New geothermometry using laser-Raman data on carbonaceous material from low and intermediate grade rocks on Santa Catalina Island, California, together with existing thermobarometric data, show that there is a quasi-continuous increase in peak metamorphic temperature from 327 ± 8°C in lawsonite blueschist facies rocks at the lowest structural levels, through ∼433°C in overlying epidote blueschists, 546 ± 20°C in albite-epidote amphibolite facies rocks, to 650–730°C in amphibolite facies rocks at the top of the sequence. Rocks of different metamorphic grade are separated from one another by tectonic contacts across which temperature increases by ∼100°C in each case. Previously published geochronological data indicate that peak metamorphism in the highest grade rocks at 115 Ma preceded deposition of blueschist facies metasediments by ∼15 million years, so that the present inverted grade sequence does not represent an original inverted temperature gradient. The present structure results from progressive underplating of oceanic rocks in a cooling subduction zone following a high-T metamorphic event at 115 Ma. An inverted temperature gradient of ≥100°C/km across the subduction channel likely existed during the high-T event, decreased during underplating, and reached zero by ∼90 Ma.
{"title":"Is the Inverted Field Gradient in the Catalina Schist Terrane Primary or Constructional?","authors":"John P. Platt, William L. Schmidt","doi":"10.1029/2023tc008021","DOIUrl":"https://doi.org/10.1029/2023tc008021","url":null,"abstract":"New geothermometry using laser-Raman data on carbonaceous material from low and intermediate grade rocks on Santa Catalina Island, California, together with existing thermobarometric data, show that there is a quasi-continuous increase in peak metamorphic temperature from 327 ± 8°C in lawsonite blueschist facies rocks at the lowest structural levels, through ∼433°C in overlying epidote blueschists, 546 ± 20°C in albite-epidote amphibolite facies rocks, to 650–730°C in amphibolite facies rocks at the top of the sequence. Rocks of different metamorphic grade are separated from one another by tectonic contacts across which temperature increases by ∼100°C in each case. Previously published geochronological data indicate that peak metamorphism in the highest grade rocks at 115 Ma preceded deposition of blueschist facies metasediments by ∼15 million years, so that the present inverted grade sequence does not represent an original inverted temperature gradient. The present structure results from progressive underplating of oceanic rocks in a cooling subduction zone following a high-T metamorphic event at 115 Ma. An inverted temperature gradient of ≥100°C/km across the subduction channel likely existed during the high-T event, decreased during underplating, and reached zero by ∼90 Ma.","PeriodicalId":22351,"journal":{"name":"Tectonics","volume":"7 1","pages":""},"PeriodicalIF":4.2,"publicationDate":"2024-02-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139757377","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}
J. M. Rosera, S. P. Gaynor, A. Ulianov, U. Schaltegger
The southern Rocky Mountains in Colorado and northern New Mexico hosted intracontinental magmatism that developed during a tectonic transition from shortening (Laramide orogeny, ca. 75 to 40 Ma) through extension and rifting. We present a novel approach that uses stochastic weighted bootstrap simulations of a large set of new and historical geochronology data to better understand how regional anisotropies responsible for focusing magma emplacement evolved through time. This technique can detect subtle trends in directional distributions, including multi-modal orientations, and can be filtered from regional to local scales. Our results indicate that magmatism followed first the northeast trend of the Colorado mineral belt between 75 and 40 Ma and deviated afterward. These deviations vary depending on the scale of the analysis. At the smallest scale we evaluated (<75 km), the orientation of magmatism from 45 to 30 Ma rotated counter-clockwise before aligning with the north-south trend of the modern Rio Grande rift. Larger, regional-scale analyses indicate magma centers between 40 to 35 Ma and 25 to 20 Ma were dominantly oriented southwest-northeast, whereas magmatism between 35 and 25 Ma had north-south orientation. The large areal footprint of magmatism and shifting regional patterns suggest that ancient zones of weakness in the North American lithosphere accommodated magma flow at different moments in time, rather than controlled by a retreating interface of the Farallon and North American plates.
科罗拉多州南部落基山脉和新墨西哥州北部的大陆内岩浆活动是在从缩短（拉氏造山运动，约 75 至 40 Ma）到延伸和断裂的构造转变过程中形成的。我们提出了一种新颖的方法，利用随机加权自举模拟大量新的和历史的地质年代数据，以更好地了解造成岩浆集中喷出的区域各向异性是如何随着时间的推移而演变的。这种技术可以发现方向性分布的微妙趋势，包括多模式定向，并且可以从区域尺度到局部尺度进行过滤。我们的研究结果表明，在 75 至 40 马年之间，岩浆活动首先沿着科罗拉多矿物带的东北方向进行，之后出现了偏离。这些偏差随分析尺度的不同而变化。在我们评估的最小尺度（75 千米）上，45 至 30 Ma 期间岩浆活动的走向先是逆时针旋转，然后才与现代格兰德河裂谷的南北走向一致。更大的区域尺度分析表明，40 至 35 Ma 和 25 至 20 Ma 之间的岩浆中心主要呈西南-东北走向，而 35 至 25 Ma 之间的岩浆活动呈南北走向。岩浆活动的大面积足迹和区域模式的变化表明，北美岩石圈的古代薄弱区在不同时期容纳了岩浆流，而不是受法拉隆板块和北美板块退缩界面的控制。
{"title":"Using Stochastic Point Pattern Analysis to Track Regional Orientations of Magmatism During the Transition to Cenozoic Extension and Rio Grande Rifting, Southern Rocky Mountains","authors":"J. M. Rosera, S. P. Gaynor, A. Ulianov, U. Schaltegger","doi":"10.1029/2023tc007902","DOIUrl":"https://doi.org/10.1029/2023tc007902","url":null,"abstract":"The southern Rocky Mountains in Colorado and northern New Mexico hosted intracontinental magmatism that developed during a tectonic transition from shortening (Laramide orogeny, ca. 75 to 40 Ma) through extension and rifting. We present a novel approach that uses stochastic weighted bootstrap simulations of a large set of new and historical geochronology data to better understand how regional anisotropies responsible for focusing magma emplacement evolved through time. This technique can detect subtle trends in directional distributions, including multi-modal orientations, and can be filtered from regional to local scales. Our results indicate that magmatism followed first the northeast trend of the Colorado mineral belt between 75 and 40 Ma and deviated afterward. These deviations vary depending on the scale of the analysis. At the smallest scale we evaluated (<75 km), the orientation of magmatism from 45 to 30 Ma rotated counter-clockwise before aligning with the north-south trend of the modern Rio Grande rift. Larger, regional-scale analyses indicate magma centers between 40 to 35 Ma and 25 to 20 Ma were dominantly oriented southwest-northeast, whereas magmatism between 35 and 25 Ma had north-south orientation. The large areal footprint of magmatism and shifting regional patterns suggest that ancient zones of weakness in the North American lithosphere accommodated magma flow at different moments in time, rather than controlled by a retreating interface of the Farallon and North American plates.","PeriodicalId":22351,"journal":{"name":"Tectonics","volume":"5 1","pages":""},"PeriodicalIF":4.2,"publicationDate":"2024-02-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139757255","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}
Yiming Zhang, Eben B. Hodgin, Tadesse Alemu, James Pierce, Anthony Fuentes, Nicholas L. Swanson-Hysell
The paleogeography of Laurentia throughout the Neoproterozoic is critical for reconstructing global paleogeography due to its central position in the supercontinent Rodinia. We develop a new paleomagnetic pole from red siltstones and fine-grained sandstones of the early Neoproterozoic Jacobsville Formation which is now constrained to be ca. 990 Ma in age. High-resolution thermal demagnetization experiments resolve detrital remanent magnetizations held by hematite. These directions were reoriented within siltstone intraclasts and pass intraformational conglomerate tests—giving confidence that the magnetization is detrital and primary. An inclination-corrected mean paleomagnetic pole position for the Jacobsville Formation indicates that Laurentia's motion slowed down significantly following the onset of the Grenvillian orogeny. Prior rapid plate motion associated with closure of the Unimos Ocean between 1,110 and 1,090 Ma transitioned to slow drift of Laurentia across the equator in the late Mesoproterozoic to early Neoproterozoic. We interpret the distinct position of this well-dated pole from those in the Grenville orogen that have been assigned a similar age to indicate that the ages of the poles associated with the Grenville Loop likely need to be revised to be younger due to prolonged exhumation.
{"title":"Tracking Rodinia Into the Neoproterozoic: New Paleomagnetic Constraints From the Jacobsville Formation","authors":"Yiming Zhang, Eben B. Hodgin, Tadesse Alemu, James Pierce, Anthony Fuentes, Nicholas L. Swanson-Hysell","doi":"10.1029/2023tc007866","DOIUrl":"https://doi.org/10.1029/2023tc007866","url":null,"abstract":"The paleogeography of Laurentia throughout the Neoproterozoic is critical for reconstructing global paleogeography due to its central position in the supercontinent Rodinia. We develop a new paleomagnetic pole from red siltstones and fine-grained sandstones of the early Neoproterozoic Jacobsville Formation which is now constrained to be ca. 990 Ma in age. High-resolution thermal demagnetization experiments resolve detrital remanent magnetizations held by hematite. These directions were reoriented within siltstone intraclasts and pass intraformational conglomerate tests—giving confidence that the magnetization is detrital and primary. An inclination-corrected mean paleomagnetic pole position for the Jacobsville Formation indicates that Laurentia's motion slowed down significantly following the onset of the Grenvillian orogeny. Prior rapid plate motion associated with closure of the Unimos Ocean between 1,110 and 1,090 Ma transitioned to slow drift of Laurentia across the equator in the late Mesoproterozoic to early Neoproterozoic. We interpret the distinct position of this well-dated pole from those in the Grenville orogen that have been assigned a similar age to indicate that the ages of the poles associated with the Grenville Loop likely need to be revised to be younger due to prolonged exhumation.","PeriodicalId":22351,"journal":{"name":"Tectonics","volume":"68 1","pages":""},"PeriodicalIF":4.2,"publicationDate":"2024-02-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139757206","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}
M. L. Anderson, R. J. Blakely, R. E. Wells, J. D. Dragovich
Detailed understanding of crustal components and tectonic history of forearcs is important due to their geological complexity and high seismic hazard. The principal component of the Cascadia forearc is Siletzia, a composite basaltic terrane of oceanic origin. Much is known about the lithology and age of the province. However, glacial sediments blanketing the Puget Lowland obscure its lateral extent and internal structure, hindering our ability to fully understand its tectonic history and its influence on modern deformation. In this study, we apply map-view interpretation and two-dimensional modeling of aeromagnetic and gravity data to the magnetically stratified Siletzia terrane revealing its internal structure and characterizing its eastern boundary. These analyses suggest the contact between Siletzia (Crescent Formation) and the Eocene accretionary prism trends northward under Lake Washington. North of Seattle, this boundary dips east where it crosses the Kingston arch, whereas south of Seattle the contact dips west where it crosses the Seattle uplift (SU). This westward dip is opposite the dip of the Eocene subduction interface, implying obduction of Siletzia upper crust at this southern location. Elongate pairs of high and low magnetic anomalies over the SU suggest imbrication of steeply-dipping, deeply rooted slices of Crescent Formation within Siletzia. We hypothesize these features result from duplication of Crescent Formation in an accretionary fold-thrust belt during the Eocene. The active Seattle fault divides this Eocene fold-thrust belt into two zones with different structural trends and opposite frontal ramp dips, suggesting the Seattle fault may have originated as a tear fault during accretion.
{"title":"Deep Structure of Siletzia in the Puget Lowland: Imaging an Obducted Plateau and Accretionary Thrust Belt With Potential Fields","authors":"M. L. Anderson, R. J. Blakely, R. E. Wells, J. D. Dragovich","doi":"10.1029/2022tc007720","DOIUrl":"https://doi.org/10.1029/2022tc007720","url":null,"abstract":"Detailed understanding of crustal components and tectonic history of forearcs is important due to their geological complexity and high seismic hazard. The principal component of the Cascadia forearc is Siletzia, a composite basaltic terrane of oceanic origin. Much is known about the lithology and age of the province. However, glacial sediments blanketing the Puget Lowland obscure its lateral extent and internal structure, hindering our ability to fully understand its tectonic history and its influence on modern deformation. In this study, we apply map-view interpretation and two-dimensional modeling of aeromagnetic and gravity data to the magnetically stratified Siletzia terrane revealing its internal structure and characterizing its eastern boundary. These analyses suggest the contact between Siletzia (Crescent Formation) and the Eocene accretionary prism trends northward under Lake Washington. North of Seattle, this boundary dips east where it crosses the Kingston arch, whereas south of Seattle the contact dips west where it crosses the Seattle uplift (SU). This westward dip is opposite the dip of the Eocene subduction interface, implying obduction of Siletzia upper crust at this southern location. Elongate pairs of high and low magnetic anomalies over the SU suggest imbrication of steeply-dipping, deeply rooted slices of Crescent Formation within Siletzia. We hypothesize these features result from duplication of Crescent Formation in an accretionary fold-thrust belt during the Eocene. The active Seattle fault divides this Eocene fold-thrust belt into two zones with different structural trends and opposite frontal ramp dips, suggesting the Seattle fault may have originated as a tear fault during accretion.","PeriodicalId":22351,"journal":{"name":"Tectonics","volume":"100 1","pages":""},"PeriodicalIF":4.2,"publicationDate":"2024-02-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139757443","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}
Yiran Wang, Michael E. Oskin, Youli Li, Xiu Hu, Jinghao Lei, Fei Liu
Understanding the propagation of shortening, especially the interaction of shallow and deep structural levels in space and time is important to understand the accretion process of a compressional orogen as well as to fully understand earthquake hazards to populated foreland basins. Here we combine evidence from geologic maps and stream-terrace surveys to construct a set of retrodeformable cross-sections of the western North Qilian Shan foreland. The uplifted, severely tilted Mesozoic and older rock units suggest the presence of both deep and shallow décollements in western and central part of our research area, and that these structures alternated activity since commencement of the latest phase of the North Qilian Shan uplift. Conversely, in the east, the absence of foreland fold-and-thrust belt and the moderately tilted Mesozoic rocks indicate the deformation is dominated by thick-skinned uplift. Based on our cross-sections, we estimate the long-term shortening rate of the Jiuxi foreland basin of 1.2–1.8 m/Kyr. Deformed foreland terraces show that, from west to east in our research area, active deformation switches between different structural levels. This trade-off between deformation styles in time and space shows that two décollement levels bound a crustal-scale duplex as the foreland is incorporated into the orogen. We suggest the complex and out-of-sequence deformation pattern may relate to pre-existing weakness within the basement rocks and is likely a common characteristic of the North Qilian foreland. This may impose an additional challenge for seismic hazard estimation of the region.
{"title":"Crustal-Scale Duplex Development During Accretion of the Jiuxi Foreland Basin, North Qilian Shan","authors":"Yiran Wang, Michael E. Oskin, Youli Li, Xiu Hu, Jinghao Lei, Fei Liu","doi":"10.1029/2023tc008160","DOIUrl":"https://doi.org/10.1029/2023tc008160","url":null,"abstract":"Understanding the propagation of shortening, especially the interaction of shallow and deep structural levels in space and time is important to understand the accretion process of a compressional orogen as well as to fully understand earthquake hazards to populated foreland basins. Here we combine evidence from geologic maps and stream-terrace surveys to construct a set of retrodeformable cross-sections of the western North Qilian Shan foreland. The uplifted, severely tilted Mesozoic and older rock units suggest the presence of both deep and shallow décollements in western and central part of our research area, and that these structures alternated activity since commencement of the latest phase of the North Qilian Shan uplift. Conversely, in the east, the absence of foreland fold-and-thrust belt and the moderately tilted Mesozoic rocks indicate the deformation is dominated by thick-skinned uplift. Based on our cross-sections, we estimate the long-term shortening rate of the Jiuxi foreland basin of 1.2–1.8 m/Kyr. Deformed foreland terraces show that, from west to east in our research area, active deformation switches between different structural levels. This trade-off between deformation styles in time and space shows that two décollement levels bound a crustal-scale duplex as the foreland is incorporated into the orogen. We suggest the complex and out-of-sequence deformation pattern may relate to pre-existing weakness within the basement rocks and is likely a common characteristic of the North Qilian foreland. This may impose an additional challenge for seismic hazard estimation of the region.","PeriodicalId":22351,"journal":{"name":"Tectonics","volume":"2 1","pages":""},"PeriodicalIF":4.2,"publicationDate":"2024-01-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139657660","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}
Chunyang Wang, Weiwei Ding, Wouter P. Schellart, Zhengyi Tong, Chongzhi Dong, Yinxia Fang, Jiabiao Li
The impact of along-trench asymmetric subduction on plate kinematic evolution (e.g., plate rotation and trench migration) remains enigmatic. In this study, analog experiments were performed to investigate the effects of symmetric and asymmetric subduction initiation on slab kinematics and trench migration. In cases when subduction was started with a cylindric slab perturbation, the plate showed little rotation during the entire subduction process, resulting in a trench shape that was symmetric with respect to the center-line of the plate. However, if subduction started with a non-cylindrical slab perturbation, the trench shape changed substantially. During the free sinking stage, the more deeply subducted part of the slab had a higher trench-normal retreat velocity (VT⊥) and subduction velocity (VS⊥) than the shallow part, which induced trench and plate rotations in the same direction. This along-trench gradient in VT⊥ increased until the deeper portion of the slab tip first touched the bottom, after which a marked decrease in VS⊥ occurred at this location; the other side of the slab had not yet reached the bottom, so experienced no recorded reduction of subduction velocity at this time. This along-strike diachronous arrival of the slab tip could induce a marked along-strike reversal in magnitude of the subduction velocity and a rotation torque centered on the point of first contact between slab and 660-km discontinuity. This could lead to instability and rotation of the subducting slab, potentially causing a reversal in the direction of trench rotation direction, but rarely in the direction of plate rotation. Our modeling results may provide useful understanding for the processes driving the rotations of the trench and plate in natural subduction zones.
{"title":"Effects of Along-Trench Asymmetric Subduction Initiation on Plate Rotation and Trench Migration: A Laboratory Modeling Perspective","authors":"Chunyang Wang, Weiwei Ding, Wouter P. Schellart, Zhengyi Tong, Chongzhi Dong, Yinxia Fang, Jiabiao Li","doi":"10.1029/2023tc007941","DOIUrl":"https://doi.org/10.1029/2023tc007941","url":null,"abstract":"The impact of along-trench asymmetric subduction on plate kinematic evolution (e.g., plate rotation and trench migration) remains enigmatic. In this study, analog experiments were performed to investigate the effects of symmetric and asymmetric subduction initiation on slab kinematics and trench migration. In cases when subduction was started with a cylindric slab perturbation, the plate showed little rotation during the entire subduction process, resulting in a trench shape that was symmetric with respect to the center-line of the plate. However, if subduction started with a non-cylindrical slab perturbation, the trench shape changed substantially. During the free sinking stage, the more deeply subducted part of the slab had a higher trench-normal retreat velocity (<i>V</i><sub>T⊥</sub>) and subduction velocity (<i>V</i><sub>S⊥</sub>) than the shallow part, which induced trench and plate rotations in the same direction. This along-trench gradient in <i>V</i><sub>T⊥</sub> increased until the deeper portion of the slab tip first touched the bottom, after which a marked decrease in <i>V</i><sub>S⊥</sub> occurred at this location; the other side of the slab had not yet reached the bottom, so experienced no recorded reduction of subduction velocity at this time. This along-strike diachronous arrival of the slab tip could induce a marked along-strike reversal in magnitude of the subduction velocity and a rotation torque centered on the point of first contact between slab and 660-km discontinuity. This could lead to instability and rotation of the subducting slab, potentially causing a reversal in the direction of trench rotation direction, but rarely in the direction of plate rotation. Our modeling results may provide useful understanding for the processes driving the rotations of the trench and plate in natural subduction zones.","PeriodicalId":22351,"journal":{"name":"Tectonics","volume":"32 1","pages":""},"PeriodicalIF":4.2,"publicationDate":"2024-01-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139589783","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}
Jane A. Gilotti, William C. McClelland, Wentao Cao, Matthew A. Coble
Ultrahigh-pressure (UHP) rocks in North-East Greenland lie within a larger region of high-pressure Laurentian crust formed in the overthickened upper plate of the collision with Baltica. Coesite-bearing zircon dates UHP metamorphism to 365–350 Ma, which formed at the end of the Caledonian collision as a result of intracontinental subduction facilitated by strike-slip faults that broke the lithosphere. Rutile is the stable Ti-bearing phase at UHP, while titanite forms on the retrograde path. Trace elements and U-Pb in titanite were analyzed for six UHP gneisses. Zr-in-titanite temperatures range from 764 to 803°C and lie on the isobaric part of the pressure-temperature path at 1.2 GPa, which fits Ti-phase stability determined by thermodynamic modeling. Large (>600 μm), zoned titanite preserves three distinct trace element patterns that are due to metamorphism, melting and garnet breakdown. Weighted mean 206Pb/238U ages range from 347 ± 5 Ma to 320 ± 11 Ma, but age variation as a function of trace element domain for individual samples is not resolvable within uncertainty. Titanite records a prolonged period of exhumation that is also seen in the zircon record, where phengite decompression melting started at ca. 347 Ma, leucosome emplacement accompanied retrograde metamorphism from 350 to 330 Ma; and titanite grew during isobaric cooling from 345 to 320 Ma when the UHP rocks stalled at lower crustal levels. The same transforms that originally break the lithosphere play a significant role in channeling the UHP rocks back to the lower crust via buoyancy driven exhumation, after which time titanite formed.
格陵兰东北部的超高压（UHP）岩石位于与波罗的海碰撞的上板块过厚形成的更大区域的高压劳伦地壳中。含沸石的超高压变质岩的年代为 365-350 Ma，形成于喀里多尼亚碰撞末期，是岩石圈断裂的走向滑动断层促进大陆内部俯冲的结果。金红石是超高压的稳定含钛相，而榍石则形成于逆行路径上。对六块超高压片麻岩进行了钛铁矿中微量元素和铀-铅分析。钛铁矿中Zr的温度范围为764至803°C，位于1.2 GPa压力-温度路径的等压部分，这符合热力学模型确定的钛相稳定性。大块（>600 μm）带状榍石保留了三种不同的微量元素模式，分别是变质作用、熔融作用和石榴石分解作用造成的。206Pb/238U 加权平均年龄从 347 ± 5 Ma 到 320 ± 11 Ma 不等，但单个样品的年龄变化与微量元素域的函数关系在不确定范围内无法确定。钛铁矿记录了一段较长的剥蚀期，这在锆石记录中也可以看到。钛铁矿记录了一段漫长的剥蚀期，这在锆石记录中也可以看到，其中辉石减压熔融开始于约 347 Ma，白云母置换伴随着 350 Ma 至 330 Ma 的逆行变质作用；而榍石则是在 345 Ma 至 320 Ma 的等压冷却过程中生长的，当时超高压岩石停滞在较低的地壳水平。最初打破岩石圈的同样的转变在通过浮力驱动的掘起将超高压岩石引回下地壳方面发挥了重要作用，此后榍石形成。
{"title":"Exhumation of an Ultrahigh-Pressure Slice From the Upper Plate of the Caledonian Orogen—A Record From Titanite in North-East Greenland","authors":"Jane A. Gilotti, William C. McClelland, Wentao Cao, Matthew A. Coble","doi":"10.1029/2023tc007810","DOIUrl":"https://doi.org/10.1029/2023tc007810","url":null,"abstract":"Ultrahigh-pressure (UHP) rocks in North-East Greenland lie within a larger region of high-pressure Laurentian crust formed in the overthickened upper plate of the collision with Baltica. Coesite-bearing zircon dates UHP metamorphism to 365–350 Ma, which formed at the end of the Caledonian collision as a result of intracontinental subduction facilitated by strike-slip faults that broke the lithosphere. Rutile is the stable Ti-bearing phase at UHP, while titanite forms on the retrograde path. Trace elements and U-Pb in titanite were analyzed for six UHP gneisses. Zr-in-titanite temperatures range from 764 to 803°C and lie on the isobaric part of the pressure-temperature path at 1.2 GPa, which fits Ti-phase stability determined by thermodynamic modeling. Large (>600 μm), zoned titanite preserves three distinct trace element patterns that are due to metamorphism, melting and garnet breakdown. Weighted mean <sup>206</sup>Pb/<sup>238</sup>U ages range from 347 ± 5 Ma to 320 ± 11 Ma, but age variation as a function of trace element domain for individual samples is not resolvable within uncertainty. Titanite records a prolonged period of exhumation that is also seen in the zircon record, where phengite decompression melting started at ca. 347 Ma, leucosome emplacement accompanied retrograde metamorphism from 350 to 330 Ma; and titanite grew during isobaric cooling from 345 to 320 Ma when the UHP rocks stalled at lower crustal levels. The same transforms that originally break the lithosphere play a significant role in channeling the UHP rocks back to the lower crust via buoyancy driven exhumation, after which time titanite formed.","PeriodicalId":22351,"journal":{"name":"Tectonics","volume":"15 1","pages":""},"PeriodicalIF":4.2,"publicationDate":"2024-01-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139517758","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}
Danya Zhou, Shaofeng Liu, Lianbin Wang, Neng Wan, Ronald Steel
Variability in subsidence rates within Upper Cretaceous strata of the Western Interior Basin offers crucial insights into the response of surface sedimentation styles to Sevier-to-Laramide tectonics and related deep mantle processes. The formation mechanisms of the Late Cretaceous Western Interior Basin in North America have long been a subject of debate. A re-evaluation of the basin's subsidence history reveals rapid subsidence pulses lasting ca. 2 Myr within longer-term (average 5.7 Myr) progradational or aggradational clastic wedges. The timing of these wedges, especially the widespread marine flooding resulting from subsidence, is constrained through the calibration of ammonite zonation with absolute dates. Sevier wedges exhibit a different architecture compared to the Laramide wedges. The former recorded initial rapid and widespread marine transgressions followed by long-term coastal progradation, whereas the latter developed by initial erosional and progradational growth followed by aggradation and long-term coastal transgression. The Sevier clastic wedges, initially accumulated within a N-S elongated, long-wavelength tectonic subsidence zone close to the thrust belt, gradually migrated cratonward. Starting in the early Campanian (ca. 82 Ma), the Laramide Orogeny developed along a NW-SE trend and then migrated northeastward, roughly consistent with coeval long-wavelength frontal basin subsidence. The spatio-temporal variations in long-wavelength tectonic subsidence indicate a shift in the dynamic subsidence's migration direction from eastward to northeastward, driven by changes in Farallon subduction direction and mode. Our work shows how repeated subsidence behavior in the Sevier-to-Laramide transition records evolving architectural responses and the trajectory of coeval dynamic topography.
{"title":"Late Cretaceous Sevier Versus Laramide Orogenies in Wyoming-Utah-Colorado, USA: New Insights From Basin Subsidence History","authors":"Danya Zhou, Shaofeng Liu, Lianbin Wang, Neng Wan, Ronald Steel","doi":"10.1029/2023tc007946","DOIUrl":"https://doi.org/10.1029/2023tc007946","url":null,"abstract":"Variability in subsidence rates within Upper Cretaceous strata of the Western Interior Basin offers crucial insights into the response of surface sedimentation styles to Sevier-to-Laramide tectonics and related deep mantle processes. The formation mechanisms of the Late Cretaceous Western Interior Basin in North America have long been a subject of debate. A re-evaluation of the basin's subsidence history reveals rapid subsidence pulses lasting ca. 2 Myr within longer-term (average 5.7 Myr) progradational or aggradational clastic wedges. The timing of these wedges, especially the widespread marine flooding resulting from subsidence, is constrained through the calibration of ammonite zonation with absolute dates. Sevier wedges exhibit a different architecture compared to the Laramide wedges. The former recorded initial rapid and widespread marine transgressions followed by long-term coastal progradation, whereas the latter developed by initial erosional and progradational growth followed by aggradation and long-term coastal transgression. The Sevier clastic wedges, initially accumulated within a N-S elongated, long-wavelength tectonic subsidence zone close to the thrust belt, gradually migrated cratonward. Starting in the early Campanian (ca. 82 Ma), the Laramide Orogeny developed along a NW-SE trend and then migrated northeastward, roughly consistent with coeval long-wavelength frontal basin subsidence. The spatio-temporal variations in long-wavelength tectonic subsidence indicate a shift in the dynamic subsidence's migration direction from eastward to northeastward, driven by changes in Farallon subduction direction and mode. Our work shows how repeated subsidence behavior in the Sevier-to-Laramide transition records evolving architectural responses and the trajectory of coeval dynamic topography.","PeriodicalId":22351,"journal":{"name":"Tectonics","volume":"68 1","pages":""},"PeriodicalIF":4.2,"publicationDate":"2024-01-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139506845","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}
Guodong Bao, Zhikun Ren, Guanghao Ha, Jinrui Liu, Zhiliang Zhang, Xiaoxiao Zhu, Dengyun Wu, Haomin Ji
The tectonic deformation on the eastern margin of the Qaidam Basin, which has preserved complete sedimentary records, significantly influences the evolutionary model of the northeastern margin of the Tibetan Plateau. However, the deformation history in this area during the Holocene remains unclear. This study is based on the high-precision digital elevation model obtained through drone mapping technology, which identifies three active faults on the eastern margin of the Qaidam Basin: the Xiariha Fault (XRHF) and Yingdeerkang Fault Yingdeerkang Fault (YKF) are NW‒SE-orientated dextral faults, whereas the Reshui-Taosituohe Fault (RTF) is a nearly east‒west-orientated sinistral fault. Based on the optically stimulated luminescence dating of the landform surfaces, the rates of strike-slip offset are as follows: those of the XRHF range from 1.12 ± 0.07 to 1.68 ± 0.12 mm/yr and those of the YKF are from 0.99 ± 0.06 to 2.29 ± 0.13 mm/yr. Recent paleoseismic events occurred along the RTF at approximately 714–1,792 years BP and at 700 ± 18 years BP, implying a recurring millennial pattern. Together, these faults possibly form a complex cross-fault system along the southeastern edge of the basin, heightening seismic risk. Deformation in the western part of the northeastern Tibetan Plateau is driven by slip on the Altyn Tagh Fault and compression in the Qaidam Basin. The central part experiences slip on the East Kunlun Fault, along with secondary faults, shortening, and block rotation. The eastern part primarily experiences slip along the Haiyuan Fault.
{"title":"New Evidence of Late Quaternary Tectonic Activity Along the Eastern Margin of the Qaidam Basin","authors":"Guodong Bao, Zhikun Ren, Guanghao Ha, Jinrui Liu, Zhiliang Zhang, Xiaoxiao Zhu, Dengyun Wu, Haomin Ji","doi":"10.1029/2023tc007906","DOIUrl":"https://doi.org/10.1029/2023tc007906","url":null,"abstract":"The tectonic deformation on the eastern margin of the Qaidam Basin, which has preserved complete sedimentary records, significantly influences the evolutionary model of the northeastern margin of the Tibetan Plateau. However, the deformation history in this area during the Holocene remains unclear. This study is based on the high-precision digital elevation model obtained through drone mapping technology, which identifies three active faults on the eastern margin of the Qaidam Basin: the Xiariha Fault (XRHF) and Yingdeerkang Fault Yingdeerkang Fault (YKF) are NW‒SE-orientated dextral faults, whereas the Reshui-Taosituohe Fault (RTF) is a nearly east‒west-orientated sinistral fault. Based on the optically stimulated luminescence dating of the landform surfaces, the rates of strike-slip offset are as follows: those of the XRHF range from 1.12 ± 0.07 to 1.68 ± 0.12 mm/yr and those of the YKF are from 0.99 ± 0.06 to 2.29 ± 0.13 mm/yr. Recent paleoseismic events occurred along the RTF at approximately 714–1,792 years BP and at 700 ± 18 years BP, implying a recurring millennial pattern. Together, these faults possibly form a complex cross-fault system along the southeastern edge of the basin, heightening seismic risk. Deformation in the western part of the northeastern Tibetan Plateau is driven by slip on the Altyn Tagh Fault and compression in the Qaidam Basin. The central part experiences slip on the East Kunlun Fault, along with secondary faults, shortening, and block rotation. The eastern part primarily experiences slip along the Haiyuan Fault.","PeriodicalId":22351,"journal":{"name":"Tectonics","volume":"63 1","pages":""},"PeriodicalIF":4.2,"publicationDate":"2024-01-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139498059","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}
Magdalena Ellis Curry, Michael R. Hudec, Frank J. Peel, Naiara Fernandez, Gillian Apps, John W. Snedden
We present the first sequential structural restoration with flexural backstripping of the Gulf of Mexico US-Mexico conjugate margin salt basin. We construct four large-scale (100s of km) balanced, sequential structural restorations to investigate spatio-temporal patterns of subsidence, geometry of the original salt basin, feedbacks between post-salt structural and stratigraphic evolution, paleo-bathymetry, and crustal configurations. The restorations are based on interpretations of 2D and 3D seismic data, and include sequential sedimentary decompaction, flexural isostatic backstripping, and thermal isostatic corrections. The spatially variable crustal thinning factor is directly measured from seismic data, and lithologic parameters are determined by well penetrations. We present a model for the original salt basin and discuss evidence for and implications of a deep water salt basin setting for the GoM. Our analysis suggests a salt basin that contained ∼1–2 km thick salt in a basin 175–390 km across with ∼1 km of bathymetry after salt deposition. The base of salt is mostly smooth with <1 km of local relief in the form of normal faults that disrupt a pre-salt sedimentary section. We find that supra-salt extension and shortening are not balanced, with measurable extension exceeding shortening by 18–30 km on each cross-section. Our subsidence analysis reveals anomalous subsidence totaling 1–2 km during Late Jurassic and Early Cretaceous times that may reflect dynamic topography or depth-dependent thinning. We offer an interpretation of crustal breakup invoking pre-salt clastic sedimentation, salt deposition in a deep water syn-thinning basin, and post-salt lower-crustal exhumation.
{"title":"Structural Restorations of the Complete Conjugate US-Mexico Eastern Gulf of Mexico Margin","authors":"Magdalena Ellis Curry, Michael R. Hudec, Frank J. Peel, Naiara Fernandez, Gillian Apps, John W. Snedden","doi":"10.1029/2023tc007897","DOIUrl":"https://doi.org/10.1029/2023tc007897","url":null,"abstract":"We present the first sequential structural restoration with flexural backstripping of the Gulf of Mexico US-Mexico conjugate margin salt basin. We construct four large-scale (100s of km) balanced, sequential structural restorations to investigate spatio-temporal patterns of subsidence, geometry of the original salt basin, feedbacks between post-salt structural and stratigraphic evolution, paleo-bathymetry, and crustal configurations. The restorations are based on interpretations of 2D and 3D seismic data, and include sequential sedimentary decompaction, flexural isostatic backstripping, and thermal isostatic corrections. The spatially variable crustal thinning factor is directly measured from seismic data, and lithologic parameters are determined by well penetrations. We present a model for the original salt basin and discuss evidence for and implications of a deep water salt basin setting for the GoM. Our analysis suggests a salt basin that contained ∼1–2 km thick salt in a basin 175–390 km across with ∼1 km of bathymetry after salt deposition. The base of salt is mostly smooth with <1 km of local relief in the form of normal faults that disrupt a pre-salt sedimentary section. We find that supra-salt extension and shortening are not balanced, with measurable extension exceeding shortening by 18–30 km on each cross-section. Our subsidence analysis reveals anomalous subsidence totaling 1–2 km during Late Jurassic and Early Cretaceous times that may reflect dynamic topography or depth-dependent thinning. We offer an interpretation of crustal breakup invoking pre-salt clastic sedimentation, salt deposition in a deep water syn-thinning basin, and post-salt lower-crustal exhumation.","PeriodicalId":22351,"journal":{"name":"Tectonics","volume":"13 1","pages":""},"PeriodicalIF":4.2,"publicationDate":"2024-01-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139498056","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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