The SHRIMP U-Pb ages are reported for two volcanic rocks from the Longwangshan and the Dawangshan formations respectively, Ningwu area, Jiangsu Province. The Dawangshan formation (NB-01) is dated at (127 3) Ma, and th...The SHRIMP U-Pb ages are reported for two volcanic rocks from the Longwangshan and the Dawangshan formations respectively, Ningwu area, Jiangsu Province. The Dawangshan formation (NB-01) is dated at (127 3) Ma, and the Longwangshan formation (NL-01), (131 4) Ma. Besides, a few Archean zircons are also found in the Longwangshan formation, which suggests a possible Archean basement in the region.展开更多
Zircon U-Pb ages and geochemical data of volcanic rocks in the Suifenhe Formation in eastern Heilongjiang Province are reported, and their petrogenesis is discussed in this paper. The Suifenhe Formation mainly consist...Zircon U-Pb ages and geochemical data of volcanic rocks in the Suifenhe Formation in eastern Heilongjiang Province are reported, and their petrogenesis is discussed in this paper. The Suifenhe Formation mainly consists of basalt, andesite, and dacite. Zircon from andesite and dacite are euhedral in shape and show typical oscillatory zoning with high Th/U ratios （0.18-0.57）, implying its magmatic origin. Zircon U-Pb dating results by laser ablation inductively coupled plasma mass spectrometer （LA-ICP-MS） indicate that the ^206Pb/^238U ages of zircons from andesite range within 105- 106 Ma, yielding a weighted mean age of 105.5±0.8 Ma （n=14）, and that ^206pb/^238U ages of zircons from dacite are between 90-96 Ma, yielding a weighted mean age of 93.2±1.3 Ma （n =13）. The volcanic rocks from the Snifenhe Formation are subalkaline series and show a calc-alkaline evolutionary trend with SiO2 content of 47.69%-65.47%, MgO contents of 1.42%-6.80% （Mg^#= 45-53）, and Na2O/K2O ratios of 1.83-3.63. They are characterized by enrichment in large ion lithophile elements （LILE） and lightrare-earth elements （LREE）, depletion in heavy rare earth elements （HREE） and high field strength elements （HFSE） （e.g., Nb, Ta, Ti）, and low initial ^87Sr/^86Sr ratios （0.7041-0.7057） and positive εNd（t） ValUes （0.39-4.08）, implying that they could be derived from a depleted magma source. Taken together, these results suggest that the primary magma of the volcanic rocks might originate from partial melting of the mantle wedge metasomatized by fluids derived from subducted slab under a tectonic setting of active continental margin.展开更多
Mesozoic volcanic rocks in the eastern part of the North Dabi e Mountains are rich in Na (Na\-2O=\{4.03%\}, Na\-2O/K\-2O=\{1.31\}), Sr and Ba , and high in Sr/Y ratio but low in Nb, Y and H REE. They have experienced ...Mesozoic volcanic rocks in the eastern part of the North Dabi e Mountains are rich in Na (Na\-2O=\{4.03%\}, Na\-2O/K\-2O=\{1.31\}), Sr and Ba , and high in Sr/Y ratio but low in Nb, Y and H REE. They have experienced strong fractionation of REE \, and are similar to adakite in geochemical characteristics. The U-Pb dating of zircon from the volcanic rocks is Ma, belonging to Early Cretaceous. These rocks are similar to the volcanic rocks of North Huaiyang not only in age and rare-earth element and trace element geochemistry, but also in the formati on temperature and pressure of the minerals. The results indicated that the dela mination of mountain root and underplating of mafic-ultramafic magma had happen ed in the Dabie orogen before Early Cretaceous. Mesozoic magmatism was intense i n the North Dabie Mountains, including the intrusion of mafic-ultramafic magma, uplifting of gneiss dome, explosion of volcanic rocks and intrusion of granitic magma. The Mesozoic volcanic rocks in the eastern part of the North Dabie Mount ains may be one part of the Mesozoic volcano-intrusive complex belt of North Hu aiyang. The existence of Mesozoic volcanic remnant cap means the denudation of t he Dabie orogenic belt was not very strong since Early Cretaceous.展开更多
文摘The SHRIMP U-Pb ages are reported for two volcanic rocks from the Longwangshan and the Dawangshan formations respectively, Ningwu area, Jiangsu Province. The Dawangshan formation (NB-01) is dated at (127 3) Ma, and the Longwangshan formation (NL-01), (131 4) Ma. Besides, a few Archean zircons are also found in the Longwangshan formation, which suggests a possible Archean basement in the region.
基金the National Natural Science Foundation of China （Grant No. 40672038） the Special Grant of 0il ＆ Gas Research （XQ-2004-07）.
文摘Zircon U-Pb ages and geochemical data of volcanic rocks in the Suifenhe Formation in eastern Heilongjiang Province are reported, and their petrogenesis is discussed in this paper. The Suifenhe Formation mainly consists of basalt, andesite, and dacite. Zircon from andesite and dacite are euhedral in shape and show typical oscillatory zoning with high Th/U ratios （0.18-0.57）, implying its magmatic origin. Zircon U-Pb dating results by laser ablation inductively coupled plasma mass spectrometer （LA-ICP-MS） indicate that the ^206Pb/^238U ages of zircons from andesite range within 105- 106 Ma, yielding a weighted mean age of 105.5±0.8 Ma （n=14）, and that ^206pb/^238U ages of zircons from dacite are between 90-96 Ma, yielding a weighted mean age of 93.2±1.3 Ma （n =13）. The volcanic rocks from the Snifenhe Formation are subalkaline series and show a calc-alkaline evolutionary trend with SiO2 content of 47.69%-65.47%, MgO contents of 1.42%-6.80% （Mg^#= 45-53）, and Na2O/K2O ratios of 1.83-3.63. They are characterized by enrichment in large ion lithophile elements （LILE） and lightrare-earth elements （LREE）, depletion in heavy rare earth elements （HREE） and high field strength elements （HFSE） （e.g., Nb, Ta, Ti）, and low initial ^87Sr/^86Sr ratios （0.7041-0.7057） and positive εNd（t） ValUes （0.39-4.08）, implying that they could be derived from a depleted magma source. Taken together, these results suggest that the primary magma of the volcanic rocks might originate from partial melting of the mantle wedge metasomatized by fluids derived from subducted slab under a tectonic setting of active continental margin.
基金theChineseAcademyofGeologicalSciences (No .I50C0 0 2 0 04)ChineseContinentalSienceDrill (No .2 0 0 0 4 0 90 )
文摘Mesozoic volcanic rocks in the eastern part of the North Dabi e Mountains are rich in Na (Na\-2O=\{4.03%\}, Na\-2O/K\-2O=\{1.31\}), Sr and Ba , and high in Sr/Y ratio but low in Nb, Y and H REE. They have experienced strong fractionation of REE \, and are similar to adakite in geochemical characteristics. The U-Pb dating of zircon from the volcanic rocks is Ma, belonging to Early Cretaceous. These rocks are similar to the volcanic rocks of North Huaiyang not only in age and rare-earth element and trace element geochemistry, but also in the formati on temperature and pressure of the minerals. The results indicated that the dela mination of mountain root and underplating of mafic-ultramafic magma had happen ed in the Dabie orogen before Early Cretaceous. Mesozoic magmatism was intense i n the North Dabie Mountains, including the intrusion of mafic-ultramafic magma, uplifting of gneiss dome, explosion of volcanic rocks and intrusion of granitic magma. The Mesozoic volcanic rocks in the eastern part of the North Dabie Mount ains may be one part of the Mesozoic volcano-intrusive complex belt of North Hu aiyang. The existence of Mesozoic volcanic remnant cap means the denudation of t he Dabie orogenic belt was not very strong since Early Cretaceous.
