B. Fairey, Aidan Kerrison, P. Meere, Kieran F. Mulchrone, M. Zieger-Hofmann, A. Gärtner, Benita-Lisette Sonntag, U. Linnemann, Klaudia F. Kuiper, M. Ennis, Chris Mark, N. Cogné, David Chew
The Devonian Old Red Sandstone (ORS) magnafacies of southern Ireland is hosted in the Lower Devonian Dingle Basin and the Upper Devonian Munster Basin. Following the closure of the Iapetus Ocean during the Caledonian Orogeny, the Dingle Basin developed as a pull-apart structure before being deformed by Acadian tectonic activity. The Munster Basin developed as a half-graben structure in response to post-Acadian N-S extension in the region. Thus, the Irish ORS provides insights into the region's tectonic history due to its temporal and spatial proximity to the Caledonian (∼475-425 Ma), Acadian (∼400-390 Ma) and Variscan orogenic events (∼390-290 Ma). This study presents the first detrital zircon and apatite U-Pb geochronological data for the UORS in southern Ireland in addition to detrital white mica 40 Ar/ 39 Ar geochronological data to help unravel the depositional history of the Irish UORS and to assess the possible role of sedimentary recycling in Upper Devonian basin development. Most Upper ORS (UORS) samples contain few late Neoproterozoic detrital zircon grains and are instead dominated by early Palaeozoic and ca. 1.1 Ga zircons. These populations represent recycling of northerly-derived Ordovician to Silurian strata of the Southern-Uplands-Longford-Down terrane which are of Laurentian affinity, and not recycling of Lower ORS (which contain a significant number of late Neoproterozoic detrital zircons) as previously thought. Similar detrital zircon dates have been observed in Givetian-Frasnian quartzites of the Pulo do Lobo Zone on the Iberian Peninsula, providing a possible Rheic Ocean link with the UORS.
爱尔兰南部泥盆纪老红砂岩（ORS）岩相位于下泥盆纪丁格尔盆地和上泥盆纪明斯特盆地。在喀里多尼亚造山运动期间伊阿佩图斯洋关闭之后，丁格尔盆地在受到阿卡迪亚构造活动的影响而发生变形之前，发展成为一个拉裂构造。芒斯特盆地在该地区后阿卡迪亚N-S伸展过程中形成了半堑壕结构。因此，爱尔兰ORS在时间和空间上接近于加里东期（475-425 Ma）、阿卡迪亚期（400-390 Ma）和瓦里斯坎期（390-290 Ma）的造山活动，为了解该地区的构造历史提供了线索。本研究首次提出了爱尔兰南部上ORS的锆英石和磷灰石U-Pb地质年代数据，以及白云母40 Ar/ 39 Ar地质年代数据，以帮助揭示爱尔兰上ORS的沉积历史，并评估沉积循环在上泥盆纪盆地发展中可能发挥的作用。 大多数上泥盆纪（UORS）样本几乎不含新近纪晚期的碎屑锆石颗粒，而是以早古生代和大约 1.1 Ga 的锆石为主。这些锆石群代表了具有劳伦伦亲缘关系的南部-高地-隆福-下地层的奥陶纪至志留纪北源地层的再循环，而不是以前认为的下奥陶纪地层的再循环（其中含有大量新近纪晚期的碎屑锆石）。在伊比利亚半岛 Pulo do Lobo 区的给统-新生代石英岩中也观察到了类似的碎屑锆石日期，这提供了莱茵洋与 UORS 的可能联系。
{"title":"Sedimentary provenance of the Upper Devonian Old Red Sandstone of southern Ireland: An integrated multi-proxy detrital geochronology study","authors":"B. Fairey, Aidan Kerrison, P. Meere, Kieran F. Mulchrone, M. Zieger-Hofmann, A. Gärtner, Benita-Lisette Sonntag, U. Linnemann, Klaudia F. Kuiper, M. Ennis, Chris Mark, N. Cogné, David Chew","doi":"10.1144/jgs2023-110","DOIUrl":"https://doi.org/10.1144/jgs2023-110","url":null,"abstract":"\u0000 The Devonian Old Red Sandstone (ORS) magnafacies of southern Ireland is hosted in the Lower Devonian Dingle Basin and the Upper Devonian Munster Basin. Following the closure of the Iapetus Ocean during the Caledonian Orogeny, the Dingle Basin developed as a pull-apart structure before being deformed by Acadian tectonic activity. The Munster Basin developed as a half-graben structure in response to post-Acadian N-S extension in the region. Thus, the Irish ORS provides insights into the region's tectonic history due to its temporal and spatial proximity to the Caledonian (∼475-425 Ma), Acadian (∼400-390 Ma) and Variscan orogenic events (∼390-290 Ma). This study presents the first detrital zircon and apatite U-Pb geochronological data for the UORS in southern Ireland in addition to detrital white mica\u0000 40\u0000 Ar/\u0000 39\u0000 Ar geochronological data to help unravel the depositional history of the Irish UORS and to assess the possible role of sedimentary recycling in Upper Devonian basin development.\u0000 \u0000 Most Upper ORS (UORS) samples contain few late Neoproterozoic detrital zircon grains and are instead dominated by early Palaeozoic and ca. 1.1 Ga zircons. These populations represent recycling of northerly-derived Ordovician to Silurian strata of the Southern-Uplands-Longford-Down terrane which are of Laurentian affinity, and not recycling of Lower ORS (which contain a significant number of late Neoproterozoic detrital zircons) as previously thought. Similar detrital zircon dates have been observed in Givetian-Frasnian quartzites of the Pulo do Lobo Zone on the Iberian Peninsula, providing a possible Rheic Ocean link with the UORS.","PeriodicalId":507891,"journal":{"name":"Journal of the Geological Society","volume":"97 7","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-07-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141683635","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Geologists have speculated when plate tectonics began since the dawn of that revolution, with recent estimates ranging from the last 20% of Earth history to within the first 5%. All such estimates rest on six types of evidence: preservation of modern plate tectonic features, detrital-zircon age spectra, trace element-isotope geochemistry, atmosphere-crust-mantle exchange, paleomagnetism, and model calculations. ‘Burke's Law’ suggests that the null hypothesis puts the onus on demonstrating when plate tectonics was not operating rather than requiring observation of plate tectonic features in the geologic record as assemblages presumed characteristic of plate tectonics could be lost from the geologic record (due to preservation biases) or never existed (due to secular changes). This issue has become salient as our community appears to be coalescing around the paradigm that plate tectonics began during the late Archean in the face of problematic evidence, much the same way it's done repeatedly over the past century (e.g., rejecting continental drift in preference to geosyncline theory). I summarize evidence from the six evidentiary types and conclude that we don't know when plate tectonics initiated. Claiming we do forestalls the day that we might truly understand an event at the heart of Earth history and habitability.
{"title":"We don't know when plate tectonics began","authors":"T. M. Harrison","doi":"10.1144/jgs2023-212","DOIUrl":"https://doi.org/10.1144/jgs2023-212","url":null,"abstract":"\u0000 Geologists have speculated when plate tectonics began since the dawn of that revolution, with recent estimates ranging from the last 20% of Earth history to within the first 5%. All such estimates rest on six types of evidence: preservation of modern plate tectonic features, detrital-zircon age spectra, trace element-isotope geochemistry, atmosphere-crust-mantle exchange, paleomagnetism, and model calculations. ‘Burke's Law’ suggests that the null hypothesis puts the onus on demonstrating when plate tectonics was\u0000 not\u0000 operating rather than requiring observation of plate tectonic features in the geologic record as assemblages presumed characteristic of plate tectonics could be lost from the geologic record (due to preservation biases) or never existed (due to secular changes). This issue has become salient as our community appears to be coalescing around the paradigm that plate tectonics began during the late Archean in the face of problematic evidence, much the same way it's done repeatedly over the past century (e.g., rejecting continental drift in preference to geosyncline theory). I summarize evidence from the six evidentiary types and conclude that we don't know when plate tectonics initiated. Claiming we do forestalls the day that we might truly understand an event at the heart of Earth history and habitability.\u0000","PeriodicalId":507891,"journal":{"name":"Journal of the Geological Society","volume":"56 27","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-04-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140656703","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
E. Saccani, Edoardo Barbero, M. Delavari, A. Dolati, Valentina Brombin, M. Marroni, L. Pandolfi
The Bajgan Complex in the North Makran Domain (Makran Accretionary Prism) comprises disrupted meta-ophiolitic sequences originating from oceanic crust protoliths. They include ultramafic and mafic cumulates, isotropic gabbros, plagiogranites, and basalts. Ultramafic-mafic cumulates and plagiogranites exhibit compositions akin to rocks formed in mid-ocean ridge settings. Isotropic gabbro and basalt protoliths can be subdivided in three distinct geochemical types. Type-1 rocks is sub-alkaline (Nb/Y < 0.1) with low Th, Nb, and Ta contents and La N /Yb N ratios <1, resembling those of normal-type (N-) mid-ocean ridge basalts (MORB). Type-2 rocks display slight enrichment in Th, Ta, Nb (Nb/Y = 0.36 – 0.45), and La N /Yb N = 2.12 – 3.20, resembling the chemistry of enriched-type (E-) MORB. Type-3 basalts show an alkaline nature (Nb/Y=0.88-1.82), significant Th, Ta, Nb enrichment, and high La N /Yb N ratios (7.01 – 20.08), resembling the chemistry of alkaline basalts (OIB). Petrogenetic modeling indicates that N-MORB protoliths originated from a depleted MORB mantle source, while E-MORB and OIB protoliths were generated from partial melting of sub-oceanic depleted sources that underwent varying degrees of OIB-type enrichment. The Bajgan meta-ophiolitic protoliths were formed within a Late Jurassic to Cretaceous oceanic basin influenced by mantle plume activity and plume-ridge interaction. 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.7193937
北迈克兰地区（迈克兰断积棱岩）的巴吉甘复合体由源自大洋地壳原岩的破碎元沸石序列组成。它们包括超闪长岩和黑云母积岩、各向同性辉长岩、斜长岩和玄武岩。超基性黑云母-黑云母积岩和长花岗岩的成分类似于在大洋中脊环境中形成的岩石。各向同性辉长岩和玄武岩原岩可细分为三种不同的地球化学类型。第一类岩石为亚碱性（Nb/Y < 0.1），Th、Nb 和 Ta 含量低，La N /Yb N 比率 < 1，与正常类型（N-）洋中脊玄武岩（MORB）相似。第二类岩石的钍、钽、铌含量略有富集（铌/镱比=0.36-0.45），镧/镱比=2.12-3.20，与富集型（E-）MORB 的化学成分相似。3型玄武岩呈碱性（Nb/Y=0.88-1.82），Th、Ta、Nb富集显著，La N /Yb N比值较高（7.01-20.08），类似于碱性玄武岩（OIB）的化学性质。岩石学模型表明，N-MORB原岩源于贫化的MORB地幔源，而E-MORB和OIB原岩则产生于经历了不同程度的OIB型富集的洋底贫化源的部分熔融。Bajgan元沸石原岩是在晚侏罗世至白垩纪大洋盆地内受地幔羽流活动和羽桥相互作用的影响而形成的。 专题文集：本文是蛇绿岩、熔岩和蓝晶岩专题集的一部分，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.7193937
{"title":"Geochemistry and magmatic petrology of meta-ophiolites from the Bajgan Complex (Makran Accretionary Prism, SE Iran): New insights on the nature of the Early Cretaceous Middle East Neotethys","authors":"E. Saccani, Edoardo Barbero, M. Delavari, A. Dolati, Valentina Brombin, M. Marroni, L. Pandolfi","doi":"10.1144/jgs2024-043","DOIUrl":"https://doi.org/10.1144/jgs2024-043","url":null,"abstract":"\u0000 The Bajgan Complex in the North Makran Domain (Makran Accretionary Prism) comprises disrupted meta-ophiolitic sequences originating from oceanic crust protoliths. They include ultramafic and mafic cumulates, isotropic gabbros, plagiogranites, and basalts. Ultramafic-mafic cumulates and plagiogranites exhibit compositions akin to rocks formed in mid-ocean ridge settings. Isotropic gabbro and basalt protoliths can be subdivided in three distinct geochemical types. Type-1 rocks is sub-alkaline (Nb/Y < 0.1) with low Th, Nb, and Ta contents and La\u0000 N\u0000 /Yb\u0000 N\u0000 ratios <1, resembling those of normal-type (N-) mid-ocean ridge basalts (MORB). Type-2 rocks display slight enrichment in Th, Ta, Nb (Nb/Y = 0.36 – 0.45), and La\u0000 N\u0000 /Yb\u0000 N\u0000 = 2.12 – 3.20, resembling the chemistry of enriched-type (E-) MORB. Type-3 basalts show an alkaline nature (Nb/Y=0.88-1.82), significant Th, Ta, Nb enrichment, and high La\u0000 N\u0000 /Yb\u0000 N\u0000 ratios (7.01 – 20.08), resembling the chemistry of alkaline basalts (OIB). Petrogenetic modeling indicates that N-MORB protoliths originated from a depleted MORB mantle source, while E-MORB and OIB protoliths were generated from partial melting of sub-oceanic depleted sources that underwent varying degrees of OIB-type enrichment. The Bajgan meta-ophiolitic protoliths were formed within a Late Jurassic to Cretaceous oceanic basin influenced by mantle plume activity and plume-ridge interaction.\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.7193937\u0000","PeriodicalId":507891,"journal":{"name":"Journal of the Geological Society","volume":"3 3","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-04-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140653701","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
R. Briant, Martin R. Bates, Jenni Robertson, J. Schwenninger, John E. Whittaker
The Solent Region and Sussex coastal plain in southern England have preserved palaeo- sea-level indicators from multiple interglacial periods, with a particularly complete record of deposition throughout the last interglacial. However, as yet, none of the research on these indicators have fully addressed the relationship of the different types of deposits preserved to mean sea-level. In this paper we apply recent approaches to estimating past relative sea-levels based on applying modern analogues to understand the indicative meaning of these indicators. We also apply a synchronous correlation model previously developed on rapidly uplifting coastlines to assess uplift rates. The uplift rates required to match the elevations of sequences suggest a significant decrease in uplift rates between the Late Wolstonian Substage and Ipswichian Stage – i.e. the c. 240 ka and c. 125 ka sea-level highstands, broadly equivalent to Marine Isotope Stages (MIS) 7 and 5e. This coincides in time with the final opening of the Straits of Dover. Supplementary material: https://doi.org/10.6084/m9.figshare.c.7172532
英格兰南部的索伦特地区和苏塞克斯沿海平原保存了多个冰期的古海平面指标，其中上 一个冰期的沉积记录尤为完整。然而，迄今为止，对这些指标的研究都没有全面探讨所保存的不同类型沉积物与平均海平面之间的关系。在本文中，我们将采用最新的方法，在应用现代类比的基础上估算过去的相对海平面，以理解这些指标的指示意义。我们还应用了之前针对快速隆升海岸线开发的同步相关模型来评估隆升率。与序列海拔相匹配的隆升率表明，在晚沃尔斯顿次阶段和伊普斯维奇阶段（即约 240 ka 和约 125 ka 的海平面高点，大致相当于海洋同位素阶段（MIS）7 和 5e）之间，隆升率显著下降。这在时间上与多佛海峡的最终开放相吻合。 补充材料：https://doi.org/10.6084/m9.figshare.c.7172532
{"title":"Indicative meanings of geological sea-level indicators in the Solent region and Sussex coast (south coast of England) and implications for uplift rates","authors":"R. Briant, Martin R. Bates, Jenni Robertson, J. Schwenninger, John E. Whittaker","doi":"10.1144/jgs2023-120","DOIUrl":"https://doi.org/10.1144/jgs2023-120","url":null,"abstract":"The Solent Region and Sussex coastal plain in southern England have preserved palaeo- sea-level indicators from multiple interglacial periods, with a particularly complete record of deposition throughout the last interglacial. However, as yet, none of the research on these indicators have fully addressed the relationship of the different types of deposits preserved to mean sea-level. In this paper we apply recent approaches to estimating past relative sea-levels based on applying modern analogues to understand the indicative meaning of these indicators. We also apply a synchronous correlation model previously developed on rapidly uplifting coastlines to assess uplift rates. The uplift rates required to match the elevations of sequences suggest a significant decrease in uplift rates between the Late Wolstonian Substage and Ipswichian Stage – i.e. the c. 240 ka and c. 125 ka sea-level highstands, broadly equivalent to Marine Isotope Stages (MIS) 7 and 5e. This coincides in time with the final opening of the Straits of Dover.\u0000 \u0000 Supplementary material:\u0000 https://doi.org/10.6084/m9.figshare.c.7172532\u0000","PeriodicalId":507891,"journal":{"name":"Journal of the Geological Society","volume":"47 52","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-04-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140701812","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
The Andean flank in central Peru is characterized by stepped profiles involving up to 20 surfaces and pediments resulting from multiple episodes of uplift and erosion. The study area exhibits the same sequence of surfaces and pediments. Moreover, the erosional features are also recognised in the Eastern Cordillera in northern Peru. This report focuses on the highest seven features in the range ∼2800-4700m. Remnants of the four surfaces at more than 3800m, which were formed during the interval ∼18-12Ma, are found only south of latitude 6°- 6.5°S. The Miocene metallogenic belt associated with the Western Cordillera terminates abruptly at that same latitude. The area north of ∼6°S. does not have any features higher than ∼3500m, which is interpreted as indicating a later initiation of uplift. It also lacks any sign of magmatic activity. On the basis of these factors the Central Andes are considered to terminate at ∼6°S, the ranges to the north being assigned to the Northern Andes. Once episodic uplift was initiated in the area north of 6°S it continued at the same rhythm as in the region to the south. Moreover, there was no apparent change in the pattern of episodic uplift when the normal subduction regime changed to a flat slab regime at ∼11Ma, probably as a result of the subduction of the Inca Plateau. The distribution of the erosion surfaces indicates that episodic uplift affected the whole of the Andean block in northern Peru. It appears that the individual episodes occurred simultaneously and produced the same amount of uplift over the whole width of the cordilleras. Moreover, there is no sign of any interruption in the process, implying continuous orogeny from the Middle Miocene onwards.
{"title":"Neogene erosion surfaces and the Andean Uplift in Northern Peru","authors":"J. J. Wilson","doi":"10.1144/jgs2023-089","DOIUrl":"https://doi.org/10.1144/jgs2023-089","url":null,"abstract":"The Andean flank in central Peru is characterized by stepped profiles involving up to 20 surfaces and pediments resulting from multiple episodes of uplift and erosion. The study area exhibits the same sequence of surfaces and pediments. Moreover, the erosional features are also recognised in the Eastern Cordillera in northern Peru. This report focuses on the highest seven features in the range ∼2800-4700m. Remnants of the four surfaces at more than 3800m, which were formed during the interval ∼18-12Ma, are found only south of latitude 6°- 6.5°S. The Miocene metallogenic belt associated with the Western Cordillera terminates abruptly at that same latitude. The area north of ∼6°S. does not have any features higher than ∼3500m, which is interpreted as indicating a later initiation of uplift. It also lacks any sign of magmatic activity. On the basis of these factors the Central Andes are considered to terminate at ∼6°S, the ranges to the north being assigned to the Northern Andes. Once episodic uplift was initiated in the area north of 6°S it continued at the same rhythm as in the region to the south. Moreover, there was no apparent change in the pattern of episodic uplift when the normal subduction regime changed to a flat slab regime at ∼11Ma, probably as a result of the subduction of the Inca Plateau. The distribution of the erosion surfaces indicates that episodic uplift affected the whole of the Andean block in northern Peru. It appears that the individual episodes occurred simultaneously and produced the same amount of uplift over the whole width of the cordilleras. Moreover, there is no sign of any interruption in the process, implying continuous orogeny from the Middle Miocene onwards.","PeriodicalId":507891,"journal":{"name":"Journal of the Geological Society","volume":"36 10","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-04-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140701640","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
J. Ormazabal, S. Principi, F. Palma, D. Bran, J. Isola, F. Esteban, A. Tassone
The North Scotia Ridge is the offshore morphostructural expression of the left-lateral transcurrent South America-Scotia Plate Boundary. Several blocks compose the ridge, including the scarcely studied Namuncurá Bank (NB, also known as Burdwood). We present the first detailed study of active structures on the seafloor of the western NB from a database of 3D and 2D seismic data, multibeam bathymetry, and sub-bottom profiles. This work assesses the architecture, style of deformation and Cenozoic evolution of NB, where several groups of faults, and en echelon folding, affects the seabed and shallow sub-bottom. These features compound the northernmost structures associated with a releasing bend, fitting well with a left-lateral Riedel shear model oriented at N74°E, slightly rotated with respect to the present-day plate boundary stress regime. The current tectonic scenario started with a main deformational phase in the Neogene, partially distributed by the Malvinas Fold-Thrust Belt, while modern deformation continues to be conditioned by pre-existing structures. This study allows for a better understanding of the tectonics of the North Scotia Ridge, a morphostructure that influences the circulation of the Antarctic Circumpolar Current thus impacting the global climate.
北斯科舍海脊是左侧横贯南美-斯科舍板块边界的近海形态结构表现。该海脊由多个区块组成，其中包括鲜有研究的 Namuncurá Bank（NB，又称 Burdwood）。我们通过三维和二维地震数据数据库、多波束测深数据和海底剖面图，首次详细研究了 NB 西部海底的活动结构。这项工作评估了北部湾的结构、变形方式和新生代演化，北部湾的几组断层和梯状褶皱影响着海底和浅海底。这些特征复合了与释放弯曲相关的最北端结构，非常符合位于 N74°E 的左侧里德尔剪切模型，相对于当今板块边界应力机制略有旋转。目前的构造情况始于新近纪的一个主要变形阶段，马尔维纳斯褶皱-推力带是这一阶段的部分分布区，而现代变形继续受先前存在的构造的制约。这项研究有助于更好地了解北斯科舍海脊的构造，这一形态结构影响着南极环极洋流的环流，从而对全球气候产生影响。
{"title":"Neotectonics on the Namuncurá (Burdwood) Bank: Unveiling seafloor strike-slip processes along the North Scotia Ridge","authors":"J. Ormazabal, S. Principi, F. Palma, D. Bran, J. Isola, F. Esteban, A. Tassone","doi":"10.1144/jgs2023-215","DOIUrl":"https://doi.org/10.1144/jgs2023-215","url":null,"abstract":"\u0000 The North Scotia Ridge is the offshore morphostructural expression of the left-lateral transcurrent South America-Scotia Plate Boundary. Several blocks compose the ridge, including the scarcely studied Namuncurá Bank (NB, also known as Burdwood). We present the first detailed study of active structures on the seafloor of the western NB from a database of 3D and 2D seismic data, multibeam bathymetry, and sub-bottom profiles. This work assesses the architecture, style of deformation and Cenozoic evolution of NB, where several groups of faults, and\u0000 en echelon\u0000 folding, affects the seabed and shallow sub-bottom. These features compound the northernmost structures associated with a releasing bend, fitting well with a left-lateral Riedel shear model oriented at N74°E, slightly rotated with respect to the present-day plate boundary stress regime. The current tectonic scenario started with a main deformational phase in the Neogene, partially distributed by the Malvinas Fold-Thrust Belt, while modern deformation continues to be conditioned by pre-existing structures. This study allows for a better understanding of the tectonics of the North Scotia Ridge, a morphostructure that influences the circulation of the Antarctic Circumpolar Current thus impacting the global climate.\u0000","PeriodicalId":507891,"journal":{"name":"Journal of the Geological Society","volume":"309 2","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-04-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140703633","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
The formation and dynamics of granitoids in an intra-continental setting are crucial for understanding the architecture and evolution of continental crust. Here, we report geochronological, geochemical, and Sr-Nd-Hf isotopic data for newly discovered late Mesozoic granitic intrusions in the Tianshan belt, northwestern China. These granitoids are I-type granites derived from an igneous precursor and were emplaced during ∼145-132 Ma. They have positive ε Nd (t) values and young Nd model ages, together with relatively low Sr/Y ratios, indicating that they might have originated from partial melting of the juvenile lower crust. There is a prominent decoupling between zircon Hf and bulk rock Nd isotopes, which may have resulted from the early crystallization of Ti-rich minerals. These granitic intrusions also display subduction-related geochemical characteristics, which are likely inherited from the Paleozoic crustal sources that were metasomatized by subduction-related fluids. We conclude that these late Mesozoic granitoids were emplaced in an intra-continental setting, and were likely triggered by thermal relaxation due to crustal shortening and thickening. These data further imply that the Tianshan has changed into crustal reworking during the Mesozoic from its prominent crustal growth in the Paleozoic. Thematic collection: This article is part of the Mesozoic and Cenozoic tectonics, landscape and climate change collection available at: https://www.lyellcollection.org/topic/collections/mesozoic-and-cenozoic-tectonics-landscape-and-climate-change Supplementary material: https://doi.org/10.6084/m9.figshare.c.7167890
{"title":"First identification of Late Mesozoic intraplate magmatism in the Chinese North Tianshan: Implications for the orogenic architecture and crustal evolution","authors":"Fujun Wang, Zhiyuan He, Rongfeng Ge, Meng Luo, Bihai Zheng, Zhiyong Zhang, Rongsong Tian, Yuanyuan Cao, Wenbin Zhu","doi":"10.1144/jgs2023-176","DOIUrl":"https://doi.org/10.1144/jgs2023-176","url":null,"abstract":"\u0000 The formation and dynamics of granitoids in an intra-continental setting are crucial for understanding the architecture and evolution of continental crust. Here, we report geochronological, geochemical, and Sr-Nd-Hf isotopic data for newly discovered late Mesozoic granitic intrusions in the Tianshan belt, northwestern China. These granitoids are I-type granites derived from an igneous precursor and were emplaced during ∼145-132 Ma. They have positive\u0000 \u0000 \u0000 ε\u0000 \u0000 \u0000 Nd\u0000 (t) values and young Nd model ages, together with relatively low Sr/Y ratios, indicating that they might have originated from partial melting of the juvenile lower crust. There is a prominent decoupling between zircon Hf and bulk rock Nd isotopes, which may have resulted from the early crystallization of Ti-rich minerals. These granitic intrusions also display subduction-related geochemical characteristics, which are likely inherited from the Paleozoic crustal sources that were metasomatized by subduction-related fluids. We conclude that these late Mesozoic granitoids were emplaced in an intra-continental setting, and were likely triggered by thermal relaxation due to crustal shortening and thickening. These data further imply that the Tianshan has changed into crustal reworking during the Mesozoic from its prominent crustal growth in the Paleozoic.\u0000 \u0000 \u0000 Thematic collection:\u0000 This article is part of the Mesozoic and Cenozoic tectonics, landscape and climate change collection available at:\u0000 https://www.lyellcollection.org/topic/collections/mesozoic-and-cenozoic-tectonics-landscape-and-climate-change\u0000 \u0000 \u0000 Supplementary material:\u0000 https://doi.org/10.6084/m9.figshare.c.7167890\u0000","PeriodicalId":507891,"journal":{"name":"Journal of the Geological Society","volume":"246 3","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-04-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140720117","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Xinqian Wang, Chen Zhan, T. Algeo, Jun Shen, Zhanhong Liu
During the Late Ordovician Hirnantian Ice Age, the South China Craton experienced large changes in climate, eustasy, and environmental conditions, but their impact on the watermass architecture of the Yangtze Sea has not been thoroughly evaluated to date. Here, we reconstruct the salinity-redox structure of the Yangtze Sea based on five Upper Ordovician-lower Silurian shale successions representing a lateral transect, from a deep-water area of the Inner Yangtze Sea (IYS; Shuanghe section) across the shallow Hunan-Hubei Arch (Pengye, Jiaoye, and Qiliao sections) to the relatively deep-water Outer Yangtze Sea (OYS; Wangjiawan section). Carbon-isotope ( δ 13 C org ) profiles show that the Guanyinqiao Bed (recording peak Hirnantian glaciation) thins and is less completely preserved at sites on the flanks of the Hunan-Hubei Arch than in deeper-water areas to the SW and NE, reflecting bathymetric influences. Watermass salinities were mainly marine at Shuanghe and brackish at the other four study sites, with little variation between Interval I (pre-glaciation), Interval II (Hirnantian glaciation), and Interval III (post-glaciation). Redox proxies document mainly euxinia at Shuanghe and Wangjiawan and suboxia at the other sites during Interval I, with shifts toward more reducing (mostly euxinic) conditions at most sites during Intervals II and III, which shows that all study sections were deep enough to remain below the redoxcline during the glacio-eustatic lowstand. Two features of the Shuanghe section mark it as being unusual: it alone exhibits fully marine salinities, implying greater proximity to the open ocean than for the other four sites, and it exhibits an especially large shift toward more reducing conditions during Interval III (i.e., the post-Hirnantian transgression), implying greater water depths. These features are difficult to reconcile with the standard palaeogeographic model for the Ordovician-Silurian South China Craton, which is characterized by a geographically enclosed and restricted IYS and a more-open OYS, arguing instead for the SW end of the IYS having been connected to the global ocean and the OYS having been a restricted oceanic cul-de-sac. A review of sedimentologic and facies data for the IYS region suggests that our re-interpretation of the Ordovician-Silurian palaeogeography of the South China Craton is viable, although further vetting of this hypothesis will be needed. 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.7170648
在晚奥陶世希尔南天冰期，华南克拉通地区经历了气候、温差和环境条件的巨大变化，但这些变化对长江海水体结构的影响迄今尚未得到全面评估。在此，我们基于五个上奥陶世-下志留纪页岩演替重建了长江海的盐度-氧化还原结构，这五个页岩演替代表了一个横向剖面，从长江内海（IYS；双河剖面）的深水区穿过湘沪拱浅水区（彭野、焦野和祁辽剖面）到相对深水的长江外海（OYS；王家湾剖面）。碳同位素（δ 13 C org）剖面显示，与西南和东北深水区相比，湘湖北拱两侧的观音桥海床（记录了希南特冰川作用的高峰期）变薄，且保存不够完整，这反映了水深的影响。双河的水体盐度主要是海洋性的，而其他四个研究地点的水体盐度则是咸的，在第一期（冰期前）、第二期（平南天冰期）和第三期（冰期后）之间几乎没有变化。氧化还原代用指标表明，在第一期期间，双河和王家湾主要处于氧化还原状态，其他地点则处于亚氧化状态，而在第二期和第三期期间，大多数地点的氧化还原状态（主要是氧化还原状态）有所改变，这表明在冰期-极低位期间，所有研究断面的深度足以保持在氧化还原线以下。双河断面有两个不同寻常的特征：与其他四个地点相比，双河断面显示出完全的海洋盐度，这意味着双河断面更接近于公海；双河断面在第三期（即后希尔南天横断期）向更高的还原条件转变的幅度特别大，这意味着双河断面的水深更大。这些特征很难与奥陶纪-志留纪华南克拉通的标准古地理模型相协调，后者的特征是一个地理上封闭和受限的IYS和一个更开放的OYS，而IYS的西南端与全球海洋相连，OYS则是一个受限的大洋死胡同。对IYS地区沉积学和岩相学数据的回顾表明，我们对华南克拉通奥陶纪-志留纪古地理的重新解释是可行的，尽管这一假说还需要进一步验证。 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，可从以下网址获取： 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.7170648
{"title":"Watermass architecture of the Ordovician-Silurian Yangtze Sea (South China) and its palaeogeographic implications","authors":"Xinqian Wang, Chen Zhan, T. Algeo, Jun Shen, Zhanhong Liu","doi":"10.1144/jgs2023-024","DOIUrl":"https://doi.org/10.1144/jgs2023-024","url":null,"abstract":"\u0000 During the Late Ordovician Hirnantian Ice Age, the South China Craton experienced large changes in climate, eustasy, and environmental conditions, but their impact on the watermass architecture of the Yangtze Sea has not been thoroughly evaluated to date. Here, we reconstruct the salinity-redox structure of the Yangtze Sea based on five Upper Ordovician-lower Silurian shale successions representing a lateral transect, from a deep-water area of the Inner Yangtze Sea (IYS; Shuanghe section) across the shallow Hunan-Hubei Arch (Pengye, Jiaoye, and Qiliao sections) to the relatively deep-water Outer Yangtze Sea (OYS; Wangjiawan section). Carbon-isotope (\u0000 \u0000 \u0000 δ\u0000 \u0000 \u0000 13\u0000 C\u0000 org\u0000 ) profiles show that the Guanyinqiao Bed (recording peak Hirnantian glaciation) thins and is less completely preserved at sites on the flanks of the Hunan-Hubei Arch than in deeper-water areas to the SW and NE, reflecting bathymetric influences. Watermass salinities were mainly marine at Shuanghe and brackish at the other four study sites, with little variation between Interval I (pre-glaciation), Interval II (Hirnantian glaciation), and Interval III (post-glaciation). Redox proxies document mainly euxinia at Shuanghe and Wangjiawan and suboxia at the other sites during Interval I, with shifts toward more reducing (mostly euxinic) conditions at most sites during Intervals II and III, which shows that all study sections were deep enough to remain below the redoxcline during the glacio-eustatic lowstand. Two features of the Shuanghe section mark it as being unusual: it alone exhibits fully marine salinities, implying greater proximity to the open ocean than for the other four sites, and it exhibits an especially large shift toward more reducing conditions during Interval III (i.e., the post-Hirnantian transgression), implying greater water depths. These features are difficult to reconcile with the standard palaeogeographic model for the Ordovician-Silurian South China Craton, which is characterized by a geographically enclosed and restricted IYS and a more-open OYS, arguing instead for the SW end of the IYS having been connected to the global ocean and the OYS having been a restricted oceanic cul-de-sac. A review of sedimentologic and facies data for the IYS region suggests that our re-interpretation of the Ordovician-Silurian palaeogeography of the South China Craton is viable, although further vetting of this hypothesis will be needed.\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.7170648\u0000","PeriodicalId":507891,"journal":{"name":"Journal of the Geological Society","volume":"67 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-04-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140720304","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Zircon is a common mineral in nature that survives varied pressure and temperature conditions in the subduction process. It has excellent ability to reveal progressive metamorphic history. Hence it is useful in reconstruct the subduction tectonics in the collisional orogenic belts. In the Tso Morari Gneiss of Indus Suture Zone, Himalaya, eclogite boudins have registered imprint of subduction related ultrahigh-pressure (UHP) metamorphism, this imprint is however missing in the host gneisses. To search the missing link, zircons of the gneisses are studied. The zircons overgrowth and the numerous mineral inclusions indicating, metamorphic responses of the gneisses. The Raman spectra of minerals show, cores of the zircon consist of apatite and quartz, and in the surrounding overgrowth preserves quartz-coesite, c-polymorphs, and other metamorphic minerals. The distribution pattern of these minerals in the zircons is consistent with the Th/U ratios ranging 0.30 to 0.01 recognizes inner magmatic and outer metamorphic domains. The U-Pb ages from inner magmatic, at c. 500 Ma, and from outer metamorphic growth at c.45-42 Ma, suggests the former is the protolith age and later is metamorphic ages of the gneisses. The tectonic interpretation reveals, the subduction of Indian felsic crust to UHP depth (>100km) at c. 45 Ma. Thematic collection: This article is part of the Mesozoic and Cenozoic tectonics, landscape and climate change collection available at: https://www.lyellcollection.org/topic/collections/mesozoic-and-cenozoic-tectonics-landscape-and-climate-change
{"title":"Tracing remnant of subducted Indian felsic crust: Insight from zircon studies","authors":"B. Mukherjee, Tania Saha","doi":"10.1144/jgs2023-116","DOIUrl":"https://doi.org/10.1144/jgs2023-116","url":null,"abstract":"Zircon is a common mineral in nature that survives varied pressure and temperature conditions in the subduction process. It has excellent ability to reveal progressive metamorphic history. Hence it is useful in reconstruct the subduction tectonics in the collisional orogenic belts. In the Tso Morari Gneiss of Indus Suture Zone, Himalaya, eclogite boudins have registered imprint of subduction related ultrahigh-pressure (UHP) metamorphism, this imprint is however missing in the host gneisses. To search the missing link, zircons of the gneisses are studied. The zircons overgrowth and the numerous mineral inclusions indicating, metamorphic responses of the gneisses. The Raman spectra of minerals show, cores of the zircon consist of apatite and quartz, and in the surrounding overgrowth preserves quartz-coesite, c-polymorphs, and other metamorphic minerals. The distribution pattern of these minerals in the zircons is consistent with the Th/U ratios ranging 0.30 to 0.01 recognizes inner magmatic and outer metamorphic domains. The U-Pb ages from inner magmatic, at c. 500 Ma, and from outer metamorphic growth at c.45-42 Ma, suggests the former is the protolith age and later is metamorphic ages of the gneisses. The tectonic interpretation reveals, the subduction of Indian felsic crust to UHP depth (>100km) at c. 45 Ma.\u0000 \u0000 Thematic collection:\u0000 This article is part of the Mesozoic and Cenozoic tectonics, landscape and climate change collection available at:\u0000 https://www.lyellcollection.org/topic/collections/mesozoic-and-cenozoic-tectonics-landscape-and-climate-change\u0000","PeriodicalId":507891,"journal":{"name":"Journal of the Geological Society","volume":"552 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-04-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140719282","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
P. Clift, Yifan Du, M. Mohtadi, Katharina Pahnke, Mika Sutorius, Philipp Böning
Arc-continent collision is a fundamental stage in the plate tectonic cycle that allows the continental crust to grow and can influence global climate through chemical weathering. Collision between Australia and the oceanic North Coast Range-New Britain Arc began in the Middle Miocene resulting in uplift of the modern New Guinea Highlands. The temporal evolution of this collision and its erosional and weathering impacts is reconstructed here using sedimentary archives from the Gulf of Papua. Sr and Nd isotopes show dominant erosion from igneous arc-ophiolite crust, accounting for ∼40−70% of the total flux in the Early Miocene, and rising to ∼80−90% at 8 Ma, before falling again to 72−83% by the present day. Greater erosion from Australia-derived units accelerated in the Pliocene, like the classic Taiwan collision but with greater erosion from arc rather than continental units. Chemical alteration of the sediment increased through time, especially since ∼5 Ma, consistent with increasing kaolinite indicative of more tropical weathering. Erosion was focused in the high topography where mafic arc units are preferentially exposed. Comparison of sediment with bedrock compositions implies that the source terrains have been more efficient at removing CO 2 from the atmosphere compared to Himalayan drainages. Supplementary material: https://doi.org/10.6084/m9.figshare.c.7168147
弧-大陆碰撞是板块构造循环的一个基本阶段，它使大陆地壳得以生长，并通过化学风化作用影响全球气候。澳大利亚与大洋性北海岸山脉-新不列颠弧之间的碰撞始于中新世，导致现代新几内亚高地的隆起。本文利用巴布亚湾的沉积档案重建了这一碰撞的时间演变及其侵蚀和风化影响。锶和钕同位素显示，火成岩弧鲕粒壳的侵蚀占主导地位，在早中新世占总通量的40-70%，在8Ma时上升到80-90%，到现代又下降到72-83%。在上新世，源于澳大利亚的单元加速了侵蚀，就像典型的台湾碰撞一样，但弧形单元而不是大陆单元的侵蚀更大。沉积物的化学蚀变随着时间的推移而加剧，尤其是自 5 Ma 以来，与表明热带风化加剧的高岭石增加相一致。侵蚀主要集中在地势较高的地方，那里的岩浆弧单元更容易暴露出来。沉积物与基岩成分的比较表明，与喜马拉雅山脉的排水沟相比，源地地形从大气中清除二氧化碳的效率更高。 补充材料：https://doi.org/10.6084/m9.figshare.c.7168147
{"title":"The erosional and weathering response to arc-continent collision in New Guinea","authors":"P. Clift, Yifan Du, M. Mohtadi, Katharina Pahnke, Mika Sutorius, Philipp Böning","doi":"10.1144/jgs2023-207","DOIUrl":"https://doi.org/10.1144/jgs2023-207","url":null,"abstract":"\u0000 Arc-continent collision is a fundamental stage in the plate tectonic cycle that allows the continental crust to grow and can influence global climate through chemical weathering. Collision between Australia and the oceanic North Coast Range-New Britain Arc began in the Middle Miocene resulting in uplift of the modern New Guinea Highlands. The temporal evolution of this collision and its erosional and weathering impacts is reconstructed here using sedimentary archives from the Gulf of Papua. Sr and Nd isotopes show dominant erosion from igneous arc-ophiolite crust, accounting for ∼40−70% of the total flux in the Early Miocene, and rising to ∼80−90% at 8 Ma, before falling again to 72−83% by the present day. Greater erosion from Australia-derived units accelerated in the Pliocene, like the classic Taiwan collision but with greater erosion from arc rather than continental units. Chemical alteration of the sediment increased through time, especially since ∼5 Ma, consistent with increasing kaolinite indicative of more tropical weathering. Erosion was focused in the high topography where mafic arc units are preferentially exposed. Comparison of sediment with bedrock compositions implies that the source terrains have been more efficient at removing CO\u0000 2\u0000 from the atmosphere compared to Himalayan drainages.\u0000 \u0000 \u0000 Supplementary material:\u0000 https://doi.org/10.6084/m9.figshare.c.7168147\u0000","PeriodicalId":507891,"journal":{"name":"Journal of the Geological Society","volume":"135 4","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-04-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140725337","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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