A suite of ~1.84-1.92 Ga metamafic dykes within the paragneiss suite（khondalite） of the Quanji massif in NW China, has been chosen in this study for further understanding the tectonic evolution and possible links to...A suite of ~1.84-1.92 Ga metamafic dykes within the paragneiss suite（khondalite） of the Quanji massif in NW China, has been chosen in this study for further understanding the tectonic evolution and possible links to the global Columbia supercontinent. Occurrence and field relations suggest that they were formed coevally with a previous studied ~1.83-1.85 Ga metamafic dyke swarms. Whole-rock major and trace elemental geochemistry suggests precursor magma of the amphibolites being generated from a volcanic arc-related tectonic setting rather than a back-arc environment where the metamafic dyke swarms were emplaced. The metamafic dykes show enrichment of LREE and strongly negative anomalies for Ta-Nb, Zr-Hf and Ti, have high SiO_2（49.3 wt.%-52.5 wt.%） but low MgO（6.40 wt.%-7.76 wt.%） contents and Mg~#（Mg~#=[100×（MgO/40.3）]/[MgO/40.3＋FeO/71.8]） values（45.7-52.1）, suggesting evolved precursor magma. The high values of La/Ta（22.2-42.8） and La/Nb（1.71-2.47）, mildly negative εNd（t） values（-2.51-0.15）, with depleted mantle model ages（TDM） of 2.45-2.84 Ga, suggest that their precursor magmas were possibly derived from a subduction-related fluid metasomatized Archean sub-continental lithospheric mantle. This study provides further evidence for oceanic plate subduction prevailing before or around ~1.85 Ga, which confirms a prolonged subduction-accretion-collision history in the NW China which is possibly linked to the assembly of the Columbia supercontinent.展开更多
Bulk-rock major and trace elements and zircon U-Pb data are reported for Permian metamafic rocks from Guoganjianan, in the western part of Longmuco-Shuanghu-Lancang suture zone. These results offer new insights into m...Bulk-rock major and trace elements and zircon U-Pb data are reported for Permian metamafic rocks from Guoganjianan, in the western part of Longmuco-Shuanghu-Lancang suture zone. These results offer new insights into mantle source characteristics and geodynamic setting of Permian ophiolitic fragments. U-Pb isotopic dating using SHRIMP II method reveals that the metamafic rocks were formed at 274.7± 3.9 and 279.8± 3.6 Ma. The metamafic rocks mostly show N-MORB-typed rare earth element patterns and are enrichment in large-ion lithophile elements, indicating that they are probably derived from partial melting of a depleted mantle in a back-arc basin. Our new data, together with recent studied results on Paleozoic ophiolitic fragments suggest the Paleo-Tethys Ocean in Central Qiangtang opened at Cambrian and widened between Ordovician and Devonian. Northward subduction started in the Late Devonian–Early Carboniferous and a back-arc basin developed during Permian.展开更多
The Jiao-Liao-Ji Belt within the North China Craton had undergone a complex tectonic evolution,marked by extensive Paleoproterozoic magmatism that produced a diverse range of mafic to felsic magmatic rocks.These event...The Jiao-Liao-Ji Belt within the North China Craton had undergone a complex tectonic evolution,marked by extensive Paleoproterozoic magmatism that produced a diverse range of mafic to felsic magmatic rocks.These events provide valuable geological records for understanding the tectonic evolution of the Jiao-Liao-Ji Belt.This study focuses on the Paleoproterozoic Chibaisong meta-gabbro in southern Jilin,investigating the source of mafic magma,petrogenesis,and tectonic setting through systematic petrological analysis,zircon U-Pb dating,and geochemical studies.The findings contribute to constraining the dynamic mechanisms of Paleoproterozoic extensional rifting in the Jiao-Liao-Ji orogenic belt.Geochemical data indicate that the samples exhibit low SiO₂(47.99–50.66 wt.%),TiO₂(0.75–3.20 wt.%),Nb(3.22–8.09 ppm),and Ta(0.22–0.51 ppm)contents,along with high TFeO₃(11.97–15.82 wt.%)and MgO(5.67–12.66 wt.%)concentrations.They also show low Nb/La ratios and high(Th/Nb)N values,consistent with the geochemical characteristics of tholeiitic basalts.The samples display low total rare earth element concentrations,weak or absent Eu anomalies,slight enrichment in light rare earth elements,relatively flat heavy rare earth element patterns,and depletion in Nb,Ta,and Ti.The meta-gabbro from southern Jilin exhibits geochemical similarities to Paleoproterozoic metamafic rocks from other regions of the Jiao-Liao-Ji Belt,resembling enriched mid-ocean ridge basalts(E-MORB)with Nb,Ta,and Ti depletion.Integration of previous studies and geochemical data suggests that the 2.16–2.10 Ga metamafic rocks in the Jiao-Liao-Ji Belt experienced contamination by older crustal material.These results indicate that the 2.16–2.10 Ga metamafic rocks are unlikely to be associated with island arc,continental arc,or mid-ocean ridge settings.Instead,they are more likely related to intraplate magmatism associated with continental rifting.展开更多
基金supported by the National Natural Science Foundation of China (Nos. 41172069, 41072044, and 41372075)
文摘A suite of ~1.84-1.92 Ga metamafic dykes within the paragneiss suite（khondalite） of the Quanji massif in NW China, has been chosen in this study for further understanding the tectonic evolution and possible links to the global Columbia supercontinent. Occurrence and field relations suggest that they were formed coevally with a previous studied ~1.83-1.85 Ga metamafic dyke swarms. Whole-rock major and trace elemental geochemistry suggests precursor magma of the amphibolites being generated from a volcanic arc-related tectonic setting rather than a back-arc environment where the metamafic dyke swarms were emplaced. The metamafic dykes show enrichment of LREE and strongly negative anomalies for Ta-Nb, Zr-Hf and Ti, have high SiO_2（49.3 wt.%-52.5 wt.%） but low MgO（6.40 wt.%-7.76 wt.%） contents and Mg~#（Mg~#=[100×（MgO/40.3）]/[MgO/40.3＋FeO/71.8]） values（45.7-52.1）, suggesting evolved precursor magma. The high values of La/Ta（22.2-42.8） and La/Nb（1.71-2.47）, mildly negative εNd（t） values（-2.51-0.15）, with depleted mantle model ages（TDM） of 2.45-2.84 Ga, suggest that their precursor magmas were possibly derived from a subduction-related fluid metasomatized Archean sub-continental lithospheric mantle. This study provides further evidence for oceanic plate subduction prevailing before or around ~1.85 Ga, which confirms a prolonged subduction-accretion-collision history in the NW China which is possibly linked to the assembly of the Columbia supercontinent.
基金supported by the Postdoctoral Science Foundation of China (No. 2014M561023)the National Natural Science Foundation of China (Nos. 40872146, 41072166, 41503022)the Project of China Geological Survey (Nos. 1212011086061, 1212011221093, 1212011087009)
文摘Bulk-rock major and trace elements and zircon U-Pb data are reported for Permian metamafic rocks from Guoganjianan, in the western part of Longmuco-Shuanghu-Lancang suture zone. These results offer new insights into mantle source characteristics and geodynamic setting of Permian ophiolitic fragments. U-Pb isotopic dating using SHRIMP II method reveals that the metamafic rocks were formed at 274.7± 3.9 and 279.8± 3.6 Ma. The metamafic rocks mostly show N-MORB-typed rare earth element patterns and are enrichment in large-ion lithophile elements, indicating that they are probably derived from partial melting of a depleted mantle in a back-arc basin. Our new data, together with recent studied results on Paleozoic ophiolitic fragments suggest the Paleo-Tethys Ocean in Central Qiangtang opened at Cambrian and widened between Ordovician and Devonian. Northward subduction started in the Late Devonian–Early Carboniferous and a back-arc basin developed during Permian.
基金Supported by National Natural Science Foundation of China(No.42172212).
文摘The Jiao-Liao-Ji Belt within the North China Craton had undergone a complex tectonic evolution,marked by extensive Paleoproterozoic magmatism that produced a diverse range of mafic to felsic magmatic rocks.These events provide valuable geological records for understanding the tectonic evolution of the Jiao-Liao-Ji Belt.This study focuses on the Paleoproterozoic Chibaisong meta-gabbro in southern Jilin,investigating the source of mafic magma,petrogenesis,and tectonic setting through systematic petrological analysis,zircon U-Pb dating,and geochemical studies.The findings contribute to constraining the dynamic mechanisms of Paleoproterozoic extensional rifting in the Jiao-Liao-Ji orogenic belt.Geochemical data indicate that the samples exhibit low SiO₂(47.99–50.66 wt.%),TiO₂(0.75–3.20 wt.%),Nb(3.22–8.09 ppm),and Ta(0.22–0.51 ppm)contents,along with high TFeO₃(11.97–15.82 wt.%)and MgO(5.67–12.66 wt.%)concentrations.They also show low Nb/La ratios and high(Th/Nb)N values,consistent with the geochemical characteristics of tholeiitic basalts.The samples display low total rare earth element concentrations,weak or absent Eu anomalies,slight enrichment in light rare earth elements,relatively flat heavy rare earth element patterns,and depletion in Nb,Ta,and Ti.The meta-gabbro from southern Jilin exhibits geochemical similarities to Paleoproterozoic metamafic rocks from other regions of the Jiao-Liao-Ji Belt,resembling enriched mid-ocean ridge basalts(E-MORB)with Nb,Ta,and Ti depletion.Integration of previous studies and geochemical data suggests that the 2.16–2.10 Ga metamafic rocks in the Jiao-Liao-Ji Belt experienced contamination by older crustal material.These results indicate that the 2.16–2.10 Ga metamafic rocks are unlikely to be associated with island arc,continental arc,or mid-ocean ridge settings.Instead,they are more likely related to intraplate magmatism associated with continental rifting.
