Several unconformities have been previously recognized in the Late Ordovician and early Silurian strata of southern Ontario. We examined the Georgian Bay, Queenston, Whirlpool, Manitoulin, Power Glen, Cabot Head formations and associated unconformities. Detailed sequence stratigraphic and chemostratigraphic analysis of Late Ordovician and early Silurian outcrops between Niagara, New York and Manitoulin Island, Ontario reveals new insights on the timing of the erosional unconformities and the Ordovician–Silurian boundary. We recognize three significant lowstand unconformities in this interval, which are referred to as the Cherokee, S1B and S2 unconformities. Additional small-scale surfaces are present but do not reflect any major change in sea level or pause in sedimentation. Using δ13Ccarb chemostratigraphy, biostratigraphy and sequence stratigraphy we tentatively correlate units and the mentioned unconformities from southern Ontario to other eastern North American sections of comparable age, showing how glacioeustasy had a widespread effect on the deposition and removal of strata in far-field, subtropical basins. The Cherokee Unconformity appears to be a composite erosion surface found across eastern North America that formed during the two or more episodes of glacioeustatic sea level fall in the early to middle Hirnantian. The overlying S1B and S2 unconformities can also be found across eastern North America and appear to be the result of glacioeustatic sea level fall occurring during the early Silurian. Additionally, these new insights on the timing of these erosional unconformities help better constrain the placement of the Ordovician/Silurian Boundary in Ontario.
{"title":"Analysis of the late Hirnantian and early Rhuddanian Unconformities of Southern Ontario: Evidence for Far Field Glacioeustatic Effects","authors":"C. Farnam, Carlton Brett","doi":"10.1139/cjes-2023-0041","DOIUrl":"https://doi.org/10.1139/cjes-2023-0041","url":null,"abstract":"Several unconformities have been previously recognized in the Late Ordovician and early Silurian strata of southern Ontario. We examined the Georgian Bay, Queenston, Whirlpool, Manitoulin, Power Glen, Cabot Head formations and associated unconformities. Detailed sequence stratigraphic and chemostratigraphic analysis of Late Ordovician and early Silurian outcrops between Niagara, New York and Manitoulin Island, Ontario reveals new insights on the timing of the erosional unconformities and the Ordovician–Silurian boundary. We recognize three significant lowstand unconformities in this interval, which are referred to as the Cherokee, S1B and S2 unconformities. Additional small-scale surfaces are present but do not reflect any major change in sea level or pause in sedimentation. Using δ13Ccarb chemostratigraphy, biostratigraphy and sequence stratigraphy we tentatively correlate units and the mentioned unconformities from southern Ontario to other eastern North American sections of comparable age, showing how glacioeustasy had a widespread effect on the deposition and removal of strata in far-field, subtropical basins. The Cherokee Unconformity appears to be a composite erosion surface found across eastern North America that formed during the two or more episodes of glacioeustatic sea level fall in the early to middle Hirnantian. The overlying S1B and S2 unconformities can also be found across eastern North America and appear to be the result of glacioeustatic sea level fall occurring during the early Silurian. Additionally, these new insights on the timing of these erosional unconformities help better constrain the placement of the Ordovician/Silurian Boundary in Ontario.","PeriodicalId":9567,"journal":{"name":"Canadian Journal of Earth Sciences","volume":null,"pages":null},"PeriodicalIF":1.4,"publicationDate":"2023-12-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"138994877","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 geometry and depth of the Moho beneath the Northern Canadian Cordillera and adjacent North American craton are modeled through the application of both cokriging and 3-D inversion of gravity data, integrated with sparse seismic depth estimates. Models require a regional density correction, with lower densities beneath the Cordillera than the craton. The lower densities are primarily attributed to a reduction in upper mantle density, ascribed to thermal expansion under regionally higher temperatures. The eastern margin of this low-density zone is broadly aligned with the rapid westward shallowing of the lithospheric-asthenospheric boundary. From the Cordillera to the North American craton, the Moho is broadly flat at a depth of ~32 km. A zone of deeper Moho (up to ~38 km) beneath the Mistry Creek embayment has a modeled mantle density that is of a colder cratonic signature, akin to the Mackenzie craton, and is interpreted to represent the preserved remnants of an old rift basin, that is a local focus of the diffuse seismicity. Southeast of the Fort Norman structure, seismicity is broadly focussed along the eastern edge of the low-density zone. Major structures such as the Denali and Tintina faults, with 100’s km of right-lateral displacement, separate zones of higher and lower upper mantle density, supporting the interpretation of their continuation into the upper mantle. Within the North American craton upper mantle density steadily increases towards the Great Bear magmatic zone, but increases more rapidly beneath the Slave craton in tangent with a deepening of the Moho.
{"title":"Exploring the Moho beneath the Northern Canadian Cordillera, with seismically constrained gravity inversion.","authors":"N. Hayward, Ernst M. Schetselaar","doi":"10.1139/cjes-2023-0121","DOIUrl":"https://doi.org/10.1139/cjes-2023-0121","url":null,"abstract":"The geometry and depth of the Moho beneath the Northern Canadian Cordillera and adjacent North American craton are modeled through the application of both cokriging and 3-D inversion of gravity data, integrated with sparse seismic depth estimates. Models require a regional density correction, with lower densities beneath the Cordillera than the craton. The lower densities are primarily attributed to a reduction in upper mantle density, ascribed to thermal expansion under regionally higher temperatures. The eastern margin of this low-density zone is broadly aligned with the rapid westward shallowing of the lithospheric-asthenospheric boundary. From the Cordillera to the North American craton, the Moho is broadly flat at a depth of ~32 km. A zone of deeper Moho (up to ~38 km) beneath the Mistry Creek embayment has a modeled mantle density that is of a colder cratonic signature, akin to the Mackenzie craton, and is interpreted to represent the preserved remnants of an old rift basin, that is a local focus of the diffuse seismicity. Southeast of the Fort Norman structure, seismicity is broadly focussed along the eastern edge of the low-density zone. Major structures such as the Denali and Tintina faults, with 100’s km of right-lateral displacement, separate zones of higher and lower upper mantle density, supporting the interpretation of their continuation into the upper mantle. Within the North American craton upper mantle density steadily increases towards the Great Bear magmatic zone, but increases more rapidly beneath the Slave craton in tangent with a deepening of the Moho.","PeriodicalId":9567,"journal":{"name":"Canadian Journal of Earth Sciences","volume":null,"pages":null},"PeriodicalIF":1.4,"publicationDate":"2023-12-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"138999061","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}
Albertosaurus sarcophagus specimens from the Danek Bonebed of Edmonton, Alberta, Canada were first described in 2014. Since this initial report, the University of Alberta’s annual field work has continued to yield additional tyrannosaurid material from the Danek Bonebed. In addition to nearly 200 tyrannosaurid shed teeth, five diagnostic tyrannosaurid cranial and postcranial bones have been identified to date. Three cranial bones were included in the initial description; here the newly uncovered left and right tyrannosaurid pubes (UALVP 52709 and UALVP 56262 respectively) are described and mapped in relation to the previously known material. The pubes can be confidently diagnosed as tyrannosaurid based on a posterior bow of the pubic shaft and further classified as albertosaurine by a weakly expanded obturator plate. A. sarcophagus is the only tyrannosaurid and albertosaurine known from the Horseshoe Canyon Formation, which allows for the material to be confidently assigned to this taxon. The left pubis (UALVP 52709) possesses multiple tooth traces on the medial surface that were likely made post-mortem as the medial surface of the pubis would have been deep within the body cavity of the animal and reactive (healing) bone is absent. Given the numerous large gouge-like tooth traces on the medial surface of the pubis and the abundance of cf. Albertosaurus teeth from the bonebed it seems likely that an A. sarcophagus took this opportunity to feed on a conspecific; providing evidence for the first case of cannibalism from an albertosaurine.
{"title":"ADDITIONAL ALBERTOSAURUS SARCOPHAGUS (TYRANNOSAURIDAE, ALBERTOSAURINAE) MATERIAL FROM THE DANEK BONEBED OF EDMONTON, ALBERTA, CANADA WITH EVIDENCE OF CANNIBALISM.","authors":"Colton Coppock, Philip J. Currie","doi":"10.1139/cjes-2023-0055","DOIUrl":"https://doi.org/10.1139/cjes-2023-0055","url":null,"abstract":"Albertosaurus sarcophagus specimens from the Danek Bonebed of Edmonton, Alberta, Canada were first described in 2014. Since this initial report, the University of Alberta’s annual field work has continued to yield additional tyrannosaurid material from the Danek Bonebed. In addition to nearly 200 tyrannosaurid shed teeth, five diagnostic tyrannosaurid cranial and postcranial bones have been identified to date. Three cranial bones were included in the initial description; here the newly uncovered left and right tyrannosaurid pubes (UALVP 52709 and UALVP 56262 respectively) are described and mapped in relation to the previously known material. The pubes can be confidently diagnosed as tyrannosaurid based on a posterior bow of the pubic shaft and further classified as albertosaurine by a weakly expanded obturator plate. A. sarcophagus is the only tyrannosaurid and albertosaurine known from the Horseshoe Canyon Formation, which allows for the material to be confidently assigned to this taxon. The left pubis (UALVP 52709) possesses multiple tooth traces on the medial surface that were likely made post-mortem as the medial surface of the pubis would have been deep within the body cavity of the animal and reactive (healing) bone is absent. Given the numerous large gouge-like tooth traces on the medial surface of the pubis and the abundance of cf. Albertosaurus teeth from the bonebed it seems likely that an A. sarcophagus took this opportunity to feed on a conspecific; providing evidence for the first case of cannibalism from an albertosaurine.","PeriodicalId":9567,"journal":{"name":"Canadian Journal of Earth Sciences","volume":null,"pages":null},"PeriodicalIF":1.4,"publicationDate":"2023-12-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139007819","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 Sandy Lake basin in northwestern Ontario is a potentially important area for insights into the late history of glacial Lake Agassiz because of its extensive glaciolacustrine deposits and well-preserved shoreline features of this geological episode. However, little information is available on its deglaciation history. Recent mapping shows the withdrawal of the ice from the basin center and subsequent deposition of extensive varved clay in the lake with an OSL-dated maximum age at 11.4 ± 0.9 ka. With its further recession, the ice constructed the Opasquia moraine on the northern rim of the basin sometime before the development on the moraine of the first major shoreline of the lake (The The Pas, inferred at 10.1 ka). Lowering of the lake level formed many strandlines on the moraine and elsewhere in the basin, which can be correlated with those in the main Agassiz basin based on projected water planes (The The Pas to Ponton). Radiocarbon dating on basal wood remains of surface peat in a former strait defined by the Ponton shoreline and a nearby site on the former lake floor indicates the abandonment of this shoreline and hence the withdrawal of Lake Agassiz from the Sandy Lake basin by 8.3 ± 0.1 cal ka (UOC-7883). The date although a minimum-limiting age provides the hitherto best possible age constraint for the Ponton-Kinojévis shorelines which many hypothesize represent one of the major lake levels during the final drainage of Lake Agassiz into Hudson Bay but have never been adequately dated before.
安大略省西北部的沙湖盆地是了解冰川湖阿加西晚期历史的一个潜在的重要区域，因为它具有广泛的冰川湖沉积和保存完好的这一地质事件的海岸线特征。然而，关于它的消冰历史的信息很少。最近的测绘显示，冰从盆地中心撤离，随后在湖中沉积了广泛的变质粘土，其最大年龄为11.4±0.9 ka。随着冰的进一步消退，冰在盆地北部边缘形成了奥帕斯基亚冰碛，时间比湖泊第一个主要海岸线的冰碛的形成要早(the Pas，推断于10.1 ka)。湖面的下降在冰碛上和盆地的其他地方形成了许多海岸线，这可以与阿加西斯主要盆地的预测水平面(the Pas to Ponton)相关联。在Ponton海岸线界定的前海峡和前湖底附近的一个地点，对表面泥炭的基生木材残骸进行放射性碳测年表明，该海岸线被放弃，因此阿加西湖从沙湖盆地撤出了8.3±0.1 cal ka (UOC-7883)。该日期虽然是一个最低限制年龄，但为ponton - kinojsamuvis海岸线提供了迄今为止最好的年龄限制，许多人假设它代表了阿加西湖最终流入哈德逊湾期间的主要湖泊之一，但以前从未有过充分的年代测定。
{"title":"Late history of glacial Lake Agassiz in northwestern Ontario, Canada: A case study in the Sandy Lake basin","authors":"Cunhai Gao","doi":"10.1139/cjes-2023-0014","DOIUrl":"https://doi.org/10.1139/cjes-2023-0014","url":null,"abstract":"The Sandy Lake basin in northwestern Ontario is a potentially important area for insights into the late history of glacial Lake Agassiz because of its extensive glaciolacustrine deposits and well-preserved shoreline features of this geological episode. However, little information is available on its deglaciation history. Recent mapping shows the withdrawal of the ice from the basin center and subsequent deposition of extensive varved clay in the lake with an OSL-dated maximum age at 11.4 ± 0.9 ka. With its further recession, the ice constructed the Opasquia moraine on the northern rim of the basin sometime before the development on the moraine of the first major shoreline of the lake (The The Pas, inferred at 10.1 ka). Lowering of the lake level formed many strandlines on the moraine and elsewhere in the basin, which can be correlated with those in the main Agassiz basin based on projected water planes (The The Pas to Ponton). Radiocarbon dating on basal wood remains of surface peat in a former strait defined by the Ponton shoreline and a nearby site on the former lake floor indicates the abandonment of this shoreline and hence the withdrawal of Lake Agassiz from the Sandy Lake basin by 8.3 ± 0.1 cal ka (UOC-7883). The date although a minimum-limiting age provides the hitherto best possible age constraint for the Ponton-Kinojévis shorelines which many hypothesize represent one of the major lake levels during the final drainage of Lake Agassiz into Hudson Bay but have never been adequately dated before.","PeriodicalId":9567,"journal":{"name":"Canadian Journal of Earth Sciences","volume":null,"pages":null},"PeriodicalIF":1.4,"publicationDate":"2023-12-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"138590005","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 Yarmouth Island Formation of the East Harpswell Group (EHG) is an assemblage of metamorphosed volcanic and sedimentary rocks exposed in Casco Bay, Maine. Although previously interpreted to have been deposited ca. 445 Ma, two new U–Pb zircon ages from metavolcanic rocks in the unit indicate prolonged magmatism between ca. 469–474 Ma and correlation with adjacent rocks of the more regionally extensive Casco Bay Group (CBG) in the Liberty–Orrington belt. New detrital zircon results from metasedimentary rocks in the EHG support this correlation; the age spectra indicate a peri-Gondwanan sedimentary source, consistent with earlier published results from the CBG. Detailed geochemical studies of the metavolcanic rocks in the Yarmouth Island Formation indicate a wide range of sub-alkaline compositions (SiO2 = 47.9–77.5 wt.%), flat chondrite-normalized rare earth element distributions, and a prominent negative Nb anomaly in normalized spider plots. Tectonic discrimination plots suggest eruption in a volcanic arc setting with continental crustal influence. This tectonic setting, when combined with the co-existence of marine sedimentary rocks, suggests a transitional setting between that of subduction and subsidence in a marine setting, perhaps due to the onset of back-arc rifting. Similarities in age, lithologic character, sediment provenance, and volcanic rock geochemistry indicate a strong correlation between these rocks in the Liberty–Orrington belt and those along strike in the southern portion of the Miramichi belt of eastern Maine and southern New Brunswick. These findings confirm the preservation of >500 km long, ca. 470 Ma, arc/back-arc terrane within the Ganderia superterrane in the northern Appalachians.
{"title":"Geochronology, geochemistry, and tectonic setting of Ordovician metavolcanic rocks in the Liberty–Orrington belt, Maine: implications for the evolution of peri-Gondwanan arcs in the northern Appalachians","authors":"Sophia A. Johnson, David P. West, E. Peterman","doi":"10.1139/cjes-2023-0115","DOIUrl":"https://doi.org/10.1139/cjes-2023-0115","url":null,"abstract":"The Yarmouth Island Formation of the East Harpswell Group (EHG) is an assemblage of metamorphosed volcanic and sedimentary rocks exposed in Casco Bay, Maine. Although previously interpreted to have been deposited ca. 445 Ma, two new U–Pb zircon ages from metavolcanic rocks in the unit indicate prolonged magmatism between ca. 469–474 Ma and correlation with adjacent rocks of the more regionally extensive Casco Bay Group (CBG) in the Liberty–Orrington belt. New detrital zircon results from metasedimentary rocks in the EHG support this correlation; the age spectra indicate a peri-Gondwanan sedimentary source, consistent with earlier published results from the CBG. Detailed geochemical studies of the metavolcanic rocks in the Yarmouth Island Formation indicate a wide range of sub-alkaline compositions (SiO2 = 47.9–77.5 wt.%), flat chondrite-normalized rare earth element distributions, and a prominent negative Nb anomaly in normalized spider plots. Tectonic discrimination plots suggest eruption in a volcanic arc setting with continental crustal influence. This tectonic setting, when combined with the co-existence of marine sedimentary rocks, suggests a transitional setting between that of subduction and subsidence in a marine setting, perhaps due to the onset of back-arc rifting. Similarities in age, lithologic character, sediment provenance, and volcanic rock geochemistry indicate a strong correlation between these rocks in the Liberty–Orrington belt and those along strike in the southern portion of the Miramichi belt of eastern Maine and southern New Brunswick. These findings confirm the preservation of >500 km long, ca. 470 Ma, arc/back-arc terrane within the Ganderia superterrane in the northern Appalachians.","PeriodicalId":9567,"journal":{"name":"Canadian Journal of Earth Sciences","volume":null,"pages":null},"PeriodicalIF":1.4,"publicationDate":"2023-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"138618291","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}
John F. Slack, H. Swinden, S. Piercey, R. Ayuso, C. V. van Staal, A. LeHuray
Lead isotope values for volcanogenic massive sulphide (VMS) deposits provide important insights into metal sources and the nature of pre-accretionary tectonostratigraphic terranes and underlying basements. Deposits of this type in New England formed in diverse tectonic settings including volcanic arcs and backarcs, a supra-subduction zone arc, a rifted fore-arc foreland basin, and a rifted continental margin. Following VMS mineralization on or near the seafloor, components of the tectonostratigraphic assemblages—volcanic ± sedimentary rocks, coeval intrusions, sulphide deposits, and underlying basements—were diachronously accreted to the Laurentian margin during the Paleozoic. Lead isotope data for galena show relatively large ranges for 206Pb/204Pb, 207Pb/204Pb, and 208Pb/204Pb. Evaluation of potential lead sources, using for comparison Pb-isotope data from modern and ancient settings, suggests that principal sources include the mantle, volcanic ± sedimentary rocks, and deeper basement rocks. Integration of the Pb-isotope values with published data such as Nd isotopes for the volcanic rocks and from deep seismic reflection profiles points to the involvement of several basements including those of Grenvillian, Ganderian, Avalonian, and West African (and/or Amazonian) affinity. Clustering of Pb-isotope data for VMS deposits within individual Cambrian and Ordovician volcanic and volcanosedimentary settings, delineated by differences in 206Pb/204Pb and µ (238U/204Pb) values, are consistent with lead derivation from at least four and possibly five different tectonostratigraphic assemblages with isotopically distinct basements. Collectively, our Pb-isotope data for New England VMS deposits provide a novel window into the nature of sub-arc basement rocks during pre-accretionary sulphide mineralization outboard of Laurentia during early Paleozoic time.
{"title":"Lead isotopes in New England (USA) volcanogenic massive sulphide deposits: implications for metal sources and pre-accretionary tectonostratigraphic terranes","authors":"John F. Slack, H. Swinden, S. Piercey, R. Ayuso, C. V. van Staal, A. LeHuray","doi":"10.1139/cjes-2023-0058","DOIUrl":"https://doi.org/10.1139/cjes-2023-0058","url":null,"abstract":"Lead isotope values for volcanogenic massive sulphide (VMS) deposits provide important insights into metal sources and the nature of pre-accretionary tectonostratigraphic terranes and underlying basements. Deposits of this type in New England formed in diverse tectonic settings including volcanic arcs and backarcs, a supra-subduction zone arc, a rifted fore-arc foreland basin, and a rifted continental margin. Following VMS mineralization on or near the seafloor, components of the tectonostratigraphic assemblages—volcanic ± sedimentary rocks, coeval intrusions, sulphide deposits, and underlying basements—were diachronously accreted to the Laurentian margin during the Paleozoic. Lead isotope data for galena show relatively large ranges for 206Pb/204Pb, 207Pb/204Pb, and 208Pb/204Pb. Evaluation of potential lead sources, using for comparison Pb-isotope data from modern and ancient settings, suggests that principal sources include the mantle, volcanic ± sedimentary rocks, and deeper basement rocks. Integration of the Pb-isotope values with published data such as Nd isotopes for the volcanic rocks and from deep seismic reflection profiles points to the involvement of several basements including those of Grenvillian, Ganderian, Avalonian, and West African (and/or Amazonian) affinity. Clustering of Pb-isotope data for VMS deposits within individual Cambrian and Ordovician volcanic and volcanosedimentary settings, delineated by differences in 206Pb/204Pb and µ (238U/204Pb) values, are consistent with lead derivation from at least four and possibly five different tectonostratigraphic assemblages with isotopically distinct basements. Collectively, our Pb-isotope data for New England VMS deposits provide a novel window into the nature of sub-arc basement rocks during pre-accretionary sulphide mineralization outboard of Laurentia during early Paleozoic time.","PeriodicalId":9567,"journal":{"name":"Canadian Journal of Earth Sciences","volume":null,"pages":null},"PeriodicalIF":1.4,"publicationDate":"2023-11-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139237951","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 report rhenium–osmium (Re–Os) isotope data and age information for bornite, chalcocite, and chalcopyrite from the Spar Lake and Rock Creek copper–silver (Cu–Ag) sediment-hosted deposits in the Spar Lake district, Mesoproterozoic Belt–Purcell Basin, Montana, USA. The Re–Os geochronometers in chalcocite and chalcopyrite do not record plausible mineralization ages at the Spar Lake deposit, which is currently interpreted to have formed at ca. 1410 million years ago (Ma) from prior work. However, a Re–Os isochron date of bornite (253.2 ± 26.9 Ma, n = 6) at Rock Creek with an extremely high initial 187Os/188Os ratio of 19.1 ± 0.2 can be interpreted as resetting of Re–Os in bornite that originally recorded a Mesoproterozoic timing of Cu–Ag mineralization in the Spar Lake district. The new Re–Os age of bornite at Permian–Triassic boundary time is compatible with a resetting at the time of building of the Sonoma Foreland Basin that resulted from the loading of an accretionary prism (i.e., Golconda Allochthon) onto the North American Plate. Our ca. 253 Ma bornite age does not constrain whether Cu was introduced to Spar Lake at this time or simply redistributed, but our findings open the possibility that Cu–Ag mineralization in the Spar Lake district might have taken place not only in the Mesoproterozoic, but also in addition, at Permian–Triassic boundary time. Indeed, numerous Cu–Ag, vanadium–uranium (V–U) sandstone-hosted and black shale-hosted deposits of assumed Permian to Triassic age are documented in the Midcontinent copper belt from western Texas to southern Idaho, including (1) Cu–Ag sediment-hosted deposits in western Colorado, southeastern Utah, and northern Arizona and (2) the Montpelier and Lake Alice sandstone-hosted Cu–Ag deposits in southeastern Idaho and western Wyoming, respectively.
{"title":"A Permian rhenium–osmium radiometric age for bornite at the Rock Creek deposit, Spar Lake copper–silver district (Montana, USA)—a link to the Sonoma Orogeny and the copper–silver–vanadium Midcontinent Belt?","authors":"N. Saintilan, R. Creaser","doi":"10.1139/cjes-2023-0024","DOIUrl":"https://doi.org/10.1139/cjes-2023-0024","url":null,"abstract":"We report rhenium–osmium (Re–Os) isotope data and age information for bornite, chalcocite, and chalcopyrite from the Spar Lake and Rock Creek copper–silver (Cu–Ag) sediment-hosted deposits in the Spar Lake district, Mesoproterozoic Belt–Purcell Basin, Montana, USA. The Re–Os geochronometers in chalcocite and chalcopyrite do not record plausible mineralization ages at the Spar Lake deposit, which is currently interpreted to have formed at ca. 1410 million years ago (Ma) from prior work. However, a Re–Os isochron date of bornite (253.2 ± 26.9 Ma, n = 6) at Rock Creek with an extremely high initial 187Os/188Os ratio of 19.1 ± 0.2 can be interpreted as resetting of Re–Os in bornite that originally recorded a Mesoproterozoic timing of Cu–Ag mineralization in the Spar Lake district. The new Re–Os age of bornite at Permian–Triassic boundary time is compatible with a resetting at the time of building of the Sonoma Foreland Basin that resulted from the loading of an accretionary prism (i.e., Golconda Allochthon) onto the North American Plate. Our ca. 253 Ma bornite age does not constrain whether Cu was introduced to Spar Lake at this time or simply redistributed, but our findings open the possibility that Cu–Ag mineralization in the Spar Lake district might have taken place not only in the Mesoproterozoic, but also in addition, at Permian–Triassic boundary time. Indeed, numerous Cu–Ag, vanadium–uranium (V–U) sandstone-hosted and black shale-hosted deposits of assumed Permian to Triassic age are documented in the Midcontinent copper belt from western Texas to southern Idaho, including (1) Cu–Ag sediment-hosted deposits in western Colorado, southeastern Utah, and northern Arizona and (2) the Montpelier and Lake Alice sandstone-hosted Cu–Ag deposits in southeastern Idaho and western Wyoming, respectively.","PeriodicalId":9567,"journal":{"name":"Canadian Journal of Earth Sciences","volume":null,"pages":null},"PeriodicalIF":1.4,"publicationDate":"2023-11-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139241020","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. Strauss, K. Faehnrich, William C. McClelland, Megan M. Koch, James L. Crowley, M. Melchin, Luke P. Beranek
{"title":"Reply to the discussion by Hadlari on “age and significance of the fire bay assemblage: an Ordovician arc fragment within the Clements Markham belt, northwestern Ellesmere Island, Canada”","authors":"J. Strauss, K. Faehnrich, William C. McClelland, Megan M. Koch, James L. Crowley, M. Melchin, Luke P. Beranek","doi":"10.1139/cjes-2023-0039","DOIUrl":"https://doi.org/10.1139/cjes-2023-0039","url":null,"abstract":"","PeriodicalId":9567,"journal":{"name":"Canadian Journal of Earth Sciences","volume":null,"pages":null},"PeriodicalIF":1.4,"publicationDate":"2023-11-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139241217","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}
{"title":"Discussion of “Age and significance of the fire bay assemblage: an Ordovician arc fragment within the Clements Markham belt, northwestern Ellesmere Island, Canada”","authors":"T. Hadlari","doi":"10.1139/cjes-2022-0146","DOIUrl":"https://doi.org/10.1139/cjes-2022-0146","url":null,"abstract":"","PeriodicalId":9567,"journal":{"name":"Canadian Journal of Earth Sciences","volume":null,"pages":null},"PeriodicalIF":1.4,"publicationDate":"2023-11-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139241919","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 Eocene Yulong porphyry copper belt in eastern Tibet contains more than 10 Mt of Cu metal, associated with subvolcanic to volcanic porphyry systems intruding Cenozoic sedimentary basins. Geochemical data analysis shows that all samples belonged to high-K calc-alkaline and shoshonite series with metaluminous–peraluminous characteristics, light rare earth elements and large ion lithophile elements enrichment, high field strength elements depletion, and share geochemical similarities to adakitic rocks. We have established a spatiotemporal evolution framework through geochronological data analysis, combined with calculated bulk zirconium saturation temperature, calculated crustal thickness and geophysical evidence. We identified three magmatic processes triggered by asthenospheric upwelling and thermal erosion of thickened crust: (1) ultrapotassic magma derived from metasomatized mantle; (2) coeval ultrapotassic melt which promoted the partial melting of eroded lower crust and the generation of high-K adakitic felsic melt; high-K and Mg# adakitic fertile magma was formed by interaction between the eroded sulphide-rich juvenile lower crust-derived melt and mantle peridotite; (3) high-K adakitic fertile magma was derived from sulphide-rich juvenile lower crust, triggered by injecting hydrous ultrapotassic magma into thinned lower crust. The difference between deposit size in the North/South section of Yulong belt may be caused by the temperature of magmatic source and the volume of coeval potassic–ultrapotassic magmatism. Our analysis of the YPCB suggests that magmatism after 175 Ma within Intermontane arc complex of the Canadian Cordillera has high potential for porphyry deposits.
{"title":"Petrogenesis and metallogenic implications of Eocene–Oligocene magmatism in the Yulong porphyry copper belt, eastern Tibet: A review and analysis of geochronological, geochemical and Sr–Nd–Pb–Hf isotopic data","authors":"Xiao-Qing Wang, Feng-Bao Ji","doi":"10.1139/cjes-2023-0087","DOIUrl":"https://doi.org/10.1139/cjes-2023-0087","url":null,"abstract":"The Eocene Yulong porphyry copper belt in eastern Tibet contains more than 10 Mt of Cu metal, associated with subvolcanic to volcanic porphyry systems intruding Cenozoic sedimentary basins. Geochemical data analysis shows that all samples belonged to high-K calc-alkaline and shoshonite series with metaluminous–peraluminous characteristics, light rare earth elements and large ion lithophile elements enrichment, high field strength elements depletion, and share geochemical similarities to adakitic rocks. We have established a spatiotemporal evolution framework through geochronological data analysis, combined with calculated bulk zirconium saturation temperature, calculated crustal thickness and geophysical evidence. We identified three magmatic processes triggered by asthenospheric upwelling and thermal erosion of thickened crust: (1) ultrapotassic magma derived from metasomatized mantle; (2) coeval ultrapotassic melt which promoted the partial melting of eroded lower crust and the generation of high-K adakitic felsic melt; high-K and Mg# adakitic fertile magma was formed by interaction between the eroded sulphide-rich juvenile lower crust-derived melt and mantle peridotite; (3) high-K adakitic fertile magma was derived from sulphide-rich juvenile lower crust, triggered by injecting hydrous ultrapotassic magma into thinned lower crust. The difference between deposit size in the North/South section of Yulong belt may be caused by the temperature of magmatic source and the volume of coeval potassic–ultrapotassic magmatism. Our analysis of the YPCB suggests that magmatism after 175 Ma within Intermontane arc complex of the Canadian Cordillera has high potential for porphyry deposits.","PeriodicalId":9567,"journal":{"name":"Canadian Journal of Earth Sciences","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2023-11-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135876183","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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