Pub Date : 2024-11-01Epub Date: 2024-11-21DOI: 10.1029/2024TC008412
T A Ducharme, D A Schneider, B Grasemann, V Scoging, C Bakowsky, K P Larson, A Camacho
The Almyropotamos tectonic window on southern Evia island in the NW Aegean Sea divides two high pressure-low temperature metamorphic units, representing distinct Hellenic thrust sheets. Ductile thinning along the major low-angle Evia Shear Zone has closely juxtaposed the lower (Basal Unit) marble-flysch sequence structurally below Styra marbles (Cycladic Blueschist Unit). The partially attenuated flysch comprises a matrix dominated by pelitic schist, with dispersed cm- to hm-scale blocks of marble, carbonate schist, quartzite, and metabasite. Structural investigation of the different lithotypes in the flysch reveals tectonic fabrics related to general flattening strain are developed most strongly in the pelitic matrix, whereas the compositionally diverse blocks exhibit differential preservation of older structures. Quartz c-axis distributions from quartz veins in the schists reflect an early, moderate temperature plane strain deformation. Colder deformation is evident in some pelitic schists, capturing Z-centered girdles consistent with the oblate finite strain ellipsoid inferred from macroscopic structures. New in situ 40Ar/39Ar and 87Rb/87Sr geochronology delineate the timing of the two deformation events. Geochronological data reaffirm the first-order observations of strain partitioning behavior at the scale of the shear zone, and confirm that the structure records two resolvable tectonometamorphic events: an early Oligocene HP-LT event, and a late Oligocene-early Miocene greenschist facies overprint coinciding with ductile thinning. The diffuse and discontinuous style of deformation recorded within the shear zone is unusual for major structures facilitating exhumation in the Aegean Sea, and may represent an analogue to mélange-hosted shear zones that accommodate progressive strain during subduction.
爱琴海西北部埃维亚岛南部的阿尔米罗波塔莫斯构造窗口划分出两个高压低温变质岩单元，分别代表不同的希腊推力片。沿着主要的低角度埃维亚剪切带的延展性减薄使下部（基底单元）大理岩-萤石层序在结构上紧密地并置在斯蒂拉大理岩（基克拉泽斯蓝岩单元）之下。部分衰减的萤石岩包括以辉绿岩片岩为主的基质，以及分散的厘米至百米级的大理岩、碳酸盐片岩、石英岩和偏闪长岩块。对萤石岩中不同岩型的构造调查显示，与总体扁平应变有关的构造结构在辉绿岩基质中发育得最为强烈，而成分多样的岩块则表现出对古老构造的不同保留。片岩中石英脉的石英 c 轴分布反映了早期的中温平面应变变形。在一些辉绿岩片岩中，低温变形非常明显，捕捉到了与宏观结构推断的扁圆形有限应变椭球体一致的Z中心腰带。新的原位 40Ar/39Ar 和 87Rb/87Sr 地质年代划分了两次变形事件的时间。地质年代数据再次证实了剪切带尺度上应变分区行为的一阶观测结果，并确认该构造记录了两次可解析的构造变质事件：一次是早渐新世的HP-LT事件，另一次是晚渐新世-中新世早期的绿泥石面叠加事件，与韧性变薄同时发生。在该剪切带内记录到的弥漫和不连续的变形风格，在爱琴海促进掘起的主要构造中并不常见，可能代表了在俯冲过程中容纳渐进应变的蜕变带。
{"title":"Strain Partitioning in a Flattening Shear Zone: Re-Evaluation of a Cycladic Style Detachment.","authors":"T A Ducharme, D A Schneider, B Grasemann, V Scoging, C Bakowsky, K P Larson, A Camacho","doi":"10.1029/2024TC008412","DOIUrl":"10.1029/2024TC008412","url":null,"abstract":"<p><p>The Almyropotamos tectonic window on southern Evia island in the NW Aegean Sea divides two high pressure-low temperature metamorphic units, representing distinct Hellenic thrust sheets. Ductile thinning along the major low-angle Evia Shear Zone has closely juxtaposed the lower (Basal Unit) marble-flysch sequence structurally below Styra marbles (Cycladic Blueschist Unit). The partially attenuated flysch comprises a matrix dominated by pelitic schist, with dispersed cm- to hm-scale blocks of marble, carbonate schist, quartzite, and metabasite. Structural investigation of the different lithotypes in the flysch reveals tectonic fabrics related to general flattening strain are developed most strongly in the pelitic matrix, whereas the compositionally diverse blocks exhibit differential preservation of older structures. Quartz c-axis distributions from quartz veins in the schists reflect an early, moderate temperature plane strain deformation. Colder deformation is evident in some pelitic schists, capturing Z-centered girdles consistent with the oblate finite strain ellipsoid inferred from macroscopic structures. New in situ <sup>40</sup>Ar/<sup>39</sup>Ar and <sup>87</sup>Rb/<sup>87</sup>Sr geochronology delineate the timing of the two deformation events. Geochronological data reaffirm the first-order observations of strain partitioning behavior at the scale of the shear zone, and confirm that the structure records two resolvable tectonometamorphic events: an early Oligocene HP-LT event, and a late Oligocene-early Miocene greenschist facies overprint coinciding with ductile thinning. The diffuse and discontinuous style of deformation recorded within the shear zone is unusual for major structures facilitating exhumation in the Aegean Sea, and may represent an analogue to mélange-hosted shear zones that accommodate progressive strain during subduction.</p>","PeriodicalId":22351,"journal":{"name":"Tectonics","volume":"43 11","pages":"e2024TC008412"},"PeriodicalIF":3.3,"publicationDate":"2024-11-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.ncbi.nlm.nih.gov/pmc/articles/PMC11582021/pdf/","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142711081","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Nolan R. Blackford, Sean P. Long, Jeffrey Lee, Kyle P. Larson, Gareth Seward, Julia L. Stevens, Hadeel Al Harthi
Documenting the magnitude of finite strain within ductile shear zones is critical for understanding lithospheric deformation. However, pervasive recrystallization within shear zones often destroys the deformed markers from which strain can be measured. Intensity parameters calculated from quartz crystallographic preferred orientation (CPO) distributions have been interpreted as proxies for the relative strain magnitude within shear zones, but thus far have not been calibrated to absolute strain magnitude. Here, we present equations that quantify the relationship between CPO intensity parameters (cylindricity and density norm) and finite strain magnitude, which we calculate by integrating quartz CPO analyses (n = 87) with strain ellipsoids from stretched detrital quartz clasts (n = 49) and macro-scale ductile thinning measurements (n = 7) from the footwall of the Northern Snake Range décollement (NSRD) in Nevada. The NSRD footwall exhibits a strain gradient, with Rs(XZ) values increasing from 5.4 ± 1.4 to 282 ± 122 eastward across the range. Cylindricity increases from 0.52 to 0.83 as Rs increases from 5.4 to 23.5, and increases gradually to 0.92 at Rs values between 160 and 404. Density norm increases from 1.68 to 2.97 as Rs increases from 5.4 to 23.5, but stays approximately constant until Rs values between 160 and 404. We present equations that express average finite strain as a function of average cylindricity and density norm, which provide a broadly applicable tool for estimating the first-order finite strain magnitude within any shear zone from which quartz CPO intensity can be measured. To demonstrate their utility, we apply our equations to published data from Himalayan shear zones and a Cordilleran core complex.
{"title":"Relating Quartz Crystallographic Preferred Orientation Intensity to Finite Strain Magnitude in the Northern Snake Range Metamorphic Core Complex, Nevada: A New Tool for Characterizing Strain Patterns in Ductilely Sheared Rocks","authors":"Nolan R. Blackford, Sean P. Long, Jeffrey Lee, Kyle P. Larson, Gareth Seward, Julia L. Stevens, Hadeel Al Harthi","doi":"10.1029/2023tc008166","DOIUrl":"https://doi.org/10.1029/2023tc008166","url":null,"abstract":"Documenting the magnitude of finite strain within ductile shear zones is critical for understanding lithospheric deformation. However, pervasive recrystallization within shear zones often destroys the deformed markers from which strain can be measured. Intensity parameters calculated from quartz crystallographic preferred orientation (CPO) distributions have been interpreted as proxies for the relative strain magnitude within shear zones, but thus far have not been calibrated to absolute strain magnitude. Here, we present equations that quantify the relationship between CPO intensity parameters (cylindricity and density norm) and finite strain magnitude, which we calculate by integrating quartz CPO analyses (<i>n</i> = 87) with strain ellipsoids from stretched detrital quartz clasts (<i>n</i> = 49) and macro-scale ductile thinning measurements (<i>n</i> = 7) from the footwall of the Northern Snake Range décollement (NSRD) in Nevada. The NSRD footwall exhibits a strain gradient, with Rs<sub>(XZ)</sub> values increasing from 5.4 ± 1.4 to 282 ± 122 eastward across the range. Cylindricity increases from 0.52 to 0.83 as Rs increases from 5.4 to 23.5, and increases gradually to 0.92 at Rs values between 160 and 404. Density norm increases from 1.68 to 2.97 as Rs increases from 5.4 to 23.5, but stays approximately constant until Rs values between 160 and 404. We present equations that express average finite strain as a function of average cylindricity and density norm, which provide a broadly applicable tool for estimating the first-order finite strain magnitude within any shear zone from which quartz CPO intensity can be measured. To demonstrate their utility, we apply our equations to published data from Himalayan shear zones and a Cordilleran core complex.","PeriodicalId":22351,"journal":{"name":"Tectonics","volume":"19 1","pages":""},"PeriodicalIF":4.2,"publicationDate":"2024-09-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142259899","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}
Chao Li, Zhongbao Zhao, Marie-Luce Chevalier, Yong Zheng, Dongliang Liu, Haijian Lu, Paul D. Bons, Haibing Li
The tectonic and topographic evolution of the southeastern Tibetan Plateau based on low-temperature thermochronology data is controversial, especially whether it is tectonically- or climatically-controlled, especially along the Lancang fault (LCF) that links the flat central plateau to the west with the high relief southeastern Tibetan Plateau to the east. To explore the tectonic evolution of the LCF and its role in the tectonic and topographic evolution of the southeastern Tibetan Plateau, we carried out detailed field investigation and low-temperature thermochronology (AHe, AFT, and ZHe) analyses. Field evidence indicate that the northern LCF splits into two branches, the Yangda-Yaxu and Baqing-Leiwuqi faults, the latter striking N50°W and dipping to the SW at ∼55°, exposing >100 m-wide fault rocks composed of a fault damage zone, breccia, and gouge. New thermochronology data and thermo-kinematic modeling results suggest rapid exhumation of the region located between these two fault branches during ∼22–10 Ma at an exhumation rate of ∼1.57 km/Ma, compared to slow cooling prior to 22 Ma and since 10 Ma. We propose that internal anti-clockwise block rotation triggered rapid local exhumation, and that the final merging of different parts of the LCF during the Early-Middle Miocene assisted the southeastward escape of Sundaland, which profoundly affected the evolution of the regional geomorphology.
{"title":"Lancang Fault Assists Block Extrusion in Southeastern Tibet During Early-Middle Miocene","authors":"Chao Li, Zhongbao Zhao, Marie-Luce Chevalier, Yong Zheng, Dongliang Liu, Haijian Lu, Paul D. Bons, Haibing Li","doi":"10.1029/2024tc008341","DOIUrl":"https://doi.org/10.1029/2024tc008341","url":null,"abstract":"The tectonic and topographic evolution of the southeastern Tibetan Plateau based on low-temperature thermochronology data is controversial, especially whether it is tectonically- or climatically-controlled, especially along the Lancang fault (LCF) that links the flat central plateau to the west with the high relief southeastern Tibetan Plateau to the east. To explore the tectonic evolution of the LCF and its role in the tectonic and topographic evolution of the southeastern Tibetan Plateau, we carried out detailed field investigation and low-temperature thermochronology (AHe, AFT, and ZHe) analyses. Field evidence indicate that the northern LCF splits into two branches, the Yangda-Yaxu and Baqing-Leiwuqi faults, the latter striking N50°W and dipping to the SW at ∼55°, exposing >100 m-wide fault rocks composed of a fault damage zone, breccia, and gouge. New thermochronology data and thermo-kinematic modeling results suggest rapid exhumation of the region located between these two fault branches during ∼22–10 Ma at an exhumation rate of ∼1.57 km/Ma, compared to slow cooling prior to 22 Ma and since 10 Ma. We propose that internal anti-clockwise block rotation triggered rapid local exhumation, and that the final merging of different parts of the LCF during the Early-Middle Miocene assisted the southeastward escape of Sundaland, which profoundly affected the evolution of the regional geomorphology.","PeriodicalId":22351,"journal":{"name":"Tectonics","volume":"46 1","pages":""},"PeriodicalIF":4.2,"publicationDate":"2024-09-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142209519","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. Patyniak, A. Landgraf, A. Dzhumabaeva, S. Baikulov, A. M. Williams, F. Preusser, K. E. Abdrakhmatov, J R. Arrowsmith, M. R. Strecker
This study investigates the intricate relationship between earthquake sources and seismogenic surface ruptures in a complex tectonic setting with active faults in the continental collision zone between the southern Tien Shan and the northern Pamir Mountains in Central Asia. The study focuses on the 2008 Mw 6.6 Nura earthquake along the Pamir Frontal Thrust, where the seismogenic surface rupture occurred unexpectedly within the footwall and 10 km away from the source thrust fault. This discrepancy raises questions about the interactions and potential trigger mechanisms between tectonic structures during earthquake rupture. Using unmanned aerial vehicle photography and field inspection, our investigation integrates detailed fault-zone mapping with tectono-geomorphic observations to unravel potential interactions between subsurface structures and surface-deformation phenomena. Our findings suggest that a combination of slip along deep-seated basement faults and remotely triggered flexural slip within folded Paleogene strata led to surface rupture of overlying Quaternary glacial deposits. Geomorphological and geochronological analyses coupled with systematic displacement measurements furthermore reveal evidence of similar past ruptures within the regional fault system, suggesting a recurrence interval of 1.7 kyr and a Holocene vertical offset rate of 0.4 mm/yr. The analysis of the Nura rupture zone contributes significantly to evaluate linkages between surface and subsurface structures regarding fault-zone behavior and seismic hazard assessments. Importantly, our results highlight the critical role of on-site investigations in regions with poorly defined surface ruptures, where misinterpretation may lead to the underestimation of the impact of seismic events and limitations in assessing earthquake history and strain accumulation.
{"title":"Surface Rupture of the 2008 Mw 6.6 Nura Earthquake: Triggered Flexural-Slip Faulting in the Pamir-Tien Shan Collision Zone","authors":"M. Patyniak, A. Landgraf, A. Dzhumabaeva, S. Baikulov, A. M. Williams, F. Preusser, K. E. Abdrakhmatov, J R. Arrowsmith, M. R. Strecker","doi":"10.1029/2024tc008360","DOIUrl":"https://doi.org/10.1029/2024tc008360","url":null,"abstract":"This study investigates the intricate relationship between earthquake sources and seismogenic surface ruptures in a complex tectonic setting with active faults in the continental collision zone between the southern Tien Shan and the northern Pamir Mountains in Central Asia. The study focuses on the 2008 <i>M</i><sub>w</sub> 6.6 Nura earthquake along the Pamir Frontal Thrust, where the seismogenic surface rupture occurred unexpectedly within the footwall and 10 km away from the source thrust fault. This discrepancy raises questions about the interactions and potential trigger mechanisms between tectonic structures during earthquake rupture. Using unmanned aerial vehicle photography and field inspection, our investigation integrates detailed fault-zone mapping with tectono-geomorphic observations to unravel potential interactions between subsurface structures and surface-deformation phenomena. Our findings suggest that a combination of slip along deep-seated basement faults and remotely triggered flexural slip within folded Paleogene strata led to surface rupture of overlying Quaternary glacial deposits. Geomorphological and geochronological analyses coupled with systematic displacement measurements furthermore reveal evidence of similar past ruptures within the regional fault system, suggesting a recurrence interval of 1.7 kyr and a Holocene vertical offset rate of 0.4 mm/yr. The analysis of the Nura rupture zone contributes significantly to evaluate linkages between surface and subsurface structures regarding fault-zone behavior and seismic hazard assessments. Importantly, our results highlight the critical role of on-site investigations in regions with poorly defined surface ruptures, where misinterpretation may lead to the underestimation of the impact of seismic events and limitations in assessing earthquake history and strain accumulation.","PeriodicalId":22351,"journal":{"name":"Tectonics","volume":"58 1","pages":""},"PeriodicalIF":4.2,"publicationDate":"2024-09-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142209527","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}
Mateus Rodrigues de Vargas, Julie Tugend, Geoffroy Mohn, Nick Kusznir, Lin Liang-Fu
We investigate the crustal structure of the Northeastern (NE) South China Sea (SCS) rifted margin to constrain its crustal thickness and basement nature with implications for the Mesozoic and Cenozoic evolution of the SCS. First-order interfaces interpreted from seismic reflection data were integrated into a 3D gravity inversion scheme to determine Moho depth and crustal thickness variations. A joint inversion of seismic and gravity data allowed us to determine crustal density variations along 2D profiles. The distal margin of the NE SCS is divided into two distinct crustal domains: the Southern Rift System (SRS), and the Southern High (SH). The SRS shows an extremely thinned crust on top of which thick Cenozoic sequences are observed. It is separated from the oceanic crust (∼6–8 km thick) by the SH, a comparatively thicker crustal domain (∼10–15 km thick) with significant magmatic additions. The distal NE SCS margin formed during the Cenozoic rifting of the SCS. The SH likely corresponds to a polygenic piece of crust, recording polyphase magmatic activity since the Mesozoic, with potentially significant activity during Cenozoic post-rift time. The NE SCS margin is conjugate to Palawan whose basement is considered to be part of the exotic Luconia microcontinent that collided with Eurasia during the Late Cretaceous. Basement similarities between Palawan and the SH are highlighted, suggesting that the latter might also be part of Luconia. Our results suggest that the docking/suture zone between Eurasia and Luconia might have acted as a preferred zone for the Cenozoic rift development.
{"title":"Crustal Structure of the Northeast South China Sea Rifted Margin","authors":"Mateus Rodrigues de Vargas, Julie Tugend, Geoffroy Mohn, Nick Kusznir, Lin Liang-Fu","doi":"10.1029/2024tc008399","DOIUrl":"https://doi.org/10.1029/2024tc008399","url":null,"abstract":"We investigate the crustal structure of the Northeastern (NE) South China Sea (SCS) rifted margin to constrain its crustal thickness and basement nature with implications for the Mesozoic and Cenozoic evolution of the SCS. First-order interfaces interpreted from seismic reflection data were integrated into a 3D gravity inversion scheme to determine Moho depth and crustal thickness variations. A joint inversion of seismic and gravity data allowed us to determine crustal density variations along 2D profiles. The distal margin of the NE SCS is divided into two distinct crustal domains: the Southern Rift System (SRS), and the Southern High (SH). The SRS shows an extremely thinned crust on top of which thick Cenozoic sequences are observed. It is separated from the oceanic crust (∼6–8 km thick) by the SH, a comparatively thicker crustal domain (∼10–15 km thick) with significant magmatic additions. The distal NE SCS margin formed during the Cenozoic rifting of the SCS. The SH likely corresponds to a polygenic piece of crust, recording polyphase magmatic activity since the Mesozoic, with potentially significant activity during Cenozoic post-rift time. The NE SCS margin is conjugate to Palawan whose basement is considered to be part of the exotic Luconia microcontinent that collided with Eurasia during the Late Cretaceous. Basement similarities between Palawan and the SH are highlighted, suggesting that the latter might also be part of Luconia. Our results suggest that the docking/suture zone between Eurasia and Luconia might have acted as a preferred zone for the Cenozoic rift development.","PeriodicalId":22351,"journal":{"name":"Tectonics","volume":"73 1","pages":""},"PeriodicalIF":4.2,"publicationDate":"2024-08-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142209526","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}
Sedigheh Khodaparast, Saeed Madanipour, Eva Enkelmann, Khaled Hessami, Reza Nozaem
The collisional Iranian Plateau and its recent kinematic evolution represent a natural example to study the intraplate response to the transferred deformation from an active convergent plate margin. The late Cenozoic deformation and structural evolution of the Plateau is not well understood. Here, we integrate structural, tectonostratigraphic, and morphotectonic field observations with low-temperature thermochronometric data along the NW-SE trending Kushk-e-Nosrat (KN) Fault to unravel the exhumation history and the kinematic change at the northwestern boundary of the Iranian Plateau. We found different sets of strike-slip related structures along the KN Fault zone, which are classified into four categories based on their cross-cutting relations and the superimposition of kinematic indicators. These include dextral transtension, dextral, dextral transpression, and sinistral kinematics. The unreset zircon (U-Th)/He and apatite fission track results and the reset apatite (U-Th)/He data from the restraining area along the KN Fault suggest 80–60°C of cooling during the early Miocene (∼20–18 Ma) and late Miocene–early Pliocene (∼7–5 Ma) due to dextral and dextral transpressional kinematics along the KN Fault zone, respectively. The dextral transtentional faulting was recorded as deposition of the Qom Formation within the releasing overlap areas along the KN Fault at >20–18 Ma. The kinematics of the KN Fault changed to sinistral during Pliocene–Quaternary times presumably triggered by the simultaneous clockwise rotation of central Iran, Alborz Mountains, and the South Caspian block. Our study proposes that the morphological and tectonostratigraphic evolution of the northern margin of the Iranian Plateau has mainly been controlled through local uplift and exhumation in restraining areas and local thick deposition in releasing areas of the major strike-slip faults during the late Cenozoic time.
{"title":"Time Constraints on the Late Cenozoic Fault Evolution Along the Northern Margin of the Iranian Plateau in the Arabia-Eurasia Collision Zone","authors":"Sedigheh Khodaparast, Saeed Madanipour, Eva Enkelmann, Khaled Hessami, Reza Nozaem","doi":"10.1029/2023tc008034","DOIUrl":"https://doi.org/10.1029/2023tc008034","url":null,"abstract":"The collisional Iranian Plateau and its recent kinematic evolution represent a natural example to study the intraplate response to the transferred deformation from an active convergent plate margin. The late Cenozoic deformation and structural evolution of the Plateau is not well understood. Here, we integrate structural, tectonostratigraphic, and morphotectonic field observations with low-temperature thermochronometric data along the NW-SE trending Kushk-e-Nosrat (KN) Fault to unravel the exhumation history and the kinematic change at the northwestern boundary of the Iranian Plateau. We found different sets of strike-slip related structures along the KN Fault zone, which are classified into four categories based on their cross-cutting relations and the superimposition of kinematic indicators. These include dextral transtension, dextral, dextral transpression, and sinistral kinematics. The unreset zircon (U-Th)/He and apatite fission track results and the reset apatite (U-Th)/He data from the restraining area along the KN Fault suggest 80–60°C of cooling during the early Miocene (∼20–18 Ma) and late Miocene–early Pliocene (∼7–5 Ma) due to dextral and dextral transpressional kinematics along the KN Fault zone, respectively. The dextral transtentional faulting was recorded as deposition of the Qom Formation within the releasing overlap areas along the KN Fault at >20–18 Ma. The kinematics of the KN Fault changed to sinistral during Pliocene–Quaternary times presumably triggered by the simultaneous clockwise rotation of central Iran, Alborz Mountains, and the South Caspian block. Our study proposes that the morphological and tectonostratigraphic evolution of the northern margin of the Iranian Plateau has mainly been controlled through local uplift and exhumation in restraining areas and local thick deposition in releasing areas of the major strike-slip faults during the late Cenozoic time.","PeriodicalId":22351,"journal":{"name":"Tectonics","volume":"75 1","pages":""},"PeriodicalIF":4.2,"publicationDate":"2024-08-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142209401","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}
Violeta Veliz-Borel, Vasiliki Mouslopoulou, Johannes Glodny, John Begg, Sabrina Metzger, Dimitris Sakellariou, Onno Oncken
Sets of marine terraces, sediments, and paleoshorelines are commonly found in forearc regions worldwide. A common assumption holds that crustal uplift prevents these features from littoral erosion. Here, we study the vertical deformation of Karpathos, a forearc island in the eastern Mediterranean, whose long axis extends at a high angle to the strike of the Hellenic Subduction System (HSS). We target three key coastal localities along the island to discuss spatial and temporal variability of vertical motion. We mapped sets of up to 19 marine terraces per locality, with elevations ranging from 1.5 to ∼350 masl. Ages for terraces and sediments are constrained by radiocarbon (<31 masl) and Sr-isotope (2–310 masl) dating, and range from 2.4 ka to ∼4.3 Ma. Data analysis shows that average uplift rates are up to two orders of magnitude faster over shorter (⪅100 ka) than longer (⪆100 ka) timescales, in agreement with other local and global data sets. Further, we find evidence for multiple marine reoccupations of late Pleistocene terraces, indicating that carbonate beachrock is often resistant to multiple interactions with sea-level. Neogene marine sequences that witness longer periods (∼4 Ma) show signs of alternating vertical motion. Using this novel data set, we explore the effects of various mechanisms (i.e., upper-plate normal faulting, splay-thrust faulting, basal underplating) on the spatial and temporal patterns of vertical deformation. Although the contribution of each mechanism to the net vertical deformation cannot be isolated with certainty, our results show that none alone could account for the observations.
{"title":"Exploring Uplift Mechanisms Across the Forearc of a Subduction System: Karpathos Island as a Natural Transect Across the Eastern Hellenic Margin","authors":"Violeta Veliz-Borel, Vasiliki Mouslopoulou, Johannes Glodny, John Begg, Sabrina Metzger, Dimitris Sakellariou, Onno Oncken","doi":"10.1029/2023tc008156","DOIUrl":"https://doi.org/10.1029/2023tc008156","url":null,"abstract":"Sets of marine terraces, sediments, and paleoshorelines are commonly found in forearc regions worldwide. A common assumption holds that crustal uplift prevents these features from littoral erosion. Here, we study the vertical deformation of Karpathos, a forearc island in the eastern Mediterranean, whose long axis extends at a high angle to the strike of the Hellenic Subduction System (HSS). We target three key coastal localities along the island to discuss spatial and temporal variability of vertical motion. We mapped sets of up to 19 marine terraces per locality, with elevations ranging from 1.5 to ∼350 masl. Ages for terraces and sediments are constrained by radiocarbon (<31 masl) and Sr-isotope (2–310 masl) dating, and range from 2.4 ka to ∼4.3 Ma. Data analysis shows that average uplift rates are up to two orders of magnitude faster over shorter (⪅100 ka) than longer (⪆100 ka) timescales, in agreement with other local and global data sets. Further, we find evidence for multiple marine reoccupations of late Pleistocene terraces, indicating that carbonate beachrock is often resistant to multiple interactions with sea-level. Neogene marine sequences that witness longer periods (∼4 Ma) show signs of alternating vertical motion. Using this novel data set, we explore the effects of various mechanisms (i.e., upper-plate normal faulting, splay-thrust faulting, basal underplating) on the spatial and temporal patterns of vertical deformation. Although the contribution of each mechanism to the net vertical deformation cannot be isolated with certainty, our results show that none alone could account for the observations.","PeriodicalId":22351,"journal":{"name":"Tectonics","volume":"102 1","pages":""},"PeriodicalIF":4.2,"publicationDate":"2024-08-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142209525","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}
The High-Pressure Phyllites-Quartzites (PQ) unit of the External Hellenides is exposed in tectonic windows in the central and northern Peloponnese (Greece). Understanding the deformation history of this unit is essential to interpreting the Oligo-Miocene evolution of the External Hellenides belt and its associated exhumation events. This study integrates new field observations and microtectonic analyses with previous studies to offer a comprehensive deformation model of the PQ unit since the Late Oligocene. The first deformation phase (D1), captures the progressive incorporation of the PQ into an orogenic wedge. This phase is largely overprinted and only preserved as relict features. The second phase (D2) displays coeval top-to-the-ENE and top-to-the-WSW localized ductile shear. A transition is observed from top-to-the-ENE non-coaxial deformation at the upper parts of the nappe to intense isoclinal folding (refolding S1) at the lower structural levels. We associate D2 with the ductile syn-orogenic exhumation of the PQ within an extrusion wedge, accompanied by greenschist-facies retrogression. In the third phase (D3), semi-brittle to brittle extensional fault planes cut through the previous ductile structures. D3 faults exhibit extensional kinematics in all directions on the flanks of exhumation domes. This phase correlates with a late-orogenic doming event, marking the final exhumation stage of the PQ unit in the upper crust. The exhumation of high-pressure units results from the interplay between ductile syn-orogenic extrusion and continuous underplating within the subduction zone. This underplating maintains vertical movements and uplift of the units, initiating a 3D upper-crustal extensional collapse along low-angle normal faults.
{"title":"Deformation Mechanisms During the Syn-Orogenic Extrusion of the High-Pressure Phyllites-Quartzites Unit in the Central and Northern Peloponnese, Greece","authors":"Vincent Wicker, Simon Bufféral","doi":"10.1029/2023tc008116","DOIUrl":"https://doi.org/10.1029/2023tc008116","url":null,"abstract":"The High-Pressure Phyllites-Quartzites (PQ) unit of the External Hellenides is exposed in tectonic windows in the central and northern Peloponnese (Greece). Understanding the deformation history of this unit is essential to interpreting the Oligo-Miocene evolution of the External Hellenides belt and its associated exhumation events. This study integrates new field observations and microtectonic analyses with previous studies to offer a comprehensive deformation model of the PQ unit since the Late Oligocene. The first deformation phase (D<sub>1</sub>), captures the progressive incorporation of the PQ into an orogenic wedge. This phase is largely overprinted and only preserved as relict features. The second phase (D<sub>2</sub>) displays coeval top-to-the-ENE and top-to-the-WSW localized ductile shear. A transition is observed from top-to-the-ENE non-coaxial deformation at the upper parts of the nappe to intense isoclinal folding (refolding S<sub>1</sub>) at the lower structural levels. We associate D<sub>2</sub> with the ductile syn-orogenic exhumation of the PQ within an extrusion wedge, accompanied by greenschist-facies retrogression. In the third phase (D<sub>3</sub>), semi-brittle to brittle extensional fault planes cut through the previous ductile structures. D<sub>3</sub> faults exhibit extensional kinematics in all directions on the flanks of exhumation domes. This phase correlates with a late-orogenic doming event, marking the final exhumation stage of the PQ unit in the upper crust. The exhumation of high-pressure units results from the interplay between ductile syn-orogenic extrusion and continuous underplating within the subduction zone. This underplating maintains vertical movements and uplift of the units, initiating a 3D upper-crustal extensional collapse along low-angle normal faults.","PeriodicalId":22351,"journal":{"name":"Tectonics","volume":"19 1","pages":""},"PeriodicalIF":4.2,"publicationDate":"2024-08-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142209399","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}
Yanling Zhang, Changqing Yin, Lin Ding, Shun Li, Jiahui Qian, Peng Gao, Wangchao Li
Despite a half-century of intense research, the timing and diachroneity of initial collision between India and Asia remain highly debated, largely due to different definitions of “initial collision” and correspondingly different methods adopted. This study focuses on high-pressure pelitic granulites of the Eastern Himalayan Syntaxis (EHS) to elucidate their metamorphic evolution and provide new constraints on the timing of initial India-Asia collision. Petrological examination and phase equilibria modeling show that high-pressure pelitic granulites have undergone four metamorphic stages, with the peak assemblage of garnet + K-feldspar + kyanite + biotite ± plagioclase ± rutile + ilmenite + quartz at P-T conditions of 13.1–15.7 kbar and 790–850°C. Clockwise P-T paths suggest that the Indian continent underwent tectonometamorphic processes of initial collision and subsequent continent subduction. Zircon and monazite dating results indicate that the metamorphic ages of pelitic granulites range from 60 to 15 Ma, with the oldest ones clustered at 60–58 Ma. The oldest metamorphic ages of high- to ultrahigh-pressure Himalayan metamorphic rocks can provide an upper age limit of the initial collision. Therefore, the initial India-Asia collision must have occurred before 60–58 Ma in the EHS, roughly consistent with ca. 57 Ma in the western Himalaya and 63–60 Ma in the central Himalaya. Collectively, we conclude that the northern margin of India most likely underwent a single-stage synchronous collision with the southern margin of Asia initially at around 60 Ma along the entire Yarlung-Tsangpo suture zone.
尽管经过半个世纪的深入研究，印度和亚洲之间最初碰撞的时间和非同步性仍然存在很大争议，这主要是由于对 "最初碰撞 "的定义不同，相应采用的方法也不同。本研究以东喜马拉雅山系（EHS）的高压辉绿岩花岗岩为研究对象，旨在阐明其变质演化过程，并为印度与亚洲的初始碰撞时间提供新的约束条件。岩石学检查和相平衡模型显示，高压辉绿岩花岗岩经历了四个变质阶段，在13.1-15.7千巴和790-850°C的P-T条件下，石榴石+K长石+闪长岩+生物橄榄石±斜长石±金红石+钛铁矿+石英的组合达到顶峰。顺时针的P-T路径表明，印度大陆经历了最初的碰撞和随后的大陆俯冲的构造变质过程。锆石和独居石测年结果表明，辉绿岩花岗岩的变质年龄在60-15Ma之间，最古老的集中在60-58Ma。喜马拉雅山高压至超高压变质岩的最古老变质年龄可以提供初始碰撞的年龄上限。因此，最初的印度-亚洲碰撞一定发生在 EHS 的 60-58 Ma 之前，与喜马拉雅西部的约 57 Ma 和喜马拉雅中部的 63-60 Ma 大致吻合。综上所述，我们得出结论，印度北缘很可能在60Ma左右时沿整个雅鲁藏布江缝合带与亚洲南缘发生了单阶段同步碰撞。
{"title":"Single-Stage Synchronous India-Asia Collision Model Revealed by Himalayan High-Pressure Metamorphic Rocks","authors":"Yanling Zhang, Changqing Yin, Lin Ding, Shun Li, Jiahui Qian, Peng Gao, Wangchao Li","doi":"10.1029/2024tc008253","DOIUrl":"https://doi.org/10.1029/2024tc008253","url":null,"abstract":"Despite a half-century of intense research, the timing and diachroneity of initial collision between India and Asia remain highly debated, largely due to different definitions of “initial collision” and correspondingly different methods adopted. This study focuses on high-pressure pelitic granulites of the Eastern Himalayan Syntaxis (EHS) to elucidate their metamorphic evolution and provide new constraints on the timing of initial India-Asia collision. Petrological examination and phase equilibria modeling show that high-pressure pelitic granulites have undergone four metamorphic stages, with the peak assemblage of garnet + K-feldspar + kyanite + biotite ± plagioclase ± rutile + ilmenite + quartz at <i>P</i>-<i>T</i> conditions of 13.1–15.7 kbar and 790–850°C. Clockwise <i>P</i>-<i>T</i> paths suggest that the Indian continent underwent tectonometamorphic processes of initial collision and subsequent continent subduction. Zircon and monazite dating results indicate that the metamorphic ages of pelitic granulites range from 60 to 15 Ma, with the oldest ones clustered at 60–58 Ma. The oldest metamorphic ages of high- to ultrahigh-pressure Himalayan metamorphic rocks can provide an upper age limit of the initial collision. Therefore, the initial India-Asia collision must have occurred before 60–58 Ma in the EHS, roughly consistent with ca. 57 Ma in the western Himalaya and 63–60 Ma in the central Himalaya. Collectively, we conclude that the northern margin of India most likely underwent a single-stage synchronous collision with the southern margin of Asia initially at around 60 Ma along the entire Yarlung-Tsangpo suture zone.","PeriodicalId":22351,"journal":{"name":"Tectonics","volume":"47 1","pages":""},"PeriodicalIF":4.2,"publicationDate":"2024-08-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142209528","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}
Haomin Ji, Zhikun Ren, Xiaoxiao Zhu, Mingkun Bai, Guodong Bao, Jinrui Liu, Guanghao Ha, Zhongtai He
The tectonic deformation of the southeastern margin of the Tibetan Plateau underwent significant changes before and after the Miocene, which led to the change of the deformation characteristics of the Sichuan-Yunnan block, and some local areas in the block also showed structural patterns inconsistent with the macroscopic clockwise rotation deformation. Moreover, the Chenghai fault (CF) in the Sichuan-Yunnan block was the seismogenic fault of the M 73/4 Yongsheng earthquake in 1515. However, the dense vegetation impeded the acquisition of surface deformation characteristics and small-scale horizontal offsets along the fault, resulting in its misty kinematic properties, roughly determined geometric distribution, and the highly controversial rupture parameters of the Yongsheng earthquake. Therefore, we used airborne light detection and ranging, which can penetrate vegetation to obtain high-resolution surface topography, to map the CF within 120 km. Combined with satellite images and field investigations, we determined that the CF consists of a series of secondary faults with simple geometric structures. Continuous offset linear landforms were preserved along the fault. 102 offsets below 30 m were statistically analyzed and the result revealed that the CF has a characteristic displacement of ∼6 m and it may rupture as a united rupture segment in each large earthquake or its two rupture segments cascade rupture to generate large earthquakes. The magnitude of the Yongsheng earthquake in 1515 was estimated at 7.7. Finally, based on this study, the kinematic characteristics of the Dali terrane and Sichuan-Yunnan block, where the CF is located are discussed.
{"title":"Slip Distribution Along the Chenghai Fault From Airborne LiDAR and Tectonic Implications for the 1515 Yongsheng Earthquake, China","authors":"Haomin Ji, Zhikun Ren, Xiaoxiao Zhu, Mingkun Bai, Guodong Bao, Jinrui Liu, Guanghao Ha, Zhongtai He","doi":"10.1029/2024tc008285","DOIUrl":"https://doi.org/10.1029/2024tc008285","url":null,"abstract":"The tectonic deformation of the southeastern margin of the Tibetan Plateau underwent significant changes before and after the Miocene, which led to the change of the deformation characteristics of the Sichuan-Yunnan block, and some local areas in the block also showed structural patterns inconsistent with the macroscopic clockwise rotation deformation. Moreover, the Chenghai fault (CF) in the Sichuan-Yunnan block was the seismogenic fault of the M 7<sup>3</sup>/<sub>4</sub> Yongsheng earthquake in 1515. However, the dense vegetation impeded the acquisition of surface deformation characteristics and small-scale horizontal offsets along the fault, resulting in its misty kinematic properties, roughly determined geometric distribution, and the highly controversial rupture parameters of the Yongsheng earthquake. Therefore, we used airborne light detection and ranging, which can penetrate vegetation to obtain high-resolution surface topography, to map the CF within 120 km. Combined with satellite images and field investigations, we determined that the CF consists of a series of secondary faults with simple geometric structures. Continuous offset linear landforms were preserved along the fault. 102 offsets below 30 m were statistically analyzed and the result revealed that the CF has a characteristic displacement of ∼6 m and it may rupture as a united rupture segment in each large earthquake or its two rupture segments cascade rupture to generate large earthquakes. The magnitude of the Yongsheng earthquake in 1515 was estimated at 7.7. Finally, based on this study, the kinematic characteristics of the Dali terrane and Sichuan-Yunnan block, where the CF is located are discussed.","PeriodicalId":22351,"journal":{"name":"Tectonics","volume":"35 1","pages":""},"PeriodicalIF":4.2,"publicationDate":"2024-08-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141933222","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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