Mesozoic sedimentary units within the Nanzhao and Mashiping basins record the paleogeographic and tectonic evolution of the Qinling Orogen(QO).This study uses new detrital zircon U-Pb ages and Hf isotopic data to cons...Mesozoic sedimentary units within the Nanzhao and Mashiping basins record the paleogeographic and tectonic evolution of the Qinling Orogen(QO).This study uses new detrital zircon U-Pb ages and Hf isotopic data to constrain the timing of deposition and provenance of the Taishanmiao,Taizishan,Nanzhao,and Mashiping formations of the North Qinling Orogen(NQO).The detrital zircons can be split by age peaks into five major groups,including Early Cretaceous,Late Triassic,Early Paleozoic,Neoproterozoic and Paleoproterozoic age peaks.On the basis of the youngest zircon ages and age-diagnostic fossils,we conclude that the Taishanmiao(youngest age of 234 Ma)and Taizishan(216 Ma)formations were deposited during the Late Triassic,whereas the Nanzhao Formation(110 Ma)was deposited during the Early Cretaceous rather than the Late Jurassic as previously thought.The Mashiping Formation(110 Ma)was also deposited during the Early Cretaceous.Combined with zircon Hf isotopic compositions,zircons from Late Triassic units were generally derived from the NQO,South Qinling Orogen(SQO),and North China Craton(NCC),with minor amounts derived from the Xing-Meng Orogenic Belt.The sediments within the Nanzhao Formation were mainly derived from the QO,with a minor contribution from the NCC.The Early Cretaceous conglomerates of the Mashiping Formation were generally derived from recycled earlier detritus.This implies that Late Triassic deposition was related to the final closure of the Mianlue Ocean,whereas Early Cretaceous deposition was correlated to the continued intercontinental subduction of the Yangtze Craton beneath the QO.The change in provenance within these Mesozoic sediments suggests the QO underwent two periods of significant uplift,which was a process generated sediments that were deposited in a series of basins of this area.展开更多
Accretionary orogens are sites of extensive continental crustal growth and modification.The mechanism by which mafic crust is transformed into silicic melts(i.e.,maturation of continental crust)is important for unders...Accretionary orogens are sites of extensive continental crustal growth and modification.The mechanism by which mafic crust is transformed into silicic melts(i.e.,maturation of continental crust)is important for understanding the formation of the continental crust.The North Qinling Orogen(NQO)is a composite orogenic belt and contains an early Paleozoic accretion-dominated orogenic system,which is ideal for investigating continental crustal maturation.We obtained zircon and monazite U–Pb age and O isotope data,zircon Lu–Hf isotope data,and whole-rock major-and trace-element and Sr–Nd isotope data for early Paleozoic granitoids of the NQO.The granitoids are divided into three groups.Group 1 includes the Taiping tonalite(445±3 Ma),the Manziying syenogranite(445±2 Ma),and the Huoshenmiao granodiorite(436±2 Ma).The Taiping and Huoshenmiao plutons have relatively high SiO_(2)contents(68.64–71.67 wt.%)and Na_(2)O/K_(2)O ratios(1.15–4.19),with enrichments in Rb,Ba,Th,and U and depletions in Nb,Ta,P,and Ti,and they are geochemically similar to sodic arc magmas.The Manziying syenogranite is a peraluminous potassic granite with high K_(2)O contents(4.59–5.27 wt.%).Grantioids from Group 1 have similarly depleted Sr–Nd–Hf–O isotopic features(eHf[t]=+5.9 to+8.8;δ^(18)O=3.98‰–5.41‰),indicative of derivation via partial melting of oceanic arc crust,which suggests that partial melting of oceanic arc crust in a subduction system contributes to the generation of continental crust and causes its maturation.Group 2 consists of the Wuduoshan monzogranite(418±2 Ma)and the Sikeshu granodiorite(423±3 Ma).These plutons have relatively high SiO_(2)(65.59–72.06 wt.%),K_(2)O(3.26–4.79 wt.%),and Al2O3(14.65–16.12 wt.%)contents and Sr/Y(33–87)and(La/Yb)N(23–48)ratios.The Wuduoshan monzogranite has positive zircon eHf(t)(+0.4 to+3.1)and uniformδ^(18)O(6.38‰–8.07‰)values,but the Sikeshu granodiorite has more variable isotopic compositions(eHf[t]=-1.9 to+5.0;δ^(18)O=6.37‰–10.60‰).The Wuduoshan monzogranite and Sikeshu granodiorite have similar whole-rock Sr–Nd isotopic compositions to basement rocks of the NQO.These features indicate that the two plutons formed by partial melting of basement rocks(i.e.,subducted into the lower crust)of the North Qinling unit,along with juvenile crustal material.Group 3 is represented by the Xiaguan monzogranite,which formed at 434–430 Ma,and can be subdivided into heavy rare earth element(REE)-depleted and-enriched units.The former has high Sr/Y(56–98)and(La/Yb)_(N)(34–73)ratios and low MgO(0.13–0.24 wt.%),Cr(0.37–1.69 ppm),and Ni(0.32–1.09 ppm)contents,similar to adakites derived from metabasaltic sources.The heavy REE-enriched nature of the Xiaguan monzogranite may reflect modification of its source by melt or fluid.Our results show that partial melting of enriched oceanic arc crust contributed to crustal maturation in an accretionary orogen.The addition of evolved crustal material also facilitated this process;therefore,the basement rocks and crustal thickness should be considered when assessing crustal dynamics in an accretionary orogen.展开更多
基金financially supported by the Natural Science Foundation of China(41722204,42072063 and 41472052)the National Key Research and Development Program of China(2016YFC0600103)+1 种基金the research grant of State Key Laboratory of Isotope Geochemistry,Guangzhou Institute of Geochemistry,Chinese Academy of Sciences(SKLaBIGKF-18-06)Basic Scientific Research Foundation of Central Universities of China(Jilin University)。
文摘Mesozoic sedimentary units within the Nanzhao and Mashiping basins record the paleogeographic and tectonic evolution of the Qinling Orogen(QO).This study uses new detrital zircon U-Pb ages and Hf isotopic data to constrain the timing of deposition and provenance of the Taishanmiao,Taizishan,Nanzhao,and Mashiping formations of the North Qinling Orogen(NQO).The detrital zircons can be split by age peaks into five major groups,including Early Cretaceous,Late Triassic,Early Paleozoic,Neoproterozoic and Paleoproterozoic age peaks.On the basis of the youngest zircon ages and age-diagnostic fossils,we conclude that the Taishanmiao(youngest age of 234 Ma)and Taizishan(216 Ma)formations were deposited during the Late Triassic,whereas the Nanzhao Formation(110 Ma)was deposited during the Early Cretaceous rather than the Late Jurassic as previously thought.The Mashiping Formation(110 Ma)was also deposited during the Early Cretaceous.Combined with zircon Hf isotopic compositions,zircons from Late Triassic units were generally derived from the NQO,South Qinling Orogen(SQO),and North China Craton(NCC),with minor amounts derived from the Xing-Meng Orogenic Belt.The sediments within the Nanzhao Formation were mainly derived from the QO,with a minor contribution from the NCC.The Early Cretaceous conglomerates of the Mashiping Formation were generally derived from recycled earlier detritus.This implies that Late Triassic deposition was related to the final closure of the Mianlue Ocean,whereas Early Cretaceous deposition was correlated to the continued intercontinental subduction of the Yangtze Craton beneath the QO.The change in provenance within these Mesozoic sediments suggests the QO underwent two periods of significant uplift,which was a process generated sediments that were deposited in a series of basins of this area.
基金This work was financially supported by the Natural Science Foundation of China(grant Nos.42072063,41722204)Program for Jilin University Science and Technology Inovative Research Team(2021TD-05)Postgraduate Innovation Research Program of Jilin University(101832020CX199).
文摘Accretionary orogens are sites of extensive continental crustal growth and modification.The mechanism by which mafic crust is transformed into silicic melts(i.e.,maturation of continental crust)is important for understanding the formation of the continental crust.The North Qinling Orogen(NQO)is a composite orogenic belt and contains an early Paleozoic accretion-dominated orogenic system,which is ideal for investigating continental crustal maturation.We obtained zircon and monazite U–Pb age and O isotope data,zircon Lu–Hf isotope data,and whole-rock major-and trace-element and Sr–Nd isotope data for early Paleozoic granitoids of the NQO.The granitoids are divided into three groups.Group 1 includes the Taiping tonalite(445±3 Ma),the Manziying syenogranite(445±2 Ma),and the Huoshenmiao granodiorite(436±2 Ma).The Taiping and Huoshenmiao plutons have relatively high SiO_(2)contents(68.64–71.67 wt.%)and Na_(2)O/K_(2)O ratios(1.15–4.19),with enrichments in Rb,Ba,Th,and U and depletions in Nb,Ta,P,and Ti,and they are geochemically similar to sodic arc magmas.The Manziying syenogranite is a peraluminous potassic granite with high K_(2)O contents(4.59–5.27 wt.%).Grantioids from Group 1 have similarly depleted Sr–Nd–Hf–O isotopic features(eHf[t]=+5.9 to+8.8;δ^(18)O=3.98‰–5.41‰),indicative of derivation via partial melting of oceanic arc crust,which suggests that partial melting of oceanic arc crust in a subduction system contributes to the generation of continental crust and causes its maturation.Group 2 consists of the Wuduoshan monzogranite(418±2 Ma)and the Sikeshu granodiorite(423±3 Ma).These plutons have relatively high SiO_(2)(65.59–72.06 wt.%),K_(2)O(3.26–4.79 wt.%),and Al2O3(14.65–16.12 wt.%)contents and Sr/Y(33–87)and(La/Yb)N(23–48)ratios.The Wuduoshan monzogranite has positive zircon eHf(t)(+0.4 to+3.1)and uniformδ^(18)O(6.38‰–8.07‰)values,but the Sikeshu granodiorite has more variable isotopic compositions(eHf[t]=-1.9 to+5.0;δ^(18)O=6.37‰–10.60‰).The Wuduoshan monzogranite and Sikeshu granodiorite have similar whole-rock Sr–Nd isotopic compositions to basement rocks of the NQO.These features indicate that the two plutons formed by partial melting of basement rocks(i.e.,subducted into the lower crust)of the North Qinling unit,along with juvenile crustal material.Group 3 is represented by the Xiaguan monzogranite,which formed at 434–430 Ma,and can be subdivided into heavy rare earth element(REE)-depleted and-enriched units.The former has high Sr/Y(56–98)and(La/Yb)_(N)(34–73)ratios and low MgO(0.13–0.24 wt.%),Cr(0.37–1.69 ppm),and Ni(0.32–1.09 ppm)contents,similar to adakites derived from metabasaltic sources.The heavy REE-enriched nature of the Xiaguan monzogranite may reflect modification of its source by melt or fluid.Our results show that partial melting of enriched oceanic arc crust contributed to crustal maturation in an accretionary orogen.The addition of evolved crustal material also facilitated this process;therefore,the basement rocks and crustal thickness should be considered when assessing crustal dynamics in an accretionary orogen.
