Tobermory C. Mackay-Champion, Michael P. Searle, Simon Tapster, Nick M. W. Roberts, Robin K. Shail, Richard M. Palin, George H. Willment, Josh T. Evans
The Lizard ophiolite, Cornwall, South-West England, is the largest and best-preserved ophiolite within the Variscan orogenic belt. It forms part of the Rheic-Rhenohercynian suture zone, and was obducted northwestward onto the passive continental margin of Avalonia (Laurussia) during the Middle Devonian. It comprises an almost complete thrust slice of oceanic crust with sheeted dykes, gabbros, Moho transition sequence, and upper-mantle peridotites, underlain by a metamorphic sole. Despite the importance of the Lizard ophiolite in understanding Variscan tectonics, the origin and age of the Lizard ophiolite are debated. We present new field observations, structural maps and cross-sections of the Lizard ophiolite from extensive re-mapping, integrated with U–Pb geochronology, petrology, thermobarometry, and whole rock geochemistry. We report new U–Pb zircon (CA-ID-TIMS and LA-ICPMS) ages of 386.80 ± 0.25/0.31/0.52 Ma (Givetian) from a plagiogranite dyke intruding the Crousa Gabbros at Porthoustock, and 395.08 ± 0.14/0.22/0.47 Ma (Emsian) from partial melts of the metamorphic sole Landewednack Amphibolites at Mullion Cove. These ages, respectively, precisely date the formation of the Lizard ophiolite oceanic crust, and the age of cooling post peak-metamorphism of the sole. Petrological modeling on the Landewednack Amphibolites suggests peak metamorphic conditions of 10 ± 2 kbar and 600 ± 75°C. We demonstrate that the Lizard ophiolite formed as a supra-subduction zone ophiolite overlying an inverted metamorphic sole, and we combine our observations and data into a new geodynamic model for the formation and obduction of the ophiolite. The current data supports an induced subduction initiation model.
英格兰西南部康沃尔郡的蜥蜴蛇绿岩是瓦利斯坎造山带中最大、保存最完好的蛇绿岩。它是Rheic-Rhenohercynian缝合带的一部分，在中泥盆纪向西北俯冲到阿瓦鲁尼亚（劳鲁西亚）的被动大陆边缘。它由几乎完整的大洋地壳推切片组成，包含片状岩堤、辉长岩、莫霍山过渡序列和上幔橄榄岩，由变质底层覆盖。尽管蜥蜴蛇绿混杂岩对了解瓦里坎构造具有重要意义，但关于蜥蜴蛇绿混杂岩的起源和年龄仍存在争议。我们通过广泛的重新测绘，结合铀-铅地质年代学、岩石学、热压测量学和全岩地球化学，展示了对蜥蜴蛇绿岩的新的实地观察结果、结构图和横截面图。我们报告了新的U-Pb锆石（CA-ID-TIMS和LA-ICPMS）年龄，分别为386.80 ± 0.25/0.31/0.52 Ma (Givetian)，来自Porthoustock侵入Crousa辉长岩的斜长花岗岩堤；395.08 ± 0.14/0.22/0.47 Ma (Emsian)，来自Mullion Cove变质唯一的Landewednack闪长岩的部分熔体。这些年龄分别精确地确定了蜥蜴蛇绿岩大洋地壳形成的时间，以及鳎目鱼变质峰后冷却的年龄。兰德韦德纳克闪长岩的岩石学模型表明，变质峰值条件为 10 ± 2 千巴和 600 ± 75 摄氏度。我们证明蜥蜴蛇绿混杂岩是在倒置变质底岩之上形成的超俯冲带蛇绿混杂岩，并将我们的观测结果和数据结合起来，为蛇绿混杂岩的形成和俯冲建立了一个新的地球动力学模型。目前的数据支持诱导俯冲起始模型。
{"title":"Magmatic, Metamorphic and Structural History of the Variscan Lizard Ophiolite and Metamorphic Sole, Cornwall, UK","authors":"Tobermory C. Mackay-Champion, Michael P. Searle, Simon Tapster, Nick M. W. Roberts, Robin K. Shail, Richard M. Palin, George H. Willment, Josh T. Evans","doi":"10.1029/2023tc008187","DOIUrl":"https://doi.org/10.1029/2023tc008187","url":null,"abstract":"The Lizard ophiolite, Cornwall, South-West England, is the largest and best-preserved ophiolite within the Variscan orogenic belt. It forms part of the Rheic-Rhenohercynian suture zone, and was obducted northwestward onto the passive continental margin of Avalonia (Laurussia) during the Middle Devonian. It comprises an almost complete thrust slice of oceanic crust with sheeted dykes, gabbros, Moho transition sequence, and upper-mantle peridotites, underlain by a metamorphic sole. Despite the importance of the Lizard ophiolite in understanding Variscan tectonics, the origin and age of the Lizard ophiolite are debated. We present new field observations, structural maps and cross-sections of the Lizard ophiolite from extensive re-mapping, integrated with U–Pb geochronology, petrology, thermobarometry, and whole rock geochemistry. We report new U–Pb zircon (CA-ID-TIMS and LA-ICPMS) ages of 386.80 ± 0.25/0.31/0.52 Ma (Givetian) from a plagiogranite dyke intruding the Crousa Gabbros at Porthoustock, and 395.08 ± 0.14/0.22/0.47 Ma (Emsian) from partial melts of the metamorphic sole Landewednack Amphibolites at Mullion Cove. These ages, respectively, precisely date the formation of the Lizard ophiolite oceanic crust, and the age of cooling post peak-metamorphism of the sole. Petrological modeling on the Landewednack Amphibolites suggests peak metamorphic conditions of 10 ± 2 kbar and 600 ± 75°C. We demonstrate that the Lizard ophiolite formed as a supra-subduction zone ophiolite overlying an inverted metamorphic sole, and we combine our observations and data into a new geodynamic model for the formation and obduction of the ophiolite. The current data supports an induced subduction initiation model.","PeriodicalId":22351,"journal":{"name":"Tectonics","volume":"53 1","pages":""},"PeriodicalIF":4.2,"publicationDate":"2024-04-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140567707","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}
Rubén Díez Fernández, Gerardo de Vicente, Diana Moreno-Martín, Carlos Fernández, Ricardo Arenas, Francisco J. Rubio Pascual
Metamorphic basements are usually considered rigid and isotropic at a large scale. However, basements contain inherited weaknesses that may potentially accommodate superimposed contraction (e.g., fault reactivation), and that favor fold nucleation (e.g., penetrative foliations). If these conditions are met, what could be the factors that impede the development of basement folds or their recognition? Actual basement folding is rarely documented, especially for large dimensions. Here we provide a case example, discussed from the perspective of structural analysis of surface data and sustained by geophysical data. The basement of the Spanish-Portuguese Central System is defined by an Alpine mega-fold (Hiendelaencina Antiform) that trends parallel to this mountain range and affects the basement and its sedimentary cover, collectively. The wavelength of this fold matches or even surpasses the thickness of the crust that hosts it (36–41 km). The Moho under this mega-fold is displaced by an Alpine fault that accounts for incipient intraplate continental subduction. The topography of the mantle may reflect an up-warping compatible with the mega-fold observed on the surface. Mega-folding is observed in the hanging wall of the Berzosa Fault, which emerges as a SE-dipping, Variscan (Paleozoic), extensional fault reactivated as a basal decollement upon Alpine (Cenozoic) contraction. The mega-fold was formed after well-oriented planar anisotropies in the basement (foliation and bedding). The development of this fold was assisted by heterogeneous shearing (coeval thrusting) plus the buttressing effect of pre-existing, near-vertical, crustal-scale faults (Somolinos and Somosierra), which inhibited slip-upsection through the basal decollement (Berzosa Fault).
{"title":"Mega-Folding of a Basement During Incipient Intra-Plate Continental Subduction (Alpine Central Iberia)","authors":"Rubén Díez Fernández, Gerardo de Vicente, Diana Moreno-Martín, Carlos Fernández, Ricardo Arenas, Francisco J. Rubio Pascual","doi":"10.1029/2023tc008163","DOIUrl":"https://doi.org/10.1029/2023tc008163","url":null,"abstract":"Metamorphic basements are usually considered rigid and isotropic at a large scale. However, basements contain inherited weaknesses that may potentially accommodate superimposed contraction (e.g., fault reactivation), and that favor fold nucleation (e.g., penetrative foliations). If these conditions are met, what could be the factors that impede the development of basement folds or their recognition? Actual basement folding is rarely documented, especially for large dimensions. Here we provide a case example, discussed from the perspective of structural analysis of surface data and sustained by geophysical data. The basement of the Spanish-Portuguese Central System is defined by an Alpine mega-fold (Hiendelaencina Antiform) that trends parallel to this mountain range and affects the basement and its sedimentary cover, collectively. The wavelength of this fold matches or even surpasses the thickness of the crust that hosts it (36–41 km). The Moho under this mega-fold is displaced by an Alpine fault that accounts for incipient intraplate continental subduction. The topography of the mantle may reflect an up-warping compatible with the mega-fold observed on the surface. Mega-folding is observed in the hanging wall of the Berzosa Fault, which emerges as a SE-dipping, Variscan (Paleozoic), extensional fault reactivated as a basal decollement upon Alpine (Cenozoic) contraction. The mega-fold was formed after well-oriented planar anisotropies in the basement (foliation and bedding). The development of this fold was assisted by heterogeneous shearing (coeval thrusting) plus the buttressing effect of pre-existing, near-vertical, crustal-scale faults (Somolinos and Somosierra), which inhibited slip-upsection through the basal decollement (Berzosa Fault).","PeriodicalId":22351,"journal":{"name":"Tectonics","volume":"24 1","pages":""},"PeriodicalIF":4.2,"publicationDate":"2024-04-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140567322","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}
Nicholas Richard, Caroline M. Burberry, Nguyen Hoang, Le Duc Anh, Sang Q. Dinh, Lynne J. Elkins
Vietnam contains complex faults coupled with a diffuse igneous province that has been active since the mid-Miocene. However, existing fault maps demonstrate little consensus over the location of Neogene basalt flows and relative ages of mapped faults, which complicates interpretations of tectonic model for the evolution of Indochina. This paper identifies discrete tectonic blocks within Vietnam and aims to define the Neogene-Recent tectonic setting and kinematics of south-central Vietnam by analyzing the orientation, kinematics, and relative ages of faults across each block. Fault ages and relative timing are estimated using cross-cutting relationships with dated basalt flows and between slickenside sets. Remote sensing results show distinct fault trends within individual blocks that are locally related to the orientations of the basement-involved block-bounding faults. Faults observed in the field indicate an early phase of dip-slip motion and a later phase of strike-slip motion, recording the rotation of blocks within a stress field. Faulting after the change in motion of the Red River Fault Zone at ∼16 Ma is inferred, as faults cross-cut basalt flows as young as ∼0.6 Ma. Strike-slip motion on block-bounding faults is consistent with rotation and continuous extrusion of each block within south-central Vietnam. The rotation of the blocks is attributed to the “continuum rubble” behavior of small crustal blocks influenced by upper mantle flow after the collision between India and Eurasia. We infer a robust lithospheric-asthenospheric coupling in the extrusion model, which holds implications for other regions experiencing extrusion even in the absence of a free surface.
越南拥有复杂的断层，加上自中新世中期以来就十分活跃的弥散火成岩区。然而，现有的断层图显示，人们对新近纪玄武岩流的位置和所绘制断层的相对年龄几乎没有共识，这使得对印度支那演化的构造模型的解释变得复杂。本文确定了越南境内的离散构造区块，旨在通过分析每个区块内断层的走向、运动学和相对年龄，确定越南中南部的新近-近期构造环境和运动学。断层年龄和相对时间是通过与年代玄武岩流的交叉关系以及滑动岩组之间的交叉关系估算出来的。遥感结果表明，各个区块内的断层趋势截然不同，这些趋势与涉及基底的区块边界断层的走向有关。实地观测到的断层表明，早期为倾滑运动，后期为走向滑动运动，记录了应力场中岩块的旋转。推断红河断裂带在 ∼16 Ma 发生运动变化之后出现了断层，因为断层穿过的玄武岩流在 ∼0.6 Ma 时还很年轻。块体边界断层的走向滑动运动与越南中南部每个块体的旋转和持续挤压相一致。地块的旋转归因于印度和欧亚大陆碰撞后受上地幔流动影响的小地壳块体的 "连续碎石 "行为。我们推断在挤压模型中岩石圈与对流层之间存在强有力的耦合，这对其他地区即使在没有自由表面的情况下经历挤压也有影响。
{"title":"Neogene-Recent Reactivation of Pre-Existing Faults in South-Central Vietnam, With Implications for the Extrusion of Indochina","authors":"Nicholas Richard, Caroline M. Burberry, Nguyen Hoang, Le Duc Anh, Sang Q. Dinh, Lynne J. Elkins","doi":"10.1029/2023tc008231","DOIUrl":"https://doi.org/10.1029/2023tc008231","url":null,"abstract":"Vietnam contains complex faults coupled with a diffuse igneous province that has been active since the mid-Miocene. However, existing fault maps demonstrate little consensus over the location of Neogene basalt flows and relative ages of mapped faults, which complicates interpretations of tectonic model for the evolution of Indochina. This paper identifies discrete tectonic blocks within Vietnam and aims to define the Neogene-Recent tectonic setting and kinematics of south-central Vietnam by analyzing the orientation, kinematics, and relative ages of faults across each block. Fault ages and relative timing are estimated using cross-cutting relationships with dated basalt flows and between slickenside sets. Remote sensing results show distinct fault trends within individual blocks that are locally related to the orientations of the basement-involved block-bounding faults. Faults observed in the field indicate an early phase of dip-slip motion and a later phase of strike-slip motion, recording the rotation of blocks within a stress field. Faulting after the change in motion of the Red River Fault Zone at ∼16 Ma is inferred, as faults cross-cut basalt flows as young as ∼0.6 Ma. Strike-slip motion on block-bounding faults is consistent with rotation and continuous extrusion of each block within south-central Vietnam. The rotation of the blocks is attributed to the “continuum rubble” behavior of small crustal blocks influenced by upper mantle flow after the collision between India and Eurasia. We infer a robust lithospheric-asthenospheric coupling in the extrusion model, which holds implications for other regions experiencing extrusion even in the absence of a free surface.","PeriodicalId":22351,"journal":{"name":"Tectonics","volume":"43 1","pages":""},"PeriodicalIF":4.2,"publicationDate":"2024-04-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140567779","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}
Éva Oravecz, Zsolt Benkó, Róbert Arató, István Dunkl, Gábor Héja, Szilvia Kövér, Tibor Németh, László Fodor
Unraveling the age and kinematics of low temperature deformation events is crucial in understanding the late-stage evolution of orogens. However, accurate age constraints can often be challenging to obtain due to unideal outcrop conditions, large sedimentary hiatuses or the lack of well-defined thermal events. In this study, we show on the example of the Nekézseny Thrust, a poorly exposed late orogenic thrust in the southern Western Carpathians, that a combined approach of structural analysis and multi-method thermochronology can provide the necessary temporal, kinematic and thermal constraints for a detailed reconstruction of the deformation history. While structural mapping revealed that the Late Cretaceous Uppony Gosau Basin in the footwall of the Nekézseny Thrust underwent a significant post-Campanian and pre-Miocene shortening, K/Ar dating of fault gouge samples from the main fault zone constrained the primary thrusting event to the Maastrichtian. Based on the acquired apatite fission-track and (U-Th)/He ages, subsequent heating of the Upper Cretaceous sediments due to tectonic burial was limited to 75–100°C, followed by deformation-related and gradual cooling between the Eocene and Early Miocene. Considering the reconstructed deformation history, as well as the large-scale tectonic affinity of the displaced units in its footwall and hanging wall, the Nekézseny Thrust is a far-traveled (ca. 600 km) segment of the Late Cretaceous Alps-Dinarides contact zone, whose development was linked to the switch from lower plate to upper plate position with respect to the Sava Zone and Alpine Tethys sutures, respectively.
{"title":"Age, Kinematic and Thermal Constraints of Syn-Orogenic Low-Temperature Deformation Events: Insights From Thermochronology and Structural Data of the Nekézseny Thrust (Alpine-Carpathian-Dinaric Area)","authors":"Éva Oravecz, Zsolt Benkó, Róbert Arató, István Dunkl, Gábor Héja, Szilvia Kövér, Tibor Németh, László Fodor","doi":"10.1029/2023tc008189","DOIUrl":"https://doi.org/10.1029/2023tc008189","url":null,"abstract":"Unraveling the age and kinematics of low temperature deformation events is crucial in understanding the late-stage evolution of orogens. However, accurate age constraints can often be challenging to obtain due to unideal outcrop conditions, large sedimentary hiatuses or the lack of well-defined thermal events. In this study, we show on the example of the Nekézseny Thrust, a poorly exposed late orogenic thrust in the southern Western Carpathians, that a combined approach of structural analysis and multi-method thermochronology can provide the necessary temporal, kinematic and thermal constraints for a detailed reconstruction of the deformation history. While structural mapping revealed that the Late Cretaceous Uppony Gosau Basin in the footwall of the Nekézseny Thrust underwent a significant post-Campanian and pre-Miocene shortening, K/Ar dating of fault gouge samples from the main fault zone constrained the primary thrusting event to the Maastrichtian. Based on the acquired apatite fission-track and (U-Th)/He ages, subsequent heating of the Upper Cretaceous sediments due to tectonic burial was limited to 75–100°C, followed by deformation-related and gradual cooling between the Eocene and Early Miocene. Considering the reconstructed deformation history, as well as the large-scale tectonic affinity of the displaced units in its footwall and hanging wall, the Nekézseny Thrust is a far-traveled (ca. 600 km) segment of the Late Cretaceous Alps-Dinarides contact zone, whose development was linked to the switch from lower plate to upper plate position with respect to the Sava Zone and Alpine Tethys sutures, respectively.","PeriodicalId":22351,"journal":{"name":"Tectonics","volume":"28 1","pages":""},"PeriodicalIF":4.2,"publicationDate":"2024-03-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140324773","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}
Dan Sandiford, Peter Betts, Joanne Whittaker, Louis Moresi
The Pacific Plate underwent a significant change in motion during the early Eocene. This change has been linked to plate boundary reconfiguration, particularly in relation to subduction margins. The reconfiguration also resulted in a new Pacific-Australian plate boundary section transecting Zealandia. Following the Eocene transition, the relative rotation axis was located within continental Zealandia, and it has been hypothesized that this region acted as a pivot point. Here we investigate the extent to which collision resistance along the intra-continental Zealandia margin (length ∼1,000 km) might have impacted the motion of the Pacific Plate, which is characterized by trench lengths more than an order of magnitude greater. We first highlight the relatively large radial component in the Pacific Plate absolute rotation during the period ca. 47 and 32 Ma (i.e., the spin around the plate centroid axis). We then consider how parameterized plate boundary forces impact the tangential and radial components of the net torque (i.e., the fictitious and true torque components). We show that during this period, both the Zealandia and Izu-Bonin-Marianas (IBM) margins of the Pacific Plate were well-oriented in terms of partitioning boundary normal forces into counter-clockwise (CCW) radial torques. This analysis is supported by results from recent global-scale numerical models. The role of Zealandia cannot be established unambiguously, based on our analysis, but effects can be quantified under different assumptions. Collision resistance along the Zealandia margin could plausibly constitute a “first order” effect on Eocene Pacific Plate rotation, albeit only on the radial component.
在始新世早期，太平洋板块的运动发生了重大变化。这一变化与板块边界重构有关，特别是与俯冲边缘有关。板块边界的重新配置还导致新的太平洋-澳大利亚板块边界剖面横穿西兰岛。在始新世过渡之后，相对旋转轴位于西兰岛大陆内，因此有人推测该地区是一个支点。在此，我们研究了沿大陆内部的西兰西亚边缘（长度∼1,000 km）的碰撞阻力可能在多大程度上影响了太平洋板块的运动，而太平洋板块的特点是海沟长度超过一个数量级。我们首先强调了太平洋板块在大约 47 至 32 Ma 期间的绝对旋转（即围绕板块中心轴的旋转）中相对较大的径向分量。然后，我们考虑了参数化的板块边界力如何影响净力矩的切向和径向分量（即虚构力矩分量和真实力矩分量）。我们的研究表明，在这一时期，太平洋板块的西兰岛边缘和伊豆-波宁-马里亚纳（IBM）边缘在将边界法向力划分为逆时针（CCW）径向力矩方面方向良好。最近的全球尺度数值模型的结果支持了这一分析。根据我们的分析，无法明确确定西兰岛的作用，但可以在不同的假设条件下量化其影响。沿西兰岛边缘的碰撞阻力有可能对始新世太平洋板块的旋转产生 "一阶 "影响，尽管只是径向分量的影响。
{"title":"A Push in the Right Direction: Exploring the Role of Zealandia Collision in Eocene Pacific-Australia Plate Motion Changes","authors":"Dan Sandiford, Peter Betts, Joanne Whittaker, Louis Moresi","doi":"10.1029/2023tc007958","DOIUrl":"https://doi.org/10.1029/2023tc007958","url":null,"abstract":"The Pacific Plate underwent a significant change in motion during the early Eocene. This change has been linked to plate boundary reconfiguration, particularly in relation to subduction margins. The reconfiguration also resulted in a new Pacific-Australian plate boundary section transecting Zealandia. Following the Eocene transition, the relative rotation axis was located within continental Zealandia, and it has been hypothesized that this region acted as a pivot point. Here we investigate the extent to which collision resistance along the intra-continental Zealandia margin (length ∼1,000 km) might have impacted the motion of the Pacific Plate, which is characterized by trench lengths more than an order of magnitude greater. We first highlight the relatively large radial component in the Pacific Plate absolute rotation during the period ca. 47 and 32 Ma (i.e., the spin around the plate centroid axis). We then consider how parameterized plate boundary forces impact the tangential and radial components of the net torque (i.e., the fictitious and true torque components). We show that during this period, both the Zealandia and Izu-Bonin-Marianas (IBM) margins of the Pacific Plate were well-oriented in terms of partitioning boundary normal forces into counter-clockwise (CCW) radial torques. This analysis is supported by results from recent global-scale numerical models. The role of Zealandia cannot be established unambiguously, based on our analysis, but effects can be quantified under different assumptions. Collision resistance along the Zealandia margin could plausibly constitute a “first order” effect on Eocene Pacific Plate rotation, albeit only on the radial component.","PeriodicalId":22351,"journal":{"name":"Tectonics","volume":"55 1","pages":""},"PeriodicalIF":4.2,"publicationDate":"2024-03-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140200820","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}
Bianca Heberer, Bernhard C. Salcher, Gabor Tari, Godfrid Wessely, István Dunkl, Reinhard F. Sachsenhofer, Michael Wagreich, Christoph von Hagke
Fold and thrust belt architecture may be influenced by basement geometry of the downgoing plate. This influence is notoriously difficult to assess due to a common lack of subsurface constraints and low resolution of exhumation estimates in space and time. The Bohemian Spur is a basement high at the transition from the Alps to the Carpathians. It coincides with narrowing of the foreland basin and an orogen-scale change of strike. Its location in one of the best-studied orogens in the world makes it an ideal case for understanding how basement topography influences fold and thrust belt tectonics. However, since thermochronological studies were mainly focused on the core of the Alps, timing and amount of exhumation remain poorly constrained in these peripheral parts of the orogen. We present new apatite (U-Th)/He and fission track data from the wedge above the Bohemian Spur. Thermally reset ages monitor a so far un(der)appreciated phase of prominent Late Oligocene to Miocene cooling, associated with crustal thickening, uplift and erosion during wedge propagation. Pronounced exhumation on the order of 3–4.5 km can be related to basement steps beneath the advancing wedge. The spur acted as a buttress for foreland-propagating thrusting, pinning deformation and nucleating antiformal stacking and duplexing and thus exhumation above it. We illustrate how along- and across-strike changes of sub-detachment topography impact wedge propagation and control fold and thrust belt geometries. The buttressing effect accounts for most of the exhumation, while deep-seated slab dynamics are of subordinate importance for wedge uplift.
{"title":"The Impact of the Bohemian Spur on the Cooling and Exhumation Pattern of the Eastern Alpine Wedge of the European Alps","authors":"Bianca Heberer, Bernhard C. Salcher, Gabor Tari, Godfrid Wessely, István Dunkl, Reinhard F. Sachsenhofer, Michael Wagreich, Christoph von Hagke","doi":"10.1029/2023tc008005","DOIUrl":"https://doi.org/10.1029/2023tc008005","url":null,"abstract":"Fold and thrust belt architecture may be influenced by basement geometry of the downgoing plate. This influence is notoriously difficult to assess due to a common lack of subsurface constraints and low resolution of exhumation estimates in space and time. The Bohemian Spur is a basement high at the transition from the Alps to the Carpathians. It coincides with narrowing of the foreland basin and an orogen-scale change of strike. Its location in one of the best-studied orogens in the world makes it an ideal case for understanding how basement topography influences fold and thrust belt tectonics. However, since thermochronological studies were mainly focused on the core of the Alps, timing and amount of exhumation remain poorly constrained in these peripheral parts of the orogen. We present new apatite (U-Th)/He and fission track data from the wedge above the Bohemian Spur. Thermally reset ages monitor a so far un(der)appreciated phase of prominent Late Oligocene to Miocene cooling, associated with crustal thickening, uplift and erosion during wedge propagation. Pronounced exhumation on the order of 3–4.5 km can be related to basement steps beneath the advancing wedge. The spur acted as a buttress for foreland-propagating thrusting, pinning deformation and nucleating antiformal stacking and duplexing and thus exhumation above it. We illustrate how along- and across-strike changes of sub-detachment topography impact wedge propagation and control fold and thrust belt geometries. The buttressing effect accounts for most of the exhumation, while deep-seated slab dynamics are of subordinate importance for wedge uplift.","PeriodicalId":22351,"journal":{"name":"Tectonics","volume":"1 1","pages":""},"PeriodicalIF":4.2,"publicationDate":"2024-03-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140172376","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}
G. Bonnet, F. E. Apen, M. Soret, J. Noël, B. Caron, D. Ninkabou, P. Zverev, D. Deldicque
The Snow Mountain Volcanic Complex (SMVC; northern California, USA) is a well-preserved example of a coherently-exhumed subducted seamount. This study reappraises the genesis and evolution of this complex and surrounding units through detailed field, petro-structural and geochronological analyses. This work demonstrates that the SMVC (a) erupted at ∼166 Ma as a hotspot volcano on the Farallon Plate, (b) entered the Franciscan subduction trench at ∼118 Ma, and (c) was subsequently subducted to a depth of ∼20 km (within the seismogenic zone), as shown by local blueschist-facies assemblages formed at 0.6 GPa, 240°C. Transient subduction interfaces are preserved above, within, and below the SMVC, making it an exceptional target to study seamount subduction dynamics. Like other seamounts, the subduction-related deformation was mainly accommodated along kilometer-scale internal thrust zones lubricated by serpentinite/metasediments, and within centimeter-thick crack-seal veins recording pulsed fluid flow near peak metamorphism. No unequivocal proof of seismic activity was found. The integration of other seamounts (some potentially belonging to a former seamount chain) in the Franciscan Complex suggests that exhumed seamounts are more abundant than previously thought. Moreover, pressure-temperature-time estimates of subduction metamorphism for the surrounding units, combined with previous work constrain the thermal maturation of the subduction zone through time and the in-sequence emplacement of the SMVC. Rapid changes in age of the subducted oceanic plate when subducted additionally hint to the subduction of large-offset transform faults on the former Farallon plate. Such a process might have been linked to changes in accretion dynamics and magmatic flare-ups in the arc.
{"title":"Seamount Subduction Dynamics and Long-Term Evolution of the Franciscan Active Margin","authors":"G. Bonnet, F. E. Apen, M. Soret, J. Noël, B. Caron, D. Ninkabou, P. Zverev, D. Deldicque","doi":"10.1029/2023tc008084","DOIUrl":"https://doi.org/10.1029/2023tc008084","url":null,"abstract":"The Snow Mountain Volcanic Complex (SMVC; northern California, USA) is a well-preserved example of a coherently-exhumed subducted seamount. This study reappraises the genesis and evolution of this complex and surrounding units through detailed field, petro-structural and geochronological analyses. This work demonstrates that the SMVC (a) erupted at ∼166 Ma as a hotspot volcano on the Farallon Plate, (b) entered the Franciscan subduction trench at ∼118 Ma, and (c) was subsequently subducted to a depth of ∼20 km (within the seismogenic zone), as shown by local blueschist-facies assemblages formed at 0.6 GPa, 240°C. Transient subduction interfaces are preserved above, within, and below the SMVC, making it an exceptional target to study seamount subduction dynamics. Like other seamounts, the subduction-related deformation was mainly accommodated along kilometer-scale internal thrust zones lubricated by serpentinite/metasediments, and within centimeter-thick crack-seal veins recording pulsed fluid flow near peak metamorphism. No unequivocal proof of seismic activity was found. The integration of other seamounts (some potentially belonging to a former seamount chain) in the Franciscan Complex suggests that exhumed seamounts are more abundant than previously thought. Moreover, pressure-temperature-time estimates of subduction metamorphism for the surrounding units, combined with previous work constrain the thermal maturation of the subduction zone through time and the in-sequence emplacement of the SMVC. Rapid changes in age of the subducted oceanic plate when subducted additionally hint to the subduction of large-offset transform faults on the former Farallon plate. Such a process might have been linked to changes in accretion dynamics and magmatic flare-ups in the arc.","PeriodicalId":22351,"journal":{"name":"Tectonics","volume":"15 1","pages":""},"PeriodicalIF":4.2,"publicationDate":"2024-03-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140125911","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}
I. Puliti, L. Benedetti, A. Pizzi, J. Fleury, M. Francescone, V. Guillou, Aster Team
Located in the easternmost portion of the Central Apennines, the Mt. Morrone normal fault system is one of the highest seismic hazards in Italy. Previous geological and geomorphological observations revealed the presence of a ∼22 km-long NW-SE right-lateral en echelon fault system made of two parallel faults affecting Quaternary deposits. Our analysis focused on the westernmost fault, which bounds the Sulmona Basin. Cumulative offsets were identified and quantified using high-resolution Digital Elevation Models derived from LiDAR, Satellite Pleiades images, and drone acquisition at the three sites. Morphological markers displaced from a few to tens of meters were dated using 36Cl exposure dating. The results would be suggesting a fault slip rate of 0.2–0.4 mm/a. The deformed markers that dated at 36–44 ka consist of alluvial terraces emplaced by the main streams flowing down from Mt. Morrone to the Sulmona Basin, subsequently incised, and preserved when the fluvial base level dropped because of the former Sulmona lake fluctuations. The yielded ages for these markers fit well with the last major aggradational event associated with the 35–40 ka Heinrich event described and dated to other fluvial basins in the Apennines. Furthermore, the estimated rate agrees with the values obtained in previous studies over shorter and longer periods (105−6 years) and within similar uncertainties. This might then suggest that the period recovered by this study encompasses the entire seismic cycle.
莫罗内山正断层系统位于亚平宁半岛中部最东端，是意大利地震危险性最高的地区之一。之前的地质和地貌观测显示，这里存在一个长达 22 公里的 NW-SE 右侧梯形断层系统，由两条平行断层组成，影响着第四纪沉积。我们的分析重点是最西端的断层，它是苏尔莫纳盆地的边界。我们在三个地点利用激光雷达、昴宿星图像和无人机采集的高分辨率数字高程模型确定并量化了累积偏移量。使用 36Cl 暴露年代测定法对位移几米到几十米的形态标记进行了年代测定。结果表明，断层滑动速率为 0.2-0.4 毫米/年。年代为 36-44 ka 的变形标记由冲积阶地组成，这些阶地由从莫罗内山流向苏尔莫纳盆地的主要溪流堆积而成，随后被切割，并在前苏尔莫纳湖波动导致河床基面下降时被保留下来。这些标志物的生成年龄与亚平宁半岛其他河川盆地所描述和测定的 35-40 ka Heinrich 事件相关的最后一次大规模增生事件非常吻合。此外，估计的速率与之前研究中获得的较短和较长时期（105-6 年）的数值一致，且不确定性相似。因此，这可能表明本研究恢复的时期涵盖了整个地震周期。
{"title":"Evidence for a Constant Slip Rate Over the Last ∼40 ka Along the Mt. Morrone Fault System in Central Apennines","authors":"I. Puliti, L. Benedetti, A. Pizzi, J. Fleury, M. Francescone, V. Guillou, Aster Team","doi":"10.1029/2023tc007871","DOIUrl":"https://doi.org/10.1029/2023tc007871","url":null,"abstract":"Located in the easternmost portion of the Central Apennines, the Mt. Morrone normal fault system is one of the highest seismic hazards in Italy. Previous geological and geomorphological observations revealed the presence of a ∼22 km-long NW-SE right-lateral en echelon fault system made of two parallel faults affecting Quaternary deposits. Our analysis focused on the westernmost fault, which bounds the Sulmona Basin. Cumulative offsets were identified and quantified using high-resolution Digital Elevation Models derived from LiDAR, Satellite Pleiades images, and drone acquisition at the three sites. Morphological markers displaced from a few to tens of meters were dated using <sup>36</sup>Cl exposure dating. The results would be suggesting a fault slip rate of 0.2–0.4 mm/a. The deformed markers that dated at 36–44 ka consist of alluvial terraces emplaced by the main streams flowing down from Mt. Morrone to the Sulmona Basin, subsequently incised, and preserved when the fluvial base level dropped because of the former Sulmona lake fluctuations. The yielded ages for these markers fit well with the last major aggradational event associated with the 35–40 ka Heinrich event described and dated to other fluvial basins in the Apennines. Furthermore, the estimated rate agrees with the values obtained in previous studies over shorter and longer periods (10<sup>5−6</sup> years) and within similar uncertainties. This might then suggest that the period recovered by this study encompasses the entire seismic cycle.","PeriodicalId":22351,"journal":{"name":"Tectonics","volume":"38 1","pages":""},"PeriodicalIF":4.2,"publicationDate":"2024-03-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140097458","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}
Ian Pierce, Ibrahim Guliyev, Gurban Yetirmishli, Rauf Muradov, Sabina Kazimova, Rashid Javanshir, Gregory P. De Pascale, Ben Johnson, Neill Marshall, Richard Walker, Paul Wordsworth
Here we present the results of the first paleoseismic study of the Kura fold-thrust belt in Azerbaijan based on field mapping, fault trenching, and Quaternary dating. Convergence at rates of ∼10 mm/yr between the Arabian and Eurasian Plates is largely accommodated by the Kura fold-thrust belt which stretches between central Azerbaijan and Georgia along the southern front of the Greater Caucasus (45–48°E). Although destructive historic earthquakes are known here, little is known about the active faults responsible for these earthquakes. A paleoseismic trench was excavated across a 2-m-high fault scarp near Agsu revealing evidence of two surface rupturing earthquakes. Radiocarbon dating of the faulted sediments limits the earthquake timing to AD 1713–1895 and AD 1872–2003. Allowing for uncertainties in dating, the two events likely correspond to historical destructive M ∼ 7 earthquakes near Shamakhi, Azerbaijan in AD 1668 and 1902. A second trench 60 km west of Agsu was excavated near Goychay also revealing evidence of at least one event that occurred 334–118 BC. Holocene shortening and dip-slip rates for the Kura fold-thrust belt are ∼8.0 and 8.5 mm/yr, respectively, based on an uplifted strath terrace west of Agsu. The only known historical devastating (M > ∼7) earthquakes in the Kura region, west of Shamakhi, occurred in 1139 and possibly 1668. The lack of reported historical ruptures from the past 4–8 centuries in the Kura, in contrast with the numerous recorded destructive earthquakes in Shamakhi, suggests that the Kura fold-thrust belt may have accumulated sufficient strain to produce a M > 7.7 earthquake.
{"title":"Surface Rupturing Earthquakes of the Greater Caucasus Frontal Thrusts, Azerbaijan","authors":"Ian Pierce, Ibrahim Guliyev, Gurban Yetirmishli, Rauf Muradov, Sabina Kazimova, Rashid Javanshir, Gregory P. De Pascale, Ben Johnson, Neill Marshall, Richard Walker, Paul Wordsworth","doi":"10.1029/2023tc007758","DOIUrl":"https://doi.org/10.1029/2023tc007758","url":null,"abstract":"Here we present the results of the first paleoseismic study of the Kura fold-thrust belt in Azerbaijan based on field mapping, fault trenching, and Quaternary dating. Convergence at rates of ∼10 mm/yr between the Arabian and Eurasian Plates is largely accommodated by the Kura fold-thrust belt which stretches between central Azerbaijan and Georgia along the southern front of the Greater Caucasus (45–48°E). Although destructive historic earthquakes are known here, little is known about the active faults responsible for these earthquakes. A paleoseismic trench was excavated across a 2-m-high fault scarp near Agsu revealing evidence of two surface rupturing earthquakes. Radiocarbon dating of the faulted sediments limits the earthquake timing to AD 1713–1895 and AD 1872–2003. Allowing for uncertainties in dating, the two events likely correspond to historical destructive <i>M</i> ∼ 7 earthquakes near Shamakhi, Azerbaijan in AD 1668 and 1902. A second trench 60 km west of Agsu was excavated near Goychay also revealing evidence of at least one event that occurred 334–118 BC. Holocene shortening and dip-slip rates for the Kura fold-thrust belt are ∼8.0 and 8.5 mm/yr, respectively, based on an uplifted strath terrace west of Agsu. The only known historical devastating (<i>M</i> > ∼7) earthquakes in the Kura region, west of Shamakhi, occurred in 1139 and possibly 1668. The lack of reported historical ruptures from the past 4–8 centuries in the Kura, in contrast with the numerous recorded destructive earthquakes in Shamakhi, suggests that the Kura fold-thrust belt may have accumulated sufficient strain to produce a <i>M</i> > 7.7 earthquake.","PeriodicalId":22351,"journal":{"name":"Tectonics","volume":"79 1","pages":""},"PeriodicalIF":4.2,"publicationDate":"2024-03-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140097472","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}
Yu Tang, Xiao Liang, Genhou Wang, Dian Li, Zhanhui Qing, Yipeng Feng, Wei Zhang, Ning Han, Yang Tian, Zhuosheng Wang
The poor understanding of the structural history of the Late Triassic flysch in the northeastern Tethyan Himalaya has caused many disputes regarding India-Asia collisional tectonics. Here, we conducted an integrated study including tectonostratigraphic analysis, structural analysis, and zircon U‒Pb and muscovite 40Ar/39Ar dating to unravel the structural evolution of the Late Triassic flysch. Field geological mapping revealed that the flysch can be subdivided into three structural units, including the Gyaca mélange, Qiongjie-Dengmu shear zone and Langjiexue fold-thrust belt. The three units all contain voluminous siliciclastic rocks deposited in an abyssal submarine fan environment at the Indian passive continental margin. The Gyaca mélange shows a two-stage deformation process that generated a collisional mélange resulting from the subduction of the Indian passive continental margin. 40Ar/39Ar dating of top-to-the-south shear bands and block-in-matrix structure indicate that the India-Asia collision happened no later than the Selandian (ca. 60 Ma). The divergent imbricated thrusting and folding of the Gyaca mélange and Langjiexue fold-thrust belt formed a positive flower structure. The zircon U‒Pb and 40Ar/39Ar dating of syntectonic dikes and sericite flakes within the Gyaca mélange yield ages of ca. 56–55 Ma for the genesis of the divergent structures. Moreover, the Qiongjie-Dengmu dextral shear zone yields a sericite 40Ar/39Ar age of ca. 35 Ma and thus indicates a transient strike-slip stress regime. Generally, the early India-Asia collision tectonics in the northeastern Tethyan Himalaya showed episodic evolution with changing structural styles from mélange formation to imbricate fold-thrust belt development and finally strike-slip shear generation.
{"title":"Diverse Structural Styles of the Northeastern Tethyan Himalaya in Southern Tibet Reveal the Early Collisional Tectonics of India and Asia","authors":"Yu Tang, Xiao Liang, Genhou Wang, Dian Li, Zhanhui Qing, Yipeng Feng, Wei Zhang, Ning Han, Yang Tian, Zhuosheng Wang","doi":"10.1029/2023tc007954","DOIUrl":"https://doi.org/10.1029/2023tc007954","url":null,"abstract":"The poor understanding of the structural history of the Late Triassic flysch in the northeastern Tethyan Himalaya has caused many disputes regarding India-Asia collisional tectonics. Here, we conducted an integrated study including tectonostratigraphic analysis, structural analysis, and zircon U‒Pb and muscovite <sup>40</sup>Ar/<sup>39</sup>Ar dating to unravel the structural evolution of the Late Triassic flysch. Field geological mapping revealed that the flysch can be subdivided into three structural units, including the Gyaca mélange, Qiongjie-Dengmu shear zone and Langjiexue fold-thrust belt. The three units all contain voluminous siliciclastic rocks deposited in an abyssal submarine fan environment at the Indian passive continental margin. The Gyaca mélange shows a two-stage deformation process that generated a collisional mélange resulting from the subduction of the Indian passive continental margin. <sup>40</sup>Ar/<sup>39</sup>Ar dating of top-to-the-south shear bands and block-in-matrix structure indicate that the India-Asia collision happened no later than the Selandian (ca. 60 Ma). The divergent imbricated thrusting and folding of the Gyaca mélange and Langjiexue fold-thrust belt formed a positive flower structure. The zircon U‒Pb and <sup>40</sup>Ar/<sup>39</sup>Ar dating of syntectonic dikes and sericite flakes within the Gyaca mélange yield ages of ca. 56–55 Ma for the genesis of the divergent structures. Moreover, the Qiongjie-Dengmu dextral shear zone yields a sericite <sup>40</sup>Ar/<sup>39</sup>Ar age of ca. 35 Ma and thus indicates a transient strike-slip stress regime. Generally, the early India-Asia collision tectonics in the northeastern Tethyan Himalaya showed episodic evolution with changing structural styles from mélange formation to imbricate fold-thrust belt development and finally strike-slip shear generation.","PeriodicalId":22351,"journal":{"name":"Tectonics","volume":"56 1","pages":""},"PeriodicalIF":4.2,"publicationDate":"2024-03-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140071957","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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