Chemical indexes of Paleoproterozoic sedimentary rocks from Liaohe Group,North China Craton:Implications for paleoclimate and provenance

Paleoproterozoic supracrustal materials have been widely identified in North China Craton,such as the Liaohe-,Hutuo-and Lyuliang groups.The Liaohe Group in the eastern part of the North China Craton is dominated by deformed and metamorphosed sedimentary and volcanic successions.Compared with that of the coeval volcanic rocks,geochemistry of the sedimentary rocks from the Liaohe Group has rarely been studied in detail,which can possibly provide information on the paleoclimate and provenance.The authors analyzed the whole-rock and detrital zircon geochemistry of sedimentary rocks from the Liaohe Group against a uniform process and proposed their different ways of paleoweathering of the lower and upper formations.That is to say,although the lower and upper formations within the Liaohe Group might be derived from the similar source composition in a tectonically active setting,the paleoclimate that they experienced was not exactly the same.The predominant derivations are the Paleoproterozoic granitoids and basalts within the Liaohe Group,with minor input of Archean continental crust.This study highlights the contributions of the Paleoproterozoic mafic sources,which has been generally overlooked in the previous researches.

Identification of carbonates with high positive carbon isotope excursion from the Liaohe Group in the northeastern North China Craton and implications for the Lomagundi-Jatuli Event

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.

Discovery of Late Permian Jianshanzi volcanic rocks in Qinghe valley of northern Liaoning and its geologic significance

Jianshanzi volcanic rocks at Qinghe valley in the northern Liaoning were considered belonging to Early Proterozoie Gaojiayu Formation of Liaohe Group, or to Early Cambrian Beidagou Formation of Qinghezhen Group, or Middle-Late Proterozoic Shenjiapu Formation-Complex of Kaiyuan Group-complex. Dating the zircons from the dacite with schistosity is 2 506 Ma in method of U-Pb （SHRIMP）. This evidence indicates the rocks may be referred to Late Permian in age. Discovery of the rocks is significant to re-recognize stratigraphic property of ＂Liaohe Group＂, regional geoteetonie location and revolution of orogenic zone in Qinghe valley of the northern Liaoning.