Lying at the large-scale tectonic boundary between the Yukon Tanana and northern extremity of the Stikinia and Quesnelia terranes, mafic eruptions have occurred over the past 4 million years in the Fort Selkirk area. Eruptions have included effusive (lava), explosive activity, and subglacial and subaqueous eruptions that produced hyaloclastite complexes. Eruptions have dammed or disrupted Yukon River at least five times. These volcanic rocks and interstratified sediments are collectively referred to as the Fort Selkirk Volcanic Group. Eruptions occurred from seven centers with activity progressively moving north. An explanation for the northern migration of volcanism is elusive at present.
{"title":"Eruptive History of the Fort Selkirk Area, Central Yukon","authors":"Lionel L. Jackson, C. Huscroft","doi":"10.1139/cjes-2022-0124","DOIUrl":"https://doi.org/10.1139/cjes-2022-0124","url":null,"abstract":"Lying at the large-scale tectonic boundary between the Yukon Tanana and northern extremity of the Stikinia and Quesnelia terranes, mafic eruptions have occurred over the past 4 million years in the Fort Selkirk area. Eruptions have included effusive (lava), explosive activity, and subglacial and subaqueous eruptions that produced hyaloclastite complexes. Eruptions have dammed or disrupted Yukon River at least five times. These volcanic rocks and interstratified sediments are collectively referred to as the Fort Selkirk Volcanic Group. Eruptions occurred from seven centers with activity progressively moving north. An explanation for the northern migration of volcanism is elusive at present.","PeriodicalId":9567,"journal":{"name":"Canadian Journal of Earth Sciences","volume":"22 1","pages":""},"PeriodicalIF":1.4,"publicationDate":"2023-04-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"74580410","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
The Erie Interstade is generally accepted to have been a relatively warm period associated with retreat of the Laurentian ice sheet (LIS) into the Ontario basin, followed by a readvance to the Valley Heads ice front in central New York. Recent investigations in the Cayuga basin indicate that this ice front retreated only to the Ithaca area during the Erie Interstade. In the Cayuga trough Erie lacustrine strata underlie Valley Heads deposits. Plant assemblages in these strata indicate a sub-arctic environment. Erie deposits also occur in the Fall Creek Valley, where a varved sequence below Valley Heads till and above Nissouri till indicate deposition close to a retreating ice front. Remanent magnetic declination in the varves, best correlated with lower Newport beds of the Middleville fm in the Mohawk Valley, suggest an age of 17.7±0.1 ka cal for the peak of the Erie retreat. Retreat only to the Ithaca area is based on lack of Erie deposits north of Ithaca, oscillation of the ice front around the south end of Cayuga Lake and the lack of a fluvial interval in the Cayuga trough that would have marked retreat into the Ontario basin. Ice core data from Greenland and sea level studies demonstrate that the Erie Interstade was neither a warm period nor a time of significant sea level rise. The Erie Interstade retreat/Valley Heads readvance appears instead to represent a minor reversal in the general, slow ice front retreat from the Last Glacial Maximum ( LGM).
伊利冰川期被普遍认为是一个相对温暖的时期，与劳伦斯冰盖(LIS)退缩到安大略盆地有关，随后进入纽约中部的谷头冰锋。最近对卡尤加盆地的调查表明，在伊利间期，这一冰锋只退到了伊萨卡地区。在卡尤加槽伊利湖地层下的谷头矿床。这些地层中的植物组合表明亚北极环境。伊利沉积物也出现在福尔克里克山谷，在那里，山谷头以下和密苏里州上方有一个弯曲的序列，表明沉积物靠近退缩的冰锋。与莫霍克山谷米德尔维尔地层下部纽波特层最相关的残余磁偏角表明，伊利撤退的峰值年龄为17.7±0.1 ka cal。只退到伊萨卡地区是基于伊萨卡北部缺乏伊利沉积物，卡尤加湖南端周围的冰阵振荡，以及卡尤加海槽中缺乏标志着退到安大略盆地的河流间隔。来自格陵兰岛的冰芯数据和海平面研究表明，Erie interstage既不是一个温暖期，也不是一个海平面显著上升的时期。Erie Interstade退缩/Valley Heads前进似乎代表了末次盛冰期(LGM)冰锋总体缓慢退缩的一个小逆转。
{"title":"A REASSESSMENT OF THE ERIE INTERSTADE FROM FIELD WORK IN THE CAYUGA BASIN, CENTRAL NEW YORK","authors":"D. Karig","doi":"10.1139/cjes-2022-0104","DOIUrl":"https://doi.org/10.1139/cjes-2022-0104","url":null,"abstract":"The Erie Interstade is generally accepted to have been a relatively warm period associated with retreat of the Laurentian ice sheet (LIS) into the Ontario basin, followed by a readvance to the Valley Heads ice front in central New York. Recent investigations in the Cayuga basin indicate that this ice front retreated only to the Ithaca area during the Erie Interstade. In the Cayuga trough Erie lacustrine strata underlie Valley Heads deposits. Plant assemblages in these strata indicate a sub-arctic environment. Erie deposits also occur in the Fall Creek Valley, where a varved sequence below Valley Heads till and above Nissouri till indicate deposition close to a retreating ice front. Remanent magnetic declination in the varves, best correlated with lower Newport beds of the Middleville fm in the Mohawk Valley, suggest an age of 17.7±0.1 ka cal for the peak of the Erie retreat. Retreat only to the Ithaca area is based on lack of Erie deposits north of Ithaca, oscillation of the ice front around the south end of Cayuga Lake and the lack of a fluvial interval in the Cayuga trough that would have marked retreat into the Ontario basin. Ice core data from Greenland and sea level studies demonstrate that the Erie Interstade was neither a warm period nor a time of significant sea level rise. The Erie Interstade retreat/Valley Heads readvance appears instead to represent a minor reversal in the general, slow ice front retreat from the Last Glacial Maximum ( LGM).","PeriodicalId":9567,"journal":{"name":"Canadian Journal of Earth Sciences","volume":"1 3","pages":""},"PeriodicalIF":1.4,"publicationDate":"2023-04-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"72547802","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Ali Yaghoubi, Catherine J. Hickson, Yuri Leonenko, Maurice B. Dusseault
{"title":"Correction: Probabilistic assessment of induced seismicity at the Alberta No. 1 geothermal project site","authors":"Ali Yaghoubi, Catherine J. Hickson, Yuri Leonenko, Maurice B. Dusseault","doi":"10.1139/cjes-2023-0028","DOIUrl":"https://doi.org/10.1139/cjes-2023-0028","url":null,"abstract":"","PeriodicalId":9567,"journal":{"name":"Canadian Journal of Earth Sciences","volume":"57 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-04-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135117499","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
R. Berman, J. Cutts, W. Davis, A. Camacho, M. Sanborn-Barrie, M. Smit
Petrological modeling and geochronology (Lu-Hf garnet, U-Pb monazite, zircon and titanite) for seven mid-amphibolite to granulite-facies metamorphic rocks in the Thelon tectonic zone (Ttz) provide new insights into its orogenc evolution. A Grt-Sp-Sil diatexite records 2.01-2.00 Ga garnet and monazite growth during >830oC contact metamorphism associated with voluminous convergent margin plutonism. The most widespread, 1.96–1.90 Ga metamorphism is associated with clockwise P-T paths, indicating it was driven by crustal thickening. Earlier (1.96–1.92 Ga) and lower temperature (630 -730 oC; 6-8 kbar) metamorphism in the eastern Slave craton contrast with ~860 oC (7.5 kbar), 1.91–1.90 Ga diatexites in the central, Paleoproterozoic plutonic rock-dominated, core of the Ttz. These differences are interpreted to reflect lower versus upper plate settings, respectively. A contribution of mantle heat is suggested by the counter-clockwise P-T path and 885 oC (5.7 kbar) conditions recorded by diatexite associated with c. 1.9 Ga peraluminous leucogranite that dominates a corridor along the Ttz – Rae craton boundary. A tectonic model is proposed wherein the Ttz evolved at an accretionary margin after rifting of Ttz microcontinent (mTtz) off the Rae craton at c. 2.2–2.1 Ga. Voluminous plutonism at 2.01 – 1.98 Ga formed via east-dipping subduction under mTtz. Following 1.97 Ga collision of the Slave craton and mTtz, west-dipping subduction generated 1.96–1.95 Ga plutonism in the composite mTtz-Slave upper plate. Collision of Rae craton at 1.95–1.94 Ga led to crustal thickening, widespread 1.91-1.90 Ga high-grade metamorphism and extensive crustal melting in the central Ttz.
{"title":"The tectonic evolution of Thelon tectonic zone, Canada: a new model based on petrological modeling linked with Lu-Hf garnet and U-Pb accessory mineral geochronology","authors":"R. Berman, J. Cutts, W. Davis, A. Camacho, M. Sanborn-Barrie, M. Smit","doi":"10.1139/cjes-2022-0147","DOIUrl":"https://doi.org/10.1139/cjes-2022-0147","url":null,"abstract":"Petrological modeling and geochronology (Lu-Hf garnet, U-Pb monazite, zircon and titanite) for seven mid-amphibolite to granulite-facies metamorphic rocks in the Thelon tectonic zone (Ttz) provide new insights into its orogenc evolution. A Grt-Sp-Sil diatexite records 2.01-2.00 Ga garnet and monazite growth during >830oC contact metamorphism associated with voluminous convergent margin plutonism. The most widespread, 1.96–1.90 Ga metamorphism is associated with clockwise P-T paths, indicating it was driven by crustal thickening. Earlier (1.96–1.92 Ga) and lower temperature (630 -730 oC; 6-8 kbar) metamorphism in the eastern Slave craton contrast with ~860 oC (7.5 kbar), 1.91–1.90 Ga diatexites in the central, Paleoproterozoic plutonic rock-dominated, core of the Ttz. These differences are interpreted to reflect lower versus upper plate settings, respectively. A contribution of mantle heat is suggested by the counter-clockwise P-T path and 885 oC (5.7 kbar) conditions recorded by diatexite associated with c. 1.9 Ga peraluminous leucogranite that dominates a corridor along the Ttz – Rae craton boundary. A tectonic model is proposed wherein the Ttz evolved at an accretionary margin after rifting of Ttz microcontinent (mTtz) off the Rae craton at c. 2.2–2.1 Ga. Voluminous plutonism at 2.01 – 1.98 Ga formed via east-dipping subduction under mTtz. Following 1.97 Ga collision of the Slave craton and mTtz, west-dipping subduction generated 1.96–1.95 Ga plutonism in the composite mTtz-Slave upper plate. Collision of Rae craton at 1.95–1.94 Ga led to crustal thickening, widespread 1.91-1.90 Ga high-grade metamorphism and extensive crustal melting in the central Ttz.","PeriodicalId":9567,"journal":{"name":"Canadian Journal of Earth Sciences","volume":"1 1","pages":""},"PeriodicalIF":1.4,"publicationDate":"2023-03-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"85097011","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
The strata exposed near Pasley Bay on south-western Boothia Peninsula were previously named the Franklin Strait Formation, spanning Lower Ordovician through early Silurian and dissected by two disconformities. The interpretation of the age and correlation were based on limited fossil evidence. New detailed field investigations and sampling at the Pasley Bay section resulted in a finding of over 1000 identifiable conodont specimens representing 37 species among 28 genera. Five Lower Ordovician and four Upper Ordovician North American standard conodont Zone-equivalent faunas are documented from the section, namely: Lower Ordovician Cordylodus angulatus, Rossodus manitouensis, Acodus deltatus/ Oneotodus costatus, Oepikodus communis, Reutterodus andinus, and Upper Ordovician Belodina confluens, Oulodus velicuspis, Oulodus robustus, and Amorphognathus ordovicicus Zone-equivalent faunas. These faunas enable a new understanding of the age and stratigraphic position of the Franklin Strait Formation: (1) it is now correlated to the Turner Cliffs (upper part of lower member and upper member), Ship Point, Thumb Mountain, Irene Bay, and Allen Bay (lower member) formations straddling Lower to upper Upper Ordovician with the Middle and lower Upper Ordovician missing; (2) it biostratigraphically overlaps with the simultaneously named Netsilik Formation for the strata containing the Cordylodus angulatus, Rossodus manitouensis, Acodus deltatus/Oneotodus costatus, and lower Oepikodus communis Zone-equivalent faunas, and lithostratigraphically for the upper part of lower member and upper member of the Turner Cliffs Formation and lower Ship Point Formation. This study also provides stratigraphic support for the tectonic model that advocates the Boothia Uplift to be a deep-seated, east-dipping thrust block. Additionally, the conodont Colour Alteration Index is used to estimate the increased heat effects close to the fault zones in the environs of the Boothia Uplift.
{"title":"Lower and Upper Ordovician conodont biostratigraphy and revised lithostratigraphy in the fault and fold zones of the Boothia Uplift, south-western Boothia Peninsula, Nunavut","authors":"Shunxin Zhang","doi":"10.1139/cjes-2022-0134","DOIUrl":"https://doi.org/10.1139/cjes-2022-0134","url":null,"abstract":"The strata exposed near Pasley Bay on south-western Boothia Peninsula were previously named the Franklin Strait Formation, spanning Lower Ordovician through early Silurian and dissected by two disconformities. The interpretation of the age and correlation were based on limited fossil evidence. New detailed field investigations and sampling at the Pasley Bay section resulted in a finding of over 1000 identifiable conodont specimens representing 37 species among 28 genera. Five Lower Ordovician and four Upper Ordovician North American standard conodont Zone-equivalent faunas are documented from the section, namely: Lower Ordovician Cordylodus angulatus, Rossodus manitouensis, Acodus deltatus/ Oneotodus costatus, Oepikodus communis, Reutterodus andinus, and Upper Ordovician Belodina confluens, Oulodus velicuspis, Oulodus robustus, and Amorphognathus ordovicicus Zone-equivalent faunas. These faunas enable a new understanding of the age and stratigraphic position of the Franklin Strait Formation: (1) it is now correlated to the Turner Cliffs (upper part of lower member and upper member), Ship Point, Thumb Mountain, Irene Bay, and Allen Bay (lower member) formations straddling Lower to upper Upper Ordovician with the Middle and lower Upper Ordovician missing; (2) it biostratigraphically overlaps with the simultaneously named Netsilik Formation for the strata containing the Cordylodus angulatus, Rossodus manitouensis, Acodus deltatus/Oneotodus costatus, and lower Oepikodus communis Zone-equivalent faunas, and lithostratigraphically for the upper part of lower member and upper member of the Turner Cliffs Formation and lower Ship Point Formation. This study also provides stratigraphic support for the tectonic model that advocates the Boothia Uplift to be a deep-seated, east-dipping thrust block. Additionally, the conodont Colour Alteration Index is used to estimate the increased heat effects close to the fault zones in the environs of the Boothia Uplift.","PeriodicalId":9567,"journal":{"name":"Canadian Journal of Earth Sciences","volume":"23 1","pages":""},"PeriodicalIF":1.4,"publicationDate":"2023-03-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"85266869","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
We have estimated the geochemical equilibration depth and temperature of the widespread Neogene alkaline basalts in the Cordillera of Alaska, NW Canada and in Mexico using geobarometry on bulk compositions that have been minimally differentiated in upward transit. The method has uncertainties of about ±10 km and < 70 oC. The regional averages of geochemical equilibration depth for 12 sites in Alaska vary from 50±10 to 84±2 km, somewhat broader than those from the Cordillera of western Canada, western USA, and Mexico. There are no associations of depth with terranes or geological provinces. The final equilibration depth of lavas with the surrounding mantle is concluded to be where partial melt percolating from greater depths ponds at the lithosphere-asthenosphere boundary (LAB) until it becomes gravitationally unstable and moves upward in conduits. The top of the low velocity zone from seismic receiver functions, taken to be the LAB in regions of Alaska where Neogene volcanism occurs, varies from 60 - 85 km, covering the range of geochemical equilibration depths of the alkaline lavas. A mean lava equilibration depth of 65 ±10 km occurs in 24 of 36 alkaline volcanic centers from Alaska to Mexico, and several other global locations, suggesting the LAB may be controlled to a first order by the change in H2O storage capacity and viscosity across the garnet-spinel peridotite phase change at this depth. The scatter and variation in equilibration depths and temperatures are a factor of two greater than the recognized uncertainties, and are not yet explained.
{"title":"Equilibration Depth and Temperature of Neogene Alkaline Lavas in the Cordillera of Alaska and Canada as a Constraint on the Lithosphere-Asthenosphere Boundary","authors":"D. Canil, R. Hyndman","doi":"10.1139/cjes-2023-0005","DOIUrl":"https://doi.org/10.1139/cjes-2023-0005","url":null,"abstract":"We have estimated the geochemical equilibration depth and temperature of the widespread Neogene alkaline basalts in the Cordillera of Alaska, NW Canada and in Mexico using geobarometry on bulk compositions that have been minimally differentiated in upward transit. The method has uncertainties of about ±10 km and < 70 oC. The regional averages of geochemical equilibration depth for 12 sites in Alaska vary from 50±10 to 84±2 km, somewhat broader than those from the Cordillera of western Canada, western USA, and Mexico. There are no associations of depth with terranes or geological provinces. The final equilibration depth of lavas with the surrounding mantle is concluded to be where partial melt percolating from greater depths ponds at the lithosphere-asthenosphere boundary (LAB) until it becomes gravitationally unstable and moves upward in conduits. The top of the low velocity zone from seismic receiver functions, taken to be the LAB in regions of Alaska where Neogene volcanism occurs, varies from 60 - 85 km, covering the range of geochemical equilibration depths of the alkaline lavas. A mean lava equilibration depth of 65 ±10 km occurs in 24 of 36 alkaline volcanic centers from Alaska to Mexico, and several other global locations, suggesting the LAB may be controlled to a first order by the change in H2O storage capacity and viscosity across the garnet-spinel peridotite phase change at this depth. The scatter and variation in equilibration depths and temperatures are a factor of two greater than the recognized uncertainties, and are not yet explained.","PeriodicalId":9567,"journal":{"name":"Canadian Journal of Earth Sciences","volume":"42 1","pages":""},"PeriodicalIF":1.4,"publicationDate":"2023-03-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"77819719","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
J. Bazarnik, K. Kośmińska, W. McClelland, J. Strauss, K. Piepjohn, S. Elvevold, G. Zielinski, J. Majka
Tectonic models for development of the Svalbard Caledonides depend on reliable assessment of the metamorphic evolution of the various basement provinces involved. The Mosselhalvøya Group (MG) and the Atomfjella Complex (AC) have previously been assigned to the Nordaustlandet and West Ny-Friesland terranes, respectively. New analytical data and petrographic observations indicate that both units experienced 2-stage metamorphism under similar pressure-temperature (P-T) conditions. Two stages of amphibolite facies metamorphism (M1 and M2) are clearly recorded by garnet and staurolite porphyroblast textures. The results of thermodynamic phase equilibrium modelling indicate that peak M2 metamorphism occurred at ~7-7.5 kbar and 590-600°C in both units. Zirconium-in-rutile trace element thermometry confirms the temperature estimates for M1 and M2 stages of metamorphism. Monazite chemical Th-U-Pb dates from the MG resolve a 2-stage garnet growth at 444 ± 7 Ma (M1) and 423 ± 6 Ma (M2). In contrast, monazite dated in the AC define a single age of 420 ± 4 Ma interpreted as M2 growth. We suggest M2 was coeval with early strike-slip motion along the Billefjorden Fault Zone, whereas M1 reflects initial tectonic burial of the studied units. The similarity in metamorphic history between the both units suggest that the boundary between them is a subordinate thrust fault within the Atomfjella thrust stack rather than a major boundary separating the Nordaustlandet and West Ny-Friesland terranes. The MG is included within West Ny-Friesland terrane and the tectonic boundary with the Nordaustlandet terrane is likely the Eolussletta Shear Zone.
斯瓦尔巴喀里多尼德发育的构造模式依赖于对所涉及的各个基底省的变质演化的可靠评估。Mosselhalvøya Group (MG)和Atomfjella Complex (AC)此前分别被分配到Nordaustlandet和West Ny-Friesland区块。新的分析资料和岩石学观察表明，两个单元在相似的压力-温度(P-T)条件下经历了2期变质作用。石榴石和橄榄石斑岩结构清楚地记录了角闪岩相变质作用的两个阶段(M1和M2)。热力学相平衡模拟结果表明，在~7 ~ 7.5 kbar和590 ~ 600℃的温度下，两个单元的M2变质作用均达到峰值。金红石中锆微量元素测温证实了变质作用M1和M2阶段的温度估计。单氮石化学Th-U-Pb数据来自MG，在444±7 Ma (M1)和423±6 Ma (M2)的两个阶段石榴石生长。相比之下，在AC中定年的独居石定义了420±4 Ma的单一年龄，解释为M2生长。我们认为M2与Billefjorden断裂带的早期走滑运动同时发生，而M1反映了研究单元的初始构造埋藏。两者变质史的相似性表明，它们之间的边界是阿托姆菲耶拉逆冲叠组内的次级逆冲断层，而不是分隔北达斯特兰地体和西纽弗里斯兰地体的主边界。MG被包括在西Ny-Friesland地体中，与nordastlandet地体的构造边界可能是Eolussletta剪切带。
{"title":"Reinterpretation of a major terrane boundary in the northern Svalbard Caledonides based on metamorphic fingerprinting of rocks in northern Spitsbergen","authors":"J. Bazarnik, K. Kośmińska, W. McClelland, J. Strauss, K. Piepjohn, S. Elvevold, G. Zielinski, J. Majka","doi":"10.1139/cjes-2022-0002","DOIUrl":"https://doi.org/10.1139/cjes-2022-0002","url":null,"abstract":"Tectonic models for development of the Svalbard Caledonides depend on reliable assessment of the metamorphic evolution of the various basement provinces involved. The Mosselhalvøya Group (MG) and the Atomfjella Complex (AC) have previously been assigned to the Nordaustlandet and West Ny-Friesland terranes, respectively. New analytical data and petrographic observations indicate that both units experienced 2-stage metamorphism under similar pressure-temperature (P-T) conditions. Two stages of amphibolite facies metamorphism (M1 and M2) are clearly recorded by garnet and staurolite porphyroblast textures. The results of thermodynamic phase equilibrium modelling indicate that peak M2 metamorphism occurred at ~7-7.5 kbar and 590-600°C in both units. Zirconium-in-rutile trace element thermometry confirms the temperature estimates for M1 and M2 stages of metamorphism. Monazite chemical Th-U-Pb dates from the MG resolve a 2-stage garnet growth at 444 ± 7 Ma (M1) and 423 ± 6 Ma (M2). In contrast, monazite dated in the AC define a single age of 420 ± 4 Ma interpreted as M2 growth. We suggest M2 was coeval with early strike-slip motion along the Billefjorden Fault Zone, whereas M1 reflects initial tectonic burial of the studied units. The similarity in metamorphic history between the both units suggest that the boundary between them is a subordinate thrust fault within the Atomfjella thrust stack rather than a major boundary separating the Nordaustlandet and West Ny-Friesland terranes. The MG is included within West Ny-Friesland terrane and the tectonic boundary with the Nordaustlandet terrane is likely the Eolussletta Shear Zone.","PeriodicalId":9567,"journal":{"name":"Canadian Journal of Earth Sciences","volume":"34 1","pages":""},"PeriodicalIF":1.4,"publicationDate":"2023-03-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"73351619","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Nikola Koglin, Solveig Estrada, A. Läufer, A. Ruppel, G. Jacques
The Caledonian and Ellesmerian orogenies were followed by extension and development of intracontinental rift basins since the late Paleozoic, as represented by the Sverdrup Basin along the Canadian Arctic Islands. The initial rifting was accompanied by pulses of volcanic activity during the Carboniferous and Permian. A new occurrence of mafic volcanic rocks, the “Taconite volcanics” (informal name), was discovered on northern Ellesmere Island between the head of Ayles Fiord and M’Clintock Inlet. The mainly alkali-picritic lavas are exposed within the central part of the Pearya Terrane as an outcrop in faulted contact with Upper Carboniferous red beds of the Canyon Fiord Formation. The contact to the Ordovician island-arc volcanic rocks of the Pearya Terrane is unclear. The outcrop is characterized by a small circular magnetic anomaly. Ar–Ar whole-rock geochronology on the volcanic rocks yielded an age of 290±19 Ma suggesting emplacement of the lavas during the early Permian. Whole rock geochemical analyses for eight samples revealed a geochemical affinity to ocean-island basalt (OIB) and indicate variable mixing of low-degree melts in the fields of garnet and spinel peridotite (~ 90-80 km depths). The involvement of a metasomatized subcontinental lithospheric mantle is indicated by high Pb, Nb and Ta concentrations. Geochemical differences (as enrichments in Ti, Nb, Zr, and the light REE) to the known Carboniferous and Permian spilitic altered basalt occurrences of northwestern Ellesmere and northern Axel Heiberg islands are probably based on differences in the mantle source. The Sr isotope ratios of the Taconite volcanics are primitive ((87Sr/86Sr)t: 0.7037–0.7042) and its Nd isotope ratios are moderately depleted (εNd(t): +2.20 – +2.85) in contrast to the enriched εNd(t) values of the Permian Esayoo formation.
{"title":"Alkaline picritic volcanism on northern Ellesmere Island associated with initial rifting of the Sverdrup Basin, Canadian Arctic","authors":"Nikola Koglin, Solveig Estrada, A. Läufer, A. Ruppel, G. Jacques","doi":"10.1139/cjes-2022-0106","DOIUrl":"https://doi.org/10.1139/cjes-2022-0106","url":null,"abstract":"The Caledonian and Ellesmerian orogenies were followed by extension and development of intracontinental rift basins since the late Paleozoic, as represented by the Sverdrup Basin along the Canadian Arctic Islands. The initial rifting was accompanied by pulses of volcanic activity during the Carboniferous and Permian. A new occurrence of mafic volcanic rocks, the “Taconite volcanics” (informal name), was discovered on northern Ellesmere Island between the head of Ayles Fiord and M’Clintock Inlet. The mainly alkali-picritic lavas are exposed within the central part of the Pearya Terrane as an outcrop in faulted contact with Upper Carboniferous red beds of the Canyon Fiord Formation. The contact to the Ordovician island-arc volcanic rocks of the Pearya Terrane is unclear. The outcrop is characterized by a small circular magnetic anomaly. Ar–Ar whole-rock geochronology on the volcanic rocks yielded an age of 290±19 Ma suggesting emplacement of the lavas during the early Permian. Whole rock geochemical analyses for eight samples revealed a geochemical affinity to ocean-island basalt (OIB) and indicate variable mixing of low-degree melts in the fields of garnet and spinel peridotite (~ 90-80 km depths). The involvement of a metasomatized subcontinental lithospheric mantle is indicated by high Pb, Nb and Ta concentrations. Geochemical differences (as enrichments in Ti, Nb, Zr, and the light REE) to the known Carboniferous and Permian spilitic altered basalt occurrences of northwestern Ellesmere and northern Axel Heiberg islands are probably based on differences in the mantle source. The Sr isotope ratios of the Taconite volcanics are primitive ((87Sr/86Sr)t: 0.7037–0.7042) and its Nd isotope ratios are moderately depleted (εNd(t): +2.20 – +2.85) in contrast to the enriched εNd(t) values of the Permian Esayoo formation.","PeriodicalId":9567,"journal":{"name":"Canadian Journal of Earth Sciences","volume":"86 1","pages":""},"PeriodicalIF":1.4,"publicationDate":"2023-03-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"83352730","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
The magmatic source of the Late Triassic granites in the East Kunlun Orogenic Belt (EKOB) is controversial, which restricts our understanding of crustal evolution and geodynamic evolution in the EKOB. Therefore, this study conducts zircon U‒Pb isotope dating, major and trace geochemical analysis, electron microprobe analysis (EMPA) of feldspar and amphibole, and in-situ zircon Hf isotope analysis of Xiangride host granites and their mafic microgranular enclaves (MMEs) in the EKOB to reveal their magmatic source and geodynamic implications. Zircon U‒Pb dating shows that the Xiangride host granites and the MMEs crystallized simultaneously at ca. 228-223 Ma. The MMEs show an igneous texture, finer grain size, higher crystallization temperature and water content, and lower oxygen fugacity than those of the host granite, suggesting that they were probably derived from two distinct primitive magmas. Therefore, the MMEs are considered the products of magma mixing between granitic and mafic magmas. The Xiangride host granites show high Sr/Y (42.0-73.1) and (La/Yb)N (12.7 to 30.7) ratios, showing affinity with adakites derived from a thickened lower crust. Combined with the indistinguishable εHf(t) values (−3.47 to +0.08) from the coeval mafic rocks, it is concluded that they are derived from partial melting of juvenile thickened lower crust. The adakitic features of the Xiangride host granites and widespread coeval granites indicate the existence of a thickened lower crust before 228 Ma and delamination of the lower lithosphere is likely the geodynamic process resulting in the postcollisional extension regime.
{"title":"Late Triassic granites with mafic microenclaves in the East Kunlun Orogenic Belt, northwestern China: Petrogenesis and implications for continental crust evolution and geodynamic evolution","authors":"Wei Xin, Zhengjiang Ding, Yuanku Meng, Jun-wei Bo, Liang Li, Guangzhou Mao","doi":"10.1139/cjes-2022-0132","DOIUrl":"https://doi.org/10.1139/cjes-2022-0132","url":null,"abstract":"The magmatic source of the Late Triassic granites in the East Kunlun Orogenic Belt (EKOB) is controversial, which restricts our understanding of crustal evolution and geodynamic evolution in the EKOB. Therefore, this study conducts zircon U‒Pb isotope dating, major and trace geochemical analysis, electron microprobe analysis (EMPA) of feldspar and amphibole, and in-situ zircon Hf isotope analysis of Xiangride host granites and their mafic microgranular enclaves (MMEs) in the EKOB to reveal their magmatic source and geodynamic implications. Zircon U‒Pb dating shows that the Xiangride host granites and the MMEs crystallized simultaneously at ca. 228-223 Ma. The MMEs show an igneous texture, finer grain size, higher crystallization temperature and water content, and lower oxygen fugacity than those of the host granite, suggesting that they were probably derived from two distinct primitive magmas. Therefore, the MMEs are considered the products of magma mixing between granitic and mafic magmas. The Xiangride host granites show high Sr/Y (42.0-73.1) and (La/Yb)N (12.7 to 30.7) ratios, showing affinity with adakites derived from a thickened lower crust. Combined with the indistinguishable εHf(t) values (−3.47 to +0.08) from the coeval mafic rocks, it is concluded that they are derived from partial melting of juvenile thickened lower crust. The adakitic features of the Xiangride host granites and widespread coeval granites indicate the existence of a thickened lower crust before 228 Ma and delamination of the lower lithosphere is likely the geodynamic process resulting in the postcollisional extension regime.","PeriodicalId":9567,"journal":{"name":"Canadian Journal of Earth Sciences","volume":"36 1","pages":""},"PeriodicalIF":1.4,"publicationDate":"2023-03-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"88170766","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Zhongjie Xu, Jintao Kong, N. Sun, Rihui Cheng, Li Zhang
Whole-rock geochemical and U–Pb–Hf isotopic data were used to investigate the age, petrogenesis, and tectonic setting of a suite of gabbro–diorite–monzonite–syenite rock exposed in Qinsai area, Hainan Island. Zircon U–Pb dating shows that the gabbro and monzonite, respectively, crystallized at 179.5 ± 2.7 and 179.0 ± 2.3 Ma. The suite consists of shoshonitic alkaline intrusive rocks with SiO2 content ranging from 41.7 to 63.4 wt%, with high U, K, and Pb and low Nb, Ta, and Ti. The suite is enriched in light rare earth elements relative to heavy rare earth elements. The gabbro has no obvious Eu anomaly but a positive Eu anomaly is evident in intermediate rocks. Zircon εHf( t) values are positive and have a wide variation (gabbro εHf( t) = +5.2 ± 8.2, monzonite εHf( t) = +4.7 ± 7.1). Gabbro and syenite are both likely derived from an enriched lithospheric mantle that was metasomatized by subduction fluids. Syenite evolved from the differentiation of gabbro, monzonite, and diorite. Collectively, these intrusive rocks formed in an extensional regime within an arc formed by subduction of the ancient Pacific plate beneath the Asian margin, which was accompanied by extensional thinning of the lithosphere.
{"title":"Petrogenesis and geodynamic significance of late Early Jurassic complex in Qinsai, Hainan Island, South China Sea","authors":"Zhongjie Xu, Jintao Kong, N. Sun, Rihui Cheng, Li Zhang","doi":"10.1139/cjes-2022-0097","DOIUrl":"https://doi.org/10.1139/cjes-2022-0097","url":null,"abstract":"Whole-rock geochemical and U–Pb–Hf isotopic data were used to investigate the age, petrogenesis, and tectonic setting of a suite of gabbro–diorite–monzonite–syenite rock exposed in Qinsai area, Hainan Island. Zircon U–Pb dating shows that the gabbro and monzonite, respectively, crystallized at 179.5 ± 2.7 and 179.0 ± 2.3 Ma. The suite consists of shoshonitic alkaline intrusive rocks with SiO2 content ranging from 41.7 to 63.4 wt%, with high U, K, and Pb and low Nb, Ta, and Ti. The suite is enriched in light rare earth elements relative to heavy rare earth elements. The gabbro has no obvious Eu anomaly but a positive Eu anomaly is evident in intermediate rocks. Zircon εHf( t) values are positive and have a wide variation (gabbro εHf( t) = +5.2 ± 8.2, monzonite εHf( t) = +4.7 ± 7.1). Gabbro and syenite are both likely derived from an enriched lithospheric mantle that was metasomatized by subduction fluids. Syenite evolved from the differentiation of gabbro, monzonite, and diorite. Collectively, these intrusive rocks formed in an extensional regime within an arc formed by subduction of the ancient Pacific plate beneath the Asian margin, which was accompanied by extensional thinning of the lithosphere.","PeriodicalId":9567,"journal":{"name":"Canadian Journal of Earth Sciences","volume":"77 1","pages":""},"PeriodicalIF":1.4,"publicationDate":"2023-03-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"85563154","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"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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