Lunar impact glasses have been identified as crucial indicators of geochemical information regarding their source regions. Impact glasses can be categorized as either local or exotic. Those preserving geochemical sign...Lunar impact glasses have been identified as crucial indicators of geochemical information regarding their source regions. Impact glasses can be categorized as either local or exotic. Those preserving geochemical signatures matching local lithologies (e.g., mare basalts or their single minerals) or regolith bulk soil compositions are classified as “local”. Otherwise, they could be defined as “exotic”. The analysis of exotic glasses provides the opportunity to explore previously unsampled lunar areas. This study focuses on the identification of exotic glasses within the Chang’e-5 (CE-5) soil sample by analyzing the trace elements of 28 impact glasses with distinct major element compositions in comparison with the CE-5 bulk soil. However, the results indicate that 18 of the analyzed glasses exhibit trace element compositions comparable to those of the local CE-5 materials. In particular, some of them could match the local single mineral component in major and trace elements, suggesting a local origin. Therefore, it is recommended that the investigation be expanded from using major elements to including nonvolatile trace elements, with a view to enhancing our understanding on the provenance of lunar impact glasses. To achieve a more accurate identification of exotic glasses within the CE-5 soil sample, a novel classification plot of Mg# versus La is proposed. The remaining 10 glasses, which exhibit diverse trace element variations, were identified as exotic. A comparative analysis of their chemical characteristics with remote sensing data indicates that they may have originated from the Aristarchus, Mairan, Sharp, or Pythagoras craters. This study elucidates the classification and possible provenance of exotic materials within the CE-5 soil sample, thereby providing constraints for the enhanced identification of local and exotic components at the CE-5 landing site.展开更多
0 INTRODUCTION Subduction of oceanic plate is vital for carbon redistribution and recycling between Earth's surface and mantle,which plays a critical role in shaping carbon budgets and terrestrial habitability thr...0 INTRODUCTION Subduction of oceanic plate is vital for carbon redistribution and recycling between Earth's surface and mantle,which plays a critical role in shaping carbon budgets and terrestrial habitability through geological time(e.g.,Plank and Manning,2019;Sverjensky et al.,2014;Dasgupta and Hirschmann,2010).The long-term subduction of Pacific/Paleo-Pacific Plate from Late Mesozoic to Cenozoic beneath Northeast China makes this area an ideal candidate for exploring ancient carbon recycling and its impact on Earth's surface environment.展开更多
Ziyang County, Shaanxi Province, China is a world known selenium（Se）-enriched area, and a severe selenosis incident was reported in Naore Village during the 1990 s. This study investigated the geochemical characteri...Ziyang County, Shaanxi Province, China is a world known selenium（Se）-enriched area, and a severe selenosis incident was reported in Naore Village during the 1990 s. This study investigated the geochemical characteristics of Se and its fractions in Se-enriched rocks from Ziyang. Se distribution is uneven, ranging from 0.23 to 57.00 μg/g（17.29±15.52 μg/g）. Se content is higher in slate than chert, and even lower in carbonate rocks. Cd, As and V are enriched but Pb is depleted in Se-enriched strata. Se has different correlations both with TS（total sulfur）（R^2=0.59 for chert） and TC（total carbon）（R^2=0.77 for slate, R^2=0.87 for carbonate）. Se has significant positive correlations with V（r=0.65）, As（r=0.485）, Cd（r=0.459） and Pb（r=0.405）. The Se level correlates with mineral content, positively with pyrite, chlorite and illite, negatively with albite. Se associated with sulfide/selenide and elemental Se are the predominant fractions of total recovered Se, suggesting that a reducing environment and the formation of sulfides were significant to Se deposition during its geochemical cycle. Although low concentration of bio-available Se（average 5.62%±3.69%） may reduce the risk of Se poisoning in the target area, utilization of Se-rich rock as natural fertilizer should be restricted.展开更多
U-Pb geochronology of calcite using laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) is an emerging method,with potential applications to a vast array of geological problems.Due to the low level...U-Pb geochronology of calcite using laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) is an emerging method,with potential applications to a vast array of geological problems.Due to the low levels of U and Pb in calcite,measurement using higher-sensitivity instruments,such as sector field (SF) ICP-MS,have advantages over more commonly used quadrupole (Q) ICP-MS instruments.Using a Thermo Element XR ICP-MS,we demonstrate that the Jet+X cone combination with the N_(2) enhancement technique provides the best sensitivity for measuring U and Pb isotopes.This higher sensitivity improves the precision of calcite U-Pb isotope measurements,and permits dating at high spatial resolutions (<110μm) and for samples containing low contents of^(238)U (<1μg g^(–1)) and/or^(207)Pb (i.e.,young samples<10 Ma).Using a spot size of 85μm with a low fluence (~2.0 J cm^(–2)),the laser-induced elemental fractionation of^(206)Pb/^(238)U in the NIST SRM 614,ARM-3 and WC-1 reference materials are insignificant (<2.2%).Adopting the optimized instrument parameters,we analysed four commonly-used calcite U-Pb reference materials (WC-1,Duff Brown Tank,JT,and ASH-15).The results match well with published isotope dilution data,demonstrating the reliability of our technique.ARM-3,an andesitic glass,is shown to be an appropriate reference material for both^(207)Pb/^(206)Pb calibration and instrument optimization because of its moderate contents of U(~3.75μg g^(–1)) and Pb (~12.7μg g^(–1)).We further demonstrate that the image-guided approach using LA-ICP-MS elemental mapping is an efficient tool in obtaining robust ages.展开更多
To meet the rapid development of zircon U-Pb geochronology and Hf-O isotope geochemistry,it is imperative to develop well-characterized zircon reference materials for microbeam analysis.Here,zircon KV01 separated from...To meet the rapid development of zircon U-Pb geochronology and Hf-O isotope geochemistry,it is imperative to develop well-characterized zircon reference materials for microbeam analysis.Here,zircon KV01 separated from the Kaap Valley pluton,South Africa is introduced as a potential Archean reference material for microbeam U-Pb age and Hf-O isotope determination.SIMS and LA-ICP-MS U-Pb isotopic measurements gave grand mean 207Pb/206Pb ages of 3233±16 Ma(2 s,n=90)and 3230±26 Ma(2 s,n=52),which are consistent with reported CA-ID-TIMS results.Slight heterogeneity of oxygen isotopes is revealed by SIMS analyses that yielded a relatively largeδ18O range of 4.61–6.51‰.Among them,the zircon grains with clear oscillatory zones give a grand meanδ18O value of 6.17±0.33‰(2 s),which is suggested to record the primary O isotopic compositions.The homogeneity in the Hf isotopic compositions of KV01 zircon was checked by the laser ablation and solution MC-ICP-MS methods.They yielded consistent results with a recommended 176Hf/177Hf ratio of 0.280810±0.000013(2 s).The results reported here demonstrate that KV01 zircon could be a reliable reference material for microbeam 207Pb/206Pb age and Hf isotope determinations of ancient zircons,and be suitable as a quality monitor for SIMS oxygen isotopic analysis.展开更多
In situ carbonate U-Pb dating is gaining popularity,and it has great potential for application in petroleum geology.However,the low U content(<10μg/g)and high common Pb content of carbonate minerals,along with the...In situ carbonate U-Pb dating is gaining popularity,and it has great potential for application in petroleum geology.However,the low U content(<10μg/g)and high common Pb content of carbonate minerals,along with the uneven distribution of U and Pb and the lack of matrix-matched reference material make carbonate U-Pb dating inaccurate and less successful,which limits the widespread application in geosciences.This study evaluated the limitations of in situ carbonate U-Pb dating and proposed a method to rationally determine the laser ablation parameters of samples by improving the experimental approach based on the laser ablation sector field inductively coupled plasma mass spectrometry(LA-SF-ICP-MS).By setting a different spot size and laser frequency for the reference material and unknown samples in the same session based on the U content of the sample,the ablation craters of the reference material and unknown samples were given the same depth/width ratio,avoiding systematic offset caused by differences in down-hole element fractionation and reducing the consume of reference material.Depending on the heterogeneous distribution of U and Pb contents in carbonate minerals,the method of grid screening and setting ablation spots during screening were used to quickly select domains with high U and low common Pb,which improves the efficiency of setting laser spots and the success rate of dating,as well as reduces the experimental time and economic cost.The accuracy and success rate of carbonate U-Pb dating were effectively improved by improving the experimental method,and the technique was applied to two carbonate samples with low U and high common Pb contents that were difficult to date by traditional methods.The two samples are the saddle dolomite in the central Sichuan Basin and the calcite cement in the sandstone reservoir of the Cretaceous Qingshuihe Formation in the South Junggar Basin.The robust ages have been obtained,which constrains the timing of the diagenetic and hydrocarbon accumulation process in the studied area.展开更多
Mica exhibits a relatively high Rb/Sr ratio and possesses a closure temperature for the Rb-Sr isotope system that is higher than the ore-forming temperature range of low-to medium-temperature deposits.Consequently,uti...Mica exhibits a relatively high Rb/Sr ratio and possesses a closure temperature for the Rb-Sr isotope system that is higher than the ore-forming temperature range of low-to medium-temperature deposits.Consequently,utilizing the laser ablation(LA)technique for in situ Rb-Sr dating in mica constitutes a significant methodology for resolving the mineralization chronology of low-to medium-temperature hydrothermal ore deposits.In this study,we employed a combination of a triple quadrupole inductively coupled plasma mass spectrometer(ICP-MS/MS)and 193 nm LA system with SF_6as the reaction gas to achieve interference removal of~(87)Rb~+on~(87)Sr~+.We then developed an in situ Rb-Sr dating method for mica.In addition,an investigation was conducted to identify the factors that could influence the analytical accuracy of the method.Subsequently,we applied the developed method to carry out in situ Rb-Sr dating for the ZBH-25 biotite,a national primary reference material(GBW04439)for K-Ar dating,and yielded a younger age(ca.12%,relative standard deviation,RSD)than the reference K-Ar age when using NIST SRM 610 as the reference material for external calibration.This finding indicated that in the process of determining Rb-Sr ages for mica by LA-ICP-MS/MS,there are significant matrix effects between the NIST SRM 610 and the mica samples,resulting in inaccurate Rb-Sr ages.In response to this issue,a two-step calibration method is proposed here.Based on external calibration using NIST SRM 610,ZBH-25 biotite is employed as a second external reference material to perform a second calibration of the sample data to correct the matrix effect between the glass standards and the natural mica samples,thereby improving the accuracy of Rb-Sr dating by LA-ICP-MS/MS.Using the proposed method,in situ Rb-Sr dating by LA-ICP-MS/MS was performed on mica samples from monzonite exposed in Mt.Dromedary,New South Wales,Australia,porphyritic granodiorite in Fangshan pluton and albionite granite in the Gyirong area of Xizang.The obtained Rb-Sr age results show agreement with the recommended values within the analytical uncertainty,which serves to validate the accuracy and effectiveness of the proposed method.展开更多
In-situ dating of the zircons, titanites, and apatites in the rock fragments of approximately 1 cm2in size from the Acasta Gneiss Complex was performed using secondary ion mass spectrometry or laser ablation inductive...In-situ dating of the zircons, titanites, and apatites in the rock fragments of approximately 1 cm2in size from the Acasta Gneiss Complex was performed using secondary ion mass spectrometry or laser ablation inductively coupled plasma mass spectrometry to provide constraints on the thermal history of the Acasta Gneiss Complex. The zircons in these rock fragments typically exhibit multiple age populations, reflecting the presence of inherited zircons or the post-crystallization process of zircon overgrowth. Combined with previous studies, our zircon dating results reveal multiple magmatic events that occurred in the Acasta Gneiss Complex, specifically at >3.96, ~3.72, and ~3.57 Ga, respectively. A titanite Pb-Pb isochron age of2911±22 Ma(95% confidence level, MSWD=1.5) for sample AY199 is identified, consistent with the timing of the latest Archean magmatism in the Acasta Gneiss Complex. The titanite U-Pb ages for samples AC478 and AY066 are 1932±270 Ma(95% confidence level, MSWD=2.3) and 1813±45 Ma(95% confidence level, MSWD=2.3), respectively. The apatites in sample P090803-C exhibit a Pb-Pb isochron age of 1833±26 Ma(95% confidence level, MSWD=1.4). The apatite U-Pb ages for samples AC478, AY199, and AY066 are 1850±20 Ma(95% confidence level, MSWD=1.3), 1827±100 Ma(95% confidence level, MSWD=6.3), and 1807±58 Ma(95% confidence level, MSWD=3.9), respectively. Titanites in samples AC478 and AY066, as well as the apatites in all four investigated samples, show a uniform age(Pb-Pb or U-Pb age) of ~1.9–1.8 Ga,indicating U-Pb system reset in these minerals due to the Wopmay orogeny and documenting that the peak temperature condition associated with the Wopmay orogeny exceeded the apatite U-Pb closure temperature and approached or exceeded that of titanite.展开更多
基金funded by the National Natural Science Foundation of China (Grant Nos. 42241103 and 62227901)the Key Research Program of the Institute of Geology and Geophysics, Chinese Academy of Sciences (Grant Nos. IGGCAS-202101 and IGGCAS-202401)
文摘Lunar impact glasses have been identified as crucial indicators of geochemical information regarding their source regions. Impact glasses can be categorized as either local or exotic. Those preserving geochemical signatures matching local lithologies (e.g., mare basalts or their single minerals) or regolith bulk soil compositions are classified as “local”. Otherwise, they could be defined as “exotic”. The analysis of exotic glasses provides the opportunity to explore previously unsampled lunar areas. This study focuses on the identification of exotic glasses within the Chang’e-5 (CE-5) soil sample by analyzing the trace elements of 28 impact glasses with distinct major element compositions in comparison with the CE-5 bulk soil. However, the results indicate that 18 of the analyzed glasses exhibit trace element compositions comparable to those of the local CE-5 materials. In particular, some of them could match the local single mineral component in major and trace elements, suggesting a local origin. Therefore, it is recommended that the investigation be expanded from using major elements to including nonvolatile trace elements, with a view to enhancing our understanding on the provenance of lunar impact glasses. To achieve a more accurate identification of exotic glasses within the CE-5 soil sample, a novel classification plot of Mg# versus La is proposed. The remaining 10 glasses, which exhibit diverse trace element variations, were identified as exotic. A comparative analysis of their chemical characteristics with remote sensing data indicates that they may have originated from the Aristarchus, Mairan, Sharp, or Pythagoras craters. This study elucidates the classification and possible provenance of exotic materials within the CE-5 soil sample, thereby providing constraints for the enhanced identification of local and exotic components at the CE-5 landing site.
基金supported by the National Natural Science Foundation of China(Nos.42130310 and 41972055)。
文摘0 INTRODUCTION Subduction of oceanic plate is vital for carbon redistribution and recycling between Earth's surface and mantle,which plays a critical role in shaping carbon budgets and terrestrial habitability through geological time(e.g.,Plank and Manning,2019;Sverjensky et al.,2014;Dasgupta and Hirschmann,2010).The long-term subduction of Pacific/Paleo-Pacific Plate from Late Mesozoic to Cenozoic beneath Northeast China makes this area an ideal candidate for exploring ancient carbon recycling and its impact on Earth's surface environment.
基金supported by the Foundation of China Geological Survey(Nos.12120113087100,12120113022600)the Basic Scientific Research of the Institute of Geophysical Geochemical Exploration,Chinese Academy of Geological Sciences(No.WHS201302)
文摘Ziyang County, Shaanxi Province, China is a world known selenium（Se）-enriched area, and a severe selenosis incident was reported in Naore Village during the 1990 s. This study investigated the geochemical characteristics of Se and its fractions in Se-enriched rocks from Ziyang. Se distribution is uneven, ranging from 0.23 to 57.00 μg/g（17.29±15.52 μg/g）. Se content is higher in slate than chert, and even lower in carbonate rocks. Cd, As and V are enriched but Pb is depleted in Se-enriched strata. Se has different correlations both with TS（total sulfur）（R^2=0.59 for chert） and TC（total carbon）（R^2=0.77 for slate, R^2=0.87 for carbonate）. Se has significant positive correlations with V（r=0.65）, As（r=0.485）, Cd（r=0.459） and Pb（r=0.405）. The Se level correlates with mineral content, positively with pyrite, chlorite and illite, negatively with albite. Se associated with sulfide/selenide and elemental Se are the predominant fractions of total recovered Se, suggesting that a reducing environment and the formation of sulfides were significant to Se deposition during its geochemical cycle. Although low concentration of bio-available Se（average 5.62%±3.69%） may reduce the risk of Se poisoning in the target area, utilization of Se-rich rock as natural fertilizer should be restricted.
基金co-supported by the National Key R&D Program of China (Grant No. 2018YFA0702602)the National Natural Science Foundation of China (Grant Nos. 41903024, 41525012)the Youth Innovation Promotion Association of the Chinese Academy of Sciences (Grant No. 2022066)。
文摘U-Pb geochronology of calcite using laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) is an emerging method,with potential applications to a vast array of geological problems.Due to the low levels of U and Pb in calcite,measurement using higher-sensitivity instruments,such as sector field (SF) ICP-MS,have advantages over more commonly used quadrupole (Q) ICP-MS instruments.Using a Thermo Element XR ICP-MS,we demonstrate that the Jet+X cone combination with the N_(2) enhancement technique provides the best sensitivity for measuring U and Pb isotopes.This higher sensitivity improves the precision of calcite U-Pb isotope measurements,and permits dating at high spatial resolutions (<110μm) and for samples containing low contents of^(238)U (<1μg g^(–1)) and/or^(207)Pb (i.e.,young samples<10 Ma).Using a spot size of 85μm with a low fluence (~2.0 J cm^(–2)),the laser-induced elemental fractionation of^(206)Pb/^(238)U in the NIST SRM 614,ARM-3 and WC-1 reference materials are insignificant (<2.2%).Adopting the optimized instrument parameters,we analysed four commonly-used calcite U-Pb reference materials (WC-1,Duff Brown Tank,JT,and ASH-15).The results match well with published isotope dilution data,demonstrating the reliability of our technique.ARM-3,an andesitic glass,is shown to be an appropriate reference material for both^(207)Pb/^(206)Pb calibration and instrument optimization because of its moderate contents of U(~3.75μg g^(–1)) and Pb (~12.7μg g^(–1)).We further demonstrate that the image-guided approach using LA-ICP-MS elemental mapping is an efficient tool in obtaining robust ages.
基金supported by the National Key R&D Program of China(Grant No.2016YFC0600109)the B-type Strategic Priority Program of the Chinese Academy of Sciences(Grant No.XDB41000000)+2 种基金the National Natural Science Foundation of China(Grant Nos.41973035&41688103)the Youth Innovation Promotion Association of the Chinese Academy of Sciences(Grant No.2020068)the State Key Laboratory of Lithospheric Evolution(Grant No.SKL-Z201901-YT)。
文摘To meet the rapid development of zircon U-Pb geochronology and Hf-O isotope geochemistry,it is imperative to develop well-characterized zircon reference materials for microbeam analysis.Here,zircon KV01 separated from the Kaap Valley pluton,South Africa is introduced as a potential Archean reference material for microbeam U-Pb age and Hf-O isotope determination.SIMS and LA-ICP-MS U-Pb isotopic measurements gave grand mean 207Pb/206Pb ages of 3233±16 Ma(2 s,n=90)and 3230±26 Ma(2 s,n=52),which are consistent with reported CA-ID-TIMS results.Slight heterogeneity of oxygen isotopes is revealed by SIMS analyses that yielded a relatively largeδ18O range of 4.61–6.51‰.Among them,the zircon grains with clear oscillatory zones give a grand meanδ18O value of 6.17±0.33‰(2 s),which is suggested to record the primary O isotopic compositions.The homogeneity in the Hf isotopic compositions of KV01 zircon was checked by the laser ablation and solution MC-ICP-MS methods.They yielded consistent results with a recommended 176Hf/177Hf ratio of 0.280810±0.000013(2 s).The results reported here demonstrate that KV01 zircon could be a reliable reference material for microbeam 207Pb/206Pb age and Hf isotope determinations of ancient zircons,and be suitable as a quality monitor for SIMS oxygen isotopic analysis.
基金supported by the Scientific Research and Technological Development Project of China National Petroleum Corporation (Grant Nos.2021DJ0105,2021DJ0203,2021DJ0303)the National Natural Science Foundation of China (Grant Nos.42172164,42002177)。
文摘In situ carbonate U-Pb dating is gaining popularity,and it has great potential for application in petroleum geology.However,the low U content(<10μg/g)and high common Pb content of carbonate minerals,along with the uneven distribution of U and Pb and the lack of matrix-matched reference material make carbonate U-Pb dating inaccurate and less successful,which limits the widespread application in geosciences.This study evaluated the limitations of in situ carbonate U-Pb dating and proposed a method to rationally determine the laser ablation parameters of samples by improving the experimental approach based on the laser ablation sector field inductively coupled plasma mass spectrometry(LA-SF-ICP-MS).By setting a different spot size and laser frequency for the reference material and unknown samples in the same session based on the U content of the sample,the ablation craters of the reference material and unknown samples were given the same depth/width ratio,avoiding systematic offset caused by differences in down-hole element fractionation and reducing the consume of reference material.Depending on the heterogeneous distribution of U and Pb contents in carbonate minerals,the method of grid screening and setting ablation spots during screening were used to quickly select domains with high U and low common Pb,which improves the efficiency of setting laser spots and the success rate of dating,as well as reduces the experimental time and economic cost.The accuracy and success rate of carbonate U-Pb dating were effectively improved by improving the experimental method,and the technique was applied to two carbonate samples with low U and high common Pb contents that were difficult to date by traditional methods.The two samples are the saddle dolomite in the central Sichuan Basin and the calcite cement in the sandstone reservoir of the Cretaceous Qingshuihe Formation in the South Junggar Basin.The robust ages have been obtained,which constrains the timing of the diagenetic and hydrocarbon accumulation process in the studied area.
基金supported by the National Natural Science Foundation of China(Grant No.42173035)the Chinese Academy of Sciences“Key Technology Talent”Project。
文摘Mica exhibits a relatively high Rb/Sr ratio and possesses a closure temperature for the Rb-Sr isotope system that is higher than the ore-forming temperature range of low-to medium-temperature deposits.Consequently,utilizing the laser ablation(LA)technique for in situ Rb-Sr dating in mica constitutes a significant methodology for resolving the mineralization chronology of low-to medium-temperature hydrothermal ore deposits.In this study,we employed a combination of a triple quadrupole inductively coupled plasma mass spectrometer(ICP-MS/MS)and 193 nm LA system with SF_6as the reaction gas to achieve interference removal of~(87)Rb~+on~(87)Sr~+.We then developed an in situ Rb-Sr dating method for mica.In addition,an investigation was conducted to identify the factors that could influence the analytical accuracy of the method.Subsequently,we applied the developed method to carry out in situ Rb-Sr dating for the ZBH-25 biotite,a national primary reference material(GBW04439)for K-Ar dating,and yielded a younger age(ca.12%,relative standard deviation,RSD)than the reference K-Ar age when using NIST SRM 610 as the reference material for external calibration.This finding indicated that in the process of determining Rb-Sr ages for mica by LA-ICP-MS/MS,there are significant matrix effects between the NIST SRM 610 and the mica samples,resulting in inaccurate Rb-Sr ages.In response to this issue,a two-step calibration method is proposed here.Based on external calibration using NIST SRM 610,ZBH-25 biotite is employed as a second external reference material to perform a second calibration of the sample data to correct the matrix effect between the glass standards and the natural mica samples,thereby improving the accuracy of Rb-Sr dating by LA-ICP-MS/MS.Using the proposed method,in situ Rb-Sr dating by LA-ICP-MS/MS was performed on mica samples from monzonite exposed in Mt.Dromedary,New South Wales,Australia,porphyritic granodiorite in Fangshan pluton and albionite granite in the Gyirong area of Xizang.The obtained Rb-Sr age results show agreement with the recommended values within the analytical uncertainty,which serves to validate the accuracy and effectiveness of the proposed method.
基金supported by the National Natural Science Foundation of China(Grants Nos.42103011,4207303442288201)the B-type Strategic Priority Program of the Chinese Academy of Sciences(Grants No.XDB41000000)。
文摘In-situ dating of the zircons, titanites, and apatites in the rock fragments of approximately 1 cm2in size from the Acasta Gneiss Complex was performed using secondary ion mass spectrometry or laser ablation inductively coupled plasma mass spectrometry to provide constraints on the thermal history of the Acasta Gneiss Complex. The zircons in these rock fragments typically exhibit multiple age populations, reflecting the presence of inherited zircons or the post-crystallization process of zircon overgrowth. Combined with previous studies, our zircon dating results reveal multiple magmatic events that occurred in the Acasta Gneiss Complex, specifically at >3.96, ~3.72, and ~3.57 Ga, respectively. A titanite Pb-Pb isochron age of2911±22 Ma(95% confidence level, MSWD=1.5) for sample AY199 is identified, consistent with the timing of the latest Archean magmatism in the Acasta Gneiss Complex. The titanite U-Pb ages for samples AC478 and AY066 are 1932±270 Ma(95% confidence level, MSWD=2.3) and 1813±45 Ma(95% confidence level, MSWD=2.3), respectively. The apatites in sample P090803-C exhibit a Pb-Pb isochron age of 1833±26 Ma(95% confidence level, MSWD=1.4). The apatite U-Pb ages for samples AC478, AY199, and AY066 are 1850±20 Ma(95% confidence level, MSWD=1.3), 1827±100 Ma(95% confidence level, MSWD=6.3), and 1807±58 Ma(95% confidence level, MSWD=3.9), respectively. Titanites in samples AC478 and AY066, as well as the apatites in all four investigated samples, show a uniform age(Pb-Pb or U-Pb age) of ~1.9–1.8 Ga,indicating U-Pb system reset in these minerals due to the Wopmay orogeny and documenting that the peak temperature condition associated with the Wopmay orogeny exceeded the apatite U-Pb closure temperature and approached or exceeded that of titanite.
