J. Spencer, S. Richard, A. Bykerk-Kauffman, K. Constenius, V. Valencia
Oligocene and early Miocene displacement on the Catalina–San Pedro detachment fault and its northern correlatives uncovered mylonitic fabrics that form the greater Catalina metamorphic core complex in southeastern Arizona, USA. Gently to moderately dipping mylonitic foliations in the complex are strongly lineated, with a lineation-azimuth average of 064–244° and dominantly top-southwest shear sense over the entire 115-km-long mylonite belt. Reconstruction of detachment fault displacement based on a variety of features indicates 40–60 km of displacement, with greater displacement in more southern areas. Widespread 26–28 Ma volcanism during early extensional basin genesis was followed by 24–26 Ma granitoid magmatism. Cooling of footwall mylonites continued until 22–24 Ma, as indicated by 40Ar/39Ar mica dates. Lower temperature thermochronometers suggest that footwall exhumation was still underway at ca. 20 Ma. Tectonic reconstruction places a variety of unmetamorphosed supracrustal units in the Tucson and Silver Bell Mountains above equivalent units that were metamorphosed and penetratively deformed in the Tortolita and Santa Catalina Mountains. This restored juxtaposition is interpreted as a consequence of older Laramide thrust burial of the deformed units, with northeast-directed thrusting occurring along the Wildhorse Mountain thrust in the Rincon Mountains and related but largely concealed thrusts to the northwest. Effective extensional exhumation of lower plate rocks resulted from a general lack of internal extension of the upper plate wedge. This is attributed to a stable sliding regime during the entire period of extension, with metamorphic core complex inflation by deep crustal flow leading to maintenance of wedge surface slope and detachment fault dip that favored stable sliding rather than internal wedge extension.
{"title":"Structure, chronology, kinematics, and geodynamics of tectonic extension in the greater Catalina metamorphic core complex, southeastern Arizona, USA","authors":"J. Spencer, S. Richard, A. Bykerk-Kauffman, K. Constenius, V. Valencia","doi":"10.1130/ges02485.1","DOIUrl":"https://doi.org/10.1130/ges02485.1","url":null,"abstract":"Oligocene and early Miocene displacement on the Catalina–San Pedro detachment fault and its northern correlatives uncovered mylonitic fabrics that form the greater Catalina metamorphic core complex in southeastern Arizona, USA. Gently to moderately dipping mylonitic foliations in the complex are strongly lineated, with a lineation-azimuth average of 064–244° and dominantly top-southwest shear sense over the entire 115-km-long mylonite belt. Reconstruction of detachment fault displacement based on a variety of features indicates 40–60 km of displacement, with greater displacement in more southern areas. Widespread 26–28 Ma volcanism during early extensional basin genesis was followed by 24–26 Ma granitoid magmatism. Cooling of footwall mylonites continued until 22–24 Ma, as indicated by 40Ar/39Ar mica dates. Lower temperature thermochronometers suggest that footwall exhumation was still underway at ca. 20 Ma. Tectonic reconstruction places a variety of unmetamorphosed supracrustal units in the Tucson and Silver Bell Mountains above equivalent units that were metamorphosed and penetratively deformed in the Tortolita and Santa Catalina Mountains. This restored juxtaposition is interpreted as a consequence of older Laramide thrust burial of the deformed units, with northeast-directed thrusting occurring along the Wildhorse Mountain thrust in the Rincon Mountains and related but largely concealed thrusts to the northwest. Effective extensional exhumation of lower plate rocks resulted from a general lack of internal extension of the upper plate wedge. This is attributed to a stable sliding regime during the entire period of extension, with metamorphic core complex inflation by deep crustal flow leading to maintenance of wedge surface slope and detachment fault dip that favored stable sliding rather than internal wedge extension.","PeriodicalId":55100,"journal":{"name":"Geosphere","volume":" ","pages":""},"PeriodicalIF":2.5,"publicationDate":"2022-09-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"45491448","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Katherine A. Alexander, C. Amos, G. Balco, W. Amidon, D. Clark, A. Meigs, Reyne K. Lesnau
New cosmogenic 3He chronologies and geologic mapping of faulted glacial drift provide new constraints for the slip rates of active faulting in the central Cascade arc, Oregon, USA. The White Branch and Dilman Meadows fault zones cut deposits created by three distinct glacial advances, which provide timing, kinematics, and rate constraints for fault motion. New cosmogenic 3He data from landforms comprising the youngest and most widespread deposits have ages between 19.4 +10.1/–6.2 ka and 21.3 ± 4.9 ka; therefore, they were deposited during the last glacial maximum (LGM). A second, older outwash surface reveals an age of 74.2 ± 3.8 ka, which suggests glaciation possibly associated with marine isotope stage (MIS) 5b. Dip-slip displacement across fault scarps expressed by lidar data reveal similar magnitudes of extensional deformation for LGM and older glacial deposits on the White Branch fault zone, which implies a lack of earthquake ruptures between the oldest and LGM advances. In contrast, scarp profiles along the Dilman Meadows fault zone reveal progressive cumulative slip for surfaces of increasing age. Taken together, our measurements provide the first constraints on the rate of extensional faulting derived from Quaternary geochronology along the White Branch and Dilman Meadows faults, which total 0.1–0.4 mm/yr since ca. 75 ka and 0.6 ± 0.04 mm/yr since the LGM, respectively. The White Branch fault zone accommodates predominately fault-normal extension, whereas right-oblique slip characterizes the Dilman Meadows fault zone. Active deformation across the central Cascade Range thus reflects the combined effects of ongoing crustal block rotation and arc magmatism.
{"title":"Implications of glacial deposit ages for the timing and rate of active crustal faulting in the central Cascade arc, Oregon, USA","authors":"Katherine A. Alexander, C. Amos, G. Balco, W. Amidon, D. Clark, A. Meigs, Reyne K. Lesnau","doi":"10.1130/ges02476.1","DOIUrl":"https://doi.org/10.1130/ges02476.1","url":null,"abstract":"New cosmogenic 3He chronologies and geologic mapping of faulted glacial drift provide new constraints for the slip rates of active faulting in the central Cascade arc, Oregon, USA. The White Branch and Dilman Meadows fault zones cut deposits created by three distinct glacial advances, which provide timing, kinematics, and rate constraints for fault motion. New cosmogenic 3He data from landforms comprising the youngest and most widespread deposits have ages between 19.4 +10.1/–6.2 ka and 21.3 ± 4.9 ka; therefore, they were deposited during the last glacial maximum (LGM). A second, older outwash surface reveals an age of 74.2 ± 3.8 ka, which suggests glaciation possibly associated with marine isotope stage (MIS) 5b. Dip-slip displacement across fault scarps expressed by lidar data reveal similar magnitudes of extensional deformation for LGM and older glacial deposits on the White Branch fault zone, which implies a lack of earthquake ruptures between the oldest and LGM advances. In contrast, scarp profiles along the Dilman Meadows fault zone reveal progressive cumulative slip for surfaces of increasing age. Taken together, our measurements provide the first constraints on the rate of extensional faulting derived from Quaternary geochronology along the White Branch and Dilman Meadows faults, which total 0.1–0.4 mm/yr since ca. 75 ka and 0.6 ± 0.04 mm/yr since the LGM, respectively. The White Branch fault zone accommodates predominately fault-normal extension, whereas right-oblique slip characterizes the Dilman Meadows fault zone. Active deformation across the central Cascade Range thus reflects the combined effects of ongoing crustal block rotation and arc magmatism.","PeriodicalId":55100,"journal":{"name":"Geosphere","volume":" ","pages":""},"PeriodicalIF":2.5,"publicationDate":"2022-09-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"47373391","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
M. Lamb, T. Hickson, P. Umhoefer, Zachary W. Anderson, C. Pomerleau, Katrina S. Souders, L. Lee, N. Dunbar, W. Mcintosh
Miocene basins of the Lake Mead region (southwestern United States) contain a well-exposed record of rifting and the evolving paleogeography of the eastern central Basin and Range. The middle Miocene Horse Spring Formation and red sandstone unit allow for detailed stratigraphic, chronostratigraphic, and structural analysis for better understanding the geologic history of extension in this region. We present new data from the White Basin and Lovell Wash areas (Nevada) to interpret the evolution of faulting, basin fill, and paleogeography. We conclude that tectonics strongly influenced sedimentation and hypothesize that climate may have played a secondary but important role in creating stratigraphic variations. Deposited from 14.5 to 13.86 Ma, the microbialitic Bitter Ridge Limestone Member of the Horse Spring Formation, the stratigraphically lowest unit in this study, records a widespread shallow and uniform lake which had moderate and steady sedimentation rates, both of which were controlled by a few faults. The persistent lake was broken up by fault reorganization followed by deposition of the highly variable fluvial-lacustrine facies of the Lovell Wash Member from 13.86 to 12.7 Ma. During this time, faulting shifted from the northeast-trending, oblique normal left-lateral White Basin fault to the northwest-trending, normal Muddy Peak fault and other smaller northwest-trending faults. The lower and middle portions of the red sandstone unit, 12.7–11.4 Ma, record an increase in the sedimentation rate of basin fill near the Muddy Peak fault as well as the return to widespread lacustrine conditions. Sedimentation and faulting slowed during deposition of the uppermost red sandstone unit, but some deformation occurred post–11.4 Ma. This study records basin-fill evolution including variations in depositional environments laterally and vertically, documents changes in the location and magnitude of faulting, supports earlier work that hypothesized faulting proceeded in discrete westward steps across the Lake Mead area, and helps constrain the paleogeographic and tectonic evolution of the region.
{"title":"Middle Miocene faulting and basin evolution during central Basin and Range extension: A detailed record from the upper Horse Spring Formation and red sandstone unit, Lake Mead region, Nevada, USA","authors":"M. Lamb, T. Hickson, P. Umhoefer, Zachary W. Anderson, C. Pomerleau, Katrina S. Souders, L. Lee, N. Dunbar, W. Mcintosh","doi":"10.1130/ges02463.1","DOIUrl":"https://doi.org/10.1130/ges02463.1","url":null,"abstract":"Miocene basins of the Lake Mead region (southwestern United States) contain a well-exposed record of rifting and the evolving paleogeography of the eastern central Basin and Range. The middle Miocene Horse Spring Formation and red sandstone unit allow for detailed stratigraphic, chronostratigraphic, and structural analysis for better understanding the geologic history of extension in this region. We present new data from the White Basin and Lovell Wash areas (Nevada) to interpret the evolution of faulting, basin fill, and paleogeography. We conclude that tectonics strongly influenced sedimentation and hypothesize that climate may have played a secondary but important role in creating stratigraphic variations. Deposited from 14.5 to 13.86 Ma, the microbialitic Bitter Ridge Limestone Member of the Horse Spring Formation, the stratigraphically lowest unit in this study, records a widespread shallow and uniform lake which had moderate and steady sedimentation rates, both of which were controlled by a few faults. The persistent lake was broken up by fault reorganization followed by deposition of the highly variable fluvial-lacustrine facies of the Lovell Wash Member from 13.86 to 12.7 Ma. During this time, faulting shifted from the northeast-trending, oblique normal left-lateral White Basin fault to the northwest-trending, normal Muddy Peak fault and other smaller northwest-trending faults. The lower and middle portions of the red sandstone unit, 12.7–11.4 Ma, record an increase in the sedimentation rate of basin fill near the Muddy Peak fault as well as the return to widespread lacustrine conditions. Sedimentation and faulting slowed during deposition of the uppermost red sandstone unit, but some deformation occurred post–11.4 Ma. This study records basin-fill evolution including variations in depositional environments laterally and vertically, documents changes in the location and magnitude of faulting, supports earlier work that hypothesized faulting proceeded in discrete westward steps across the Lake Mead area, and helps constrain the paleogeographic and tectonic evolution of the region.","PeriodicalId":55100,"journal":{"name":"Geosphere","volume":" ","pages":""},"PeriodicalIF":2.5,"publicationDate":"2022-08-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"44244726","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Fault traces and offsets, cross-section length changes, paleomagnetic inclination and declination anomalies, and stress-direction indicators with ages back to 90 Ma are collected from the geologic literature on the western United States and northern Mexico. Finite-element program Restore simulates paleokinematics by weighted least squares and integrates displacements, strains, and rotations back in time, producing paleogeologic maps, as well as maps of velocity, heave rate, strain rate, and stress direction at 6 m.y. intervals. After calibrating three program parameters against neotectonic velocities from geodesy, all classes of data except inclination anomalies are fit reasonably well. The kink in the San Andreas fault near San Gorgonio Pass has been gradually restored by slip on adjacent faults and automated smoothing. Piercing-point pairs successfully restored along the San Andreas–Gulf of California plate boundary include the Pelona and Orocopia Schists at 6 Ma, the Pinnacles and Neenach Volcanics at 21 Ma, and the Jolla Vieja and Poway conglomerates adjacent to their Sonoran source at 48–42 Ma. During 18–6 Ma, rapid extension on the Oceanside detachment fault system was restored, placing present San Nicolas Island adjacent to present Rosarito, Baja California, at 18 Ma. Since ca. 18 Ma, the western Transverse Ranges have rotated 70° clockwise, restoration of which implies that sinistral faults in this province originated with NNE trends. The first contact between the Pacific and North America plates at ca. 28 Ma was not associated with any dramatic increase in dextral faulting on land; instead, the primary result was extension in the Plush Ranch–Vasquez-Diligencia basins and Colorado River corridor, probably driven by an unstable triple-junction and accelerated by heating and uplift of North America above enlarging slab windows.
{"title":"Kinematics and paleogeology of the western United States and northern Mexico computed from geologic and paleomagnetic data: 0 to 48 Ma","authors":"P. Bird, R. Ingersoll","doi":"10.1130/ges02474.1","DOIUrl":"https://doi.org/10.1130/ges02474.1","url":null,"abstract":"Fault traces and offsets, cross-section length changes, paleomagnetic inclination and declination anomalies, and stress-direction indicators with ages back to 90 Ma are collected from the geologic literature on the western United States and northern Mexico. Finite-element program Restore simulates paleokinematics by weighted least squares and integrates displacements, strains, and rotations back in time, producing paleogeologic maps, as well as maps of velocity, heave rate, strain rate, and stress direction at 6 m.y. intervals. After calibrating three program parameters against neotectonic velocities from geodesy, all classes of data except inclination anomalies are fit reasonably well. The kink in the San Andreas fault near San Gorgonio Pass has been gradually restored by slip on adjacent faults and automated smoothing. Piercing-point pairs successfully restored along the San Andreas–Gulf of California plate boundary include the Pelona and Orocopia Schists at 6 Ma, the Pinnacles and Neenach Volcanics at 21 Ma, and the Jolla Vieja and Poway conglomerates adjacent to their Sonoran source at 48–42 Ma. During 18–6 Ma, rapid extension on the Oceanside detachment fault system was restored, placing present San Nicolas Island adjacent to present Rosarito, Baja California, at 18 Ma. Since ca. 18 Ma, the western Transverse Ranges have rotated 70° clockwise, restoration of which implies that sinistral faults in this province originated with NNE trends. The first contact between the Pacific and North America plates at ca. 28 Ma was not associated with any dramatic increase in dextral faulting on land; instead, the primary result was extension in the Plush Ranch–Vasquez-Diligencia basins and Colorado River corridor, probably driven by an unstable triple-junction and accelerated by heating and uplift of North America above enlarging slab windows.","PeriodicalId":55100,"journal":{"name":"Geosphere","volume":"1 1","pages":""},"PeriodicalIF":2.5,"publicationDate":"2022-08-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"63751835","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Kendra E. Murray, Andrea L. Stevens Goddard, Alyssa L. Abbey, M. Wildman
Advances in low-temperature thermochronology, and the wide range of geologic problems that it is used to investigate, have prompted the routine use of thermal history (time-temperature, tT) models to quantitatively explore and evaluate rock cooling ages. As a result, studies that investigate topics ranging from Proterozoic tectonics to Pleistocene erosion now commonly require a substantial numerical modeling effort that combines the empirical understanding of chronometer thermochemical behavior (kinetics) with independent knowledge or hypotheses about a study area’s geologic history (geologic constraints). Although relatively user-friendly programs, such as HeFTy and QTQt, are available to facilitate thermal history modeling, there is a critical need to provide the geoscience community with more accessible entry points for using these tools. This contribution addresses this need by offering an explicit discussion of modeling strategies in the program HeFTy. Using both synthetic data and real examples, we illustrate the opportunities and limitations of thermal history modeling. We highlight the importance of testing the sensitivity of model results to model design choices and describe a strategy for classifying model results that we call the Path Family Approach. More broadly, we demonstrate how HeFTy can be used to build an intuitive understanding of the thermochronologic data types and model design strategies that are capable of discriminating among geologic hypotheses.
{"title":"Thermal history modeling techniques and interpretation strategies: Applications using HeFTy","authors":"Kendra E. Murray, Andrea L. Stevens Goddard, Alyssa L. Abbey, M. Wildman","doi":"10.1130/ges02500.1","DOIUrl":"https://doi.org/10.1130/ges02500.1","url":null,"abstract":"Advances in low-temperature thermochronology, and the wide range of geologic problems that it is used to investigate, have prompted the routine use of thermal history (time-temperature, tT) models to quantitatively explore and evaluate rock cooling ages. As a result, studies that investigate topics ranging from Proterozoic tectonics to Pleistocene erosion now commonly require a substantial numerical modeling effort that combines the empirical understanding of chronometer thermochemical behavior (kinetics) with independent knowledge or hypotheses about a study area’s geologic history (geologic constraints). Although relatively user-friendly programs, such as HeFTy and QTQt, are available to facilitate thermal history modeling, there is a critical need to provide the geoscience community with more accessible entry points for using these tools. This contribution addresses this need by offering an explicit discussion of modeling strategies in the program HeFTy. Using both synthetic data and real examples, we illustrate the opportunities and limitations of thermal history modeling. We highlight the importance of testing the sensitivity of model results to model design choices and describe a strategy for classifying model results that we call the Path Family Approach. More broadly, we demonstrate how HeFTy can be used to build an intuitive understanding of the thermochronologic data types and model design strategies that are capable of discriminating among geologic hypotheses.","PeriodicalId":55100,"journal":{"name":"Geosphere","volume":" ","pages":""},"PeriodicalIF":2.5,"publicationDate":"2022-08-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"47209476","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Holger Petermann, T. Lyson, Ian M. Miller, J. Hagadorn
We propose a new proxy that employs assemblages of fossil turtle shells to estimate the timing and depth at which fossilization and lithification occur in shallowly buried terrestrial strata. This proxy, the Turtle Compaction Index (TCI), leverages the mechanical failure properties of extant turtle shells and the material properties of sediments that encase fossil turtle shells to estimate the burial depths over which turtle shells become compacted. Because turtle shells are one of the most abundant macroscopic terrestrial fossils in late Mesozoic and younger strata, the compactional attributes of a suite of turtle shells can be paired with geochronologic and stratigraphic data to constrain burial histories of continental settings—a knowledge gap unfilled by traditional burial-depth proxies, most of which are more sensitive to deeper burial depths. Pilot TCI studies of suites of shallowly buried turtle shells from the Denver and Williston basins suggest that such assemblages are sensitive indicators of the depths (~10–500 m) at which fossils and their encasing sediment become sufficiently lithified to inhibit further shell compaction, which is when taphonomic processes correspondingly wane. This work also confirms previously hypothesized shallow Cenozoic burial histories for each of these basins. TCI from mudstone-encased turtle shells can be paired with thicknesses and ages of overlying strata to create geohistorical burial curves that indicate when such post-burial processes were active.
{"title":"Crushed turtle shells: Proxies for lithification and burial-depth histories","authors":"Holger Petermann, T. Lyson, Ian M. Miller, J. Hagadorn","doi":"10.1130/ges02513.1","DOIUrl":"https://doi.org/10.1130/ges02513.1","url":null,"abstract":"We propose a new proxy that employs assemblages of fossil turtle shells to estimate the timing and depth at which fossilization and lithification occur in shallowly buried terrestrial strata. This proxy, the Turtle Compaction Index (TCI), leverages the mechanical failure properties of extant turtle shells and the material properties of sediments that encase fossil turtle shells to estimate the burial depths over which turtle shells become compacted. Because turtle shells are one of the most abundant macroscopic terrestrial fossils in late Mesozoic and younger strata, the compactional attributes of a suite of turtle shells can be paired with geochronologic and stratigraphic data to constrain burial histories of continental settings—a knowledge gap unfilled by traditional burial-depth proxies, most of which are more sensitive to deeper burial depths. Pilot TCI studies of suites of shallowly buried turtle shells from the Denver and Williston basins suggest that such assemblages are sensitive indicators of the depths (~10–500 m) at which fossils and their encasing sediment become sufficiently lithified to inhibit further shell compaction, which is when taphonomic processes correspondingly wane. This work also confirms previously hypothesized shallow Cenozoic burial histories for each of these basins. TCI from mudstone-encased turtle shells can be paired with thicknesses and ages of overlying strata to create geohistorical burial curves that indicate when such post-burial processes were active.","PeriodicalId":55100,"journal":{"name":"Geosphere","volume":" ","pages":""},"PeriodicalIF":2.5,"publicationDate":"2022-08-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"45406911","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
A. Pamukçu, B. Schoene, C. Deering, C. B. Keller, M. Eddy
Exposed at the Lake City caldera (Colorado, USA) is the ca. 23 Ma reversely stratified (rhyolite to trachyte) Sunshine Peak Tuff and post-collapse syenite and monzonite resurgent intrusions. Existing models for this system suggest that the rhyolites are related to the trachyte and resurgent syenite through fractional crystallization, separation, and remobilization (crystal mush model), and that multiple magma batches were involved in the system (Hon, 1987; Kennedy et al., 2016; Lubbers et al., 2020). We use U-Pb zircon CA-ID-TIMS-TEA and zircon trace-element modeling to further probe age and geochemical relationships between the extrusive and intrusive units. Zircon ages and compositions from the erupted units and the syenite overlap, suggesting these magmas were related and may have mixed prior to eruption. Results from the monzonite suggest it was a contemporaneous but distinct magma batch that mixed with parts of the larger system. Trends in zircon geochemistry are decoupled from time, reflecting a complex history of accessory mineral saturation and mixing of magma batches, and a distinct high-Hf population of zircon grains hints at the existence of an additional, independent batch of rhyolitic magma in the system. The new ages we present shorten the lifetime of the Lake City magmatic system from 80 to 300 k.y. (Bove et al., 2001) to 60 to 220 k.y. and suggest the high-silica rhyolite magma crystallized over a minimum of ~160 k.y. This latter timescale likely reflects a protracted history that includes differentiation of a parent melt prior to extraction of eruptible high-silica rhyolite magma.
暴露在Lake City破火山口（美国科罗拉多州）的是约23 Ma的反向分层（从流纹岩到粗晶岩）Sunshine Peak Tuff和坍塌后的正长岩和二长岩复活侵入体。该系统的现有模型表明，流纹岩通过分级结晶、分离和再活化与粗晶岩和复活正长岩有关（晶浆模型），并且该系统涉及多个岩浆批次（Hon，1987；Kennedy等人，2016；Lubbers等人，2020）。我们使用U-Pb锆石CA-ID-TIMS-TEA和锆石微量元素建模来进一步探测喷出单元和侵入单元之间的年龄和地球化学关系。喷发单元和正长岩的锆石年龄和成分重叠，表明这些岩浆是相关的，可能在喷发前混合。二长岩的结果表明，它是一个同时代但不同的岩浆批次，与较大系统的部分混合。锆石地球化学的趋势与时间脱钩，反映了副矿物饱和和岩浆批次混合的复杂历史，锆石颗粒的明显高Hf群体暗示系统中存在额外的、独立的一批流纹岩岩浆。我们提出的新年龄将Lake City岩浆系统的寿命从80至300千年（Bove et al.，2001）缩短至60至220千年，并表明高硅流纹岩岩浆的结晶时间至少为160千年。后一个时间尺度可能反映了一个漫长的历史，包括在提取可喷发的高硅流纹岩岩浆之前母熔体的分化。
{"title":"Volcano-pluton connections at the Lake City magmatic center (Colorado, USA)","authors":"A. Pamukçu, B. Schoene, C. Deering, C. B. Keller, M. Eddy","doi":"10.1130/ges02467.1","DOIUrl":"https://doi.org/10.1130/ges02467.1","url":null,"abstract":"Exposed at the Lake City caldera (Colorado, USA) is the ca. 23 Ma reversely stratified (rhyolite to trachyte) Sunshine Peak Tuff and post-collapse syenite and monzonite resurgent intrusions. Existing models for this system suggest that the rhyolites are related to the trachyte and resurgent syenite through fractional crystallization, separation, and remobilization (crystal mush model), and that multiple magma batches were involved in the system (Hon, 1987; Kennedy et al., 2016; Lubbers et al., 2020). We use U-Pb zircon CA-ID-TIMS-TEA and zircon trace-element modeling to further probe age and geochemical relationships between the extrusive and intrusive units. Zircon ages and compositions from the erupted units and the syenite overlap, suggesting these magmas were related and may have mixed prior to eruption. Results from the monzonite suggest it was a contemporaneous but distinct magma batch that mixed with parts of the larger system. Trends in zircon geochemistry are decoupled from time, reflecting a complex history of accessory mineral saturation and mixing of magma batches, and a distinct high-Hf population of zircon grains hints at the existence of an additional, independent batch of rhyolitic magma in the system. The new ages we present shorten the lifetime of the Lake City magmatic system from 80 to 300 k.y. (Bove et al., 2001) to 60 to 220 k.y. and suggest the high-silica rhyolite magma crystallized over a minimum of ~160 k.y. This latter timescale likely reflects a protracted history that includes differentiation of a parent melt prior to extraction of eruptible high-silica rhyolite magma.","PeriodicalId":55100,"journal":{"name":"Geosphere","volume":" ","pages":""},"PeriodicalIF":2.5,"publicationDate":"2022-08-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"44659101","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Leigh H. van Drecht, L. Beranek, M. Colpron, Adam C. Wiest
The Whitehorse trough is a synorogenic basin in the northern Cordillera that resulted from arc-collision processes along the northwestern margin of North America, but its filling history and tectonic significance remain uncertain. New detrital zircon U-Pb-Hf isotope analyses of 12 rock samples, including six basal sandstones that sit unconformably on Triassic rocks of Stikinia, were combined with published detrital zircon and fossil data to establish the depositional ages of synorogenic Laberge Group strata in Yukon and test proposed links between Intermontane terrane exhumation and basin-filling events. Laberge Group strata yielded 205–170 Ma and 390–252 Ma detrital zircon populations that indicate derivation from local Late Triassic to Middle Jurassic arc and syncollisional plutons and metamorphosed Paleozoic basement rocks of the Stikinia and Yukon-Tanana terranes. Basal sandstone units have Early Jurassic depositional ages that show the Whitehorse trough filled during early Sinemurian, late Sinemurian to Pliensbachian, and Toarcian subsidence events. Late Triassic to Early Jurassic detrital zircon grains confirm that syn-collisional plutons near the northern trough were exhumed at 0.5–7.5 mm/yr and replicate their excursion to subchondritic Hf isotope compositions as a result of increasing crustal contributions from Rhaetian to Sinemurian time. The new detrital zircon data, combined with recent constraints for Triassic– Jurassic metamorphism and magmatism in Yukon, require modification of published forearc to syncollisional basin models for the Whitehorse trough. We reinterpret Jurassic subsidence patterns and architecture of the Whitehorse trough to reflect sinistral transtension within a transform fault system that resulted from the reorganization of subduction after end-on arc collision.
{"title":"Development of the Whitehorse trough as a strike-slip basin during Early to Middle Jurassic arc-continent collision in the Canadian Cordillera","authors":"Leigh H. van Drecht, L. Beranek, M. Colpron, Adam C. Wiest","doi":"10.1130/ges02510.1","DOIUrl":"https://doi.org/10.1130/ges02510.1","url":null,"abstract":"The Whitehorse trough is a synorogenic basin in the northern Cordillera that resulted from arc-collision processes along the northwestern margin of North America, but its filling history and tectonic significance remain uncertain. New detrital zircon U-Pb-Hf isotope analyses of 12 rock samples, including six basal sandstones that sit unconformably on Triassic rocks of Stikinia, were combined with published detrital zircon and fossil data to establish the depositional ages of synorogenic Laberge Group strata in Yukon and test proposed links between Intermontane terrane exhumation and basin-filling events. Laberge Group strata yielded 205–170 Ma and 390–252 Ma detrital zircon populations that indicate derivation from local Late Triassic to Middle Jurassic arc and syncollisional plutons and metamorphosed Paleozoic basement rocks of the Stikinia and Yukon-Tanana terranes. Basal sandstone units have Early Jurassic depositional ages that show the Whitehorse trough filled during early Sinemurian, late Sinemurian to Pliensbachian, and Toarcian subsidence events. Late Triassic to Early Jurassic detrital zircon grains confirm that syn-collisional plutons near the northern trough were exhumed at 0.5–7.5 mm/yr and replicate their excursion to subchondritic Hf isotope compositions as a result of increasing crustal contributions from Rhaetian to Sinemurian time. The new detrital zircon data, combined with recent constraints for Triassic– Jurassic metamorphism and magmatism in Yukon, require modification of published forearc to syncollisional basin models for the Whitehorse trough. We reinterpret Jurassic subsidence patterns and architecture of the Whitehorse trough to reflect sinistral transtension within a transform fault system that resulted from the reorganization of subduction after end-on arc collision.","PeriodicalId":55100,"journal":{"name":"Geosphere","volume":" ","pages":""},"PeriodicalIF":2.5,"publicationDate":"2022-08-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"43263805","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
New lithologic and detrital zircon (DZ) U-Pb data from Devonian–Triassic strata on St. Lawrence Island in the Bering Sea and from the western Brooks Range of Alaska suggest affinities between these two areas. The Brooks Range constitutes part of the Arctic Alaska–Chukotka microplate, but the tectonic and paleogeographic affinities of St. Lawrence Island are unknown or at best speculative. Strata on St. Lawrence Island form a Devonian–Triassic carbonate succession and a Mississippian(?)–Triassic clastic succession that are subdivided according to three distinctive DZ age distributions. The Devonian–Triassic carbonate succession has Mississippian-age quartz arenite beds with Silurian, Cambrian, Neoproterozoic, and Mesoproterozoic DZ age modes, and it exhibits similar age distributions and lithologic and biostratigraphic characteristics as Mississippian-age Utukok Formation strata in the Kelly River allochthon of the western Brooks Range. Consistent late Neoproterozoic, Cambrian, and Silurian ages in each of the Mississippian-age units suggest efficient mixing of the DZ prior to deposition, and derivation from strata exposed by the pre-Mississippian unconformity and/or Endicott Group strata that postdate the unconformity. The Mississippian(?)–Triassic clastic succession is subdivided into feldspathic and graywacke subunits. The feldspathic subunit has a unimodal DZ age mode at 2.06 Ga, identical to Nuka Formation strata in the Nuka Ridge allochthon of the western Brooks Range, and it records a distinctive depositional episode related to late Paleozoic juxtaposition of a Paleoproterozoic terrane along the most distal parts of the Arctic Alaska–Chukotka microplate. The graywacke subunit has Triassic maximum depositional ages and abundant late Paleozoic grains, likely sourced from fringing arcs and/or continent-scale paleorivers draining Eurasia, and it has similar age distributions to Triassic strata from the Lisburne Peninsula (northwestern Alaska), Chukotka and Wrangel Island (eastern Russia), and the northern Sverdrup Basin (Canadian Arctic), but, unlike the Devonian–Triassic carbonate succession and feldspathic subunit of the Mississippian(?)–Triassic clastic succession, it has no obvious analogue in the western Brooks Range allochthon stack. These correlations establish St. Lawrence Island as conclusively belonging to the Arctic Alaska–Chukotka microplate, thus enhancing our understanding of the circum-Arctic region in late Paleozoic–Triassic time.
{"title":"Detrital zircon ages from upper Paleozoic–Triassic clastic strata on St. Lawrence Island, Alaska: An enigmatic component of the Arctic Alaska–Chukotka microplate","authors":"J. Amato, J. Dumoulin, E. S. Gottlieb, T. Moore","doi":"10.1130/ges02490.1","DOIUrl":"https://doi.org/10.1130/ges02490.1","url":null,"abstract":"New lithologic and detrital zircon (DZ) U-Pb data from Devonian–Triassic strata on St. Lawrence Island in the Bering Sea and from the western Brooks Range of Alaska suggest affinities between these two areas. The Brooks Range constitutes part of the Arctic Alaska–Chukotka microplate, but the tectonic and paleogeographic affinities of St. Lawrence Island are unknown or at best speculative. Strata on St. Lawrence Island form a Devonian–Triassic carbonate succession and a Mississippian(?)–Triassic clastic succession that are subdivided according to three distinctive DZ age distributions. The Devonian–Triassic carbonate succession has Mississippian-age quartz arenite beds with Silurian, Cambrian, Neoproterozoic, and Mesoproterozoic DZ age modes, and it exhibits similar age distributions and lithologic and biostratigraphic characteristics as Mississippian-age Utukok Formation strata in the Kelly River allochthon of the western Brooks Range. Consistent late Neoproterozoic, Cambrian, and Silurian ages in each of the Mississippian-age units suggest efficient mixing of the DZ prior to deposition, and derivation from strata exposed by the pre-Mississippian unconformity and/or Endicott Group strata that postdate the unconformity. The Mississippian(?)–Triassic clastic succession is subdivided into feldspathic and graywacke subunits. The feldspathic subunit has a unimodal DZ age mode at 2.06 Ga, identical to Nuka Formation strata in the Nuka Ridge allochthon of the western Brooks Range, and it records a distinctive depositional episode related to late Paleozoic juxtaposition of a Paleoproterozoic terrane along the most distal parts of the Arctic Alaska–Chukotka microplate. The graywacke subunit has Triassic maximum depositional ages and abundant late Paleozoic grains, likely sourced from fringing arcs and/or continent-scale paleorivers draining Eurasia, and it has similar age distributions to Triassic strata from the Lisburne Peninsula (northwestern Alaska), Chukotka and Wrangel Island (eastern Russia), and the northern Sverdrup Basin (Canadian Arctic), but, unlike the Devonian–Triassic carbonate succession and feldspathic subunit of the Mississippian(?)–Triassic clastic succession, it has no obvious analogue in the western Brooks Range allochthon stack. These correlations establish St. Lawrence Island as conclusively belonging to the Arctic Alaska–Chukotka microplate, thus enhancing our understanding of the circum-Arctic region in late Paleozoic–Triassic time.","PeriodicalId":55100,"journal":{"name":"Geosphere","volume":" ","pages":""},"PeriodicalIF":2.5,"publicationDate":"2022-07-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"47659273","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
A series of large earthquakes in 1899 affected southeastern Alaska near Yakutat and Disenchantment Bays. The largest of the series, a MW 8.2 event on 10 September 1899, generated an ~12-m-high tsunami and as much as 14.4 m of coseismic uplift in Yakutat Bay, the largest coseismic uplift ever measured. Several complex fault systems in the area are associated with the Yakutat terrane collision with North America and the termination of the Fairweather strike-slip system, but because faults local to Yakutat Bay have been incompletely or poorly mapped, it is unclear which fault system(s) ruptured during the 10 September 1899 event. Using marine geophysical data collected in August 2012, we provide an improved tectonic framework for the Yakutat area, which advances our understanding of earthquake hazards. We combined 153 line km of 2012 high-resolution multichannel seismic (MCS) reflection data with compressed high-intensity radar pulse (Chirp) profiles, basin-scale MCS data, 2018 seafloor bathymetry, published geodetic models and thermochronology data, and previous measurements of coseismic uplift to better constrain fault geometry and subsurface structure in the Yakutat Bay area. We did not observe any active or concealed faults crossing Yakutat Bay in our high-resolution data, requiring faults to be located entirely onshore or nearshore. We interpreted onshore faults east of Yakutat Bay to be associated with the transpressional termination of the Fairweather fault system, forming a series of splay faults that exhibit a horsetail geometry. Thrust and reverse faults on the west side of the bay are related to Yakutat terrane underthrusting and collision with North America. Our results include an updated fault map, structural model of Yakutat Bay, and quantitative assessment of uncertainties for legacy geologic coseismic uplift measurements. Additionally, our results indicate the 10 September 1899 rupture was possibly related to stress loading from the earlier Yakutat terrane underthrusting event of 4 September 1899, with the majority of 10 September coseismic slip occurring on the Esker Creek system on the northwest side of Yakutat Bay. Limited (~2 m) coseismic or postseismic slip associated with the 1899 events occurred on faults located east of Yakutat Bay.
{"title":"Revisiting the 1899 earthquake series using integrative geophysical analysis in Yakutat Bay, Alaska","authors":"M. Walton, S. Gulick, P. Haeussler","doi":"10.1130/ges02423.1","DOIUrl":"https://doi.org/10.1130/ges02423.1","url":null,"abstract":"A series of large earthquakes in 1899 affected southeastern Alaska near Yakutat and Disenchantment Bays. The largest of the series, a MW 8.2 event on 10 September 1899, generated an ~12-m-high tsunami and as much as 14.4 m of coseismic uplift in Yakutat Bay, the largest coseismic uplift ever measured. Several complex fault systems in the area are associated with the Yakutat terrane collision with North America and the termination of the Fairweather strike-slip system, but because faults local to Yakutat Bay have been incompletely or poorly mapped, it is unclear which fault system(s) ruptured during the 10 September 1899 event. Using marine geophysical data collected in August 2012, we provide an improved tectonic framework for the Yakutat area, which advances our understanding of earthquake hazards. We combined 153 line km of 2012 high-resolution multichannel seismic (MCS) reflection data with compressed high-intensity radar pulse (Chirp) profiles, basin-scale MCS data, 2018 seafloor bathymetry, published geodetic models and thermochronology data, and previous measurements of coseismic uplift to better constrain fault geometry and subsurface structure in the Yakutat Bay area. We did not observe any active or concealed faults crossing Yakutat Bay in our high-resolution data, requiring faults to be located entirely onshore or nearshore. We interpreted onshore faults east of Yakutat Bay to be associated with the transpressional termination of the Fairweather fault system, forming a series of splay faults that exhibit a horsetail geometry. Thrust and reverse faults on the west side of the bay are related to Yakutat terrane underthrusting and collision with North America. Our results include an updated fault map, structural model of Yakutat Bay, and quantitative assessment of uncertainties for legacy geologic coseismic uplift measurements. Additionally, our results indicate the 10 September 1899 rupture was possibly related to stress loading from the earlier Yakutat terrane underthrusting event of 4 September 1899, with the majority of 10 September coseismic slip occurring on the Esker Creek system on the northwest side of Yakutat Bay. Limited (~2 m) coseismic or postseismic slip associated with the 1899 events occurred on faults located east of Yakutat Bay.","PeriodicalId":55100,"journal":{"name":"Geosphere","volume":" ","pages":""},"PeriodicalIF":2.5,"publicationDate":"2022-07-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"46462082","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"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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