The Great Oxidation Event(GOE)during the early Paleoproterozoic represents the first significant buildup in Earth’s atmospheric oxygen and resulted in a series of significant changes in the Earth’s surface environme...The Great Oxidation Event(GOE)during the early Paleoproterozoic represents the first significant buildup in Earth’s atmospheric oxygen and resulted in a series of significant changes in the Earth’s surface environment.Among them is the 2.22(or 2.33)–2.06 Ga Lomagundi-Jatuli Event(LJE),which is globally,the largest magnitude and longest duration,marine carbonate positive carbon isotope excursion(δ^(13)C_(V-PDB)>10‰)known.This event has attracted the attention of scholars all over the world.However,except for a high positive carbon isotope excursion(δ^(13)C_(V-PDB)>10‰)recently identified from marine carbonate rocks within the Daposhan Formation in the lower Fanhe Group(or the Sanchazi Group)in the Longgang Block in the northeast North China Craton(NCC),Paleoproterozoic carbonates in the NCC are characterized by a low-amplitude positive carbon isotope excursion(δ^(13)C_(V-PDB)<5‰).This feature is significantly different from the high positive carbon isotope excursion characteristics of carbonates deposited during the LJE period in other cratons.To determine whether there are large-scale and reliable sedimentary records of the LJE in the NCC and the reasons for the low positive δ^(13)C excursion of the Paleoproterozoic carbonates obtained by the previous studies,we conducted field investigations,carbon-oxygen isotopes,and whole-rock major and trace element geochemical analyses of Liaohe Group carbonate rocks from the Anshan area in the northwestern margin of the Jiao-Liao-Ji Belt in the northeast NCC.Our results show that the Gaojiayu Formation of the Liaohe Group in the Anshan area has high positive δ^(13)C_(V-PDB) values from 8.6‰ to 12.4‰ and δ^(18)O_(V-SMOW) values of 17.9‰-27.4‰(δ^(18)O_(V-PDB) values ranging from−12.6‰to -3.4‰).This provides solid evidence for the preservation of reliable sedimentary records of the LJE in the northeastern NCC.Deposition of the high positive δ^(13)C excursion(>10‰)of marine carbonate rocks occurred at about 2.15 Ga.Lithological comparisons of different sections and whole-rock geochemical results show that the high positive δ^(13)C excursion is mainly controlled by the stratigraphic interval and depositional ages;the changes of sedimentary facies and diagenesis have no significant effects on reducing of the δ^(13)C values.The intrusion of mafic sills into carbonates has resulted in synchronous decrease of C-O isotopes near the contact zones,but the decreasing amplitude of δ^(13)C is less than 3‰.Therefore,our study firstly identified marine carbonates with high positive δ^(13)C excursion(>10‰)from the Gaojiayu Formation,which provides robust evidence for global correlation of the LJE,which has implications for its genesis and global significance.Moreover,due to global near-synchronization of the LJE,the carbon-oxygen isotope chemical stratigraphy of carbonate rocks deposited during the LJE period,combined with geochronological data,can provide new constraints on the stratigraphic subdivision and correlations of Paleoproterozoic sedimentary successions in the NCC.展开更多
The Qingchengzi ore field is an important gold-polymetallic center of the North China Cra-ton.It has been recognized that the gold deposits in Qingchengzi were controlled by structures like litho-logical interfaces an...The Qingchengzi ore field is an important gold-polymetallic center of the North China Cra-ton.It has been recognized that the gold deposits in Qingchengzi were controlled by structures like litho-logical interfaces and fractures along mechanically weak bedding and foliation planes,but it still remains poorly understood how the structures affected the localization of the gold deposits.Finite element based numerical modeling was used to reproduce the deformation process of the Baiyun gold deposit during the mineralization period.Paleoproterozoic schist and marble are widely exposed in Qingchengzi,and a large part of the Baiyun gold ores occurs along the interfaces between the schist and the marble.The modeling results suggest that the mechanical contrast between the schist and the marble may be a major reason why the stress was localized along their lithological interfaces under a compressional stress regime.Two parts of their lithological interfaces were identified to be easily stress-localized and first fractured:the interface between the schist and its underlying marble at shallower levels and the one between the schist and its overlying marble at deeper levels.Stress concentration in these two parts is independent on the dipping angle and direction of the interfaces.Therefore,mineralizing fluids may have been concentrated into these two parts.The first one is consistent with the present ore bodies of the Baiyun gold deposit,and the second one could be considered for deep prospecting.These findings also provide implications for the structural controls of lithological interfaces on the mineralization in other gold deposits of this region.展开更多
基金financially supported by the National Natural Science Foundation of China(Grant Nos.41920104004,U2244213,41725011)the Fundamental Research Fund of Chinese Academy of Geological Sciences(Grant No.JKYZD202320)。
文摘The Great Oxidation Event(GOE)during the early Paleoproterozoic represents the first significant buildup in Earth’s atmospheric oxygen and resulted in a series of significant changes in the Earth’s surface environment.Among them is the 2.22(or 2.33)–2.06 Ga Lomagundi-Jatuli Event(LJE),which is globally,the largest magnitude and longest duration,marine carbonate positive carbon isotope excursion(δ^(13)C_(V-PDB)>10‰)known.This event has attracted the attention of scholars all over the world.However,except for a high positive carbon isotope excursion(δ^(13)C_(V-PDB)>10‰)recently identified from marine carbonate rocks within the Daposhan Formation in the lower Fanhe Group(or the Sanchazi Group)in the Longgang Block in the northeast North China Craton(NCC),Paleoproterozoic carbonates in the NCC are characterized by a low-amplitude positive carbon isotope excursion(δ^(13)C_(V-PDB)<5‰).This feature is significantly different from the high positive carbon isotope excursion characteristics of carbonates deposited during the LJE period in other cratons.To determine whether there are large-scale and reliable sedimentary records of the LJE in the NCC and the reasons for the low positive δ^(13)C excursion of the Paleoproterozoic carbonates obtained by the previous studies,we conducted field investigations,carbon-oxygen isotopes,and whole-rock major and trace element geochemical analyses of Liaohe Group carbonate rocks from the Anshan area in the northwestern margin of the Jiao-Liao-Ji Belt in the northeast NCC.Our results show that the Gaojiayu Formation of the Liaohe Group in the Anshan area has high positive δ^(13)C_(V-PDB) values from 8.6‰ to 12.4‰ and δ^(18)O_(V-SMOW) values of 17.9‰-27.4‰(δ^(18)O_(V-PDB) values ranging from−12.6‰to -3.4‰).This provides solid evidence for the preservation of reliable sedimentary records of the LJE in the northeastern NCC.Deposition of the high positive δ^(13)C excursion(>10‰)of marine carbonate rocks occurred at about 2.15 Ga.Lithological comparisons of different sections and whole-rock geochemical results show that the high positive δ^(13)C excursion is mainly controlled by the stratigraphic interval and depositional ages;the changes of sedimentary facies and diagenesis have no significant effects on reducing of the δ^(13)C values.The intrusion of mafic sills into carbonates has resulted in synchronous decrease of C-O isotopes near the contact zones,but the decreasing amplitude of δ^(13)C is less than 3‰.Therefore,our study firstly identified marine carbonates with high positive δ^(13)C excursion(>10‰)from the Gaojiayu Formation,which provides robust evidence for global correlation of the LJE,which has implications for its genesis and global significance.Moreover,due to global near-synchronization of the LJE,the carbon-oxygen isotope chemical stratigraphy of carbonate rocks deposited during the LJE period,combined with geochronological data,can provide new constraints on the stratigraphic subdivision and correlations of Paleoproterozoic sedimentary successions in the NCC.
基金The work was financially funded by the National Key R&D Program of China(No.2018YFC0603802)the Basic Research Fund for Central Research Institutes(No.JYYWF20180602)the National Natural Science Foundation of China(No.41822206).
文摘The Qingchengzi ore field is an important gold-polymetallic center of the North China Cra-ton.It has been recognized that the gold deposits in Qingchengzi were controlled by structures like litho-logical interfaces and fractures along mechanically weak bedding and foliation planes,but it still remains poorly understood how the structures affected the localization of the gold deposits.Finite element based numerical modeling was used to reproduce the deformation process of the Baiyun gold deposit during the mineralization period.Paleoproterozoic schist and marble are widely exposed in Qingchengzi,and a large part of the Baiyun gold ores occurs along the interfaces between the schist and the marble.The modeling results suggest that the mechanical contrast between the schist and the marble may be a major reason why the stress was localized along their lithological interfaces under a compressional stress regime.Two parts of their lithological interfaces were identified to be easily stress-localized and first fractured:the interface between the schist and its underlying marble at shallower levels and the one between the schist and its overlying marble at deeper levels.Stress concentration in these two parts is independent on the dipping angle and direction of the interfaces.Therefore,mineralizing fluids may have been concentrated into these two parts.The first one is consistent with the present ore bodies of the Baiyun gold deposit,and the second one could be considered for deep prospecting.These findings also provide implications for the structural controls of lithological interfaces on the mineralization in other gold deposits of this region.
