Donghai Guo, Shan Li, H. Permana, Y. Lai, I. Setiawan
The central part of Java, Indonesia, is located on the southern margin of Sundaland, and records the tectonic-magmatic history of the easternmost Neo-Tethys. Elucidating the petrogenesis and its tectonic setting of the Cretaceous Luk Ulo granites in Central Java is key to reconstructing the late subduction-accretion history of the easternmost Neo-Tethys. This study reports for the first time the zircon U-Pb geochronology, Hf-O isotope, whole-rock major and trace elements, and Sr-Nd isotope geochemistry of two granitoid episodes from Central Java. Zircon U-Pb dating results show that the Luk Ulo granites formed in two Cretaceous episodes at ca. 115 Ma and ca. 70 Ma. These two Cretaceous granitoid episodes contain both calc-alkaline with enriched large-ion lithophile elements and light rare earth elements and depleted high field strength elements, exhibiting arc geochemical signatures. The older (ca. 115 Ma) granites show slightly higher (87Sr/86Sr)i values of 0.70772 to 0.70784 and weakly negative εNd(t) values of −2.37 to −1.67, indicating the contribution of ancient crust. However, the scattered zircon εHf(t) values of +0.23 to +11.39 suggest a probable mixture of ancient crustal components and juvenile crustal additions in the magma source. The high zircon δ18O values (+8.86‰ to +14.24‰) show the possible incorporation of supracrustal components (sediments and fluids) in the magma formation. In contrast, the younger (ca. 70 Ma) granites show low (87Sr/86Sr)i values of 0.70427−0.70442, strong positive εNd(t) values of +3.89 to +4.03, and zircon εHf(t) values of +14.04 to +17.38 and slightly higher zircon δ18O values of +5.01‰ to +6.49‰ than the depleted mantle, indicating that the magma was predominantly derived from the juvenile crust with negligible supracrustal involvement. In general, zircon εHf(t) values and whole-rock εNd(t) values of the Late Cretaceous (after ca. 90 Ma) granitic rocks in the southwest margin of Sundaland were higher than those of the Early Cretaceous granitoids, suggesting a change in the source region from ancient to the juvenile in response to the rollback of the Neo-Tethys ocean. Our findings from the two Cretaceous granitoid episodes in Central Java provide new insights into the tectono-magmatic evolution along the southwestern margin of Sundaland and the two different episodes of crustal growth in the easternmost Tethys during the Cretaceous.
{"title":"Petrogenesis of two Cretaceous granitoid episodes in the Luk Ulo region, Central Java, Indonesia, and its implication for the tectonic evolution of the easternmost Neo-Tethys","authors":"Donghai Guo, Shan Li, H. Permana, Y. Lai, I. Setiawan","doi":"10.1130/b36781.1","DOIUrl":"https://doi.org/10.1130/b36781.1","url":null,"abstract":"The central part of Java, Indonesia, is located on the southern margin of Sundaland, and records the tectonic-magmatic history of the easternmost Neo-Tethys. Elucidating the petrogenesis and its tectonic setting of the Cretaceous Luk Ulo granites in Central Java is key to reconstructing the late subduction-accretion history of the easternmost Neo-Tethys. This study reports for the first time the zircon U-Pb geochronology, Hf-O isotope, whole-rock major and trace elements, and Sr-Nd isotope geochemistry of two granitoid episodes from Central Java. Zircon U-Pb dating results show that the Luk Ulo granites formed in two Cretaceous episodes at ca. 115 Ma and ca. 70 Ma. These two Cretaceous granitoid episodes contain both calc-alkaline with enriched large-ion lithophile elements and light rare earth elements and depleted high field strength elements, exhibiting arc geochemical signatures. The older (ca. 115 Ma) granites show slightly higher (87Sr/86Sr)i values of 0.70772 to 0.70784 and weakly negative εNd(t) values of −2.37 to −1.67, indicating the contribution of ancient crust. However, the scattered zircon εHf(t) values of +0.23 to +11.39 suggest a probable mixture of ancient crustal components and juvenile crustal additions in the magma source. The high zircon δ18O values (+8.86‰ to +14.24‰) show the possible incorporation of supracrustal components (sediments and fluids) in the magma formation. In contrast, the younger (ca. 70 Ma) granites show low (87Sr/86Sr)i values of 0.70427−0.70442, strong positive εNd(t) values of +3.89 to +4.03, and zircon εHf(t) values of +14.04 to +17.38 and slightly higher zircon δ18O values of +5.01‰ to +6.49‰ than the depleted mantle, indicating that the magma was predominantly derived from the juvenile crust with negligible supracrustal involvement. In general, zircon εHf(t) values and whole-rock εNd(t) values of the Late Cretaceous (after ca. 90 Ma) granitic rocks in the southwest margin of Sundaland were higher than those of the Early Cretaceous granitoids, suggesting a change in the source region from ancient to the juvenile in response to the rollback of the Neo-Tethys ocean. Our findings from the two Cretaceous granitoid episodes in Central Java provide new insights into the tectono-magmatic evolution along the southwestern margin of Sundaland and the two different episodes of crustal growth in the easternmost Tethys during the Cretaceous.","PeriodicalId":55104,"journal":{"name":"Geological Society of America Bulletin","volume":" ","pages":""},"PeriodicalIF":4.9,"publicationDate":"2023-08-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"42445338","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}
C. Caudill, G. Osinski, L. Tornabene, F. Longstaffe, D. Mccarty, H. Sapers
The presence of extensive clay minerals in the ancient Noachian terrains of Mars is often used to invoke past climatic conditions that were warmer and supported surface-stable liquid water. These clay-rich regions are also heavily cratered, leading to the possibility of a causal relationship. The aim of this study is to better understand the impact excavation and generation of clays and whether there are any mineralogical or geochemical indicators that could differentiate between these two origins, both on Earth and, by analogy, Mars. Here, we present a detailed field and laboratory investigation of the composition, texture, and setting of clay minerals in impactites at the well-preserved Ries impact structure, Germany. Authigenic impactite (syn- and post-impact) clay minerals in impact melt-bearing breccia deposits are compared with sedimentary-derived clay mineral-bearing units preserved from the time of the impact event. Our findings indicate: (1) impact-generated deposits comprise compositionally diverse, Al-dominant smectitic clay minerals that could have formed without appreciable exogenous volatiles through a combination of autometamorphism, hydrothermal alteration, and devitrification; and (2) the pre-impact sedimentary clay mineral assemblages were similar in composition to those in the impact-generated deposits such that only detailed, successive laboratory treatments and analyses could discern the two sample types. NASA’s Perseverance Mars rover mission is presently investigating its first science campaign and has identified secondary alteration products, including possible clay minerals. Our study suggests that the rover may explore impact-generated clay minerals in situ, though their provenance might only be determined from analysis of the returned samples in Earth laboratories.
{"title":"Pre- and syn-impact formation of clay minerals at the Ries impact structure, Germany: Implications for clay minerals on Mars","authors":"C. Caudill, G. Osinski, L. Tornabene, F. Longstaffe, D. Mccarty, H. Sapers","doi":"10.1130/b36699.1","DOIUrl":"https://doi.org/10.1130/b36699.1","url":null,"abstract":"The presence of extensive clay minerals in the ancient Noachian terrains of Mars is often used to invoke past climatic conditions that were warmer and supported surface-stable liquid water. These clay-rich regions are also heavily cratered, leading to the possibility of a causal relationship. The aim of this study is to better understand the impact excavation and generation of clays and whether there are any mineralogical or geochemical indicators that could differentiate between these two origins, both on Earth and, by analogy, Mars. Here, we present a detailed field and laboratory investigation of the composition, texture, and setting of clay minerals in impactites at the well-preserved Ries impact structure, Germany. Authigenic impactite (syn- and post-impact) clay minerals in impact melt-bearing breccia deposits are compared with sedimentary-derived clay mineral-bearing units preserved from the time of the impact event. Our findings indicate: (1) impact-generated deposits comprise compositionally diverse, Al-dominant smectitic clay minerals that could have formed without appreciable exogenous volatiles through a combination of autometamorphism, hydrothermal alteration, and devitrification; and (2) the pre-impact sedimentary clay mineral assemblages were similar in composition to those in the impact-generated deposits such that only detailed, successive laboratory treatments and analyses could discern the two sample types. NASA’s Perseverance Mars rover mission is presently investigating its first science campaign and has identified secondary alteration products, including possible clay minerals. Our study suggests that the rover may explore impact-generated clay minerals in situ, though their provenance might only be determined from analysis of the returned samples in Earth laboratories.","PeriodicalId":55104,"journal":{"name":"Geological Society of America Bulletin","volume":" ","pages":""},"PeriodicalIF":4.9,"publicationDate":"2023-08-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"49137587","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}
Jiahui Ma, Tianshui Yang, Wenxiao Peng, W. Bian, Suo Wang, Fei Han, Jiacheng Liang, Xianwei Jiao, Jingjie Jin, Shihong Zhang, Huaichun Wu, Haiyan Li, Yiming Ma
To better clarify the reliability of redbed paleomagnetic datasets from the Tibetan Plateau and shape of the Qiangtang Terrane (QT) prior to the India-Asia collision, a combined paleomagnetic and detrital zircon U-Pb geochronologic study is conducted on the Upper Cretaceous Abushan Formation (Fm) redbeds, dated to be within 89.1−83.6 Ma, in the Anduo area. The tilt-corrected grand mean direction for 37 sites is Ds = 0.9°, Is = +36.4°, k = 43.6, α95 = 3.6°, which provides a paleopole at 78.2°N, 266.8°E (A95 = 3.6°), corresponding to a paleolatitude of 20.5° ± 3.6°N for the study area (32.3°N, 91.4°E). Reliable demagnetization curves, positive fold, and conglomerate tests support the interpretation that characteristic remanent magnetization directions recorded primary magnetizations carried by detrital hematite and did not suffer from the influence of distortional strains. Our paleomagnetic results indicate that the mean inclination observed from the southwest dipping limb (Is = +44.2°) is clearly steeper than that from the north dipping limb (Is = +34.2°). The results of syntectonic-sedimentation-correction and the fluvial gravel deposits present in the Abushan Fm redbeds sampled support the contention that the apparent inclination discrepancy is attributed to the syntectonic growth strata and that the paleomagnetic datasets observed from two limbs of folds are still reliable. Furthermore, reliable Late Cretaceous paleomagnetic datasets show that the shape of the QT west of the Eastern Himalaya Syntaxis (EHS) during the Late Cretaceous was similar to its present-day relatively E-W alignment, and that around the EHS, its shape changed from the Late Cretaceous NE-SW alignment to the present-day approximately NW-SE alignment.
{"title":"New Late Cretaceous paleomagnetic and geochronologic results from the southern Qiangtang Terrane: Contributions to the reliability of redbed paleomagnetic datasets from the Tibetan Plateau and shape of the Qiangtang Terrane","authors":"Jiahui Ma, Tianshui Yang, Wenxiao Peng, W. Bian, Suo Wang, Fei Han, Jiacheng Liang, Xianwei Jiao, Jingjie Jin, Shihong Zhang, Huaichun Wu, Haiyan Li, Yiming Ma","doi":"10.1130/b37023.1","DOIUrl":"https://doi.org/10.1130/b37023.1","url":null,"abstract":"To better clarify the reliability of redbed paleomagnetic datasets from the Tibetan Plateau and shape of the Qiangtang Terrane (QT) prior to the India-Asia collision, a combined paleomagnetic and detrital zircon U-Pb geochronologic study is conducted on the Upper Cretaceous Abushan Formation (Fm) redbeds, dated to be within 89.1−83.6 Ma, in the Anduo area. The tilt-corrected grand mean direction for 37 sites is Ds = 0.9°, Is = +36.4°, k = 43.6, α95 = 3.6°, which provides a paleopole at 78.2°N, 266.8°E (A95 = 3.6°), corresponding to a paleolatitude of 20.5° ± 3.6°N for the study area (32.3°N, 91.4°E). Reliable demagnetization curves, positive fold, and conglomerate tests support the interpretation that characteristic remanent magnetization directions recorded primary magnetizations carried by detrital hematite and did not suffer from the influence of distortional strains. Our paleomagnetic results indicate that the mean inclination observed from the southwest dipping limb (Is = +44.2°) is clearly steeper than that from the north dipping limb (Is = +34.2°). The results of syntectonic-sedimentation-correction and the fluvial gravel deposits present in the Abushan Fm redbeds sampled support the contention that the apparent inclination discrepancy is attributed to the syntectonic growth strata and that the paleomagnetic datasets observed from two limbs of folds are still reliable. Furthermore, reliable Late Cretaceous paleomagnetic datasets show that the shape of the QT west of the Eastern Himalaya Syntaxis (EHS) during the Late Cretaceous was similar to its present-day relatively E-W alignment, and that around the EHS, its shape changed from the Late Cretaceous NE-SW alignment to the present-day approximately NW-SE alignment.","PeriodicalId":55104,"journal":{"name":"Geological Society of America Bulletin","volume":" ","pages":""},"PeriodicalIF":4.9,"publicationDate":"2023-08-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"44765682","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}
A. Montanari, K. Farley, R. Coccioni, N. Sabatino, D. Bice, M. Yesko, M. Sinnesael, N. D. de Winter
In this paper, we report on a biostratigraphic, magnetostratigraphic, and stable isotope (δ13C and 3He) analysis across three pelagic limestone sections of the Campanian Scaglia Rossa Formation exposed in the classic Bottaccione Gorge at Gubbio (Umbria region), near the village of Furlo, and near the town of Apiro (both in the Marche region), all located in the Umbria-Marche basin of the northeastern Apennines of central Italy. These sections record the coincidental occurrence of an extraterrestrial 3He (3HeET) anomaly known as K1 and a negative shift in the δ13C record known as the early Campanian event. Cyclostratigraphic spectral analysis of the Furlo section based on a high-resolution magnetic susceptibility record in these pelagic limestones revealed that the regular orbitally forced Milankovitch cycles are somewhat disturbed or blurred through the interval of the coincident 3HeET K1 anomaly and the early Campanian event isotopic anomaly, suggesting a causal effect resulting from the enhanced influx of extraterrestrial material (i.e., interplanetary dust particles and a myriad of small meteorite impacts). This would have altered the transparency of the atmosphere, causing a short-lived climate change event.
{"title":"Cosmogenic 3He anomaly K1 vs. the early Campanian isotopic event (ECE) as recorded in pelagic limestones of the Umbria-Marche succession (Italy)","authors":"A. Montanari, K. Farley, R. Coccioni, N. Sabatino, D. Bice, M. Yesko, M. Sinnesael, N. D. de Winter","doi":"10.1130/b36952.1","DOIUrl":"https://doi.org/10.1130/b36952.1","url":null,"abstract":"In this paper, we report on a biostratigraphic, magnetostratigraphic, and stable isotope (δ13C and 3He) analysis across three pelagic limestone sections of the Campanian Scaglia Rossa Formation exposed in the classic Bottaccione Gorge at Gubbio (Umbria region), near the village of Furlo, and near the town of Apiro (both in the Marche region), all located in the Umbria-Marche basin of the northeastern Apennines of central Italy. These sections record the coincidental occurrence of an extraterrestrial 3He (3HeET) anomaly known as K1 and a negative shift in the δ13C record known as the early Campanian event. Cyclostratigraphic spectral analysis of the Furlo section based on a high-resolution magnetic susceptibility record in these pelagic limestones revealed that the regular orbitally forced Milankovitch cycles are somewhat disturbed or blurred through the interval of the coincident 3HeET K1 anomaly and the early Campanian event isotopic anomaly, suggesting a causal effect resulting from the enhanced influx of extraterrestrial material (i.e., interplanetary dust particles and a myriad of small meteorite impacts). This would have altered the transparency of the atmosphere, causing a short-lived climate change event.","PeriodicalId":55104,"journal":{"name":"Geological Society of America Bulletin","volume":" ","pages":""},"PeriodicalIF":4.9,"publicationDate":"2023-08-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"43551543","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}
Arnold García Zavaleta, N. Hauser, M. Roddaz, G. Gonçalves, Pamela A. Aparicio González, P. Baby, W. Reimold, Felipe Puma, P. Bravo, Melvy Humerez
The western margin of SW Gondwana was a place of active convergence between the Gondwana shield and the oceanic lithosphere of the Panthalassa Ocean during most of the Paleozoic. However, several studies have indicated that especially to the north of latitude 22°S, the Devonian−early Carboniferous was a time of relative quiescence without magmatic activity, metamorphism, or deformation. This interval has been termed the “Devonian Problem.” As the Devonian−Carboniferous is extensively well represented by over 4000-m-thick sedimentary sequences in the Tarija Basin in the Southern Bolivian Subandean Zone, provenance analyses—U-Pb isotope analysis on detrital zircon, Sr-Nd whole-rock isotope analysis, and X-ray diffraction (XRD)—were conducted on stratigraphically controlled sedimentary units to attempt to constrain the tectonic setting of the basin during that time. U-Pb on zircon provenance analysis indicates that only the Carboniferous units show input from comparatively young sources (<14%), with ages between 420 Ma and 320 Ma, which can be correlated with a Devonian magmatic arc. The dominant source areas for Devonian−Carboniferous sediment were the Sierras Pampeanas to the southwest and the Arequipa-Antofalla Massif and Famatinian Arc to the west, besides a few zircon grains (<18% of dates) that were possibly derived from pre-Andean inliers with ages typically >1800 Ma. The combined Sr-Nd isotope and XRD results for the pelites and the multidimensional scaling (MDS) analysis indicate that the Carboniferous units most likely represent reworked material from older units, with a minor contribution from the western part of the basin. All currently available data lead us to propose that the Tarija Basin developed during the Devonian−Carboniferous in a foreland basin setting related to the convergent margin, with important glacial sedimentary input from the continent during the Carboniferous. The absence of a contribution from a concomitant magmatic arc for the Devonian units of the Tarija Basin and the scarce magmatic zircon input (<14%) into the Carboniferous units indicate a shift from flat-slab subduction during the Devonian to normal subduction during the Carboniferous following complete delamination of the flat slab. Our comparison of the detrital record for the Tarija Basin with that of the Paraná, Chaco-Paraná, Sauce Grande, Paganzo, Navidad Arizaro, Madre de Dios, and Karoo basins supports an active margin setting for the SW margin of Gondwana during this time interval.
在古生代的大部分时间里，西南冈瓦纳西缘是冈瓦纳地盾与泛海洋岩石圈的活跃交汇之地。然而，一些研究表明，特别是在北纬22°S以北，泥盆纪-早石炭世是一个相对平静的时期，没有岩浆活动、变质作用或变形。这个区间被称为“泥盆纪问题”。由于玻利维亚南部Subandean带的Tarija盆地泥盆纪-石炭系广泛地代表了超过4000 m厚的沉积层序，因此对地层控制的沉积单元进行了物源分析——碎屑锆石u - pb同位素分析、Sr-Nd全岩同位素分析和x射线衍射(XRD)分析，试图约束该时期盆地的构造背景。锆石U-Pb物源分析表明，只有石炭系单元具有相对年轻的源输入(1800 Ma)。岩石的Sr-Nd同位素、XRD和多维标度(MDS)分析结果表明，石炭系单元极有可能是旧单元的再加工物质，盆地西部的贡献较小。根据现有资料，塔里木盆地发育于泥盆纪—石炭世，是一个与会聚边缘有关的前陆盆地，石炭世有大量来自大陆的冰川沉积。塔里木盆地泥盆系单元缺少岩浆弧的贡献，石炭系单元缺少岩浆锆石的输入(<14%)，表明在平板完全剥离后，从泥盆系的平板俯冲向石炭系的正常俯冲转变。我们将Tarija盆地的碎屑记录与帕拉纳、chaco -帕拉纳、Sauce Grande、Paganzo、Navidad Arizaro、Madre de Dios和Karoo盆地的碎屑记录进行比较，支持冈瓦纳西南边缘在这段时间内的活动边缘设置。
{"title":"Provenance of Devonian−Carboniferous sedimentary rocks of the Tarija Basin, southern Bolivia: Implications for the geodynamic evolution of the southwestern margin of Gondwana","authors":"Arnold García Zavaleta, N. Hauser, M. Roddaz, G. Gonçalves, Pamela A. Aparicio González, P. Baby, W. Reimold, Felipe Puma, P. Bravo, Melvy Humerez","doi":"10.1130/b36701.1","DOIUrl":"https://doi.org/10.1130/b36701.1","url":null,"abstract":"The western margin of SW Gondwana was a place of active convergence between the Gondwana shield and the oceanic lithosphere of the Panthalassa Ocean during most of the Paleozoic. However, several studies have indicated that especially to the north of latitude 22°S, the Devonian−early Carboniferous was a time of relative quiescence without magmatic activity, metamorphism, or deformation. This interval has been termed the “Devonian Problem.” As the Devonian−Carboniferous is extensively well represented by over 4000-m-thick sedimentary sequences in the Tarija Basin in the Southern Bolivian Subandean Zone, provenance analyses—U-Pb isotope analysis on detrital zircon, Sr-Nd whole-rock isotope analysis, and X-ray diffraction (XRD)—were conducted on stratigraphically controlled sedimentary units to attempt to constrain the tectonic setting of the basin during that time. U-Pb on zircon provenance analysis indicates that only the Carboniferous units show input from comparatively young sources (<14%), with ages between 420 Ma and 320 Ma, which can be correlated with a Devonian magmatic arc. The dominant source areas for Devonian−Carboniferous sediment were the Sierras Pampeanas to the southwest and the Arequipa-Antofalla Massif and Famatinian Arc to the west, besides a few zircon grains (<18% of dates) that were possibly derived from pre-Andean inliers with ages typically >1800 Ma. The combined Sr-Nd isotope and XRD results for the pelites and the multidimensional scaling (MDS) analysis indicate that the Carboniferous units most likely represent reworked material from older units, with a minor contribution from the western part of the basin. All currently available data lead us to propose that the Tarija Basin developed during the Devonian−Carboniferous in a foreland basin setting related to the convergent margin, with important glacial sedimentary input from the continent during the Carboniferous. The absence of a contribution from a concomitant magmatic arc for the Devonian units of the Tarija Basin and the scarce magmatic zircon input (<14%) into the Carboniferous units indicate a shift from flat-slab subduction during the Devonian to normal subduction during the Carboniferous following complete delamination of the flat slab. Our comparison of the detrital record for the Tarija Basin with that of the Paraná, Chaco-Paraná, Sauce Grande, Paganzo, Navidad Arizaro, Madre de Dios, and Karoo basins supports an active margin setting for the SW margin of Gondwana during this time interval.","PeriodicalId":55104,"journal":{"name":"Geological Society of America Bulletin","volume":" ","pages":""},"PeriodicalIF":4.9,"publicationDate":"2023-08-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"48619705","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}
Submarine landslides are significant geohazards, capable of displacing large volumes of sediment from continental margins to deposit mass transport complexes (MTCs) and generate offshore tsunamis. However, the reactivation of MTCs after their initial failure has long been overlooked. By analyzing high-quality three-dimensional seismic reflection data and seismic attribute maps, as well as comparing the geometry of different MTCs, we investigate the development of long-term slope instability and its hazardous consequences on the northwest flank of the Storegga Slide on the Norwegian margin. Our results demonstrate that the reactivation of MTCs can deform both their inner structure and overlying strata, promoting the formation of sinuous channels and local slope failures on the seafloor. These findings further reveal the MTCs that are underconsolidated or comprise slide blocks may remain unstable for a long time after their initial failure, particularly when affected by slope undercutting and a corresponding reduction in lateral support. This study shows that MTC-prone sequences are more likely to comprise regions of continental slopes with long-term instability and recurring marine geohazards.
{"title":"Long-term slope instability induced by the reactivation of mass transport complexes: An underestimated geohazard on the Norwegian continental margin","authors":"Song Jing, T. Alves, K. Omosanya, Wei Li","doi":"10.1130/b36816.1","DOIUrl":"https://doi.org/10.1130/b36816.1","url":null,"abstract":"Submarine landslides are significant geohazards, capable of displacing large volumes of sediment from continental margins to deposit mass transport complexes (MTCs) and generate offshore tsunamis. However, the reactivation of MTCs after their initial failure has long been overlooked. By analyzing high-quality three-dimensional seismic reflection data and seismic attribute maps, as well as comparing the geometry of different MTCs, we investigate the development of long-term slope instability and its hazardous consequences on the northwest flank of the Storegga Slide on the Norwegian margin. Our results demonstrate that the reactivation of MTCs can deform both their inner structure and overlying strata, promoting the formation of sinuous channels and local slope failures on the seafloor. These findings further reveal the MTCs that are underconsolidated or comprise slide blocks may remain unstable for a long time after their initial failure, particularly when affected by slope undercutting and a corresponding reduction in lateral support. This study shows that MTC-prone sequences are more likely to comprise regions of continental slopes with long-term instability and recurring marine geohazards.","PeriodicalId":55104,"journal":{"name":"Geological Society of America Bulletin","volume":" ","pages":""},"PeriodicalIF":4.9,"publicationDate":"2023-08-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"42805440","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}
H. Rochín-Bañaga, R. Gastaldo, D. Davis, J. Neveling, S. Kamo, C. Looy, J. Geissman
We report U-Pb age determinations of carbonate nodules from an in situ paleosol horizon in the Upper Permian Balfour Formation and from several horizons of pedogenic nodule conglomerate (PNC) in the Triassic Katberg Formation, Karoo Basin, South Africa, using laser ablation−inductively coupled plasma−mass spectrometry (LA-ICP-MS). The paleosol sample yields an age of 252 ± 3 Ma, which overlaps with a previous high-precision U-Pb zircon date from a volcanic ash deposit 2 m above the paleosol. This relationship demonstrates the reliability of using LA-ICP-MS dating techniques on terrestrial pedogenic calcite. Two PNC samples collected at the base of the Katberg Formation within the same sandstone unit yield ages of 255 ± 3 Ma and 251 ± 3 Ma. The age of 251 ± 3 Ma overlaps with the high-precision U-Pb zircon date below the PNC and is a maximum age estimate of deposition for the base of the Katberg Formation. Our results show that reworked nodules in the same concentrated conglomerate lag can be of different ages, but that similarly aged nodules are spatially associated. In addition, two PNC samples collected higher in the section yield ages of 249 ± 3 Ma and 241 ± 3 Ma, providing maximum depositional ages for the lower to middle Katberg Formation for the first time. We demonstrate that pedogenic carbonate nodules can be dated with meaningful precision, providing another mechanism for constraining the age of sedimentary sequences and studying events associated with the Permian−Triassic transition in the central Karoo Basin, even though the extinction boundary may not be preserved in this area.
{"title":"U-Pb dating of pedogenic calcite near the Permian−Triassic boundary, Karoo Basin, South Africa","authors":"H. Rochín-Bañaga, R. Gastaldo, D. Davis, J. Neveling, S. Kamo, C. Looy, J. Geissman","doi":"10.1130/b36968.1","DOIUrl":"https://doi.org/10.1130/b36968.1","url":null,"abstract":"We report U-Pb age determinations of carbonate nodules from an in situ paleosol horizon in the Upper Permian Balfour Formation and from several horizons of pedogenic nodule conglomerate (PNC) in the Triassic Katberg Formation, Karoo Basin, South Africa, using laser ablation−inductively coupled plasma−mass spectrometry (LA-ICP-MS). The paleosol sample yields an age of 252 ± 3 Ma, which overlaps with a previous high-precision U-Pb zircon date from a volcanic ash deposit 2 m above the paleosol. This relationship demonstrates the reliability of using LA-ICP-MS dating techniques on terrestrial pedogenic calcite. Two PNC samples collected at the base of the Katberg Formation within the same sandstone unit yield ages of 255 ± 3 Ma and 251 ± 3 Ma. The age of 251 ± 3 Ma overlaps with the high-precision U-Pb zircon date below the PNC and is a maximum age estimate of deposition for the base of the Katberg Formation. Our results show that reworked nodules in the same concentrated conglomerate lag can be of different ages, but that similarly aged nodules are spatially associated. In addition, two PNC samples collected higher in the section yield ages of 249 ± 3 Ma and 241 ± 3 Ma, providing maximum depositional ages for the lower to middle Katberg Formation for the first time. We demonstrate that pedogenic carbonate nodules can be dated with meaningful precision, providing another mechanism for constraining the age of sedimentary sequences and studying events associated with the Permian−Triassic transition in the central Karoo Basin, even though the extinction boundary may not be preserved in this area.","PeriodicalId":55104,"journal":{"name":"Geological Society of America Bulletin","volume":" ","pages":""},"PeriodicalIF":4.9,"publicationDate":"2023-08-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"45955353","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}
We extend two hypotheses based on studies of 1st- to 3rd-order Piedmont watersheds of southeastern Pennsylvania, USA, by collecting data in a larger 3rd- to 5th-order watershed nearby. One hypothesis posits that presettlement river corridors were dominated by wetlands, and the other suggests that river valleys were filled by millpond sedimentation following European settlement. Both hypotheses support new river restoration practices, so their generality is important to assess. Ten lithofacies indicate depositional environments, while pedostratigraphic criteria and 14C dating define presettlement and postsettlement stratigraphic units. Basal gravels similar to modern stream bed sediments represent presettlement channels with active bedload transport. Wedge-shaped gravel deposits resembling modern bars further document presettlement bedload transport by channelized flows. Extensive presettlement and postsettlement units of massive, organic-poor, fine-grained sediment formed when overbank flows inundated floodplains. Peat deposits, exposed at a single site (but absent elsewhere), represent a presettlement wetland. Decimeter-thick, discontinuous, massive carbonaceous fine-grained sediments occasionally overlie basal gravels; these may represent localized wetlands adjacent to presettlement channels or hydraulic backwater environments. Laminated sand and mud accumulated behind one 3-m-high mill dam, but these millpond deposits are absent at other sites. Instead of being dominated by wetlands, presettlement river corridors are better described as a complex mosaic of riparian environments including older colluvial landforms, floodplains (some of which may have been seasonally inundated wetlands), primary (and possibly secondary) channels, and depending on geomorphic setting, either localized or valley-spanning wetlands. After European settlement, millponds were important locally, but their deposits represent a minor component of the stratigraphic record.
{"title":"Pre- and postsettlement depositional processes and environments of the 3rd- to 5th-order White Clay Creek watershed, Piedmont Province, Pennsylvania and Delaware, USA","authors":"J. Pizzuto, M. E. Huffman, E. Symes","doi":"10.1130/b37032.1","DOIUrl":"https://doi.org/10.1130/b37032.1","url":null,"abstract":"We extend two hypotheses based on studies of 1st- to 3rd-order Piedmont watersheds of southeastern Pennsylvania, USA, by collecting data in a larger 3rd- to 5th-order watershed nearby. One hypothesis posits that presettlement river corridors were dominated by wetlands, and the other suggests that river valleys were filled by millpond sedimentation following European settlement. Both hypotheses support new river restoration practices, so their generality is important to assess. Ten lithofacies indicate depositional environments, while pedostratigraphic criteria and 14C dating define presettlement and postsettlement stratigraphic units. Basal gravels similar to modern stream bed sediments represent presettlement channels with active bedload transport. Wedge-shaped gravel deposits resembling modern bars further document presettlement bedload transport by channelized flows. Extensive presettlement and postsettlement units of massive, organic-poor, fine-grained sediment formed when overbank flows inundated floodplains. Peat deposits, exposed at a single site (but absent elsewhere), represent a presettlement wetland. Decimeter-thick, discontinuous, massive carbonaceous fine-grained sediments occasionally overlie basal gravels; these may represent localized wetlands adjacent to presettlement channels or hydraulic backwater environments. Laminated sand and mud accumulated behind one 3-m-high mill dam, but these millpond deposits are absent at other sites. Instead of being dominated by wetlands, presettlement river corridors are better described as a complex mosaic of riparian environments including older colluvial landforms, floodplains (some of which may have been seasonally inundated wetlands), primary (and possibly secondary) channels, and depending on geomorphic setting, either localized or valley-spanning wetlands. After European settlement, millponds were important locally, but their deposits represent a minor component of the stratigraphic record.","PeriodicalId":55104,"journal":{"name":"Geological Society of America Bulletin","volume":" ","pages":""},"PeriodicalIF":4.9,"publicationDate":"2023-08-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"46658263","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}
Yang Bai, Mengmeng Cui, B. Su, Xia Liu, Yan Xiao, P. Robinson, X. Gu
Although the involvement of hydrous fluids has been frequently invoked in the formation of stratiform chromitites in layered intrusions, there is a lack of natural evidence to signify their presence and mechanism. Here, Fourier-transform infrared spectroscopy (FTIR) of H2O in silicate minerals in the lowermost layer and G chromitite layer of the Stillwater complex, Montana, USA, shows that olivine grains have 20−55 ppm H2O, orthopyroxene has 30−45 ppm H2O, and clinopyroxene has 144−489 ppm H2O. The jointly increasing H2O contents of olivine and orthopyroxene in silicate cumulates along with magma differentiation record a negative correlation in chromitites. On the basis of poikilitic clinopyroxene, we calculated that the interstitial melts had averages of 1.3 wt% and 2.3 wt% H2O in dunite and chromitite, respectively, showing significant differences between chromitites and silicate cumulates. More than 10% of the chromite grains contained polymineralic inclusions up to 100 μm in size that were composed mainly of orthopyroxene, hornblende, plagioclase, and phlogopite. Most of these minerals were characterized by higher MgO and fluid-mobile element contents, such as Na and K, than minerals in associated silicates. Based on the mineral modes of the hydrous phases and their compositions, the trapped fluids contained ∼2.6 wt% H2O, consistent with the FTIR estimates, indicating the inclusion compositions represent interstitial melts instead of parental magmas. These observations indicate that the chromite microlites collected fluids during early crystallization, leading to a heterogeneous fluid redistribution in the melt. The fluids were collected on the surface of chromite grains during crystallization and then dissolved into poikilitic pyroxene. Chromite grains could also be efficiently floated by these fluids, causing them to migrate away from the silicate minerals in the magma channel and leading to the formation of nearly monomineralic chromitite seams. This process serves as a kinetic model indicating that chromite could be completely separated from silicates during mechanical sorting in layered intrusions.
{"title":"FTIR study of H2O in silicate minerals and mineral inclusions in chromite from the peridotite zone of the Stillwater complex (Montana, USA): Evidence for chromitite formation in an H2O-rich environment","authors":"Yang Bai, Mengmeng Cui, B. Su, Xia Liu, Yan Xiao, P. Robinson, X. Gu","doi":"10.1130/b36733.1","DOIUrl":"https://doi.org/10.1130/b36733.1","url":null,"abstract":"Although the involvement of hydrous fluids has been frequently invoked in the formation of stratiform chromitites in layered intrusions, there is a lack of natural evidence to signify their presence and mechanism. Here, Fourier-transform infrared spectroscopy (FTIR) of H2O in silicate minerals in the lowermost layer and G chromitite layer of the Stillwater complex, Montana, USA, shows that olivine grains have 20−55 ppm H2O, orthopyroxene has 30−45 ppm H2O, and clinopyroxene has 144−489 ppm H2O. The jointly increasing H2O contents of olivine and orthopyroxene in silicate cumulates along with magma differentiation record a negative correlation in chromitites. On the basis of poikilitic clinopyroxene, we calculated that the interstitial melts had averages of 1.3 wt% and 2.3 wt% H2O in dunite and chromitite, respectively, showing significant differences between chromitites and silicate cumulates. More than 10% of the chromite grains contained polymineralic inclusions up to 100 μm in size that were composed mainly of orthopyroxene, hornblende, plagioclase, and phlogopite. Most of these minerals were characterized by higher MgO and fluid-mobile element contents, such as Na and K, than minerals in associated silicates. Based on the mineral modes of the hydrous phases and their compositions, the trapped fluids contained ∼2.6 wt% H2O, consistent with the FTIR estimates, indicating the inclusion compositions represent interstitial melts instead of parental magmas. These observations indicate that the chromite microlites collected fluids during early crystallization, leading to a heterogeneous fluid redistribution in the melt. The fluids were collected on the surface of chromite grains during crystallization and then dissolved into poikilitic pyroxene. Chromite grains could also be efficiently floated by these fluids, causing them to migrate away from the silicate minerals in the magma channel and leading to the formation of nearly monomineralic chromitite seams. This process serves as a kinetic model indicating that chromite could be completely separated from silicates during mechanical sorting in layered intrusions.","PeriodicalId":55104,"journal":{"name":"Geological Society of America Bulletin","volume":" ","pages":""},"PeriodicalIF":4.9,"publicationDate":"2023-08-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"48401670","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}
Miao Sun, Junwu Tang, R. Klemd, Bin Lin, Pan Tang, Zebin Zhang, Wei Chen, Fa-qiao Li, Jing Qi, Han Chen, Feng-hua Gu
The large magma reservoirs underlying world-class porphyry deposits are one of the key factors in their formation, which thus led to the present study focusing on the unmineralized intrusive rocks underlying the porphyry molybdenum-copper orebody of the post-collisional Jiama porphyry-skarn copper-polymetallic deposit in southern Tibet. The Jiama porphyry intrusion comprises intermediate-silica quartz diorite, monzogranite, and granodiorite porphyries, as well a high-silica granite porphyry. The intrusive rocks suite exhibits similar whole-rock Sr-Nd isotopic compositions [εNd(t) = −3.9 to −0.8], suggesting a common, non-radiogenic magma source. Yet, these rocks have distinct geochemical characteristics. The intermediate-silica rocks are relatively enriched in Ba and Sr with minor Eu anomalies, and show adakite-like geochemical characteristics. In contrast, the high-silica granite porphyry is strongly depleted in Ba, Sr, and Eu, and lacks adakite-like geochemical characteristics. We propose that the high-silica granite porphyry represents highly fractionated melt extracted from a silicic mush reservoir (crystallinity of ∼40%−65%), and that the monzogranite and granodiorite porphyries constitute the complementary residual silicic cumulates. High crystallinity facilitates the formation of connected fluid pathways, allowing the efficient removal of volatiles from the remaining silicic melt and a rapid flux of the ore-forming fluids toward the apical parts of the large magma reservoir. Less-evolved mafic melt is believed to have repeatedly intruded the base of the magma reservoir, thereby releasing volatiles and water into the silicic mush systems. The volatiles migrated upward through the fluid channels and accumulated in the apical part of the magma reservoir, subsequently, as a result of the overpressure in the roof zone, ore-forming fluids and successive batches of magma were expelled together, thereby forming the Jiama porphyry-skarn deposit.
{"title":"The formation of a giant post-collision porphyry copper system: A case study of the Jiama deposit, Tibet","authors":"Miao Sun, Junwu Tang, R. Klemd, Bin Lin, Pan Tang, Zebin Zhang, Wei Chen, Fa-qiao Li, Jing Qi, Han Chen, Feng-hua Gu","doi":"10.1130/b36924.1","DOIUrl":"https://doi.org/10.1130/b36924.1","url":null,"abstract":"The large magma reservoirs underlying world-class porphyry deposits are one of the key factors in their formation, which thus led to the present study focusing on the unmineralized intrusive rocks underlying the porphyry molybdenum-copper orebody of the post-collisional Jiama porphyry-skarn copper-polymetallic deposit in southern Tibet. The Jiama porphyry intrusion comprises intermediate-silica quartz diorite, monzogranite, and granodiorite porphyries, as well a high-silica granite porphyry. The intrusive rocks suite exhibits similar whole-rock Sr-Nd isotopic compositions [εNd(t) = −3.9 to −0.8], suggesting a common, non-radiogenic magma source. Yet, these rocks have distinct geochemical characteristics. The intermediate-silica rocks are relatively enriched in Ba and Sr with minor Eu anomalies, and show adakite-like geochemical characteristics. In contrast, the high-silica granite porphyry is strongly depleted in Ba, Sr, and Eu, and lacks adakite-like geochemical characteristics. We propose that the high-silica granite porphyry represents highly fractionated melt extracted from a silicic mush reservoir (crystallinity of ∼40%−65%), and that the monzogranite and granodiorite porphyries constitute the complementary residual silicic cumulates. High crystallinity facilitates the formation of connected fluid pathways, allowing the efficient removal of volatiles from the remaining silicic melt and a rapid flux of the ore-forming fluids toward the apical parts of the large magma reservoir. Less-evolved mafic melt is believed to have repeatedly intruded the base of the magma reservoir, thereby releasing volatiles and water into the silicic mush systems. The volatiles migrated upward through the fluid channels and accumulated in the apical part of the magma reservoir, subsequently, as a result of the overpressure in the roof zone, ore-forming fluids and successive batches of magma were expelled together, thereby forming the Jiama porphyry-skarn deposit.","PeriodicalId":55104,"journal":{"name":"Geological Society of America Bulletin","volume":" ","pages":""},"PeriodicalIF":4.9,"publicationDate":"2023-08-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"49369587","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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