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}
Mervin J. Bartholomew, Demin Liu, Andrew M. Mickelson, Lian Brugere, Tammy Rittenour, Guo Q. Sun
The Yushu fault, part of the Yushu–Ganzi fault zone, is one of several E-W-trending left-lateral, strike-slip fault zones that extend across the Tibetan Plateau accommodating lateral transfer of crustal material out of the collision zone between the Indian and Eurasian plates. Discontinuous left-lateral surface rupture occurred along WNW-ESE-striking, near-vertical faults during two Mw 6.9 14 April 2010 Yushu earthquakes. Geomorphic and surface-rupture characteristics change at the base of a red cliff separating the Guoqiong and Buqionggei segments. Excavations across these segments near the Jinsha River show: (a) more continuous deposition on the down-dropped side; and (b) how frequently these surface-rupture histories were linked or sequential (major to great earthquakes) versus not linked (moderate/strong to large earthquakes). Trench CUG-2011-1 and roadcut CUG-2012-1 (Guoqiong segment) were on older fan surfaces and Trench CUG-2012-2 (Buqionggei segment) crossed a narrow graben. On the Guoqiong segment, using OxCal v.4.4 that works with IntCal20 database for Bayesian-ordered ages from four 14C and nine OSL ages, surface ruptures occurred during earthquakes at 2010CE, ∼200BCE, ∼2400BCE, ∼4250BCE, ∼6750BCE, ∼7400BCE and ∼10400BCE consistent with an ∼2200-year Holocene recurrence interval. For the Buqionggei segment, Bayesian-ordered ages from six OSL ages indicate three Holocene surface ruptures occurred at 2010CE, ∼4600BCE and ∼6750BCE. Surface ruptures on both segments (suggesting linked or sequential major to great earthquakes) only occurred two to three times at 2010CE, ∼4500BCE and/or ∼6750BCE. Thus, risk of infrequent major to great Holocene earthquakes is ∼2400–∼8800 years along the Yushu fault.
{"title":"Timing of Holocene Surface-Ruptures Across Adjacent Rupture-Segments Where the Jinsha River Crosses the Yushu Fault, Qinghai Province, China","authors":"Mervin J. Bartholomew, Demin Liu, Andrew M. Mickelson, Lian Brugere, Tammy Rittenour, Guo Q. Sun","doi":"10.1029/2023tc007922","DOIUrl":"https://doi.org/10.1029/2023tc007922","url":null,"abstract":"The Yushu fault, part of the Yushu–Ganzi fault zone, is one of several E-W-trending left-lateral, strike-slip fault zones that extend across the Tibetan Plateau accommodating lateral transfer of crustal material out of the collision zone between the Indian and Eurasian plates. Discontinuous left-lateral surface rupture occurred along WNW-ESE-striking, near-vertical faults during two Mw 6.9 14 April 2010 Yushu earthquakes. Geomorphic and surface-rupture characteristics change at the base of a red cliff separating the Guoqiong and Buqionggei segments. Excavations across these segments near the Jinsha River show: (a) more continuous deposition on the down-dropped side; and (b) how frequently these surface-rupture histories were linked or sequential (<i>major to great</i> earthquakes) versus not linked (<i>moderate/strong to large</i> earthquakes). Trench CUG-2011-1 and roadcut CUG-2012-1 (Guoqiong segment) were on older fan surfaces and Trench CUG-2012-2 (Buqionggei segment) crossed a narrow graben. On the Guoqiong segment, using OxCal v.4.4 that works with IntCal20 database for Bayesian-ordered ages from four <sup>14</sup>C and nine OSL ages, surface ruptures occurred during earthquakes at 2010CE, ∼200BCE, ∼2400BCE, ∼4250BCE, ∼6750BCE, ∼7400BCE and ∼10400BCE consistent with an ∼2200-year Holocene recurrence interval. For the Buqionggei segment, Bayesian-ordered ages from six OSL ages indicate three Holocene surface ruptures occurred at 2010CE, ∼4600BCE and ∼6750BCE. Surface ruptures on both segments (suggesting linked or sequential <i>major to great</i> earthquakes) only occurred two to three times at 2010CE, ∼4500BCE and/or ∼6750BCE. Thus, risk of infrequent <i>major to great</i> Holocene earthquakes is ∼2400–∼8800 years along the Yushu fault.","PeriodicalId":22351,"journal":{"name":"Tectonics","volume":"35 1","pages":""},"PeriodicalIF":4.2,"publicationDate":"2024-07-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141551243","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}
R. Quiroga, L. Giambiagi, A. Echaurren, J. Mescua, H. Pingel, G. Fuentes, M. Peña, J. Suriano, F. Martínez, C. Mpodozis, M. R. Strecker
We present a study in the southern Puna (26°30′–27°30′S), aiming to explore the late Cenozoic evolution of the deformation and the stress field during its uplift. Through U-Pb geochronology, structural observations, paleostress analysis, and balanced cross-sections, we propose an structural evolutionary model over the past 24 million years, separated in four stages: Stage 1, in the late Oligocene to middle Miocene, the region experienced E-W compression. Stage 2, from middle to late Miocene, a transition from predominant compression to an incipient strike-slip regime is observed. Stage 3, from late Miocene to early Pliocene, showed a further shift in the stress field, resulting in a combination of a predominant strike-slip regime, and less predominant compressional regime. Finally, Stage 4, from late Pliocene to Quaternary, featured a dominance of strike-slip regimes. Our results show that the stress field in each stage is associated with the orogen's internal architecture and its evolution. Vertical stress variations are linked to plateau uplift, creating topographic gradients across the orogen. Horizontal rotations of the principal stress axes are caused mainly by an edge effect resulting from the growth of the plateau while it reaches a critical crustal thickness and elevation. This leads to a transfer of compression from high-lying areas to lower regions. The southernmost Puna region shows no significant evidence of normal faulting, suggesting it is not undergoing orogenic collapse associated with a regional tensional stress regime.
{"title":"Boundary Effects of Orogenic Plateaus in the Evolution of the Stress Field: The Southern Puna Study Case (26°30′–27°30′S)","authors":"R. Quiroga, L. Giambiagi, A. Echaurren, J. Mescua, H. Pingel, G. Fuentes, M. Peña, J. Suriano, F. Martínez, C. Mpodozis, M. R. Strecker","doi":"10.1029/2023tc008185","DOIUrl":"https://doi.org/10.1029/2023tc008185","url":null,"abstract":"We present a study in the southern Puna (26°30′–27°30′S), aiming to explore the late Cenozoic evolution of the deformation and the stress field during its uplift. Through U-Pb geochronology, structural observations, paleostress analysis, and balanced cross-sections, we propose an structural evolutionary model over the past 24 million years, separated in four stages: Stage 1, in the late Oligocene to middle Miocene, the region experienced E-W compression. Stage 2, from middle to late Miocene, a transition from predominant compression to an incipient strike-slip regime is observed. Stage 3, from late Miocene to early Pliocene, showed a further shift in the stress field, resulting in a combination of a predominant strike-slip regime, and less predominant compressional regime. Finally, Stage 4, from late Pliocene to Quaternary, featured a dominance of strike-slip regimes. Our results show that the stress field in each stage is associated with the orogen's internal architecture and its evolution. Vertical stress variations are linked to plateau uplift, creating topographic gradients across the orogen. Horizontal rotations of the principal stress axes are caused mainly by an edge effect resulting from the growth of the plateau while it reaches a critical crustal thickness and elevation. This leads to a transfer of compression from high-lying areas to lower regions. The southernmost Puna region shows no significant evidence of normal faulting, suggesting it is not undergoing orogenic collapse associated with a regional tensional stress regime.","PeriodicalId":22351,"journal":{"name":"Tectonics","volume":"40 1","pages":""},"PeriodicalIF":4.2,"publicationDate":"2024-06-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141508358","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}
A. Ceccato, W. M. Behr, A. S. Zappone, L. Tavazzani, A. Giuliani
The rheology of crystalline units controls the large-scale deformation geometry and dynamics of collisional orogens. Defining a time-constrained rheological evolution of such units may help unravel the details of collisional dynamics. Here, we integrate field analysis, pseudosection calculations and in situ garnet U–Pb and mica Rb–Sr geochronology to define the structural and rheological evolution of the Rotondo granite (Gotthard nappe, Central Alps). We identify a sequence of four (D1–D4) deformation stages. Pre-collisional D1 brittle faults developed before Alpine peak metamorphism, which occurred at 34–20 Ma (U–Pb garnet ages) at 590 ± 25°C and 0.9 ± 0.1 GPa. The reactivation of D1 structures controlled the rheological evolution, from D2 reverse mylonitic shearing at amphibolite facies (520 ± 40°C and 0.8 ± 0.1 GPa) at 18–20 Ma (white mica Rb–Sr ages), to strike-slip, brittle-ductile shearing at greenschist-facies D3 (395 ± 25°C and 0.4 ± 0.1 GPa) at 14–15 Ma (white mica and biotite Rb–Sr ages), and then to D4 strike-slip faulting at shallow conditions. Although highly misoriented for the Alpine collisional stress orientation, D1 brittle structures controlled the localization of D2 ductile mylonites accommodating fast (∼3 mm/yr) exhumation rates due to their weak shear strength (<10 MPa). This structural and rheological evolution is common across External Crystalline Massifs (e.g., Aar, Mont Blanc), suggesting that the European upper crust was extremely weak during Alpine collision, its strength controlled by weak ductile shear zones localized on pre-collisional deformation structures, that in turn controlled localized exhumation at the scale of the orogen.
{"title":"Structural Evolution, Exhumation Rates, and Rheology of the European Crust During Alpine Collision: Constraints From the Rotondo Granite—Gotthard Nappe","authors":"A. Ceccato, W. M. Behr, A. S. Zappone, L. Tavazzani, A. Giuliani","doi":"10.1029/2023tc008219","DOIUrl":"https://doi.org/10.1029/2023tc008219","url":null,"abstract":"The rheology of crystalline units controls the large-scale deformation geometry and dynamics of collisional orogens. Defining a time-constrained rheological evolution of such units may help unravel the details of collisional dynamics. Here, we integrate field analysis, pseudosection calculations and in situ garnet U–Pb and mica Rb–Sr geochronology to define the structural and rheological evolution of the Rotondo granite (Gotthard nappe, Central Alps). We identify a sequence of four (D<sub>1</sub>–D<sub>4</sub>) deformation stages. Pre-collisional D<sub>1</sub> brittle faults developed before Alpine peak metamorphism, which occurred at 34–20 Ma (U–Pb garnet ages) at 590 ± 25°C and 0.9 ± 0.1 GPa. The reactivation of D<sub>1</sub> structures controlled the rheological evolution, from D<sub>2</sub> reverse mylonitic shearing at amphibolite facies (520 ± 40°C and 0.8 ± 0.1 GPa) at 18–20 Ma (white mica Rb–Sr ages), to strike-slip, brittle-ductile shearing at greenschist-facies D<sub>3</sub> (395 ± 25°C and 0.4 ± 0.1 GPa) at 14–15 Ma (white mica and biotite Rb–Sr ages), and then to D<sub>4</sub> strike-slip faulting at shallow conditions. Although highly misoriented for the Alpine collisional stress orientation, D<sub>1</sub> brittle structures controlled the localization of D<sub>2</sub> ductile mylonites accommodating fast (∼3 mm/yr) exhumation rates due to their weak shear strength (<10 MPa). This structural and rheological evolution is common across External Crystalline Massifs (e.g., Aar, Mont Blanc), suggesting that the European upper crust was extremely weak during Alpine collision, its strength controlled by weak ductile shear zones localized on pre-collisional deformation structures, that in turn controlled localized exhumation at the scale of the orogen.","PeriodicalId":22351,"journal":{"name":"Tectonics","volume":"193 1","pages":""},"PeriodicalIF":4.2,"publicationDate":"2024-06-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141508359","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 interplay between regional tectonics and the development of a major ocean gateway between the Pacific and the Atlantic Ocean has resulted in numerous paleogeographic reconstruction studies that describe the Cenozoic tectonic history of the Scotia Sea region. Despite the multitude of published tectonic reconstructions and the variety of geological and geophysical data available from the Scotia Sea, the geological history remains ambiguous. We present a comparative paleogeographic analysis of previously published tectonic reconstructions to identify agreements and conflicts between these reconstructions. We propose an alternative model to explain the Cenozoic evolution of the Scotia Sea region. The paleogeographic comparison shows that most reconstructions agree on the tectonic evolution of the South Scotia Ridge and the East Scotia Ridge. Major differences between the reconstructions are the role of the westward subducting plate below the South Sandwich plate, and the age and origin of the Central Scotia Sea. Tectonic reconstructions assume that the Central Scotia Sea is either part of a Cenozoic back-arc basin, or a captured piece of Cretaceous oceanic crust. We propose a new alternative tectonic reconstruction that brings these two prevailing hypotheses elegantly together. Here, we identified new geographical blocks consisting of thinned continental or Cretaceous oceanic fragments that originate from the Paleo-Pacific Weddell Sea gateway from high-resolution bathymetry. These fragments are now part of the Central Scotia Sea and have been affected by early back-arc tectonic activity of the South Sandwich subduction zone, leading locally to the formation of Cenozoic-aged crust in the Central Scotia Sea.
{"title":"Cretaceous Crust in the Scotia Sea: Missing Pieces in a Geological Puzzle?","authors":"J. H. Oldenhage, W. P. Schellart, A. Beniest","doi":"10.1029/2023tc008079","DOIUrl":"https://doi.org/10.1029/2023tc008079","url":null,"abstract":"The interplay between regional tectonics and the development of a major ocean gateway between the Pacific and the Atlantic Ocean has resulted in numerous paleogeographic reconstruction studies that describe the Cenozoic tectonic history of the Scotia Sea region. Despite the multitude of published tectonic reconstructions and the variety of geological and geophysical data available from the Scotia Sea, the geological history remains ambiguous. We present a comparative paleogeographic analysis of previously published tectonic reconstructions to identify agreements and conflicts between these reconstructions. We propose an alternative model to explain the Cenozoic evolution of the Scotia Sea region. The paleogeographic comparison shows that most reconstructions agree on the tectonic evolution of the South Scotia Ridge and the East Scotia Ridge. Major differences between the reconstructions are the role of the westward subducting plate below the South Sandwich plate, and the age and origin of the Central Scotia Sea. Tectonic reconstructions assume that the Central Scotia Sea is either part of a Cenozoic back-arc basin, or a captured piece of Cretaceous oceanic crust. We propose a new alternative tectonic reconstruction that brings these two prevailing hypotheses elegantly together. Here, we identified new geographical blocks consisting of thinned continental or Cretaceous oceanic fragments that originate from the Paleo-Pacific Weddell Sea gateway from high-resolution bathymetry. These fragments are now part of the Central Scotia Sea and have been affected by early back-arc tectonic activity of the South Sandwich subduction zone, leading locally to the formation of Cenozoic-aged crust in the Central Scotia Sea.","PeriodicalId":22351,"journal":{"name":"Tectonics","volume":"12 1","pages":""},"PeriodicalIF":4.2,"publicationDate":"2024-06-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141508360","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}
Max M. Garvue, James A. Spotila, Michele L. Cooke, Elizabeth R. Curtiss
Restraining bends influence topography, strike-slip evolution, and earthquake rupture dynamics, however the specific factors governing their geometry and development in the crust are not well established. These relationships are challenging to investigate in field examples due to cannibalization and erosion of earlier structures with cumulative strain. To address this knowledge gap, we investigated the structure, morphology, and kinematics of 22 basement-cored restraining bends on low net-slip faults (<10 km) within the southern Eastern California shear zone (SECSZ) via mapping, topographic analyses, and 3D numerical modeling. The bends are self-similar in form with most exhibiting focused relief between high-angle bounding faults with an arrowhead shape in map view and a “whaleback” longitudinal profile. Slight changes in that form occur with increasing size indicating predictable growth that appears to be primarily controlled by local fault geometries (i.e., bifurcation angle), rather than the influence of fault obliquity relative to far-field plate motion, due to inefficient slip-transfer across interconnected irregularly trending closely spaced faults. Modeling results indicate that the self-similar fault-bound geometry of SECSZ restraining bends may arise from elevated shear strain at the outer corners of single transpressional fault bends with increasing cumulative slip. This, in turn, promotes growth of a new fault leading to efficient accommodation of local convergent strain via uplift between bounding faults. Finally, our results indicate that the kilometer-scale restraining bends contribute minimally to regional contraction as they only penetrate the upper third of the seismogenic crust and are therefore also unlikely to impede large earthquake surface ruptures.
{"title":"What Controls Early Restraining Bend Growth? Structural, Morphometric, and Numerical Modeling Analyses From the Eastern California Shear Zone","authors":"Max M. Garvue, James A. Spotila, Michele L. Cooke, Elizabeth R. Curtiss","doi":"10.1029/2023tc008148","DOIUrl":"https://doi.org/10.1029/2023tc008148","url":null,"abstract":"Restraining bends influence topography, strike-slip evolution, and earthquake rupture dynamics, however the specific factors governing their geometry and development in the crust are not well established. These relationships are challenging to investigate in field examples due to cannibalization and erosion of earlier structures with cumulative strain. To address this knowledge gap, we investigated the structure, morphology, and kinematics of 22 basement-cored restraining bends on low net-slip faults (<10 km) within the southern Eastern California shear zone (SECSZ) via mapping, topographic analyses, and 3D numerical modeling. The bends are self-similar in form with most exhibiting focused relief between high-angle bounding faults with an arrowhead shape in map view and a “whaleback” longitudinal profile. Slight changes in that form occur with increasing size indicating predictable growth that appears to be primarily controlled by local fault geometries (i.e., bifurcation angle), rather than the influence of fault obliquity relative to far-field plate motion, due to inefficient slip-transfer across interconnected irregularly trending closely spaced faults. Modeling results indicate that the self-similar fault-bound geometry of SECSZ restraining bends may arise from elevated shear strain at the outer corners of single transpressional fault bends with increasing cumulative slip. This, in turn, promotes growth of a new fault leading to efficient accommodation of local convergent strain via uplift between bounding faults. Finally, our results indicate that the kilometer-scale restraining bends contribute minimally to regional contraction as they only penetrate the upper third of the seismogenic crust and are therefore also unlikely to impede large earthquake surface ruptures.","PeriodicalId":22351,"journal":{"name":"Tectonics","volume":"50 1","pages":""},"PeriodicalIF":4.2,"publicationDate":"2024-05-31","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141191799","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}
Wen-Huang Chen, Yi Yan, Andrew Carter, Peter D. Clift, Chi-Yue Huang, Graciano P. Yumul, Carla B. Dimalanta, Jillian Aira S. Gabo-Ratio, Le Zhang, Ming-Huei Wang, Xin-Chang Zhang
The evolution of arc-continent collision between the Palawan microcontinental block and the Cagayan Ridge in the southeastern margin of the South China Sea (SCS) is vital to understand how this collision correlated with seafloor spreading of the SCS. To address the evolution of arc-continent collision, we studied the biostratigraphy and provenance of syn-collisional sediments in the Isugod Basin in central-southern Palawan. Microfossil analysis indicates a Late Miocene age (11.5–5.6 Ma) for the Isugod and Alfonso XIII Formations and rapid subsidence during initiation of the basin which may have been triggered by local extensional collapse of the wedge in response to forearc uplift. Multidisciplinary provenance analysis reveals that the Isugod and Alfonso XIII Formations were derived from the Middle Eocene–lower Oligocene Panas-Pandian Formation on the Palawan wedge and the Late Eocene Central Palawan Ophiolite. These results suggest the emergence of both the orogenic wedge and obducted forearc ophiolite at ∼11.5 Ma, implying collision onset before ∼11.5 Ma. The collision initiation in Palawan could be better constrained to ∼18 Ma, based on the drowning of the Nido carbonate platform in the foreland. Therefore, the gravitational collapse of the Palawan wedge and the subsidence/formation of the Isugod Basin might reflect a significant uplift pulse in the hinterland of the wedge beginning within 13.4–11.5 Ma in the late stage of collision. It indicates that although compression originated from spreading of the SCS had ceased at 16–15 Ma, arc-continent collision in Palawan did not stop and was sustained by compression from the upper plate afterward.
巴拉望微大陆块与南中国海（SCS）东南缘卡加延海脊之间的弧-大陆碰撞演化，对于了解这种碰撞如何与南中国海的海底扩张相关至关重要。针对弧-大陆碰撞的演化，我们研究了巴拉望岛中南部伊苏戈德盆地同步碰撞沉积物的生物地层学和产状。微化石分析表明，伊苏古德和阿方索十三世地层的年代为晚中新世（11.5-5.6Ma），在盆地形成过程中出现了快速下沉，这可能是由于前弧隆升导致楔块局部伸展塌陷而引发的。多学科成因分析表明，伊苏古德地层和阿方索十三世地层源自巴拉望楔上的中始新世-下新世帕纳斯-潘迪亚地层和晚始新世巴拉望中部蛇绿岩。这些结果表明，造山楔和俯冲前弧蛇绿混杂岩都在∼11.5Ma出现，这意味着碰撞发生在∼11.5Ma之前。根据尼多碳酸盐平台在前陆的淹没情况，巴拉望岛的碰撞起始时间可以更好地确定为 ∼18 Ma。因此，巴拉望楔块的重力塌陷和伊苏古德盆地的下沉/形成可能反映了楔块腹地在碰撞晚期的13.4-11.5 Ma内开始的显著隆升脉冲。这表明，虽然源于南中国海扩张的挤压在 16-15 Ma 时已经停止，但巴拉望的弧-大陆碰撞并未停止，而是在之后由上板块的挤压维持着。
{"title":"Evolution of Arc-Continent Collision in the Southeastern Margin of the South China Sea: Insight From the Isugod Basin in Central-Southern Palawan","authors":"Wen-Huang Chen, Yi Yan, Andrew Carter, Peter D. Clift, Chi-Yue Huang, Graciano P. Yumul, Carla B. Dimalanta, Jillian Aira S. Gabo-Ratio, Le Zhang, Ming-Huei Wang, Xin-Chang Zhang","doi":"10.1029/2023tc008078","DOIUrl":"https://doi.org/10.1029/2023tc008078","url":null,"abstract":"The evolution of arc-continent collision between the Palawan microcontinental block and the Cagayan Ridge in the southeastern margin of the South China Sea (SCS) is vital to understand how this collision correlated with seafloor spreading of the SCS. To address the evolution of arc-continent collision, we studied the biostratigraphy and provenance of syn-collisional sediments in the Isugod Basin in central-southern Palawan. Microfossil analysis indicates a Late Miocene age (11.5–5.6 Ma) for the Isugod and Alfonso XIII Formations and rapid subsidence during initiation of the basin which may have been triggered by local extensional collapse of the wedge in response to forearc uplift. Multidisciplinary provenance analysis reveals that the Isugod and Alfonso XIII Formations were derived from the Middle Eocene–lower Oligocene Panas-Pandian Formation on the Palawan wedge and the Late Eocene Central Palawan Ophiolite. These results suggest the emergence of both the orogenic wedge and obducted forearc ophiolite at ∼11.5 Ma, implying collision onset before ∼11.5 Ma. The collision initiation in Palawan could be better constrained to ∼18 Ma, based on the drowning of the Nido carbonate platform in the foreland. Therefore, the gravitational collapse of the Palawan wedge and the subsidence/formation of the Isugod Basin might reflect a significant uplift pulse in the hinterland of the wedge beginning within 13.4–11.5 Ma in the late stage of collision. It indicates that although compression originated from spreading of the SCS had ceased at 16–15 Ma, arc-continent collision in Palawan did not stop and was sustained by compression from the upper plate afterward.","PeriodicalId":22351,"journal":{"name":"Tectonics","volume":"36 1","pages":""},"PeriodicalIF":4.2,"publicationDate":"2024-05-31","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141191771","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}
Yazhou Miao, Jian Zhang, Karel Schulmann, Alexandra Guy, Igor Soejono, Yingde Jiang, Min Sun, Shuhui Zhang, Zhiyong Li
The geodynamic evolution of the East Junggar is examined by means of satellite imaging and field-based structural studies, U-Pb zircon geochronology and analysis of potential field geophysical data in the Yemaquan arc and the Dulate back-arc systems. The northern Yemaquan arc shows a pervasive WNW–ESE steep S1 foliation that is related to the exhumation of Armantai ophiolitic mélange in an F1 antiformal structure. The bedding of the Dulate sequences is folded by N–S-trending F1 upright folds that are preserved in low strain domains. The timing of D1 is estimated between 310 and 280 Ma. During D2, previously folded Dulate sequences were orthogonally refolded by E–W-trending F2 upright folds, resulting in Type-1 basin and dome interference pattern and pervasive E–W trending S2 cleavage zones. The age of D2 is constrained to be 270–250 Ma based on the dating of syn-tectonic pegmatites and deposition of syn-orogenic sedimentary rocks. The boundary between the Yemaquan arc and Dulate back-arc basin experienced reactivation through D2 dextral transpressive shear zones. The D1 fabrics are the consequence of the closure of the Dulate back-arc basin due to the advancing mode of Kalamaili subduction. Almost orthogonal Permian D2 fabrics were generated by the N–S shortening of the East Junggar and the northward movement of the Junggar Block indenter. This D2 deformation was associated with the anticlockwise rotation of the southern limb of the Mongolian Orocline, the scissor-like closure of the northerly Mongol-Okhotsk Ocean and the collision of the Mongolian and the Tarim–North China craton collages.
通过卫星成像和野外构造研究、U-Pb锆石地质年代以及对叶马泉弧和Dulate后弧系统潜在野外地球物理数据的分析，研究了东准噶尔的地球动力演化。叶马泉弧北部显示出普遍的 WNW-ESE 陡峭 S1 褶皱，这与阿曼台蛇绿岩夹层在 F1 反形貌结构中的出露有关。Dulate序列的基底被保留在低应变域中的N-S向F1直立褶皱所褶皱。D1 的时间估计在 310 至 280 Ma 之间。在D2期间，先前褶皱的Dulate序列被东西走向的F2直立褶皱正交再褶皱，形成了1型盆地和穹隆干扰模式以及普遍的东西走向S2劈裂带。根据同步构造伟晶岩的年代测定和同步成因沉积岩的沉积，D2 的年龄被推定为 270-250 Ma。Yemaquan弧与Dulate后弧盆地之间的边界通过D2右旋转位剪切带重新激活。D1 构造是由于卡拉麦里俯冲模式的推进导致迪特后弧盆地关闭的结果。几乎正交的二叠纪 D2 构造是由东准噶尔北-南向缩短和准噶尔地块压头北移产生的。这种D2变形与蒙古鄂伦春山脉南缘的逆时针旋转、蒙古-奥霍次克洋向北的剪刀状闭合以及蒙古和塔里木-华北克拉通碰撞有关。
{"title":"Switching From Subduction Zone Advance to Retreat Explains the Late Paleozoic Evolution of the East Junggar System, Central Asian Orogenic Belt","authors":"Yazhou Miao, Jian Zhang, Karel Schulmann, Alexandra Guy, Igor Soejono, Yingde Jiang, Min Sun, Shuhui Zhang, Zhiyong Li","doi":"10.1029/2024tc008254","DOIUrl":"https://doi.org/10.1029/2024tc008254","url":null,"abstract":"The geodynamic evolution of the East Junggar is examined by means of satellite imaging and field-based structural studies, U-Pb zircon geochronology and analysis of potential field geophysical data in the Yemaquan arc and the Dulate back-arc systems. The northern Yemaquan arc shows a pervasive WNW–ESE steep S<sub>1</sub> foliation that is related to the exhumation of Armantai ophiolitic mélange in an F<sub>1</sub> antiformal structure. The bedding of the Dulate sequences is folded by N–S-trending F<sub>1</sub> upright folds that are preserved in low strain domains. The timing of D<sub>1</sub> is estimated between 310 and 280 Ma. During D<sub>2</sub>, previously folded Dulate sequences were orthogonally refolded by E–W-trending F<sub>2</sub> upright folds, resulting in Type-1 basin and dome interference pattern and pervasive E–W trending S<sub>2</sub> cleavage zones. The age of D<sub>2</sub> is constrained to be 270–250 Ma based on the dating of syn-tectonic pegmatites and deposition of syn-orogenic sedimentary rocks. The boundary between the Yemaquan arc and Dulate back-arc basin experienced reactivation through D<sub>2</sub> dextral transpressive shear zones. The D<sub>1</sub> fabrics are the consequence of the closure of the Dulate back-arc basin due to the advancing mode of Kalamaili subduction. Almost orthogonal Permian D<sub>2</sub> fabrics were generated by the N–S shortening of the East Junggar and the northward movement of the Junggar Block indenter. This D<sub>2</sub> deformation was associated with the anticlockwise rotation of the southern limb of the Mongolian Orocline, the scissor-like closure of the northerly Mongol-Okhotsk Ocean and the collision of the Mongolian and the Tarim–North China craton collages.","PeriodicalId":22351,"journal":{"name":"Tectonics","volume":"36 1","pages":""},"PeriodicalIF":4.2,"publicationDate":"2024-05-31","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141191797","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}
Kevin P. Furlong, Antonio Villaseñor, Harley M. Benz, Kirsty A. McKenzie
The northward migration of the Mendocino triple junction (MTJ) drives a fundamental plate boundary transformation from convergence to translation; producing a series of strike-slip faults, that become the San Andreas plate boundary. We find that the 3-D structure of the Pacific plate lithosphere in the vicinity of the MTJ controls the location of San Andreas plate boundary formation. At the time of initiation of the Pacific-North America plate boundary (∼30 Ma), the sequential interaction with the western margin of North America of the Pioneer Fracture Zone, soon followed by the Mendocino Fracture Zone, led to the capture of a small segment of partially subducted Farallon lithosphere by the Pacific plate, termed the Pioneer Fragment (PF). Since that time, the PF has translated with the Pacific Plate along the western margin of North America. Recently developed, high-resolution seismic-tomographic imagery of northern California indicates that (a) the PF is extant, occupying the western half of the slab window, immediately south of the MTJ; (b) the eastern edge of the PF lies beneath the newly forming Maacama fault system, which develops to become the locus for the primary plate boundary structure after approximately 6–10 Ma; and (c) the location of the translating PF adjacent to the asthenosphere of the slab window generates a shear zone within and below the crust that develops into the plate boundary faults. As a result, the San Andreas plate boundary forms interior to the western margin of North America, rather than at its western edge.
{"title":"Formation and Evolution of the Pacific-North American (San Andreas) Plate Boundary: Constraints From the Crustal Architecture of Northern California","authors":"Kevin P. Furlong, Antonio Villaseñor, Harley M. Benz, Kirsty A. McKenzie","doi":"10.1029/2023tc007963","DOIUrl":"https://doi.org/10.1029/2023tc007963","url":null,"abstract":"The northward migration of the Mendocino triple junction (MTJ) drives a fundamental plate boundary transformation from convergence to translation; producing a series of strike-slip faults, that become the San Andreas plate boundary. We find that the 3-D structure of the Pacific plate lithosphere in the vicinity of the MTJ controls the location of San Andreas plate boundary formation. At the time of initiation of the Pacific-North America plate boundary (∼30 Ma), the sequential interaction with the western margin of North America of the Pioneer Fracture Zone, soon followed by the Mendocino Fracture Zone, led to the capture of a small segment of partially subducted Farallon lithosphere by the Pacific plate, termed the Pioneer Fragment (PF). Since that time, the PF has translated with the Pacific Plate along the western margin of North America. Recently developed, high-resolution seismic-tomographic imagery of northern California indicates that (a) the PF is extant, occupying the western half of the slab window, immediately south of the MTJ; (b) the eastern edge of the PF lies beneath the newly forming Maacama fault system, which develops to become the locus for the primary plate boundary structure after approximately 6–10 Ma; and (c) the location of the translating PF adjacent to the asthenosphere of the slab window generates a shear zone within and below the crust that develops into the plate boundary faults. As a result, the San Andreas plate boundary forms interior to the western margin of North America, rather than at its western edge.","PeriodicalId":22351,"journal":{"name":"Tectonics","volume":"50 1","pages":""},"PeriodicalIF":4.2,"publicationDate":"2024-05-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141191772","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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