G. Ghorbani, H. S. Moghadam, Y. Dilek, Shoji Arai, M. Khedr
We investigate in this paper mineral compositions and geochemical evolution of the mantle wedge peridotites preserved in the Late Cretaceous Zagros ophiolites of SW Iran. Mantle peridotites above subduction zones commonly experience distinct melting, depletion, and refertilization processes as a result of the circulation of fluids derived from subducting slabs and flux melting. Our results reveal that the mantle wedge peridotites in the Zagros ophiolites are characterized mainly by residual and impregnated types. Residual peridotites resulted from early depletion and later refertilization processes, whereas impregnated peridotites developed due to episodic melt impregnations within and across the mantle. Mg#s and NiO contents, spinel Cr#, Mg#, and TiO 2 in olivines, Mg# and Al 2 O 3 contents of orthopyroxenes, and Mg#, TiO 2 , and Al 2 O 3 contents in clinopyroxenes of dunites, harzburgites and lherzolites indicate the significant role of re-equilibration processes among different mineral phases and interactions with basaltic melts percolating within the host peridotites. The observed geochemical variations in the mineral chemistry of the Zagros peridotites reflect changes in magma chemistry and fluctuations in the degree of melt extraction and melt–rock interactions within the mantle peridotites. However, our data suggest that Mg-Fe distribution in the spinels of some dunites and harzburgites might also have resulted from subsolidus redistribution and exchange with surrounding olivine grains. Spinel and clinopyroxene phases in gabbroic rocks and ultramafic cumulates within the Zagros ophiolites also show significant variations in their compositions, suggesting that their magmas evolved from MORB-like to IAT, calc-alkaline, and boninite suites, typical of subduction initiation generated melts. Hence, the Zagros ophiolites present a case study of time–progressive melt evolution of the forearc oceanic lithosphere. Thematic collection: This article is part of the Ophiolites, melanges and blueschists collection available at: https://www.lyellcollection.org/topic/collections/ophiolites-melanges-and-blueschists Supplementary material: https://doi.org/10.6084/m9.figshare.c.7093528
本文研究了伊朗西南部晚白垩世扎格罗斯蛇绿岩中保存的地幔楔橄榄岩的矿物成分和地球化学演化。由于来自俯冲板块的流体循环和通量熔融，俯冲带上方的地幔橄榄岩通常会经历不同的熔融、贫化和再富集过程。我们的研究结果表明，扎格罗斯蛇绿岩中的地幔楔橄榄岩主要分为残余型和浸渍型。残积橄榄岩是早期贫化和后期再富集过程的结果，而浸渍橄榄岩则是由于地幔内部和地幔之间的偶发性熔体浸渍而形成的。橄榄石中的 Mg#s 和 NiO 含量、尖晶石中的 Cr#、Mg#和 TiO 2 含量，正长石中的 Mg# 和 Al 2 O 3 含量，以及辉绿岩、哈氏堡岩和黑沸石中的 Mg#、TiO 2 和 Al 2 O 3 含量，都表明不同矿物相之间的再平衡过程以及与主橄榄岩内部渗入的玄武岩熔体之间的相互作用发挥了重要作用。观察到的扎格罗斯橄榄岩矿物化学的地球化学变化反映了岩浆化学的变化以及地幔橄榄岩内部熔体萃取和熔岩相互作用程度的波动。不过，我们的数据表明，某些辉长岩和哈兹堡岩尖晶石中的镁-铁分布也可能是由于亚固结物的重新分布以及与周围橄榄石晶粒的交换造成的。扎格罗斯蛇绿混杂岩中辉长岩和超基性岩中的尖晶石和挛辉石相在成分上也显示出显著的差异，这表明它们的岩浆从类似于MORB的岩浆演化为IAT、钙碱性和倭黑石岩浆，是典型的俯冲起始生成熔体。因此，扎格罗斯蛇绿混杂岩是弧前海洋岩石圈熔融演化的一个案例研究。 专题文集：本文是蛇绿岩、熔岩和蓝晶岩文集的一部分，可在以下网址查阅： https://www.lyellcollection.org/topic/collections/ophiolites-melanges-and-blueschists 补充材料： https://doi.org/10.6084/m9.figshare.c.7093528
{"title":"Mineral chemistry and melt evolution of the mantle wedge peridotites in the Late Cretaceous Zagros Belt ophiolites (Iran): clues for the subduction initiation–induced forearc magmatism","authors":"G. Ghorbani, H. S. Moghadam, Y. Dilek, Shoji Arai, M. Khedr","doi":"10.1144/jgs2023-209","DOIUrl":"https://doi.org/10.1144/jgs2023-209","url":null,"abstract":"\u0000 We investigate in this paper mineral compositions and geochemical evolution of the mantle wedge peridotites preserved in the Late Cretaceous Zagros ophiolites of SW Iran. Mantle peridotites above subduction zones commonly experience distinct melting, depletion, and refertilization processes as a result of the circulation of fluids derived from subducting slabs and flux melting. Our results reveal that the mantle wedge peridotites in the Zagros ophiolites are characterized mainly by residual and impregnated types. Residual peridotites resulted from early depletion and later refertilization processes, whereas impregnated peridotites developed due to episodic melt impregnations within and across the mantle. Mg#s and NiO contents, spinel Cr#, Mg#, and TiO\u0000 2\u0000 in olivines, Mg# and Al\u0000 2\u0000 O\u0000 3\u0000 contents of orthopyroxenes, and Mg#, TiO\u0000 2\u0000 , and Al\u0000 2\u0000 O\u0000 3\u0000 contents in clinopyroxenes of dunites, harzburgites and lherzolites indicate the significant role of re-equilibration processes among different mineral phases and interactions with basaltic melts percolating within the host peridotites. The observed geochemical variations in the mineral chemistry of the Zagros peridotites reflect changes in magma chemistry and fluctuations in the degree of melt extraction and melt–rock interactions within the mantle peridotites. However, our data suggest that Mg-Fe distribution in the spinels of some dunites and harzburgites might also have resulted from subsolidus redistribution and exchange with surrounding olivine grains. Spinel and clinopyroxene phases in gabbroic rocks and ultramafic cumulates within the Zagros ophiolites also show significant variations in their compositions, suggesting that their magmas evolved from MORB-like to IAT, calc-alkaline, and boninite suites, typical of subduction initiation generated melts. Hence, the Zagros ophiolites present a case study of time–progressive melt evolution of the forearc oceanic lithosphere.\u0000 \u0000 \u0000 Thematic collection:\u0000 This article is part of the Ophiolites, melanges and blueschists collection available at:\u0000 https://www.lyellcollection.org/topic/collections/ophiolites-melanges-and-blueschists\u0000 \u0000 \u0000 Supplementary material:\u0000 https://doi.org/10.6084/m9.figshare.c.7093528\u0000","PeriodicalId":17320,"journal":{"name":"Journal of the Geological Society","volume":null,"pages":null},"PeriodicalIF":2.7,"publicationDate":"2024-02-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140412005","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
D. Gasser, Jarosław Majka, Johannes Jakob, Christopher J. Barnes
The opening and closure of the Paleozoic Iapetus Ocean, leading to the collision of Laurentia and Baltica forming the Caledonian orogen, is one of the prime examples of a Wilson Cycle. In this perspective article, we summarize and discuss the content of 10 new research articles within a 5-stage framework of the Caledonian Wilson cycle from a North Atlantic perspective. Stage 1 covers Neoproterozoic rifting of both the Laurentian and Baltican margins, where the plate tectonic configurations and the timing for the onset of rifting are far from resolved; Stage 2 covers the onset of sea-floor spreading within Iapetus, with several different oceanic basins opening at different times, and with variable geometries of the rifted margins; Stage 3 covers the narrowing of the Iapetus basins along several subduction zones, the number, location and orientation of which are debated; Stage 4 covers the main continent-continent collision, documenting advances in our understanding of (U)HP metamorphism within the Western Gneiss Region; Stage 5 covers post-orogenic extension, transitioning into stage 1 of the subsequent Atlantic Wilson cycle. We review the evolution of the Caledonian Wilson cycle in the light of the recent literature from the past decade and highlight open questions and unresolved issues. Thematic collection: This article is part of the Caledonian Wilson cycle collection available at: https://www.lyellcollection.org/topic/collections/the-caledonian-wilson-cycle
{"title":"A review of the Caledonian Wilson Cycle from a North Atlantic perspective","authors":"D. Gasser, Jarosław Majka, Johannes Jakob, Christopher J. Barnes","doi":"10.1144/jgs2023-211","DOIUrl":"https://doi.org/10.1144/jgs2023-211","url":null,"abstract":"The opening and closure of the Paleozoic Iapetus Ocean, leading to the collision of Laurentia and Baltica forming the Caledonian orogen, is one of the prime examples of a Wilson Cycle. In this perspective article, we summarize and discuss the content of 10 new research articles within a 5-stage framework of the Caledonian Wilson cycle from a North Atlantic perspective. Stage 1 covers Neoproterozoic rifting of both the Laurentian and Baltican margins, where the plate tectonic configurations and the timing for the onset of rifting are far from resolved; Stage 2 covers the onset of sea-floor spreading within Iapetus, with several different oceanic basins opening at different times, and with variable geometries of the rifted margins; Stage 3 covers the narrowing of the Iapetus basins along several subduction zones, the number, location and orientation of which are debated; Stage 4 covers the main continent-continent collision, documenting advances in our understanding of (U)HP metamorphism within the Western Gneiss Region; Stage 5 covers post-orogenic extension, transitioning into stage 1 of the subsequent Atlantic Wilson cycle. We review the evolution of the Caledonian Wilson cycle in the light of the recent literature from the past decade and highlight open questions and unresolved issues.\u0000 \u0000 Thematic collection:\u0000 This article is part of the Caledonian Wilson cycle collection available at:\u0000 https://www.lyellcollection.org/topic/collections/the-caledonian-wilson-cycle\u0000","PeriodicalId":17320,"journal":{"name":"Journal of the Geological Society","volume":null,"pages":null},"PeriodicalIF":2.7,"publicationDate":"2024-02-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140422164","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
A. Leslie, M. Krabbendam, C.W. Thomas, C.J. Banks, S. M. Clarke
Restoring primary depositional frameworks from orogenic settings is challenging. To demonstrate a robust determination of original, but now highly-deformed, depositional frameworks and their first-order sequence-stratigraphy, we analyse the Dalradian succession of Tyndrum–Glen Lyon (Breadalbane) in the south-western Grampian Highlands of Scotland. In Breadalbane, several distinctive Appin and Argyll group Dalradian formations are absent. Omission has been attributed to ductile shearing on the Boundary Slide structure, during the Grampian Orogeny (c. 470 Ma). Alternatively, we restore and describe a primary depositional framework and widely-developed intra-Dalradian basin unconformity in Breadalbane, preserved in the relatively low strain lower limb of the Grampian D2 Ben Lui Syncline. On this unconformity, locally distinctive strata of the Easdale Subgroup, and more regionally-typical strata of the Crinan Subgroup, were deposited directly on strata of the Lochaber Subgroup. North-eastwards loss of strata of the Ballachulish, Blair Atholl and Islay subgroups, observed south-west of Tyndrum, contrasts with gradual reappearance of correlative units north-eastwards from Glen Lyon. Onlap and/or overstep relationships are well-preserved – although strain is enhanced locally along pronounced stratal/rheological contrasts, the stratigraphical framework remains essentially intact. Our Scotland-wide analysis of the Dalradian depositional framework recognises other probable basin-scale unconformities that locally influenced patterns of superimposed orogenic deformation.
从造山运动环境中恢复原始沉积框架具有挑战性。为了有力地确定原始但现已高度变形的沉积框架及其一阶序列地层学，我们分析了苏格兰格兰披恩高地西南部的廷德鲁姆-格兰里昂（Breadalbane）达拉底岩演替。在 Breadalbane，几个独特的阿平组和阿盖尔组达拉地层都不存在。这些地层的消失被归因于格兰披安造山运动（约 470 Ma）期间边界滑动结构的韧性剪切。另外，我们还原并描述了布里达尔班的主要沉积框架和广泛发育的达尔拉底盆地内的不整合地层，该地层保存在格兰披安 D2 Ben Lui 叠合岩的相对低应变下缘。在这个不整合地层上，伊斯代尔亚群（Easdale Subgroup）具有地方特色的地层和克里南亚群（Crinan Subgroup）更具区域特色的地层直接沉积在洛哈博亚群（Lochaber Subgroup）的地层上。在廷德鲁姆西南部观察到巴拉丘利什亚群、布莱尔阿托尔亚群和艾莱亚群地层向东北方向消失，与此形成鲜明对比的是，相关单元从格伦里昂向东北方向逐渐重新出现。叠压和/或覆压关系保存完好--虽然地层/流变对比明显的地方应变增强，但地层框架基本保持完好。我们在苏格兰范围内对达拉地层沉积框架进行的分析确认了其他可能的盆地尺度不整合，这些不整合对叠加造山运动变形模式产生了局部影响。
{"title":"Geometrical restoration of a late Neoproterozoic depositional framework and an intrabasinal unconformity in the Laurentian margin Dalradian Supergroup, Grampian Highlands, Scotland","authors":"A. Leslie, M. Krabbendam, C.W. Thomas, C.J. Banks, S. M. Clarke","doi":"10.1144/jgs2023-208","DOIUrl":"https://doi.org/10.1144/jgs2023-208","url":null,"abstract":"Restoring primary depositional frameworks from orogenic settings is challenging. To demonstrate a robust determination of original, but now highly-deformed, depositional frameworks and their first-order sequence-stratigraphy, we analyse the Dalradian succession of Tyndrum–Glen Lyon (Breadalbane) in the south-western Grampian Highlands of Scotland.\u0000 In Breadalbane, several distinctive Appin and Argyll group Dalradian formations are absent. Omission has been attributed to ductile shearing on the Boundary Slide structure, during the Grampian Orogeny (c. 470 Ma). Alternatively, we restore and describe a primary depositional framework and widely-developed intra-Dalradian basin unconformity in Breadalbane, preserved in the relatively low strain lower limb of the Grampian D2 Ben Lui Syncline. On this unconformity, locally distinctive strata of the Easdale Subgroup, and more regionally-typical strata of the Crinan Subgroup, were deposited directly on strata of the Lochaber Subgroup. North-eastwards loss of strata of the Ballachulish, Blair Atholl and Islay subgroups, observed south-west of Tyndrum, contrasts with gradual reappearance of correlative units north-eastwards from Glen Lyon. Onlap and/or overstep relationships are well-preserved – although strain is enhanced locally along pronounced stratal/rheological contrasts, the stratigraphical framework remains essentially intact.\u0000 Our Scotland-wide analysis of the Dalradian depositional framework recognises other probable basin-scale unconformities that locally influenced patterns of superimposed orogenic deformation.","PeriodicalId":17320,"journal":{"name":"Journal of the Geological Society","volume":null,"pages":null},"PeriodicalIF":2.7,"publicationDate":"2024-02-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140426340","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Erkang Qiu, K. Larson, Alfredo Camacho, Yueqiao Zhang
Dating the timing of deformation within shear zones is critical to quantifying orogenic processes and developing time-resolved regional tectonic frameworks. Such work requires the integration of detailed microstructural analysis with in-situ geochronology to quantify when deformation mechanisms were active at the microscale. The Proterozoic, granulite-facies Strangways Metamorphic Complex was exhumed during the Devonian to Carboniferous intracontinental Alice Springs orogeny. New microstructural observations, quartz c -axis orientation analyses, mica chemistry, Ti-in-biotite thermometry, and in-situ mica Rb-Sr and titanite U-Pb geochronology outline a detailed history of ductile shearing across the complex. Movement along the north boundary shear zone of Strangways Metamorphic Complex appears to have initiated ca. 382 Ma, preceding peak metamorphism in the area during the Alice Springs orogeny. Widespread reverse-sense ductile shearing occurred within the Strangways Metamorphic Complex between ca. 365 and 355 Ma and correlates with rapid cooling of the region. Late-stage ductile deformation is recorded at ca. 335 Ma, likely reflecting the terminal exhumation of the Strangways Metamorphic Complex. Finally, the new in situ muscovite and biotite Rb-Sr data collected herein permit comparison with previous two-point mica Rb-Sr isochrons and 40 Ar- 39 Ar dates from the same specimens. In the rocks analyzed, the biotite Rb-Sr system returned dates similar to the previous 40 Ar- 39 Ar white mica dates, perhaps indicating a similar effective closure temperature. Supplementary material: https://osf.io/yjp24/?view_only=0bf5bec9f5c94a1aa4fb413320ec24e8
{"title":"Reassessing the timing of high strain deformation in the Strangways Metamorphic Complex, central Australia, by\u0000 in-situ\u0000 Mica Rb-Sr and Titanite U-Pb geochronology","authors":"Erkang Qiu, K. Larson, Alfredo Camacho, Yueqiao Zhang","doi":"10.1144/jgs2023-163","DOIUrl":"https://doi.org/10.1144/jgs2023-163","url":null,"abstract":"\u0000 Dating the timing of deformation within shear zones is critical to quantifying orogenic processes and developing time-resolved regional tectonic frameworks. Such work requires the integration of detailed microstructural analysis with\u0000 in-situ\u0000 geochronology to quantify when deformation mechanisms were active at the microscale. The Proterozoic, granulite-facies Strangways Metamorphic Complex was exhumed during the Devonian to Carboniferous intracontinental Alice Springs orogeny. New microstructural observations, quartz\u0000 c\u0000 -axis orientation analyses, mica chemistry, Ti-in-biotite thermometry, and\u0000 in-situ\u0000 mica Rb-Sr and titanite U-Pb geochronology outline a detailed history of ductile shearing across the complex. Movement along the north boundary shear zone of Strangways Metamorphic Complex appears to have initiated ca. 382 Ma, preceding peak metamorphism in the area during the Alice Springs orogeny. Widespread reverse-sense ductile shearing occurred within the Strangways Metamorphic Complex between ca. 365 and 355 Ma and correlates with rapid cooling of the region. Late-stage ductile deformation is recorded at ca. 335 Ma, likely reflecting the terminal exhumation of the Strangways Metamorphic Complex. Finally, the new\u0000 in situ\u0000 muscovite and biotite Rb-Sr data collected herein permit comparison with previous two-point mica Rb-Sr isochrons and\u0000 40\u0000 Ar-\u0000 39\u0000 Ar dates from the same specimens. In the rocks analyzed, the biotite Rb-Sr system returned dates similar to the previous\u0000 40\u0000 Ar-\u0000 39\u0000 Ar white mica dates, perhaps indicating a similar effective closure temperature.\u0000 \u0000 \u0000 Supplementary material:\u0000 https://osf.io/yjp24/?view_only=0bf5bec9f5c94a1aa4fb413320ec24e8\u0000","PeriodicalId":17320,"journal":{"name":"Journal of the Geological Society","volume":null,"pages":null},"PeriodicalIF":2.7,"publicationDate":"2024-02-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140431732","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
J. H. Metcalfe, R. Strachan, J. R. Darling, M. Fowler, G. Chapman, J. Dunlop
U-Pb apatite geochronology is increasingly recognised as a valuable tool for constraining the age of mid-crustal ductile shear zones. The crustal-scale Outer Hebrides Fault Zone (OHFZ) within the Laurentian foreland of the Scottish Caledonides has long been of uncertain age and tectonic significance. Earliest deformation within the OHFZ was associated with top-to-the-NW ductile thrusting that formed a belt of greenschist facies mylonites within host Archaean-Palaeoproterozoic basement gneisses. Previous estimates for the timing of thrusting vary between c. 1600 Ma and c. 430 Ma. The mylonitic fabrics are defined by a recrystallised assemblage of quartz + albite / oligoclase + sericite + actinolite + epidote + apatite ± calcite, consistent with deformation temperatures of 400-500 °C and within the range of reported closure temperatures for Pb diffusion in apatite. U-Pb (LA-ICP-MS) dating of two texturally distinct apatite grain types within the mylonites has yielded ages mostly in the range c. 1100 – 900 Ma. The OHFZ is therefore interpreted as a Grenville-Sveconorwegian structure that formed during the tripartite collision of Laurentia, Baltica, and Amazonia and the assembly of Rodinia. Supplementary material: https://doi.org/10.6084/m9.figshare.c.7084925
人们日益认识到，铀-铅-磷灰石地质年代学是制约中地壳韧性剪切带年龄的重要工具。长期以来，苏格兰喀里多尼亚山脉劳伦前陆的地壳尺度外赫布里底断裂带（OHFZ）的年龄和构造意义一直不确定。外赫布里底断裂带内最早的变形与自上而下向西北的韧性推力作用有关，这种推力作用在太古代-古新世基底片麻岩中形成了一条绿泥石面岩带。以前对推覆时间的估计在约 1600 Ma 到约 430 Ma 之间。绵状构造由石英+白云石/低闪长岩+绢云母+阳起石+闪长岩+磷灰石±方解石的重结晶组合所界定，与400-500 °C的变形温度相一致，并在磷灰石中铅扩散的闭合温度报告范围内。对麦饭石中两种质地不同的磷灰石晶粒类型进行铀-铅（LA-ICP-MS）测年，得出的年龄大多在约 1100 - 900 Ma 之间。因此，OHFZ被解释为在劳伦西亚、波罗的海和亚马孙三方碰撞以及罗迪尼亚组装过程中形成的格勒维尔-斯维科诺尔维格构造。 补充材料：https://doi.org/10.6084/m9.figshare.c.7084925
{"title":"U-Pb geochronology and microstructural analysis of apatite within a Proterozoic crustal-scale shear zone, Outer Hebrides, NW Scotland","authors":"J. H. Metcalfe, R. Strachan, J. R. Darling, M. Fowler, G. Chapman, J. Dunlop","doi":"10.1144/jgs2023-139","DOIUrl":"https://doi.org/10.1144/jgs2023-139","url":null,"abstract":"U-Pb apatite geochronology is increasingly recognised as a valuable tool for constraining the age of mid-crustal ductile shear zones. The crustal-scale Outer Hebrides Fault Zone (OHFZ) within the Laurentian foreland of the Scottish Caledonides has long been of uncertain age and tectonic significance. Earliest deformation within the OHFZ was associated with top-to-the-NW ductile thrusting that formed a belt of greenschist facies mylonites within host Archaean-Palaeoproterozoic basement gneisses. Previous estimates for the timing of thrusting vary between c. 1600 Ma and c. 430 Ma. The mylonitic fabrics are defined by a recrystallised assemblage of quartz + albite / oligoclase + sericite + actinolite + epidote + apatite ± calcite, consistent with deformation temperatures of 400-500 °C and within the range of reported closure temperatures for Pb diffusion in apatite. U-Pb (LA-ICP-MS) dating of two texturally distinct apatite grain types within the mylonites has yielded ages mostly in the range c. 1100 – 900 Ma. The OHFZ is therefore interpreted as a Grenville-Sveconorwegian structure that formed during the tripartite collision of Laurentia, Baltica, and Amazonia and the assembly of Rodinia.\u0000 \u0000 Supplementary material:\u0000 https://doi.org/10.6084/m9.figshare.c.7084925\u0000","PeriodicalId":17320,"journal":{"name":"Journal of the Geological Society","volume":null,"pages":null},"PeriodicalIF":2.7,"publicationDate":"2024-02-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140436492","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Xuelian Guo, G. Retallack, Bin Lü, Mingming Ma, Huairen Cao, Weibin Wang, Jinhao Liu
Detrital zircon geochronology has been used to determine provenance, but also gives maximum depositional ages that can constrain other forms of geochronology, such as magnetostratigraphy and pedostratigraphy. Pedostratigraphy and magnetostratigraphy correlate a series of global events by spacing or intensity in a fashion comparable with a commercial barcode. The Late Devonian Shaliushui Formation of NW China is poorly fossiliferous, but shows spikes in magnetic susceptibility, Al/Si ratios, Rb/Sr ratios and the depth to carbonate nodules (Bk horizon) corresponding with the timing of named Late Devonian black shale horizons. By contrast, the Ti/Al ratios show only small variations, indicating little long-term change in the source terrain or in the hydraulic sorting of heavy minerals. Most of the detrital zircon ages are older than an age model from the pedostratigraphic correlation of deep calcic horizons corresponding to global atmospheric CO 2 spikes at times of black shale expansion, but one detrital zircon age converges with the pedostratigraphic depositional ages near the top of the section. Pedostratigraphy is widely used in Quaternary sequences, but can also be a basis for age models of rocks in deep time if supported by detrital zircon ages. Supplementary material: Paleosol and geochemical data, and youngest zircon ages for a section of Devonian rocks near Ciyao, Gansu, China are available at https://doi.org/10.6084/m9.figshare.c.7008192
{"title":"Pedostratigraphic age model for Devonian red beds of NW China","authors":"Xuelian Guo, G. Retallack, Bin Lü, Mingming Ma, Huairen Cao, Weibin Wang, Jinhao Liu","doi":"10.1144/jgs2023-096","DOIUrl":"https://doi.org/10.1144/jgs2023-096","url":null,"abstract":"\u0000 Detrital zircon geochronology has been used to determine provenance, but also gives maximum depositional ages that can constrain other forms of geochronology, such as magnetostratigraphy and pedostratigraphy. Pedostratigraphy and magnetostratigraphy correlate a series of global events by spacing or intensity in a fashion comparable with a commercial barcode. The Late Devonian Shaliushui Formation of NW China is poorly fossiliferous, but shows spikes in magnetic susceptibility, Al/Si ratios, Rb/Sr ratios and the depth to carbonate nodules (Bk horizon) corresponding with the timing of named Late Devonian black shale horizons. By contrast, the Ti/Al ratios show only small variations, indicating little long-term change in the source terrain or in the hydraulic sorting of heavy minerals. Most of the detrital zircon ages are older than an age model from the pedostratigraphic correlation of deep calcic horizons corresponding to global atmospheric CO\u0000 2\u0000 spikes at times of black shale expansion, but one detrital zircon age converges with the pedostratigraphic depositional ages near the top of the section. Pedostratigraphy is widely used in Quaternary sequences, but can also be a basis for age models of rocks in deep time if supported by detrital zircon ages.\u0000 \u0000 \u0000 Supplementary material:\u0000 Paleosol and geochemical data, and youngest zircon ages for a section of Devonian rocks near Ciyao, Gansu, China are available at\u0000 https://doi.org/10.6084/m9.figshare.c.7008192\u0000","PeriodicalId":17320,"journal":{"name":"Journal of the Geological Society","volume":null,"pages":null},"PeriodicalIF":2.7,"publicationDate":"2024-02-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140445008","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
An appraisal of the Quaternary shelf-margin succession in the western Great Australian Bight has yielded new insights into the development of this prograding passive margin. Our analysis of seismic reflection and sedimentary data from the Eyre Terrace and adjacent outer shelf challenges the established view that this shelf-margin wedge represents a prograding carbonate ramp. Instead, we identify separate outer shelf and upper slope depositional systems: the outer shelf comprises an aggrading-to-prograding succession whereas the upper slope was constructed and shaped predominantly by alongslope processes driven by the major boundary currents that form the Southern Australia Current System. The latter resulted in the formation of a spectacular 500 m-thick, basin-scale, elongate-mounded carbonate contourite drift – the ‘Eyre Terrace Drift’ – and associated sediment waves. Sheeted drift and infill drift geometries are also observed. Key sedimentary attributes include fine-grained sediment, multi-scale gradational bed contacts, and pervasive bioturbation. The upper flank of the drift provided a platform across which the prograding outermost-shelf facies progressively migrated. The resulting stratigraphic pattern of the Quaternary shelf-margin clinoforms was formed by a combination of ‘conventional’ clinoform progradation from the outer shelf and ‘contouritic clinoform’ progradation and drift accretion on the upper slope.
{"title":"A Quaternary carbonate contourite drift system on the Eyre Terrace, Great Australian Bight: implications for the origin of prograding shelf-edge/upper slope clinoforms, southern Australian passive margin","authors":"M. Stoker, S. Holford, J. Totterdell","doi":"10.1144/jgs2023-135","DOIUrl":"https://doi.org/10.1144/jgs2023-135","url":null,"abstract":"An appraisal of the Quaternary shelf-margin succession in the western Great Australian Bight has yielded new insights into the development of this prograding passive margin. Our analysis of seismic reflection and sedimentary data from the Eyre Terrace and adjacent outer shelf challenges the established view that this shelf-margin wedge represents a prograding carbonate ramp. Instead, we identify separate outer shelf and upper slope depositional systems: the outer shelf comprises an aggrading-to-prograding succession whereas the upper slope was constructed and shaped predominantly by alongslope processes driven by the major boundary currents that form the Southern Australia Current System. The latter resulted in the formation of a spectacular 500 m-thick, basin-scale, elongate-mounded carbonate contourite drift – the ‘Eyre Terrace Drift’ – and associated sediment waves. Sheeted drift and infill drift geometries are also observed. Key sedimentary attributes include fine-grained sediment, multi-scale gradational bed contacts, and pervasive bioturbation. The upper flank of the drift provided a platform across which the prograding outermost-shelf facies progressively migrated. The resulting stratigraphic pattern of the Quaternary shelf-margin clinoforms was formed by a combination of ‘conventional’ clinoform progradation from the outer shelf and ‘contouritic clinoform’ progradation and drift accretion on the upper slope.","PeriodicalId":17320,"journal":{"name":"Journal of the Geological Society","volume":null,"pages":null},"PeriodicalIF":2.7,"publicationDate":"2024-02-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140451945","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Zhanhong Liu, T. Algeo, S. Arefifard, Wei Wei, Carlton Brett, E. Landing, S.M Lev
Ancient epicratonic formations, which represent the bulk of pre-Jurassic sedimentary rocks, have been widely interpreted as marine deposits, but recently developed bulk-shale elemental proxies for paleo-watermass salinity (i.e., B/Ga, Sr/Ba, and S/TOC) have shown this inference to be frequently incorrect. Here, we use these proxies to test the salinity conditions of 22 representative shale and marl formations of early Cambrian to early Silurian age from five cratons (Laurentia, Avalonia, Baltica, Iran and South China) in the context of formation-specific paleogeographic and paleoclimatic reconstructions. Our dataset shows that around half of these formations were probably deposited under brackish or mixed brackish-marine conditions rather than fully marine conditions (as previously inferred), and that one of them represents a freshwater facies (previously interpreted as marine mainly on the basis of Cruziana traces). In most cases, the development of reduced-salinity conditions can be related to the coastal and/or humid climate belt setting in which the formation of interest was deposited. Our dataset also reveals systematically low Sr/Ba values (i.e., relative to modern brackish and marine facies), suggesting that seawater Sr concentrations were lower during the Early Paleozoic than in the modern. Our findings suggest that re-evaluation of the salinity characteristics of many ancient epicratonic shale and marl formations is necessary. Thematic collection: This article is part of the Chemical Evolution of the Mid-Paleozoic Earth System and Biotic Response collection available at: https://www.lyellcollection.org/topic/collections/chemical-evolution-of-the-mid-paleozoic-earth-system Supplementary material: https://doi.org/10.6084/m9.figshare.c.7063365
古震旦系地层是侏罗纪前沉积岩的主体，被广泛解释为海相沉积，但最近开发的古水体盐度的大块页岩元素代用指标（即 B/Ga、Sr/Ba 和 S/TOC）表明这种推断经常是不正确的。在这里，我们利用这些代用指标，结合特定地层的古地理和古气候重建，测试了五个地壳（劳伦西亚、阿瓦鲁尼亚、波罗的海、伊朗和华南）22 个具有代表性的早寒武纪至早志留纪页岩和泥灰岩地层的盐度条件。我们的数据集显示，这些地层中约有一半可能是在咸水或咸海-海洋混合条件下沉积的，而不是像以前推断的那样完全是海洋条件下沉积的，其中一个地层代表了淡水层（以前主要根据克鲁兹亚纳痕迹解释为海洋层）。在大多数情况下，盐度降低条件的形成与相关地层沉积的沿海和/或潮湿气候带环境有关。我们的数据集还显示出系统性的低 Sr/Ba 值（即相对于现代咸水层和海相层而言），这表明早古生代的海水 Sr 浓度低于现代海水 Sr 浓度。我们的研究结果表明，有必要重新评估许多古震旦系页岩和泥灰岩地层的盐度特征。 专题文集：本文是中古生代地球系统化学演化与生物响应文集的一部分，可在以下网址查阅： https://www.lyellcollection.org/topic/collections/chemical-evolution-of-the-mid-paleozoic-earth-system 补充材料： https://doi.org/10.6084/m9.figshare.c.7063365
{"title":"Testing the salinity of Cambrian to Silurian epicratonic seas","authors":"Zhanhong Liu, T. Algeo, S. Arefifard, Wei Wei, Carlton Brett, E. Landing, S.M Lev","doi":"10.1144/jgs2023-217","DOIUrl":"https://doi.org/10.1144/jgs2023-217","url":null,"abstract":"\u0000 Ancient epicratonic formations, which represent the bulk of pre-Jurassic sedimentary rocks, have been widely interpreted as marine deposits, but recently developed bulk-shale elemental proxies for paleo-watermass salinity (i.e., B/Ga, Sr/Ba, and S/TOC) have shown this inference to be frequently incorrect. Here, we use these proxies to test the salinity conditions of 22 representative shale and marl formations of early Cambrian to early Silurian age from five cratons (Laurentia, Avalonia, Baltica, Iran and South China) in the context of formation-specific paleogeographic and paleoclimatic reconstructions. Our dataset shows that around half of these formations were probably deposited under brackish or mixed brackish-marine conditions rather than fully marine conditions (as previously inferred), and that one of them represents a freshwater facies (previously interpreted as marine mainly on the basis of\u0000 Cruziana\u0000 traces). In most cases, the development of reduced-salinity conditions can be related to the coastal and/or humid climate belt setting in which the formation of interest was deposited. Our dataset also reveals systematically low Sr/Ba values (i.e., relative to modern brackish and marine facies), suggesting that seawater Sr concentrations were lower during the Early Paleozoic than in the modern. Our findings suggest that re-evaluation of the salinity characteristics of many ancient epicratonic shale and marl formations is necessary.\u0000 \u0000 \u0000 Thematic collection:\u0000 This article is part of the Chemical Evolution of the Mid-Paleozoic Earth System and Biotic Response collection available at:\u0000 https://www.lyellcollection.org/topic/collections/chemical-evolution-of-the-mid-paleozoic-earth-system\u0000 \u0000 \u0000 Supplementary material:\u0000 https://doi.org/10.6084/m9.figshare.c.7063365\u0000","PeriodicalId":17320,"journal":{"name":"Journal of the Geological Society","volume":null,"pages":null},"PeriodicalIF":2.7,"publicationDate":"2024-02-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140451113","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
M. García, M. López, J. Bucher, M. Tettamanti, R. Feo, L. D'Elia, J. Franzese
In the context of Andean-type oblique convergence, strain partitioning between thrust and strike-slip tectonics is well-documented in the arc region. However, the impact of this configuration in the retroarc remains poorly understood, especially in broken foreland systems where basement structures compartmentalize the retroarc into small intermontane sedimentary basins. The spatiotemporal analysis of tectonic evolution and the role of inherited weaknesses in this area are often debated. This study addresses these uncertainties by integrating geometric and kinematic analyses of tectonic structures within the Sañicó Massif in the North Patagonian foreland. Results reveal two deformational episodes. The initial Late Cretaceous to Paleocene episode represents a contractional deformation phase, with NW-SE shortening direction causing the tectonic inversion of pre-Andean rift depocentres. The second episode records a Neogene transpressional regime with both contractional and strike-slip deformation, with E-W to NE-SW shortening direction, which progressed under reactivation of pre-existing structures and generated new faults. This work demonstrates the Neogene propagation of the strike-slip regime towards the retroarc, defining strain partitioning at various scales and highlighting its interaction with pre-existing structures. These results enhance our understanding of the complex tectonic history in oblique subduction settings, providing significant evidence of the structural inheritance in retroarc systems.
{"title":"Strain partitioning in the Patagonian Broken Foreland: influence of structural inheritance of Early Andean deformation","authors":"M. García, M. López, J. Bucher, M. Tettamanti, R. Feo, L. D'Elia, J. Franzese","doi":"10.1144/jgs2023-166","DOIUrl":"https://doi.org/10.1144/jgs2023-166","url":null,"abstract":"In the context of Andean-type oblique convergence, strain partitioning between thrust and strike-slip tectonics is well-documented in the arc region. However, the impact of this configuration in the retroarc remains poorly understood, especially in broken foreland systems where basement structures compartmentalize the retroarc into small intermontane sedimentary basins. The spatiotemporal analysis of tectonic evolution and the role of inherited weaknesses in this area are often debated. This study addresses these uncertainties by integrating geometric and kinematic analyses of tectonic structures within the Sañicó Massif in the North Patagonian foreland. Results reveal two deformational episodes. The initial Late Cretaceous to Paleocene episode represents a contractional deformation phase, with NW-SE shortening direction causing the tectonic inversion of pre-Andean rift depocentres. The second episode records a Neogene transpressional regime with both contractional and strike-slip deformation, with E-W to NE-SW shortening direction, which progressed under reactivation of pre-existing structures and generated new faults. This work demonstrates the Neogene propagation of the strike-slip regime towards the retroarc, defining strain partitioning at various scales and highlighting its interaction with pre-existing structures. These results enhance our understanding of the complex tectonic history in oblique subduction settings, providing significant evidence of the structural inheritance in retroarc systems.","PeriodicalId":17320,"journal":{"name":"Journal of the Geological Society","volume":null,"pages":null},"PeriodicalIF":2.7,"publicationDate":"2024-02-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139802249","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
M. García, M. López, J. Bucher, M. Tettamanti, R. Feo, L. D'Elia, J. Franzese
In the context of Andean-type oblique convergence, strain partitioning between thrust and strike-slip tectonics is well-documented in the arc region. However, the impact of this configuration in the retroarc remains poorly understood, especially in broken foreland systems where basement structures compartmentalize the retroarc into small intermontane sedimentary basins. The spatiotemporal analysis of tectonic evolution and the role of inherited weaknesses in this area are often debated. This study addresses these uncertainties by integrating geometric and kinematic analyses of tectonic structures within the Sañicó Massif in the North Patagonian foreland. Results reveal two deformational episodes. The initial Late Cretaceous to Paleocene episode represents a contractional deformation phase, with NW-SE shortening direction causing the tectonic inversion of pre-Andean rift depocentres. The second episode records a Neogene transpressional regime with both contractional and strike-slip deformation, with E-W to NE-SW shortening direction, which progressed under reactivation of pre-existing structures and generated new faults. This work demonstrates the Neogene propagation of the strike-slip regime towards the retroarc, defining strain partitioning at various scales and highlighting its interaction with pre-existing structures. These results enhance our understanding of the complex tectonic history in oblique subduction settings, providing significant evidence of the structural inheritance in retroarc systems.
{"title":"Strain partitioning in the Patagonian Broken Foreland: influence of structural inheritance of Early Andean deformation","authors":"M. García, M. López, J. Bucher, M. Tettamanti, R. Feo, L. D'Elia, J. Franzese","doi":"10.1144/jgs2023-166","DOIUrl":"https://doi.org/10.1144/jgs2023-166","url":null,"abstract":"In the context of Andean-type oblique convergence, strain partitioning between thrust and strike-slip tectonics is well-documented in the arc region. However, the impact of this configuration in the retroarc remains poorly understood, especially in broken foreland systems where basement structures compartmentalize the retroarc into small intermontane sedimentary basins. The spatiotemporal analysis of tectonic evolution and the role of inherited weaknesses in this area are often debated. This study addresses these uncertainties by integrating geometric and kinematic analyses of tectonic structures within the Sañicó Massif in the North Patagonian foreland. Results reveal two deformational episodes. The initial Late Cretaceous to Paleocene episode represents a contractional deformation phase, with NW-SE shortening direction causing the tectonic inversion of pre-Andean rift depocentres. The second episode records a Neogene transpressional regime with both contractional and strike-slip deformation, with E-W to NE-SW shortening direction, which progressed under reactivation of pre-existing structures and generated new faults. This work demonstrates the Neogene propagation of the strike-slip regime towards the retroarc, defining strain partitioning at various scales and highlighting its interaction with pre-existing structures. These results enhance our understanding of the complex tectonic history in oblique subduction settings, providing significant evidence of the structural inheritance in retroarc systems.","PeriodicalId":17320,"journal":{"name":"Journal of the Geological Society","volume":null,"pages":null},"PeriodicalIF":2.7,"publicationDate":"2024-02-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139862322","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
京公网安备 11010802042870号
京ICP备2023020795号-1
扫码关注我们
求助内容：
应助结果提醒方式：