642,"journal":{"name":"Geology","volume":"26 1","pages":""},"PeriodicalIF":5.8,"publicationDate":"2025-11-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145651159","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}
Braid deltas, environments that form where braided rivers meet base level, are more abundant on Holocene Earth than previously appreciated. A worldwide survey identified 786 braid deltas with feeder systems >500 m wide. Braid deltas occur at all latitudes north of the Antarctic Circle and are most abundant by land area in the 45°S−60°S and 60°N−90°N latitude bands. Marine-associated braid deltas compose 71% of the dataset, with the remainder in marginal lacustrine settings. Half of the observed braid deltas do not form radial terminal delta-plain geometry. Hierarchical clustering analysis separates braid deltas into nine clusters that define a classification scheme. Drivers of differentiation include basin type, embayment, sediment supply, and flow intermittence. The classified dataset provides analogues to ancient, nonvegetated deltaic environments and the essential framework for development of braid-delta facies models.
{"title":"Global distribution, hierarchical clustering classification, and significance of Holocene braid deltas","authors":"Jason G. Muhlbauer, Christopher M. Fedo","doi":"10.1130/g53851.1","DOIUrl":"https://doi.org/10.1130/g53851.1","url":null,"abstract":"Braid deltas, environments that form where braided rivers meet base level, are more abundant on Holocene Earth than previously appreciated. A worldwide survey identified 786 braid deltas with feeder systems &gt;500 m wide. Braid deltas occur at all latitudes north of the Antarctic Circle and are most abundant by land area in the 45°S−60°S and 60°N−90°N latitude bands. Marine-associated braid deltas compose 71% of the dataset, with the remainder in marginal lacustrine settings. Half of the observed braid deltas do not form radial terminal delta-plain geometry. Hierarchical clustering analysis separates braid deltas into nine clusters that define a classification scheme. Drivers of differentiation include basin type, embayment, sediment supply, and flow intermittence. The classified dataset provides analogues to ancient, nonvegetated deltaic environments and the essential framework for development of braid-delta facies models.","PeriodicalId":12642,"journal":{"name":"Geology","volume":"2 1","pages":""},"PeriodicalIF":5.8,"publicationDate":"2025-11-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145651156","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}
Changyeol Lee, Nestor G. Cerpa, Jaehoon Lee, Minyoung Huh
Scattered non-age-progressive intraplate volcanism (SIV) is globally widespread, yet its underlying mechanism remains poorly understood. A hypothesis posits that the magma feeding this volcanism originates from hydrous melting of upwelling mantle from the mantle transition zone (MTZ), driven by subduction-induced return flow. Here, we test this hypothesis using a two-dimensional numerical model of passive MTZ upwelling that incorporates magma formation and transport based on two-phase flow theory. Our results show that dehydration of the upwelling MTZ mantle at the 410 km discontinuity initially forms a large, horizontally elongated magmatic solitary wave. Driven by buoyancy, this wave ascends and subsequently disintegrates into multiple, smaller (∼10−20 km in diameter) magmatic solitary waves. These discrete waves ascend randomly through the asthenosphere in a process akin to “mantle rain,” reaching the lithosphere base in ∼10 m.y. Our model provides a viable explanation for SIV.
{"title":"Intraplate volcanism induced by magmatic solitary waves ascending from the mantle transition zone","authors":"Changyeol Lee, Nestor G. Cerpa, Jaehoon Lee, Minyoung Huh","doi":"10.1130/g53800.1","DOIUrl":"https://doi.org/10.1130/g53800.1","url":null,"abstract":"Scattered non-age-progressive intraplate volcanism (SIV) is globally widespread, yet its underlying mechanism remains poorly understood. A hypothesis posits that the magma feeding this volcanism originates from hydrous melting of upwelling mantle from the mantle transition zone (MTZ), driven by subduction-induced return flow. Here, we test this hypothesis using a two-dimensional numerical model of passive MTZ upwelling that incorporates magma formation and transport based on two-phase flow theory. Our results show that dehydration of the upwelling MTZ mantle at the 410 km discontinuity initially forms a large, horizontally elongated magmatic solitary wave. Driven by buoyancy, this wave ascends and subsequently disintegrates into multiple, smaller (∼10−20 km in diameter) magmatic solitary waves. These discrete waves ascend randomly through the asthenosphere in a process akin to “mantle rain,” reaching the lithosphere base in ∼10 m.y. Our model provides a viable explanation for SIV.","PeriodicalId":12642,"journal":{"name":"Geology","volume":"32 1","pages":""},"PeriodicalIF":5.8,"publicationDate":"2025-11-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145651158","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}
Adrian E. Castro, Daniel R. Viete, Stephanie Walker, Steven J. Jaret, Isabella Brunet, Katherine Morin, Dana C. Brenner, Supratik Roy, Ethan F. Baxter, Oliver M. Wolfe, Jay Thomas
The Manhattan Prong (a belt of ancient rock in southern New York, USA) underlies one of the largest population bases in North America yet its tectonometamorphic history remains poorly understood. We performed monazite U-Pb and garnet Sm-Nd petrochronology in association with garnet diffusion chronometry on a sample of the Manhattan Schist from Central Park, New York City. Monazite included in both garnet and matrix yielded a 206Pb/238U date of ca. 438 Ma, though one matrix grain yielded a distinctly younger date of ca. 391 Ma; all monazite analyzed showed identical rare earth element compositions. Garnet yielded a robust isochron date of ca. 386 Ma, interpreted to constrain the timing of garnet growth at near-peak metamorphic conditions. Retention of manganese zoning in 1-mm-scale garnet requires that near-peak metamorphic conditions at ca. 386 Ma persisted for <5 m.y. The Manhattan Schist records a polymetamorphic history involving Taconic greenschist-facies metamorphism at ca. 438 Ma, recorded by relict monazite, then short-lived Acadian kyanite-grade metamorphism at ca. 386 Ma, recorded by garnet and the major rock-forming assemblage. These results are consistent with tectonic models that involve localized, episodic heating of the middle crust, rather than gradual and more pervasive processes of heating and cooling. Our study is an example of the nuanced tectonometamorphic understanding that can be gained by combining accessory and major phase petrochronology.
{"title":"Decoupled monazite and garnet petrochronology reveals short-duration, high-temperature Acadian metamorphism in the Manhattan Schist, New York City, USA","authors":"Adrian E. Castro, Daniel R. Viete, Stephanie Walker, Steven J. Jaret, Isabella Brunet, Katherine Morin, Dana C. Brenner, Supratik Roy, Ethan F. Baxter, Oliver M. Wolfe, Jay Thomas","doi":"10.1130/g53777.1","DOIUrl":"https://doi.org/10.1130/g53777.1","url":null,"abstract":"The Manhattan Prong (a belt of ancient rock in southern New York, USA) underlies one of the largest population bases in North America yet its tectonometamorphic history remains poorly understood. We performed monazite U-Pb and garnet Sm-Nd petrochronology in association with garnet diffusion chronometry on a sample of the Manhattan Schist from Central Park, New York City. Monazite included in both garnet and matrix yielded a 206Pb/238U date of ca. 438 Ma, though one matrix grain yielded a distinctly younger date of ca. 391 Ma; all monazite analyzed showed identical rare earth element compositions. Garnet yielded a robust isochron date of ca. 386 Ma, interpreted to constrain the timing of garnet growth at near-peak metamorphic conditions. Retention of manganese zoning in 1-mm-scale garnet requires that near-peak metamorphic conditions at ca. 386 Ma persisted for &lt;5 m.y. The Manhattan Schist records a polymetamorphic history involving Taconic greenschist-facies metamorphism at ca. 438 Ma, recorded by relict monazite, then short-lived Acadian kyanite-grade metamorphism at ca. 386 Ma, recorded by garnet and the major rock-forming assemblage. These results are consistent with tectonic models that involve localized, episodic heating of the middle crust, rather than gradual and more pervasive processes of heating and cooling. Our study is an example of the nuanced tectonometamorphic understanding that can be gained by combining accessory and major phase petrochronology.","PeriodicalId":12642,"journal":{"name":"Geology","volume":"19 1","pages":""},"PeriodicalIF":5.8,"publicationDate":"2025-11-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145599612","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}
Charlie Bristow, Nicholas Lancaster, Khalid Al-Ramadan, Christina Neudorf, Amanda Keen-Zebert
Luminescence dating of interdune sabkha sediments and cross strata deposited on the lee face of a 160-m-high mega-crescentic dune in the eastern Rub’ al-Khali sand sea provides information on dune dynamics and preservation potential. Optically stimulated luminescence ages show that the rates of dune accumulation varied during the latest Pleistocene and Holocene. Sedimentary structures indicate that megadune migration was the result of strong northwesterly “Shamal” winds. During the same interval of the late Pleistocene and early Holocene, linear dunes in the northeastern United Arab Emirates were also accumulating rapidly, indicating that the period 16−9 ka was characterized by regionally widespread dune formation and/or reworking. The dune has subsequently migrated to the SSE almost 900 m since the early Holocene, at an average rate of 77 m/k.y., indicating persistence of the Shamal wind system for at least 20 k.y. Rates of megadune migration and wet sabkha accumulation reveal that, despite their very large size, less than 1% of the megadune would be preserved in a sedimentary record.
{"title":"Not much to show for it: Late Pleistocene dynamics of migrating megadunes in the Rub’ al-Khali, Saudi Arabia, indicate minimal preservation of their deposits","authors":"Charlie Bristow, Nicholas Lancaster, Khalid Al-Ramadan, Christina Neudorf, Amanda Keen-Zebert","doi":"10.1130/g53651.1","DOIUrl":"https://doi.org/10.1130/g53651.1","url":null,"abstract":"Luminescence dating of interdune sabkha sediments and cross strata deposited on the lee face of a 160-m-high mega-crescentic dune in the eastern Rub’ al-Khali sand sea provides information on dune dynamics and preservation potential. Optically stimulated luminescence ages show that the rates of dune accumulation varied during the latest Pleistocene and Holocene. Sedimentary structures indicate that megadune migration was the result of strong northwesterly “Shamal” winds. During the same interval of the late Pleistocene and early Holocene, linear dunes in the northeastern United Arab Emirates were also accumulating rapidly, indicating that the period 16−9 ka was characterized by regionally widespread dune formation and/or reworking. The dune has subsequently migrated to the SSE almost 900 m since the early Holocene, at an average rate of 77 m/k.y., indicating persistence of the Shamal wind system for at least 20 k.y. Rates of megadune migration and wet sabkha accumulation reveal that, despite their very large size, less than 1% of the megadune would be preserved in a sedimentary record.","PeriodicalId":12642,"journal":{"name":"Geology","volume":"18 1","pages":""},"PeriodicalIF":5.8,"publicationDate":"2025-11-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145560584","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}
Naixiao Xu, Hao Cheng, Geoffrey D. Bromiley, Henry J.B. Dick, Lingmin Zhang
The extent of chlorine isotope heterogeneity within Earth’s mantle remains a subject of active debate. To contribute to this discussion, we present the first in situ chlorine isotope measurements of apatite from Integrated Ocean Drilling Program Hole U1473A (Southwest Indian Ridge) gabbros. The apatites record a pristine mantle δ37Cl value of −0.51‰ ± 0.04‰, consistent with global mid-ocean ridge basalt averages. Systematic negative covariations between δ37Cl and Cl content across lithological boundaries cannot be explained by fractional crystallization alone. Compared to altered gabbros from Ocean Drilling Program Hole 735B (Atlantis Bank), apatites from U1473A show lower δ37Cl values. The preservation of euhedral textures and constant OH concentrations in these apatites, combined with amphibole geochemistry, rules out lower-temperature seawater alteration. Instead, these trends reflect high-temperature processes, including melt−rock interaction, brine assimilation, or mantle heterogeneity. Our findings demonstrate that δ37Cl variability in mantle-derived apatites records both crustal recycling and intrinsic mantle heterogeneity, confirming their utility as reliable tracers of deep Earth volatile cycling.
{"title":"Mantle chlorine isotope signature and melt−rock interaction revealed by apatite at the Southwest Indian Ridge","authors":"Naixiao Xu, Hao Cheng, Geoffrey D. Bromiley, Henry J.B. Dick, Lingmin Zhang","doi":"10.1130/g53563.1","DOIUrl":"https://doi.org/10.1130/g53563.1","url":null,"abstract":"The extent of chlorine isotope heterogeneity within Earth’s mantle remains a subject of active debate. To contribute to this discussion, we present the first in situ chlorine isotope measurements of apatite from Integrated Ocean Drilling Program Hole U1473A (Southwest Indian Ridge) gabbros. The apatites record a pristine mantle δ37Cl value of −0.51‰ ± 0.04‰, consistent with global mid-ocean ridge basalt averages. Systematic negative covariations between δ37Cl and Cl content across lithological boundaries cannot be explained by fractional crystallization alone. Compared to altered gabbros from Ocean Drilling Program Hole 735B (Atlantis Bank), apatites from U1473A show lower δ37Cl values. The preservation of euhedral textures and constant OH concentrations in these apatites, combined with amphibole geochemistry, rules out lower-temperature seawater alteration. Instead, these trends reflect high-temperature processes, including melt−rock interaction, brine assimilation, or mantle heterogeneity. Our findings demonstrate that δ37Cl variability in mantle-derived apatites records both crustal recycling and intrinsic mantle heterogeneity, confirming their utility as reliable tracers of deep Earth volatile cycling.","PeriodicalId":12642,"journal":{"name":"Geology","volume":"28 1","pages":""},"PeriodicalIF":5.8,"publicationDate":"2025-11-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145554262","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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