The Northern Junggar Basin experienced extensive subduction and a complex tectono-magmatic evolution during the Late Paleozoic,resulting in a heterogeneous distribution of volcanic rocks in the Junggar Basin.In this s...The Northern Junggar Basin experienced extensive subduction and a complex tectono-magmatic evolution during the Late Paleozoic,resulting in a heterogeneous distribution of volcanic rocks in the Junggar Basin.In this study,the Carboniferous tectono-magmatic evolution of the northern Luliang arc was described by exploring the petrography and geochemistry of Carboniferous volcanic rocks collected from well Y-2 and outcrop WW' in the northern Luliang Uplift.The distribution,types,and formation ages of these volcanic rocks were characterized and the volcanic sequence in well Y-1 was divided into upper and lower parts according to vertical variations in selected geochemical data.Then the petrogenesis and tectonic settings of different volcanic rocks were evaluated and this was used to infer the tectonomagmatic evolution of the northern Luliang arc during the Carboniferous.The results indicate that:(1) Carboniferous high-K calc-alkali andesite-dacite associations are distributed in the west of the northern Luliang Uplift,and Lower Carboniferous calc-alkali basalt-dacite-rhyolite assemblages are preserved in its east.(2) The intermediateacid volcanic rocks in wells Y-1 and Y-2 were derived from calc-alkali basaltic magma through melting of the juvenile lower crust,and geochemical variations indicate increasing addition of slab melting in a subduction-related arc environment.The bimodal volcanic rocks from outcrop WW' were derived from lithospheric underplating of basaltic magma in an intra-arc extensional setting.(3) The closure of the eastern Keramaili Oceanic basin occurred before the Early Carboniferous,and the tectono-magmatic difference between the east and the west of the northern Luliang Uplift appeared before the Carboniferous period.展开更多
The Carboniferous volcanic rocks in the Wulungu-Luliang area are mainly andesites of medium- to high-K calc-alkalic series. Volcanic rock samples have relatively high alkali(Na2O + K2 O = 4.7 % to 6.8 %) and low Ti O2...The Carboniferous volcanic rocks in the Wulungu-Luliang area are mainly andesites of medium- to high-K calc-alkalic series. Volcanic rock samples have relatively high alkali(Na2O + K2 O = 4.7 % to 6.8 %) and low Ti O2contents(0.7 % to 0.9 %), relatively high Mg O(2.5 % to 3.4 %) and Mg#(49.9 % to 67.1 %), high rare earth element(REE) contents, and relatively high K2 O contents(1.7 % to 3.1 %). Chondrite-normalized REE patterns show light REE enrichment((La/Yb)N= 4.15 to 5.19)with weak Eu anomalies(d Eu = 0.75 to 0.92). These samples are enriched in large-ion lithophile elements but relatively depleted in high field strength elements. The trace elements and REE patterns are similar to those of Setouchi and central Ryukyu high-Mg andesites, indicating a highMg andesite source. Relatively high Y contents(16.7 to24.4 ppm), and relatively low Sr/Y ratios(17.2 to 38.8) and Ti O2contents(0.7 % to 0.9 %) exclude the possibility of slab melting. Low Sr/Nd(16.6 to 42.8), Ba/Th(66.4 to266.8), and U/Th(0.2 to 0.3) indicate that the influence of slab-derived fluids is low. The ratios of Ce/Th(4.9–7.3), Ce/Pb(1.8–4.2), Ba/Rb(7.99–22.03), Ba/Th(66.4–266.8), and La/Sm(3.6–4.3) are similar to ratios found in subducting sediment melts. Relatively high ratios of K/Nb(1357–3258),Th/La(0.28–0.42), Zr/Nb(8.8–27.1), and especially Th/Nb(0.48–1.25) suggest that the magma was assimilated and contaminated by upper continental crust. These characteristics, along with the ratios of La/Yb, Sc/Ni, Th/Yb, Ta/Yb,Ce/P2O5, and Zr/Ti O2, demonstrate that the earlier Carboniferous volcanic rocks in the Wulungu-Luliang area were generated in a continental island-arc setting.展开更多
基金financially supported by the National Natural Science Foundation of China (Nos.41802182 and 42072192)Open fund of Key Laboratory of Coalbed Methane Resources and Reservoir Formation Process of the Ministry of Education,China University of Mining and Technology (No.2018-004)+1 种基金A Project Funded by the Priority Academic Program Development of Jiangsu Higher Education Institution (PAPD)China Scholarship Council。
文摘The Northern Junggar Basin experienced extensive subduction and a complex tectono-magmatic evolution during the Late Paleozoic,resulting in a heterogeneous distribution of volcanic rocks in the Junggar Basin.In this study,the Carboniferous tectono-magmatic evolution of the northern Luliang arc was described by exploring the petrography and geochemistry of Carboniferous volcanic rocks collected from well Y-2 and outcrop WW' in the northern Luliang Uplift.The distribution,types,and formation ages of these volcanic rocks were characterized and the volcanic sequence in well Y-1 was divided into upper and lower parts according to vertical variations in selected geochemical data.Then the petrogenesis and tectonic settings of different volcanic rocks were evaluated and this was used to infer the tectonomagmatic evolution of the northern Luliang arc during the Carboniferous.The results indicate that:(1) Carboniferous high-K calc-alkali andesite-dacite associations are distributed in the west of the northern Luliang Uplift,and Lower Carboniferous calc-alkali basalt-dacite-rhyolite assemblages are preserved in its east.(2) The intermediateacid volcanic rocks in wells Y-1 and Y-2 were derived from calc-alkali basaltic magma through melting of the juvenile lower crust,and geochemical variations indicate increasing addition of slab melting in a subduction-related arc environment.The bimodal volcanic rocks from outcrop WW' were derived from lithospheric underplating of basaltic magma in an intra-arc extensional setting.(3) The closure of the eastern Keramaili Oceanic basin occurred before the Early Carboniferous,and the tectono-magmatic difference between the east and the west of the northern Luliang Uplift appeared before the Carboniferous period.
文摘The Carboniferous volcanic rocks in the Wulungu-Luliang area are mainly andesites of medium- to high-K calc-alkalic series. Volcanic rock samples have relatively high alkali(Na2O + K2 O = 4.7 % to 6.8 %) and low Ti O2contents(0.7 % to 0.9 %), relatively high Mg O(2.5 % to 3.4 %) and Mg#(49.9 % to 67.1 %), high rare earth element(REE) contents, and relatively high K2 O contents(1.7 % to 3.1 %). Chondrite-normalized REE patterns show light REE enrichment((La/Yb)N= 4.15 to 5.19)with weak Eu anomalies(d Eu = 0.75 to 0.92). These samples are enriched in large-ion lithophile elements but relatively depleted in high field strength elements. The trace elements and REE patterns are similar to those of Setouchi and central Ryukyu high-Mg andesites, indicating a highMg andesite source. Relatively high Y contents(16.7 to24.4 ppm), and relatively low Sr/Y ratios(17.2 to 38.8) and Ti O2contents(0.7 % to 0.9 %) exclude the possibility of slab melting. Low Sr/Nd(16.6 to 42.8), Ba/Th(66.4 to266.8), and U/Th(0.2 to 0.3) indicate that the influence of slab-derived fluids is low. The ratios of Ce/Th(4.9–7.3), Ce/Pb(1.8–4.2), Ba/Rb(7.99–22.03), Ba/Th(66.4–266.8), and La/Sm(3.6–4.3) are similar to ratios found in subducting sediment melts. Relatively high ratios of K/Nb(1357–3258),Th/La(0.28–0.42), Zr/Nb(8.8–27.1), and especially Th/Nb(0.48–1.25) suggest that the magma was assimilated and contaminated by upper continental crust. These characteristics, along with the ratios of La/Yb, Sc/Ni, Th/Yb, Ta/Yb,Ce/P2O5, and Zr/Ti O2, demonstrate that the earlier Carboniferous volcanic rocks in the Wulungu-Luliang area were generated in a continental island-arc setting.
