It is well known that there are widespread igneous events at;100 Ma in the Eastern North China Craton;however,their tectonic environments are controversial.They were thought to be either related to an intra-continenta...It is well known that there are widespread igneous events at;100 Ma in the Eastern North China Craton;however,their tectonic environments are controversial.They were thought to be either related to an intra-continental rifting or展开更多
The timing and mechanisms of lithospheric thinning and destruction of the North China Craton(NCC)remain controversial,and the overall geodynamics of the process are poorly understood.This paper documents Late Triassic...The timing and mechanisms of lithospheric thinning and destruction of the North China Craton(NCC)remain controversial,and the overall geodynamics of the process are poorly understood.This paper documents Late Triassic igneous rocks including monzogranite,gabbro,and diorite from the Xiuyan District on the Liaodong Peninsula in the eastern NCC,which have LA-ICP-MS zircon U-Pb ages of 229.0±0.4 Ma,216.2±0.9 Ma,and 210.6±2.0 Ma,respectively.Monzogranite shows high-SiO_(2) adakite affinity,negative ε_(Hf)(t)values(-20.6 to-17.9),and old T_(DM2) ages(3.53-3.29 Ga),suggesting that their parental magma was derived from thickened Paleoarchean mafic lower crust and minor mantle materials that were also involved their generation.Gabbro is ultrapotassic,strongly enriched in LREEs and LILEs,depleted in HFSEs,and has evolved zircon Hf isotopes with negative ε_(Hf) of -10.04 to-5.85 and old T_(DM2) ages(2.59-2.22 Ga).These are diagnostic signatures of a crustal component,but their high contents of Mg O,Cr,Co,Ni indicate that the primary magma originated from enriched mantle.Diorite is enriched in LILEs and LREEs,depleted in HFSEs(with negative Nb,Ta,and Ti anomalies),and contains negative ε_(Hf)(t)values(-13.64 to-11.01).Compared with the gabbro,the diorite is relatively enriched in Nb,Ta and HREEs,and also contains younger T_(DM2) ages(2.11-1.94 Ga),suggesting that the diorite was formed by mixing between ancient lower crust-derived felsic magmas and asthenospheric mantle-derived magmas.Field observations,geochronology,geochemistry,and zircon Lu-Hf isotopes indicate that Late Triassic magmatism and tectonic activity resulted from deep subduction of the Yangtze Craton beneath the NCC in the Xiuyan area.This phase of tectonic activity was completed in the eastern NCC by the Late Triassic(216 Ma),and was subsequently followed by lithospheric thinning that began in the Late Triassic.展开更多
The variation of crustal thickness is a critical index to reveal how the continental crust evolved over its four billion years.Generally,ratios of whole-rock trace elements,such as Sr/Y,(La/Yb)n and Ce/Y,are used to c...The variation of crustal thickness is a critical index to reveal how the continental crust evolved over its four billion years.Generally,ratios of whole-rock trace elements,such as Sr/Y,(La/Yb)n and Ce/Y,are used to characterize crustal thicknesses.However,sometimes confusing results are obtained since there is no enough filtered data.Here,a state-of-the-art approach,based on a machine-learning algorithm,is proposed to predict crustal thickness using global major-and trace-element geochemical data of intermediate arc rocks and intraplate basalts,and their corresponding crustal thicknesses.After the validation processes,the root-mean-square error(RMSE)and the coefficient of determination(R2)score were used to evaluate the performance of the machine learning algorithm based on the learning dataset which has never been used during the training phase.The results demonstrate that the machine learning algorithm is more reliable in predicting crustal thickness than the conventional methods.The trained model predicts that the crustal thickness of the eastern North China Craton(ENCC)was-45 km from the Late Triassic to the Early Cretaceous,but-35 km from the Early Cretaceous,which corresponds to the paleo-elevation of 3.0±1.5 km at Early Mesozoic,and decease to the present-day elevation in the ENCC.The estimates are generally consistent with the previous studies on xenoliths from the lower crust and on the paleoenvironment of the coastal mountain of the ENCC,which indicates that the lower crust of the ENCC was delaminated abruptly at the Early Cretaceous.展开更多
Mesozoic intermediate-felsic magmatic rocks in the eastern North China Craton commonly show geochemical similarity to adakites.However,the lack of direct constraints from partial melting experiments at high pressures ...Mesozoic intermediate-felsic magmatic rocks in the eastern North China Craton commonly show geochemical similarity to adakites.However,the lack of direct constraints from partial melting experiments at high pressures and temperatures fuels a debate over the origin of these rocks.In this work,we performed partial melting experiments at 1.5 GPa and 800–950℃on amphibolite samples collected from the vicinity of the Mesozoic potassium-rich adakitic rocks in the Zhangjiakou area,northern margin of the North China Craton.The experimental melts range from granitic to granodioritic compositions,with SiO_(2)=56.4–72.6 wt.%,Al_(2)O_(3)=16.1–19.3 wt.%,FeO^(*)=2.4–9.6 wt.%,MgO=0.3–2.0 wt.%,CaO=0.6–3.8 wt.%,Na_(2)O=4.7–5.3 wt.%,and K_(2)O=2.6–3.9 wt.%,which are in the ranges of the surrounding Mesozoic potassium-rich adakitic rocks,except for the higher Al_(2)O_(3)contents and the data point at 1.5 GPa and 800℃.Trace element compositions of the melts measured by LA-ICP-MS are rich in Sr(849–1067 ppm)and light rare earth elements(LREEs)and poor in Y(<10.4 ppm)and Yb(<0.88 ppm),and have high Sr/Y(102–221)and(La/Yb)n(27–41)ratios and strongly fractionated rare earth element(REE)patterns,whereas no obvious negative Eu anomalies are observed.The geochemical characteristics show overall similarity to the Mesozoic potassium-rich adakitic rocks in the area,especially adakites with low Mg#,again except for the data point at 1.5 GPa and 800℃.The results suggest that partial melting of amphibolite can produce potassium-rich adakitic rocks with low Mg#in the eastern North China Craton under the experimental conditions of 1.5 GPa and 850–950℃.The experimental restites consist of hornblende(Hbl)+plagioclase(Pl)+garnet(Grt)±clinopyroxene(Cpx),a mineral assemblage significantly different from that of the nearby Hannuoba mafic granulite xenoliths which consist of Cpx+orthopyroxene(Opx)+Pl±Grt.Chemically,the experimental restites contain higher Al_(2)O_(3)but lower MgO and CaO than the Hannuoba mafic granulite xenoliths.We therefore argue that the Hannuoba mafic granulite xenoliths cannot represent the direct products of partial melting of the experimental amphibolite.展开更多
Lithosphere thinning and destruction in the middle-eastern North China Craton(NCC), a region susceptible to strong earthquakes, is one of the research hotspots in solid earth science. All 42 seismic wide-angle reflect...Lithosphere thinning and destruction in the middle-eastern North China Craton(NCC), a region susceptible to strong earthquakes, is one of the research hotspots in solid earth science. All 42 seismic wide-angle reflection/refraction profiles have been completed in the middle-eastern NCC. We collect all the 2-D profiling results and perform gridding of the velocity and interface depth data, building a 3-D crustal velocity structure model for the middle-eastern NCC, named HBCrust1.0, by using the Kriging interpolation method. Our result shows that the first-arrival times calculated by HBCust1.0 fit well with the observations. The result demonstrates that the upper crust is the main seismogenic layer, and the brittle-ductile transition occurs at depths near interface C(the interface between upper and lower crust). The depth of interface Moho varies beneath the source area of the Tangshan earthquake, and a low-velocity structure is found to extend from the source area to the lower crust. Based on these observations, it can be inferred that stress accumulation responsible for the Tangshan earthquake may have been closely related to the migration and deformation of the mantle materials. Comparisons of the average velocities of the whole crust, the upper and the lower crust show that the average velocity of the lower crust under the central part of the North China Basin(NCB) in the east of the craton is obviously higher than the regional average. This high-velocity probably results from long-term underplating of the mantle magma.展开更多
Based on the spatial distribution of ancient rocks and zircons, three ancient terranes older than ca. 2.6 Ga have recently been identified in the North China Craton, namely the Eastern, Southern, and Central Ancient T...Based on the spatial distribution of ancient rocks and zircons, three ancient terranes older than ca. 2.6 Ga have recently been identified in the North China Craton, namely the Eastern, Southern, and Central Ancient Terranes. The Eastern Ancient Terrane is the best studied and understood of the three ancient terranes. It has a long geological history back to ca. 3.8 Ga ago and includes the areas of Anshan-Benxi, eastern Hebei, eastern Shandong and western Shandong. In Anshan-Benxi, several different types of 3.8 Ga rocks were discovered together with 3.1-3.7 Ga rocks, whereas 2.9-3.0 Ga K-rich granites and 2.5 Ga syenogranite occur on larger scales. In eastern Hebei, 3.0-3.4 Ga rocks and older detrital and xenocrystic zircons were identified. In eastern Shandong, there are a large volumes of 2.7 Ga and 2.9 Ga rocks. In western Shandong, early Neoarchean （2.6-2.7 Ga） intrusive and supracrustal rocks are widely distributed. Whole-rock Nd and zircon Hf isotope data suggest that both mantle additions and crustal recycling played important roles within the Eastern Ancient Terrane during almost every tectono-magmatic event. Most BIFs in the North China Craton are late Neoarchean in age and are distributed on continental crust along the western margin of the Eastern Ancient Terrane, probably suggesting that a stable environment was one of the key factors for the formation of large-scale BIFs.展开更多
U-Pb zircon age, geochemical, and Sr-Nd-Pb isotopic data of mafic dykes from eastern Shandong Province, eastern China is reported herein. Laser ablation inductively coupled plasma mass spectrometry （LA-ICP-MS） U-Pb ...U-Pb zircon age, geochemical, and Sr-Nd-Pb isotopic data of mafic dykes from eastern Shandong Province, eastern China is reported herein. Laser ablation inductively coupled plasma mass spectrometry （LA-ICP-MS） U-Pb zircon analyses of two samples from the investigated mafic dykes yield consistent ages ranging from 121.9 Ma ± 0.47 Ma to 122.9 Ma ± 0.61 Ma. The mafic dykes are characterized by high （87Sr/86Sr） i ranging from 0.7087 to 0.7089, low εNd（t） values ranging from -16.9 to -17.8, 206Pb/204Pb = 17.15 to 17.17, 207Pb/204Pb = 15.45 to 15.47, and 208Pb/204Pb = 37.59 to 37.68. Results from the current study suggest that the mafic dykes are derived from partial melting of ancient lithospheric mantle that was variably hybridized by melts derived from foundered lower crustal eclogite. The mafic dykes may have been generated through subsequent insignificant crystal fractionation and very minor crustal contamination during magma ascent. Combined with previous studies, the current findings provide new evidence that the intense lithospheric thinning beneath the eastern Shandong Province of eastern China occurred at ~120 Ma, and that this condition was caused by the removal of the lower lithosphere （mantle and lower crust）.展开更多
始太古代及形成时代更古老的岩石十分稀少,任何新的发现都是对最早期陆壳形成演化研究的重要贡献。本文首次报道了华北克拉通冀东地区~3.8 Ga TTG岩石的年龄和地球化学组成。样品J2012为花岗闪长质片麻岩,J2013为侵入花岗闪长质片麻岩...始太古代及形成时代更古老的岩石十分稀少,任何新的发现都是对最早期陆壳形成演化研究的重要贡献。本文首次报道了华北克拉通冀东地区~3.8 Ga TTG岩石的年龄和地球化学组成。样品J2012为花岗闪长质片麻岩,J2013为侵入花岗闪长质片麻岩的花岗闪长岩脉,也遭受变质变形。两者的岩浆锆石年龄分别为3785±8 Ma和3773±6 Ma。尽管岩石的常量元素组成和形成时代类似,但稀土模式明显不同。样品J2012的TREE(稀土总量)和(La/Yb)n比值分别为139.2×10^(-6)和8.44,组成特征与北美4.03 Ga Acasta片麻岩类似,岩浆作用发生在相对低压的条件下,岩浆作用过程中无石榴子石参与而有斜长石存在。样品J2013的TREE和(La/Yb)n比值分别为163.5×10^(-6)和51.16。轻重稀土强烈分异要求花岗闪长岩形成于石榴子石稳定和斜长石不稳定的高压条件下。研究表明,冀东地区在~3.8 Ga时TTG岩浆作用就显示出多样性,支持了古太古代早期—冥古宙陆壳基底广泛存在的认识。根据始太古代岩石类型和组成特征等综合对比,认为鞍本和冀东是华北克拉通2个不同的古陆核形成演化中心。展开更多
基金supported by 973 (2012CB416601) and NFSC (41322018) projects
文摘It is well known that there are widespread igneous events at;100 Ma in the Eastern North China Craton;however,their tectonic environments are controversial.They were thought to be either related to an intra-continental rifting or
基金supported by the project of China Geological Survey(Grant No.DD20190438)。
文摘The timing and mechanisms of lithospheric thinning and destruction of the North China Craton(NCC)remain controversial,and the overall geodynamics of the process are poorly understood.This paper documents Late Triassic igneous rocks including monzogranite,gabbro,and diorite from the Xiuyan District on the Liaodong Peninsula in the eastern NCC,which have LA-ICP-MS zircon U-Pb ages of 229.0±0.4 Ma,216.2±0.9 Ma,and 210.6±2.0 Ma,respectively.Monzogranite shows high-SiO_(2) adakite affinity,negative ε_(Hf)(t)values(-20.6 to-17.9),and old T_(DM2) ages(3.53-3.29 Ga),suggesting that their parental magma was derived from thickened Paleoarchean mafic lower crust and minor mantle materials that were also involved their generation.Gabbro is ultrapotassic,strongly enriched in LREEs and LILEs,depleted in HFSEs,and has evolved zircon Hf isotopes with negative ε_(Hf) of -10.04 to-5.85 and old T_(DM2) ages(2.59-2.22 Ga).These are diagnostic signatures of a crustal component,but their high contents of Mg O,Cr,Co,Ni indicate that the primary magma originated from enriched mantle.Diorite is enriched in LILEs and LREEs,depleted in HFSEs(with negative Nb,Ta,and Ti anomalies),and contains negative ε_(Hf)(t)values(-13.64 to-11.01).Compared with the gabbro,the diorite is relatively enriched in Nb,Ta and HREEs,and also contains younger T_(DM2) ages(2.11-1.94 Ga),suggesting that the diorite was formed by mixing between ancient lower crust-derived felsic magmas and asthenospheric mantle-derived magmas.Field observations,geochronology,geochemistry,and zircon Lu-Hf isotopes indicate that Late Triassic magmatism and tectonic activity resulted from deep subduction of the Yangtze Craton beneath the NCC in the Xiuyan area.This phase of tectonic activity was completed in the eastern NCC by the Late Triassic(216 Ma),and was subsequently followed by lithospheric thinning that began in the Late Triassic.
基金co-funded by the National Natural Science Foundation of China(Grant Nos.42002089,41930428)the National Key R&D Program of China(Grant Nos.2016YFC0600401 and 2017YFC0602302)+1 种基金by Open Research Fund Program of Key Laboratory of Metallogenic Prediction of Nonferrous Metals and Geological Environment Monitoring(Central South University)Ministry of Education(Grant Nos.2020YSJS02,2020YSJS01).
文摘The variation of crustal thickness is a critical index to reveal how the continental crust evolved over its four billion years.Generally,ratios of whole-rock trace elements,such as Sr/Y,(La/Yb)n and Ce/Y,are used to characterize crustal thicknesses.However,sometimes confusing results are obtained since there is no enough filtered data.Here,a state-of-the-art approach,based on a machine-learning algorithm,is proposed to predict crustal thickness using global major-and trace-element geochemical data of intermediate arc rocks and intraplate basalts,and their corresponding crustal thicknesses.After the validation processes,the root-mean-square error(RMSE)and the coefficient of determination(R2)score were used to evaluate the performance of the machine learning algorithm based on the learning dataset which has never been used during the training phase.The results demonstrate that the machine learning algorithm is more reliable in predicting crustal thickness than the conventional methods.The trained model predicts that the crustal thickness of the eastern North China Craton(ENCC)was-45 km from the Late Triassic to the Early Cretaceous,but-35 km from the Early Cretaceous,which corresponds to the paleo-elevation of 3.0±1.5 km at Early Mesozoic,and decease to the present-day elevation in the ENCC.The estimates are generally consistent with the previous studies on xenoliths from the lower crust and on the paleoenvironment of the coastal mountain of the ENCC,which indicates that the lower crust of the ENCC was delaminated abruptly at the Early Cretaceous.
基金the National Natural Science Foundation of China(Grant Nos.41772043 and 41802043)the Chinese Academy of Sciences“Light of West China”Program(Dawei Fan,2017 and Jingui Xu,2019)+1 种基金the Youth Innovation Promotion Association CAS(Dawei Fan,2018434)the Innovation and Entrepreneurship Funding of High-Level Overseas Talents of Guizhou Province(Dawei Fan,[2019]10).
文摘Mesozoic intermediate-felsic magmatic rocks in the eastern North China Craton commonly show geochemical similarity to adakites.However,the lack of direct constraints from partial melting experiments at high pressures and temperatures fuels a debate over the origin of these rocks.In this work,we performed partial melting experiments at 1.5 GPa and 800–950℃on amphibolite samples collected from the vicinity of the Mesozoic potassium-rich adakitic rocks in the Zhangjiakou area,northern margin of the North China Craton.The experimental melts range from granitic to granodioritic compositions,with SiO_(2)=56.4–72.6 wt.%,Al_(2)O_(3)=16.1–19.3 wt.%,FeO^(*)=2.4–9.6 wt.%,MgO=0.3–2.0 wt.%,CaO=0.6–3.8 wt.%,Na_(2)O=4.7–5.3 wt.%,and K_(2)O=2.6–3.9 wt.%,which are in the ranges of the surrounding Mesozoic potassium-rich adakitic rocks,except for the higher Al_(2)O_(3)contents and the data point at 1.5 GPa and 800℃.Trace element compositions of the melts measured by LA-ICP-MS are rich in Sr(849–1067 ppm)and light rare earth elements(LREEs)and poor in Y(<10.4 ppm)and Yb(<0.88 ppm),and have high Sr/Y(102–221)and(La/Yb)n(27–41)ratios and strongly fractionated rare earth element(REE)patterns,whereas no obvious negative Eu anomalies are observed.The geochemical characteristics show overall similarity to the Mesozoic potassium-rich adakitic rocks in the area,especially adakites with low Mg#,again except for the data point at 1.5 GPa and 800℃.The results suggest that partial melting of amphibolite can produce potassium-rich adakitic rocks with low Mg#in the eastern North China Craton under the experimental conditions of 1.5 GPa and 850–950℃.The experimental restites consist of hornblende(Hbl)+plagioclase(Pl)+garnet(Grt)±clinopyroxene(Cpx),a mineral assemblage significantly different from that of the nearby Hannuoba mafic granulite xenoliths which consist of Cpx+orthopyroxene(Opx)+Pl±Grt.Chemically,the experimental restites contain higher Al_(2)O_(3)but lower MgO and CaO than the Hannuoba mafic granulite xenoliths.We therefore argue that the Hannuoba mafic granulite xenoliths cannot represent the direct products of partial melting of the experimental amphibolite.
基金supported by the National Natural Science Foundation of China (Grant Nos. 90814012, 91014006, 91414301, 41174052 & 41274113)
文摘Lithosphere thinning and destruction in the middle-eastern North China Craton(NCC), a region susceptible to strong earthquakes, is one of the research hotspots in solid earth science. All 42 seismic wide-angle reflection/refraction profiles have been completed in the middle-eastern NCC. We collect all the 2-D profiling results and perform gridding of the velocity and interface depth data, building a 3-D crustal velocity structure model for the middle-eastern NCC, named HBCrust1.0, by using the Kriging interpolation method. Our result shows that the first-arrival times calculated by HBCust1.0 fit well with the observations. The result demonstrates that the upper crust is the main seismogenic layer, and the brittle-ductile transition occurs at depths near interface C(the interface between upper and lower crust). The depth of interface Moho varies beneath the source area of the Tangshan earthquake, and a low-velocity structure is found to extend from the source area to the lower crust. Based on these observations, it can be inferred that stress accumulation responsible for the Tangshan earthquake may have been closely related to the migration and deformation of the mantle materials. Comparisons of the average velocities of the whole crust, the upper and the lower crust show that the average velocity of the lower crust under the central part of the North China Basin(NCB) in the east of the craton is obviously higher than the regional average. This high-velocity probably results from long-term underplating of the mantle magma.
基金financially supported by the Major State Basic Research Program of the People’s Republic of China(2012CB416600)the National Natural Science Foundation of China(41472169,41172127)the Key Program of the Ministry of Land and Resources of China(DD20160121-03,12120114021301,1212010811033,and 12120115070301)
文摘Based on the spatial distribution of ancient rocks and zircons, three ancient terranes older than ca. 2.6 Ga have recently been identified in the North China Craton, namely the Eastern, Southern, and Central Ancient Terranes. The Eastern Ancient Terrane is the best studied and understood of the three ancient terranes. It has a long geological history back to ca. 3.8 Ga ago and includes the areas of Anshan-Benxi, eastern Hebei, eastern Shandong and western Shandong. In Anshan-Benxi, several different types of 3.8 Ga rocks were discovered together with 3.1-3.7 Ga rocks, whereas 2.9-3.0 Ga K-rich granites and 2.5 Ga syenogranite occur on larger scales. In eastern Hebei, 3.0-3.4 Ga rocks and older detrital and xenocrystic zircons were identified. In eastern Shandong, there are a large volumes of 2.7 Ga and 2.9 Ga rocks. In western Shandong, early Neoarchean （2.6-2.7 Ga） intrusive and supracrustal rocks are widely distributed. Whole-rock Nd and zircon Hf isotope data suggest that both mantle additions and crustal recycling played important roles within the Eastern Ancient Terrane during almost every tectono-magmatic event. Most BIFs in the North China Craton are late Neoarchean in age and are distributed on continental crust along the western margin of the Eastern Ancient Terrane, probably suggesting that a stable environment was one of the key factors for the formation of large-scale BIFs.
基金supported by Opening Project(201206)of the State Key Laboratory of Ore deposit Geochemistry,Chinese Academia of Sciencesthe National Nature Science Foundation of China(40773020,40972071,90714010,and 40634020)
文摘U-Pb zircon age, geochemical, and Sr-Nd-Pb isotopic data of mafic dykes from eastern Shandong Province, eastern China is reported herein. Laser ablation inductively coupled plasma mass spectrometry （LA-ICP-MS） U-Pb zircon analyses of two samples from the investigated mafic dykes yield consistent ages ranging from 121.9 Ma ± 0.47 Ma to 122.9 Ma ± 0.61 Ma. The mafic dykes are characterized by high （87Sr/86Sr） i ranging from 0.7087 to 0.7089, low εNd（t） values ranging from -16.9 to -17.8, 206Pb/204Pb = 17.15 to 17.17, 207Pb/204Pb = 15.45 to 15.47, and 208Pb/204Pb = 37.59 to 37.68. Results from the current study suggest that the mafic dykes are derived from partial melting of ancient lithospheric mantle that was variably hybridized by melts derived from foundered lower crustal eclogite. The mafic dykes may have been generated through subsequent insignificant crystal fractionation and very minor crustal contamination during magma ascent. Combined with previous studies, the current findings provide new evidence that the intense lithospheric thinning beneath the eastern Shandong Province of eastern China occurred at ~120 Ma, and that this condition was caused by the removal of the lower lithosphere （mantle and lower crust）.
文摘始太古代及形成时代更古老的岩石十分稀少,任何新的发现都是对最早期陆壳形成演化研究的重要贡献。本文首次报道了华北克拉通冀东地区~3.8 Ga TTG岩石的年龄和地球化学组成。样品J2012为花岗闪长质片麻岩,J2013为侵入花岗闪长质片麻岩的花岗闪长岩脉,也遭受变质变形。两者的岩浆锆石年龄分别为3785±8 Ma和3773±6 Ma。尽管岩石的常量元素组成和形成时代类似,但稀土模式明显不同。样品J2012的TREE(稀土总量)和(La/Yb)n比值分别为139.2×10^(-6)和8.44,组成特征与北美4.03 Ga Acasta片麻岩类似,岩浆作用发生在相对低压的条件下,岩浆作用过程中无石榴子石参与而有斜长石存在。样品J2013的TREE和(La/Yb)n比值分别为163.5×10^(-6)和51.16。轻重稀土强烈分异要求花岗闪长岩形成于石榴子石稳定和斜长石不稳定的高压条件下。研究表明,冀东地区在~3.8 Ga时TTG岩浆作用就显示出多样性,支持了古太古代早期—冥古宙陆壳基底广泛存在的认识。根据始太古代岩石类型和组成特征等综合对比,认为鞍本和冀东是华北克拉通2个不同的古陆核形成演化中心。
