Zoë K. Mildon, Manuel Diercks, Gerald P. Roberts, Joanna P. Faure Walker, Athanassios Ganas, Ioannis Papanikolaou, Vassilis Sakas, Jenni Robertson, Claudia Sgambato, Sam Mitchell
Geodetically-derived deformation rates are sometimes used to infer seismic hazard, implicitly assuming that short-term (annual-decadal) deformation is representative of longer-term deformation. This is despite geological observations indicating that deformation/slip rates are variable over a range of timescales. Using geodetic data from 2016 to 2021, we observe an up to 7-fold increase in vertical deformation rate in mid-2019 across the Pisia-Skinos normal fault in Greece. We hypothesize that this deformation is aseismic as there is no temporally correlated increase in the earthquake activity (M > 1). We explore four possible physical mechanisms, and our preferred hypothesis is that the transient deformation is caused by centimeter-scale slip in the upper 5 km of the Pisia fault zone. This is the first observation of shallow tectonic (i.e., not related to human activities) aseismic deformation on a normal fault globally. Our results suggest that continental normal faults can exhibit variable deformation over shorter timescales than previously observed, and thus care should be taken when utilizing geodetic rates to quantify seismic hazard.
{"title":"Transient Aseismic Vertical Deformation Across the Steeply-Dipping Pisia-Skinos Normal Fault (Gulf of Corinth, Greece)","authors":"Zoë K. Mildon, Manuel Diercks, Gerald P. Roberts, Joanna P. Faure Walker, Athanassios Ganas, Ioannis Papanikolaou, Vassilis Sakas, Jenni Robertson, Claudia Sgambato, Sam Mitchell","doi":"10.1029/2024tc008276","DOIUrl":"https://doi.org/10.1029/2024tc008276","url":null,"abstract":"Geodetically-derived deformation rates are sometimes used to infer seismic hazard, implicitly assuming that short-term (annual-decadal) deformation is representative of longer-term deformation. This is despite geological observations indicating that deformation/slip rates are variable over a range of timescales. Using geodetic data from 2016 to 2021, we observe an up to 7-fold increase in vertical deformation rate in mid-2019 across the Pisia-Skinos normal fault in Greece. We hypothesize that this deformation is aseismic as there is no temporally correlated increase in the earthquake activity (M > 1). We explore four possible physical mechanisms, and our preferred hypothesis is that the transient deformation is caused by centimeter-scale slip in the upper 5 km of the Pisia fault zone. This is the first observation of shallow tectonic (i.e., not related to human activities) aseismic deformation on a normal fault globally. Our results suggest that continental normal faults can exhibit variable deformation over shorter timescales than previously observed, and thus care should be taken when utilizing geodetic rates to quantify seismic hazard.","PeriodicalId":22351,"journal":{"name":"Tectonics","volume":"75 1","pages":""},"PeriodicalIF":4.2,"publicationDate":"2024-08-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141884575","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}
John S. Singleton, Gloria Arancibia, Diego Morata, Ignacia Pérez De La Maza
The ∼173–164 Ma Papudo-Quintero plutonic complex near 32.5°S in central Chile records three deformation events that provide insight into the tectonic development of the early Andean margin. The first event (D1) includes: (a) high-temperature (>600°C), coaxial-dominated strain along NE- to N-striking subvertical shear zones; (b) widespread emplacement of granitic dikes that dip gently to steeply NE; and (c) development of narrow (<10 cm thick) strike-slip and oblique-reverse shear zones. These D1 structures record NW-SE to WNW-ESE transpressional shortening with a component of sinistral shear parallel to the N-S trending magmatic arc. Zircon and apatite U-Pb dates and cross-cutting relations constrain most D1 deformation to ∼166–164 Ma. The second event (D2) occurred during postmagmatic cooling in the Late Jurassic and was characterized by development of pervasive E-W-striking veins with alteration halos and minor strike-slip and normal faults that record N-S extension in a transtensional regime. Structures associated with the last deformation event (D3) include Late Jurassic to Early Cretaceous mafic dikes, veins, and conjugate strike-slip faults that record NW-SE to N-S shortening in a strike-slip regime. D1 deformation is consistent with studies from other areas that document NW-SE shortening ± sinistral transpression along the arc throughout the Jurassic, suggesting this deformation was regional in scale and driven by oblique subduction convergence. Deformation associated with oblique convergence was localized within the active magmatic arc, which was an important process in the early Andean orogeny. As the arc migrated eastward, D2 and D3 structures formed in a low-stress regime in an arc margin or forearc setting.
{"title":"Magmatism and Polyphase Deformation in the Middle Jurassic Arc of Central Chile: Implications for the Tectonic Development of the Early Andean Margin","authors":"John S. Singleton, Gloria Arancibia, Diego Morata, Ignacia Pérez De La Maza","doi":"10.1029/2023tc008241","DOIUrl":"https://doi.org/10.1029/2023tc008241","url":null,"abstract":"The ∼173–164 Ma Papudo-Quintero plutonic complex near 32.5°S in central Chile records three deformation events that provide insight into the tectonic development of the early Andean margin. The first event (D<sub>1</sub>) includes: (a) high-temperature (>600°C), coaxial-dominated strain along NE- to N-striking subvertical shear zones; (b) widespread emplacement of granitic dikes that dip gently to steeply NE; and (c) development of narrow (<10 cm thick) strike-slip and oblique-reverse shear zones. These D<sub>1</sub> structures record NW-SE to WNW-ESE transpressional shortening with a component of sinistral shear parallel to the N-S trending magmatic arc. Zircon and apatite U-Pb dates and cross-cutting relations constrain most D<sub>1</sub> deformation to ∼166–164 Ma. The second event (D<sub>2</sub>) occurred during postmagmatic cooling in the Late Jurassic and was characterized by development of pervasive E-W-striking veins with alteration halos and minor strike-slip and normal faults that record N-S extension in a transtensional regime. Structures associated with the last deformation event (D<sub>3</sub>) include Late Jurassic to Early Cretaceous mafic dikes, veins, and conjugate strike-slip faults that record NW-SE to N-S shortening in a strike-slip regime. D<sub>1</sub> deformation is consistent with studies from other areas that document NW-SE shortening ± sinistral transpression along the arc throughout the Jurassic, suggesting this deformation was regional in scale and driven by oblique subduction convergence. Deformation associated with oblique convergence was localized within the active magmatic arc, which was an important process in the early Andean orogeny. As the arc migrated eastward, D<sub>2</sub> and D<sub>3</sub> structures formed in a low-stress regime in an arc margin or forearc setting.","PeriodicalId":22351,"journal":{"name":"Tectonics","volume":"217 1","pages":""},"PeriodicalIF":4.2,"publicationDate":"2024-07-31","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141884577","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}
E. Legeay, G. Mohn, J. C. Ringenbach, W. Vetel, F. Sapin
This contribution explores the formation and evolution of hyper-extended basins, associated with the early stage of core complex formation, controlled by low-angle normal faults active at <30°. Based on a high-resolution industrial 3D seismic reflection survey along the southern margin of the South China Sea (SCS) (Dangerous Grounds), we mapped and analyzed the 3D geometry of low-angle normal fault systems and the related stratigraphy. Two main hyper-extended basins were documented, filled by up to 6 km of sediments including pre- to post-rift sequences. The observed normal faults on depth migrated seismic sections show an average dip angle of <30° and appear planar, characterized by continuous reflections with no clear steepening at depth and sole-out on distinct decollement levels. Detailed fault surface mapping reveals the occurrence of km-scale corrugations together with large wavelength undulation. The formation of these hyper-extended basins is associated with polyphased syn-rift infill during the development of the low-angle normal faults. The first syn-rift sequence appears as chaotic and discontinuous packages that has been dismembered and fragmented during the activity of low-angle normal faults. The second syn-rift package shows unexpected sedimentary wedges developing successively toward the footwall and the hangingwall. This geometry results from the interplay between the main low-angle normal fault and antithetic faults defining a so-called extensional fishtail. The deep structure of these basins shows nascent domes with limited evidence of magmatism. Eventually, these basins likely capture the earliest stage of core complex development in the proximal margin of the southern SCS.
{"title":"3D Structure of Low-Angle Normal Faults and Tectono-Sedimentary Processes of Nascent Continental Core-Complexes in the SE South China Sea","authors":"E. Legeay, G. Mohn, J. C. Ringenbach, W. Vetel, F. Sapin","doi":"10.1029/2023tc008218","DOIUrl":"https://doi.org/10.1029/2023tc008218","url":null,"abstract":"This contribution explores the formation and evolution of hyper-extended basins, associated with the early stage of core complex formation, controlled by low-angle normal faults active at <30°. Based on a high-resolution industrial 3D seismic reflection survey along the southern margin of the South China Sea (SCS) (Dangerous Grounds), we mapped and analyzed the 3D geometry of low-angle normal fault systems and the related stratigraphy. Two main hyper-extended basins were documented, filled by up to 6 km of sediments including pre- to post-rift sequences. The observed normal faults on depth migrated seismic sections show an average dip angle of <30° and appear planar, characterized by continuous reflections with no clear steepening at depth and sole-out on distinct decollement levels. Detailed fault surface mapping reveals the occurrence of km-scale corrugations together with large wavelength undulation. The formation of these hyper-extended basins is associated with polyphased syn-rift infill during the development of the low-angle normal faults. The first syn-rift sequence appears as chaotic and discontinuous packages that has been dismembered and fragmented during the activity of low-angle normal faults. The second syn-rift package shows unexpected sedimentary wedges developing successively toward the footwall and the hangingwall. This geometry results from the interplay between the main low-angle normal fault and antithetic faults defining a so-called extensional fishtail. The deep structure of these basins shows nascent domes with limited evidence of magmatism. Eventually, these basins likely capture the earliest stage of core complex development in the proximal margin of the southern SCS.","PeriodicalId":22351,"journal":{"name":"Tectonics","volume":"2 1","pages":""},"PeriodicalIF":4.2,"publicationDate":"2024-07-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141871517","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 Eastern Alps were affected by a profound post-collisional tectonic reorganisation in Neogene time, featuring indentation by the Adriatic upper plate, rapid uplift and filling of the eastern Molasse Basin, exhumation and eastward orogen-parallel transport of Paleogene metamorphic units in the orogenic core, and a shift from northward thrust propagation in the European plate to southward propagation in the Adriatic plate. We test the idea that these events were triggered by slab detachment by reconstructing the indentation process. This involves sequentially restoring N-S and E-W cross-sections of the orogenic wedge and correcting for out-of-section orogen-parallel transport with a map-view reconstruction. We propose two phases of indentation: Initially (23 and 14 Ma), the whole Adriatic crust acted as an indenter. Its northward motion was accommodated by upright folding and orogen-parallel extensional exhumation in the Tauern Window. This phase was followed (14 Ma to Present) by continued orogen-parallel transport of the orogenic wedge into the Pannonian Basin and deformation of the leading edge of the Adriatic indenter, forming the Southern Alps fold-thrust belt. The lower crust of the Southern Alps indented the base of the Venediger Nappes in the Tauern Window, forming a high-velocity (6.8–7.25 km/s) ridge in map view at 30–45 km depth. By correlating the post-23 Ma orogenic evolution with presently imaged European slab segments in P-wave teleseismic tomography, we discern two possible Neogene slab removal events: One from 23 to 19 Ma triggering tectonic reorganisation of the Eastern Alps and its foreland basin, and potentially a second event after 14 Ma.
{"title":"Post-Collisional Reorganisation of the Eastern Alps in 4D – Crust and Mantle Structure","authors":"Peter J. McPhee, Mark R. Handy","doi":"10.1029/2024tc008374","DOIUrl":"https://doi.org/10.1029/2024tc008374","url":null,"abstract":"The Eastern Alps were affected by a profound post-collisional tectonic reorganisation in Neogene time, featuring indentation by the Adriatic upper plate, rapid uplift and filling of the eastern Molasse Basin, exhumation and eastward orogen-parallel transport of Paleogene metamorphic units in the orogenic core, and a shift from northward thrust propagation in the European plate to southward propagation in the Adriatic plate. We test the idea that these events were triggered by slab detachment by reconstructing the indentation process. This involves sequentially restoring N-S and E-W cross-sections of the orogenic wedge and correcting for out-of-section orogen-parallel transport with a map-view reconstruction. We propose two phases of indentation: Initially (23 and 14 Ma), the whole Adriatic crust acted as an indenter. Its northward motion was accommodated by upright folding and orogen-parallel extensional exhumation in the Tauern Window. This phase was followed (14 Ma to Present) by continued orogen-parallel transport of the orogenic wedge into the Pannonian Basin and deformation of the leading edge of the Adriatic indenter, forming the Southern Alps fold-thrust belt. The lower crust of the Southern Alps indented the base of the Venediger Nappes in the Tauern Window, forming a high-velocity (6.8–7.25 km/s) ridge in map view at 30–45 km depth. By correlating the post-23 Ma orogenic evolution with presently imaged European slab segments in P-wave teleseismic tomography, we discern two possible Neogene slab removal events: One from 23 to 19 Ma triggering tectonic reorganisation of the Eastern Alps and its foreland basin, and potentially a second event after 14 Ma.","PeriodicalId":22351,"journal":{"name":"Tectonics","volume":"78 1","pages":""},"PeriodicalIF":4.2,"publicationDate":"2024-07-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141871516","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}
Veleda A. P. Muller, Christian Sue, Pierre G. Valla, Pietro Sternai, Thibaud Simon-Labric, Cécile Gautheron, Kurt M. Cuffey, Djordje Grujic, Matthias Bernet, Joseph Martinod, Matias C. Ghiglione, Peter Reiners, Chelsea Willett, David Shuster, Frédéric Herman, Lukas Baumgartner, Jean Braun
High-relief glacial valleys shape the modern topography of the Southern Patagonian Andes, but their formation remains poorly understood. Two Miocene plutonic complexes in the Andean retroarc, the Fitz Roy (49°S) and Torres del Paine (51°S) massifs, were emplaced between 16.9–16.4 Ma and 12.6–12.4 Ma, respectively. Subduction of oceanic ridge segments initiated ca. 16 Ma at 54°S, leading to northward opening of a slab window with associated mantle upwelling. The onset of major glaciations caused drastic topographic changes since ca. 7 Ma. To constrain the respective contributions of tectonic-mantle dynamics and fluvio-glacial erosion to rock exhumation and landscape evolution, we perform inverse thermal modeling of a new data set of zircon and apatite (U-Th)/He from the two massifs, complemented by apatite 4He/3He data for Torres del Paine. Our results show rapid rock exhumation recorded only in the Fitz Roy massif between 10 and 8 Ma, which we ascribe to local mantle upwelling forcing surface uplift and intensified erosion around 49°S. Both massifs record a pulse of rock exhumation between 7 and 4 Ma, which we interpret as enhanced erosion during the beginning of Patagonian glaciations. After a period of erosional and tectonic quiescence in the Pliocene, increased rock exhumation since 3–2 Ma is interpreted as the result of alpine glacial valley carving promoted by reinforced glacial-interglacial cycles. This study highlights that glacial erosion was the main driver to rock exhumation in the Patagonian retroarc since 7 Ma, but that mantle upwelling might be a driving force to rock exhumation as well.
高凸冰川谷塑造了南巴塔哥尼亚安第斯山脉的现代地形，但人们对它们的形成却知之甚少。安第斯弧后部的两个中新世火山岩群，即菲茨罗伊（南纬 49°）和托雷斯德尔帕恩（南纬 51°）岩块，分别在 16.9-16.4 Ma 和 12.6-12.4 Ma 之间形成。大洋脊段的俯冲开始于南纬 54°，约 16 Ma，导致板块窗口向北打开，并伴有地幔上涌。自约 7 Ma 开始的大冰川作用导致了地形的急剧变化。7 Ma。为了确定构造-地幔动力学和河流-冰川侵蚀作用各自对岩石掘起和地貌演变的贡献，我们对来自这两个山丘的锆石和磷灰石（U-Th）/He新数据集进行了逆热建模，并对托雷斯德尔潘恩的磷灰石4He/3He数据进行了补充。我们的研究结果表明，只有菲茨罗伊山丘在10-8Ma之间记录到了快速的岩石掘起，我们将其归因于当地地幔上升流迫使地表隆起和南纬49°附近的侵蚀加剧。两个山丘都记录了 7 至 4 Ma 之间的岩石掘起，我们将其解释为巴塔哥尼亚冰川期开始时侵蚀作用的加强。在经历了上新世时期的侵蚀和构造静止期之后，自 3-2 Ma 以来岩石掘出量的增加被解释为冰川-间冰期循环加强所导致的高山冰川峡谷开凿的结果。这项研究强调，冰川侵蚀是巴塔哥尼亚后弧自7Ma以来岩石掘出的主要驱动力，但地幔上升流也可能是岩石掘出的驱动力。
{"title":"Geodynamic and Climatic Forcing on Late-Cenozoic Exhumation of the Southern Patagonian Andes (Fitz Roy and Torres del Paine massifs)","authors":"Veleda A. P. Muller, Christian Sue, Pierre G. Valla, Pietro Sternai, Thibaud Simon-Labric, Cécile Gautheron, Kurt M. Cuffey, Djordje Grujic, Matthias Bernet, Joseph Martinod, Matias C. Ghiglione, Peter Reiners, Chelsea Willett, David Shuster, Frédéric Herman, Lukas Baumgartner, Jean Braun","doi":"10.1029/2023tc007914","DOIUrl":"https://doi.org/10.1029/2023tc007914","url":null,"abstract":"High-relief glacial valleys shape the modern topography of the Southern Patagonian Andes, but their formation remains poorly understood. Two Miocene plutonic complexes in the Andean retroarc, the Fitz Roy (49°S) and Torres del Paine (51°S) massifs, were emplaced between 16.9–16.4 Ma and 12.6–12.4 Ma, respectively. Subduction of oceanic ridge segments initiated ca. 16 Ma at 54°S, leading to northward opening of a slab window with associated mantle upwelling. The onset of major glaciations caused drastic topographic changes since ca. 7 Ma. To constrain the respective contributions of tectonic-mantle dynamics and fluvio-glacial erosion to rock exhumation and landscape evolution, we perform inverse thermal modeling of a new data set of zircon and apatite (U-Th)/He from the two massifs, complemented by apatite <sup>4</sup>He/<sup>3</sup>He data for Torres del Paine. Our results show rapid rock exhumation recorded only in the Fitz Roy massif between 10 and 8 Ma, which we ascribe to local mantle upwelling forcing surface uplift and intensified erosion around 49°S. Both massifs record a pulse of rock exhumation between 7 and 4 Ma, which we interpret as enhanced erosion during the beginning of Patagonian glaciations. After a period of erosional and tectonic quiescence in the Pliocene, increased rock exhumation since 3–2 Ma is interpreted as the result of alpine glacial valley carving promoted by reinforced glacial-interglacial cycles. This study highlights that glacial erosion was the main driver to rock exhumation in the Patagonian retroarc since 7 Ma, but that mantle upwelling might be a driving force to rock exhumation as well.","PeriodicalId":22351,"journal":{"name":"Tectonics","volume":"19 1","pages":""},"PeriodicalIF":4.2,"publicationDate":"2024-07-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141780107","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}
Julia C. Fonseca, Cesar R. Ranero, Paola Vannucchi, David Iacopini, Helenice Vital
The Brazilian Equatorial Margin (BEM) is interpreted as a transform margin, where the last segment opened during Gondwana rifting. However, margin evolution, and break-up age remain unconstrained. We interpret >10k km of crustal-scale seismic images extending along ∼600 km of the margin calibrated with drillholes. We determine the style and timing of tectonics across the rift system. We link changes in crustal-scale structure and age of sediment deposits to interpret variations with the style of extension and intensity of thinning across the BEM. Observations support a rift evolution where deformation is initially distributed forming a shallow basin, subsequently focusses, and later migrates basin-ward forming the deep-water domain. We interpret that tectonic activity started ∼140–136 Ma and stopped earlier in the shallow basin causing minor thinning, than in the deep-water domain with a ∼60 km wide area with 4–8 km thick crust extended in Late Aptian to Early Albian (116–110 Ma). Constraints from seismic and drilling help define an abrupt continent to ocean transition (COT) where continental crust may be abutted by oceanic crust, and breakup occurred at early Albian time. Basin sedimentation from the onset to the Late Aptian is continental, indicating an isolated environment disconnected from Atlantic oceans. During late-most Aptian to Early Albian basin sedimentation changes and indicates a comparatively rapid marine water infill. Rifting of the BEM is not dominated by transcurrent deformation as previously inferred, with strike-slip faulting limited to comparatively small sectors, whereas most of the margin extended by normal faulting deformation.
巴西赤道边缘（BEM）被解释为一个转换边缘，其最后一段在冈瓦纳断裂过程中打开。然而，边缘的演化和断裂年龄仍未确定。我们解释了沿边缘 600 千米延伸的 1 万千米地壳尺度地震图像，并用钻孔进行了校准。我们确定了整个裂谷系统的构造风格和时间。我们将地壳尺度结构的变化和沉积物沉积的年龄联系起来，以解释整个 BEM 的延伸方式和变薄强度的变化。观测结果支持这样一种断裂演化过程：变形最初分布形成浅盆地，随后集中，然后向盆地方向迁移，形成深水域。我们的解释是，构造活动开始于140-136Ma，在浅盆地较早停止，造成轻微的变薄，而在深水域，构造活动在晚奥陶纪到早阿尔卑纪（116-110Ma）延伸出一个宽60km、厚4-8km的地壳区域。地震和钻探资料有助于确定大陆向海洋的突然过渡（COT），大陆地壳可能与大洋地壳相接，断裂发生在早阿尔比世。从始新世到晚始新世的盆地沉积为大陆沉积，表明当时的环境与大西洋隔绝。在最晚始新世至早白垩世，盆地沉积发生了变化，表明海水注入相对较快。BEM的断裂并不像以前推断的那样以横断面变形为主，走向滑动断层仅限于相对较小的区域，而大部分边缘则以正断层变形延伸。
{"title":"The Tectonic Structure and Evolution of the Potiguar-Ceará Rifted Margin of Brazil","authors":"Julia C. Fonseca, Cesar R. Ranero, Paola Vannucchi, David Iacopini, Helenice Vital","doi":"10.1029/2023tc008184","DOIUrl":"https://doi.org/10.1029/2023tc008184","url":null,"abstract":"The Brazilian Equatorial Margin (BEM) is interpreted as a transform margin, where the last segment opened during Gondwana rifting. However, margin evolution, and break-up age remain unconstrained. We interpret >10k km of crustal-scale seismic images extending along ∼600 km of the margin calibrated with drillholes. We determine the style and timing of tectonics across the rift system. We link changes in crustal-scale structure and age of sediment deposits to interpret variations with the style of extension and intensity of thinning across the BEM. Observations support a rift evolution where deformation is initially distributed forming a shallow basin, subsequently focusses, and later migrates basin-ward forming the deep-water domain. We interpret that tectonic activity started ∼140–136 Ma and stopped earlier in the shallow basin causing minor thinning, than in the deep-water domain with a ∼60 km wide area with 4–8 km thick crust extended in Late Aptian to Early Albian (116–110 Ma). Constraints from seismic and drilling help define an abrupt continent to ocean transition (COT) where continental crust may be abutted by oceanic crust, and breakup occurred at early Albian time. Basin sedimentation from the onset to the Late Aptian is continental, indicating an isolated environment disconnected from Atlantic oceans. During late-most Aptian to Early Albian basin sedimentation changes and indicates a comparatively rapid marine water infill. Rifting of the BEM is not dominated by transcurrent deformation as previously inferred, with strike-slip faulting limited to comparatively small sectors, whereas most of the margin extended by normal faulting deformation.","PeriodicalId":22351,"journal":{"name":"Tectonics","volume":"8 1","pages":""},"PeriodicalIF":4.2,"publicationDate":"2024-07-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141780182","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}
D. E. Stevens, Y. L. C. McNeill, T. J. Henstock, P. M. Barnes, G. Crutchley, N. Bangs, S. Henrys, H. J. A. Van Avendonk
The southern Hikurangi subduction zone exhibits significant along-strike variation in convergence rate and obliquity, sediment thickness and, uniquely, the increasing proximity of southern Hikurangi to, and impingement on, the incoming continental Chatham Rise, an ancient Gondwana accretionary complex. There are corresponding changes in the morphology and structure of the Hikurangi accretionary prism. We combine widely spaced multichannel seismic reflection profiles with high resolution bathymetry and previous interpretations to characterize the structure and the history of the accretionary prism since 2 Ma. The southern Hikurangi margin can be divided into three segments. A northeastern segment (A) characterized by a moderately wide (∼70 km), low taper (∼5°) prism recording uninhibited outward growth in the last ∼1 Myr. Deformation resolvable in seismic reflection data accounts for ∼20 % of plate convergence, comparable with the central Hikurangi margin further North. A central segment (B) characterized by a narrow (∼30 km), moderate taper (∼8°) prism, with earlier (∼2-∼1 Ma) shortening than segment A. Outward prism growth ceased coincidentally with development of major strike-slip faults in the prism interior, reduced margin-normal convergence rate, and the onset of impingement on the incoming Chatham Rise to the south. A southwestern segment (C) marks the approximate southern termination of subduction but widens to ∼50 km due to rapid outward migration of the deformation front via fault reactivation within the now-underthrusting corner of the Chatham Rise. Segment C exhibits minimal shortening as margin-normal subduction velocity decreases and plate motion is increasingly taken up by interior thrusts and strike-slip faults.
{"title":"Structural Variation Along the Southern Hikurangi Subduction Zone, Aotearoa New Zealand, From Seismic Reflection and Retro-Deformation Analysis","authors":"D. E. Stevens, Y. L. C. McNeill, T. J. Henstock, P. M. Barnes, G. Crutchley, N. Bangs, S. Henrys, H. J. A. Van Avendonk","doi":"10.1029/2023tc008212","DOIUrl":"https://doi.org/10.1029/2023tc008212","url":null,"abstract":"The southern Hikurangi subduction zone exhibits significant along-strike variation in convergence rate and obliquity, sediment thickness and, uniquely, the increasing proximity of southern Hikurangi to, and impingement on, the incoming continental Chatham Rise, an ancient Gondwana accretionary complex. There are corresponding changes in the morphology and structure of the Hikurangi accretionary prism. We combine widely spaced multichannel seismic reflection profiles with high resolution bathymetry and previous interpretations to characterize the structure and the history of the accretionary prism since 2 Ma. The southern Hikurangi margin can be divided into three segments. A northeastern segment (A) characterized by a moderately wide (∼70 km), low taper (∼5°) prism recording uninhibited outward growth in the last ∼1 Myr. Deformation resolvable in seismic reflection data accounts for ∼20 % of plate convergence, comparable with the central Hikurangi margin further North. A central segment (B) characterized by a narrow (∼30 km), moderate taper (∼8°) prism, with earlier (∼2-∼1 Ma) shortening than segment A. Outward prism growth ceased coincidentally with development of major strike-slip faults in the prism interior, reduced margin-normal convergence rate, and the onset of impingement on the incoming Chatham Rise to the south. A southwestern segment (C) marks the approximate southern termination of subduction but widens to ∼50 km due to rapid outward migration of the deformation front via fault reactivation within the now-underthrusting corner of the Chatham Rise. Segment C exhibits minimal shortening as margin-normal subduction velocity decreases and plate motion is increasingly taken up by interior thrusts and strike-slip faults.","PeriodicalId":22351,"journal":{"name":"Tectonics","volume":"11 1","pages":""},"PeriodicalIF":4.2,"publicationDate":"2024-07-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141746370","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}
Ziqing Li, Bo Zhang, Lei Guo, Zhaoliang Hou, Bernhard Grasemann, Fulong Cai, Houqi Wang
In the southeastern Tibetan Plateau, region-scale dextral strike-slip shear zones, crucial for India-Asia convergence, were investigated along the Dulongjiang shear zone near the Eastern Himalayan Syntaxis (EHS). Structural, kinematic, and geochronological data from Dulongjiang and Nabang regions in western Yunnan, China, reveal dextral strike-slip shearing between 30 and 15 Ma. Various rocks were affected by moderate-temperature shear deformation (∼450–550°C), inferred from microstructures and quartz CPO patterns, during dextral strike-slip and exhumation of the shear zone. Combined with structures of pre-, syn-, and post-shearing leucogranites, zircon U-Pb dating indicates that the dextral shear along the shear zone began in the Early Oligocene (30–29 Ma) subsequent to the India-Asia collision. Micas in mylonitic granites yield 40Ar/39Ar ages, suggesting that the principal dextral shear deformation occurred approximately between 18 and 15 Ma. The Dulongjiang shear zone is linked to the Parlung, Nabang shear zone, and Sagaing Fault, forming a regional Cenozoic dextral shear system around the EHS. The study, combined with tomographic anomalies beneath the India-Asia collision zone, highlights distinct lithospheric-scale evolution in southeastern and eastern Tibet. Continuous intracontinental strike-slip shearing indicates a tectonic shift from Tibetan extension to block rotation around the EHS. From 30 to 15 Ma, slab tear, accompanied by clockwise rotation and dextral strike-slip shearing, suggests a warmer geodynamic setting influenced by hot mantle flow associated with ongoing subduction of the Indian lithosphere. Oligocene-Miocene dextral strike-slip shearing around the EHS, linking southwards with the Sagaing Fault, may correspond to the rotation necessary for slab to bend, stretch, and eventually tear beneath the region.
在青藏高原东南部，沿东喜马拉雅轴（EHS）附近的独龙江剪切带研究了对印度-亚洲辐合至关重要的区域尺度右旋走向滑动剪切带。来自中国云南西部独龙江和那邦地区的构造、运动学和地质年代数据揭示了 30-15 Ma 之间的右旋走向剪切。根据微结构和石英CPO模式推断，在右旋走向滑动和剪切带的剥蚀过程中，各种岩石受到中温剪切变形（450-550°C）的影响。结合剪切前、同步和剪切后白榴石的结构，锆石U-Pb年代测定表明，剪切带的右旋剪切始于印度-亚洲碰撞之后的早渐新世（30-29 Ma）。麦饭石花岗岩中的云母产生的40Ar/39Ar年龄表明，主要的右旋剪切变形大约发生在18至15Ma之间。独龙江剪切带与帕隆剪切带、纳邦剪切带和实皆断层相连，在东高止山脉周围形成了一个区域性新生代右旋剪切系统。这项研究与印度-亚洲碰撞带下的断层异常相结合，凸显了西藏东南部和东部岩石圈尺度的明显演化。持续的大陆内部走向-滑动剪切表明，构造从西藏延伸转变为EHS周围的块体旋转。从 30 到 15 Ma，板块撕裂，伴随着顺时针旋转和右旋走向剪切，表明当时的地球动力环境较为温暖，受到与印度岩石圈持续俯冲有关的热地幔流的影响。EHS周围的渐新世-中新世向南与实皆断层相连的右旋向斜剪切可能与板块在该地区下方弯曲、拉伸并最终撕裂所需的旋转相对应。
{"title":"Slab Tear of Subducted Indian Lithosphere Beneath the Eastern Himalayan Syntaxis Region","authors":"Ziqing Li, Bo Zhang, Lei Guo, Zhaoliang Hou, Bernhard Grasemann, Fulong Cai, Houqi Wang","doi":"10.1029/2024tc008248","DOIUrl":"https://doi.org/10.1029/2024tc008248","url":null,"abstract":"In the southeastern Tibetan Plateau, region-scale dextral strike-slip shear zones, crucial for India-Asia convergence, were investigated along the Dulongjiang shear zone near the Eastern Himalayan Syntaxis (EHS). Structural, kinematic, and geochronological data from Dulongjiang and Nabang regions in western Yunnan, China, reveal dextral strike-slip shearing between 30 and 15 Ma. Various rocks were affected by moderate-temperature shear deformation (∼450–550°C), inferred from microstructures and quartz CPO patterns, during dextral strike-slip and exhumation of the shear zone. Combined with structures of pre-, syn-, and post-shearing leucogranites, zircon U-Pb dating indicates that the dextral shear along the shear zone began in the Early Oligocene (30–29 Ma) subsequent to the India-Asia collision. Micas in mylonitic granites yield <sup>40</sup>Ar/<sup>39</sup>Ar ages, suggesting that the principal dextral shear deformation occurred approximately between 18 and 15 Ma. The Dulongjiang shear zone is linked to the Parlung, Nabang shear zone, and Sagaing Fault, forming a regional Cenozoic dextral shear system around the EHS. The study, combined with tomographic anomalies beneath the India-Asia collision zone, highlights distinct lithospheric-scale evolution in southeastern and eastern Tibet. Continuous intracontinental strike-slip shearing indicates a tectonic shift from Tibetan extension to block rotation around the EHS. From 30 to 15 Ma, slab tear, accompanied by clockwise rotation and dextral strike-slip shearing, suggests a warmer geodynamic setting influenced by hot mantle flow associated with ongoing subduction of the Indian lithosphere. Oligocene-Miocene dextral strike-slip shearing around the EHS, linking southwards with the Sagaing Fault, may correspond to the rotation necessary for slab to bend, stretch, and eventually tear beneath the region.","PeriodicalId":22351,"journal":{"name":"Tectonics","volume":"29 1","pages":""},"PeriodicalIF":4.2,"publicationDate":"2024-07-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141613725","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}
Autumn L. Helfrich, J. Ryan Thigpen, Victoria M. Buford-Parks, Nadine McQuarrie, Summer J. Brown, Ryan C. Goldsby
Constraining the geometry and displacement of crustal-scale normal faults has historically been challenging, owing to difficulties with geophysical imaging and inability to identify precise cut-offs at depth. Using a modified workflow previously applied to contractional systems, flexural-kinematic (Move) and thermal-kinematic (Pecube) models are integrated with apatite (U-Th)/He (AHe) and apatite fission track (AFT) data from Teton footwall transects to constrain total Teton fault displacement (Dmax). Models with slip onset at ∼10 Ma and flexure parameters that best match the observed Teton flexural profile require Dmax > 8 km to produce young (<10 Ma) AHe ages observed at low elevation footwall positions in the Tetons. For the same slip onset, models with Dmax of 11–13 km provide the best match to observed AHe data, but displacements ≥16 km are required to produce observed AFT ages (13.6–12.0 Ma) at low elevations. A more complex model with slow slip onset at ∼25 Ma followed by faster slip at ∼10 Ma yields a good match between modeled and observed AHe ages at a Dmax of 13–15 km. However, this model predicts low elevation AFT ages 6–8 Ma older than observed ages, even at Dmax values of 16–17 km. Based on this analysis and integration with previous studies, we propose a unified evolution wherein the Teton fault likely experienced 11–13 km of Miocene-recent displacement, with AFT data likely indicating a pre-to early Miocene cooling history. Importantly, this study highlights the utility of using integrated flexural- and thermal-kinematic models to resolve displacement histories in extensional systems.
由于地球物理成像方面的困难以及无法确定深度的精确截断点，对地壳尺度正断层的几何形状和位移进行约束一直是一项挑战。利用以前用于收缩系统的改进工作流程，将挠曲运动学（Move）和热运动学（Pecube）模型与来自泰顿脚墙横断面的磷灰石（U-Th）/氦（AHe）和磷灰石裂变轨迹（AFT）数据相结合，以确定泰顿断层的总位移（Dmax）。滑动起始时间为 ∼10 Ma、挠曲参数与观察到的泰顿挠曲剖面最匹配的模型需要 Dmax > 8 km 才能产生在泰顿低海拔脚墙位置观察到的年轻（<10 Ma）AHe 年龄。对于相同的滑动起始点，Dmax 为 11-13 km 的模型与观测到的 AHe 数据最匹配，但需要位移≥16 km 才能产生在低海拔地区观测到的 AFT 年龄（13.6-12.0 Ma）。一个更复杂的模型是在 ∼25 Ma 开始缓慢滑动，然后在 ∼10 Ma 开始快速滑动，结果在 Dmax 为 13-15 km 时，模型年龄与观测到的 AHe 年龄非常吻合。然而，该模型预测的低海拔AFT年龄比观测年龄早6-8 Ma，即使在Dmax值为16-17 km时也是如此。根据上述分析并结合之前的研究，我们提出了一个统一的演化过程，即泰顿断层可能经历了 11-13 千米的中新世近期位移，而 AFT 数据可能显示了中新世前至中新世早期的冷却历史。重要的是，这项研究强调了使用综合挠曲和热运动学模型来解析伸展系统位移历史的实用性。
{"title":"Constraining Displacement Magnitude on Crustal-Scale Extensional Faults Using Thermochronology Combined With Flexural-Kinematic and Thermal-Kinematic Modeling: An Example From the Teton Fault, Wyoming, USA","authors":"Autumn L. Helfrich, J. Ryan Thigpen, Victoria M. Buford-Parks, Nadine McQuarrie, Summer J. Brown, Ryan C. Goldsby","doi":"10.1029/2024tc008308","DOIUrl":"https://doi.org/10.1029/2024tc008308","url":null,"abstract":"Constraining the geometry and displacement of crustal-scale normal faults has historically been challenging, owing to difficulties with geophysical imaging and inability to identify precise cut-offs at depth. Using a modified workflow previously applied to contractional systems, flexural-kinematic (<i>Move</i>) and thermal-kinematic (<i>Pecube</i>) models are integrated with apatite (U-Th)/He (AHe) and apatite fission track (AFT) data from Teton footwall transects to constrain total Teton fault displacement (<i>D</i><sub><i>max</i></sub>). Models with slip onset at ∼10 Ma and flexure parameters that best match the observed Teton flexural profile require <i>D</i><sub><i>max</i></sub> > 8 km to produce young (<10 Ma) AHe ages observed at low elevation footwall positions in the Tetons. For the same slip onset, models with <i>D</i><sub><i>max</i></sub> of 11–13 km provide the best match to observed AHe data, but displacements ≥16 km are required to produce observed AFT ages (13.6–12.0 Ma) at low elevations. A more complex model with slow slip onset at ∼25 Ma followed by faster slip at ∼10 Ma yields a good match between modeled and observed AHe ages at a <i>D</i><sub><i>max</i></sub> of 13–15 km. However, this model predicts low elevation AFT ages 6–8 Ma older than observed ages, even at <i>D</i><sub><i>max</i></sub> values of 16–17 km. Based on this analysis and integration with previous studies, we propose a unified evolution wherein the Teton fault likely experienced 11–13 km of Miocene-recent displacement, with AFT data likely indicating a pre-to early Miocene cooling history. Importantly, this study highlights the utility of using integrated flexural- and thermal-kinematic models to resolve displacement histories in extensional systems.","PeriodicalId":22351,"journal":{"name":"Tectonics","volume":"49 1","pages":""},"PeriodicalIF":4.2,"publicationDate":"2024-07-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141613966","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 arcuate Mazatagh thrust belt (MTB) in the central Tarim Basin is one of the key regions for understanding the Cenozoic intracontinental deformation in response to the India–Eurasia collision. However, whether it was formed due to oroclinal bending and its kinematic processes remain unclear. Here, we present a detailed paleomagnetic rotation study at Hongbaishan in the middle MTB to shed new light on the deformation in this region. Positive fold and reversal tests of 50 site means suggest primary magnetizations. The paleomagnetic declinations indicate ∼14.6 ± 8.5° absolute clockwise rotation at Hongbaishan since the late Miocene (∼7.6 Ma). Together with the rotation results calculated from Hongbaishan-1 and Mazatagh magnetostratigraphic data sets in the southeastern MTB, these results reveal an increasing magnitude of clockwise rotation along the belt toward its southeastern tip. Positive oroclinal tests along the MTB suggest the occurrence of oroclinal bending that curved the originally straight MTB before and during the deposition of its lower part, and nearly half of the bending had occurred during the deposition of its upper part. This oroclinal bending is mostly attributed to the northward indentation of the West Kunlun Mountains along the décollement salt‒gypsum layers and further implies ∼7.9° absolute clockwise rotation of the Tarim Basin since the late Miocene. Integrating these findings with other lines of geological evidence around the Tarim Basin, we propose that episodic widespread tectonic deformation with basinward propagation occurred since the late Miocene due to the far-field effect of the continuous northward indentation of the Indian Plate into Eurasia.
{"title":"Late Miocene Oroclinal Bending of the Mazatagh Thrust Belt in the Central Tarim Basin and Its Tectonic Implications","authors":"Bingshuai Li, Maodu Yan, Heng Peng, Weilin Zhang, Jinbo Zan, Tao Zhang, Xiaomin Fang","doi":"10.1029/2023tc008233","DOIUrl":"https://doi.org/10.1029/2023tc008233","url":null,"abstract":"The arcuate Mazatagh thrust belt (MTB) in the central Tarim Basin is one of the key regions for understanding the Cenozoic intracontinental deformation in response to the India–Eurasia collision. However, whether it was formed due to oroclinal bending and its kinematic processes remain unclear. Here, we present a detailed paleomagnetic rotation study at Hongbaishan in the middle MTB to shed new light on the deformation in this region. Positive fold and reversal tests of 50 site means suggest primary magnetizations. The paleomagnetic declinations indicate ∼14.6 ± 8.5° absolute clockwise rotation at Hongbaishan since the late Miocene (∼7.6 Ma). Together with the rotation results calculated from Hongbaishan-1 and Mazatagh magnetostratigraphic data sets in the southeastern MTB, these results reveal an increasing magnitude of clockwise rotation along the belt toward its southeastern tip. Positive oroclinal tests along the MTB suggest the occurrence of oroclinal bending that curved the originally straight MTB before and during the deposition of its lower part, and nearly half of the bending had occurred during the deposition of its upper part. This oroclinal bending is mostly attributed to the northward indentation of the West Kunlun Mountains along the décollement salt‒gypsum layers and further implies ∼7.9° absolute clockwise rotation of the Tarim Basin since the late Miocene. Integrating these findings with other lines of geological evidence around the Tarim Basin, we propose that episodic widespread tectonic deformation with basinward propagation occurred since the late Miocene due to the far-field effect of the continuous northward indentation of the Indian Plate into Eurasia.","PeriodicalId":22351,"journal":{"name":"Tectonics","volume":"54 1","pages":""},"PeriodicalIF":4.2,"publicationDate":"2024-07-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141567671","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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