The Zhalaxiageyong lead-zinc-copper polymetallic deposit is a typical porphyry deposit of the Tuotuohe area. Whole-rock geochemical analyses,Zircon U-Pb dating and Hf isotope analysis are undertaken for the ore host t...The Zhalaxiageyong lead-zinc-copper polymetallic deposit is a typical porphyry deposit of the Tuotuohe area. Whole-rock geochemical analyses,Zircon U-Pb dating and Hf isotope analysis are undertaken for the ore host trachydacite with the aim of constraining its petrogenesis,magma source and regional tectonic setting.LA-ICP-MS zircon U-Pb dating indicates that the trachydacite was formed in 32. 68 ± 0. 50 Ma( MSWD =1. 6),i. e.,Oligocene. The trachydacite is rich in potassium and poor in Mg#( 5. 10-9. 70),belonging to the peraluminous shoshonite series. The rocks are enriched in LILE( large ion lithophile elements) Rb,Ba,K and LREE,depleted in HFSE( high field strength elements) Nb,Ta,P,Ti,with high Sr and low Y and Yb,having the characteristics of the C type adakite. It is calculated that the initial εHf( t) of the zircons range from-0. 92 to 2. 07 and their two-stage Hf model ages T_(DM2) range from 978 Ma to 1 169 Ma. The magma source should be mainly the partially melt mafic rocks of the thickened Middle Neoproterozoic lower crust of the Northern Qiangtang massif with the addition of ancient aluminosilica material in the melting process. The rocks formed in the tectonic setting of delamination of lithosphere and extension of the thickened crust. During the period of 40-32 Ma,large-scale potassium rich alkaline magmatism occurred in this area. The porphyry metallogenesis is related to the magmatic activities in this period.展开更多
Unlike the typical large igneous provinces(LIPs) that are dominated by mafic-ultramafic rocks, the Tarim large igneous province(TLIP) is characterized by a high proportion of felsic rocks, based on which the TLIP is c...Unlike the typical large igneous provinces(LIPs) that are dominated by mafic-ultramafic rocks, the Tarim large igneous province(TLIP) is characterized by a high proportion of felsic rocks, based on which the TLIP is classified as a transitional LIP. In this study, we focus on the trachydacite from the TLIP in which we report the characteristics of hisingerite employing a variety of techniques such as EMPA, LA-ICPMS, CCD single crystal diffraction, and bulk-rock oxygen isotopes. The hisingerite in this rock is associated with plagioclase, amphibole, apatite and ilmenite. These minerals occur as aggregates of fine curled fibers in micron-scale and display heavy rare earth elements(HREE) enriched signature with significant negative Eu anomalies. In the primitive mantle-normalized trace element spider diagrams, they show pronounced Th and U spikes and Nb, Zr, Hf troughs. Petrological observation and mineralogical study reveal a closely genetic relationship between hisingerite and amphibole, indicating that the hisingerite might have been derived from the breakdown of amphibole during the magma ascent. The formation of hisingerite requires excess water from the surrounding melts, suggesting a hydrous parental magma. The hisingerite and amphibole assign a hydrous crustal source for the rock, and extensive crustal melting accounts for the voluminous felsic rocks in the TLIP.展开更多
The Lhasa terrane records voluminous magmatism related to the subduction of the Neo-Tethyan oceanic lithosphere,the study of which constrains the tectonomagmatic evolution of the region.We report zircon U-Pb ages,whol...The Lhasa terrane records voluminous magmatism related to the subduction of the Neo-Tethyan oceanic lithosphere,the study of which constrains the tectonomagmatic evolution of the region.We report zircon U-Pb ages,whole-rock compositions and Sr-Nd isotopic data from volcanic rocks in the Bangba district within the central Lhasa subterrane to constrain their magmatic source and petrogenesis.Zircon U-Pb dating of two volcanic rock samples yields End Cretaceous ages of 70.0±0.8 and 74.3±1.2 Ma.The rocks have high SiO_(2)(65.41 wt.%-68.45 wt.%),Al_(2)O_(3)(16.16 wt.%-16.59 wt.%)and K_(2)O(5.00 wt.%-6.73 wt.%)contents,and low TFe2O3(2.33 wt.%-2.79 wt.%),MgO(0.64 wt.%-1.44 wt.%)and TiO_(2)(0.61 wt.%-0.65 wt.%)contents,with aluminium saturation indices(A/CNK)of 0.99-1.06.The major-and trace-element compositions of the rocks show they are metaluminous to slightly peraluminous high-K calc-alkaline trachydacite.The relatively high SiO2 and Sr-Nd isotopic compositions((^(87)Sr/^(86)Sr)_(i)=0.722654,0.722038 and 0.725787 andε_(Nd)(t)=-12.27,-12.36 and-6.09,respectively)indicate that the trachydacites formed by partial melting of crustal material.The trachydacites are relatively enriched in light rare earth elements,depleted in heavy rare earth elements,have high(La/Yb)_(N) and(Gd/Yb)_(N) ratios(>61 and>6,respectively),and low Y(<18 ppm)and Yb(<18 ppm)contents,indicating they most likely formed from partial melting of lower crust in the garnet stability field.Considering the geodynamic setting of the region during this period,partial melting of the ancient Lhasa crust was likely triggered by underplating mafic magmas during rollback of the Neo-Tethyan slab.展开更多
基金Supported by Project of China Geological Survey(No.12120114080901)
文摘The Zhalaxiageyong lead-zinc-copper polymetallic deposit is a typical porphyry deposit of the Tuotuohe area. Whole-rock geochemical analyses,Zircon U-Pb dating and Hf isotope analysis are undertaken for the ore host trachydacite with the aim of constraining its petrogenesis,magma source and regional tectonic setting.LA-ICP-MS zircon U-Pb dating indicates that the trachydacite was formed in 32. 68 ± 0. 50 Ma( MSWD =1. 6),i. e.,Oligocene. The trachydacite is rich in potassium and poor in Mg#( 5. 10-9. 70),belonging to the peraluminous shoshonite series. The rocks are enriched in LILE( large ion lithophile elements) Rb,Ba,K and LREE,depleted in HFSE( high field strength elements) Nb,Ta,P,Ti,with high Sr and low Y and Yb,having the characteristics of the C type adakite. It is calculated that the initial εHf( t) of the zircons range from-0. 92 to 2. 07 and their two-stage Hf model ages T_(DM2) range from 978 Ma to 1 169 Ma. The magma source should be mainly the partially melt mafic rocks of the thickened Middle Neoproterozoic lower crust of the Northern Qiangtang massif with the addition of ancient aluminosilica material in the melting process. The rocks formed in the tectonic setting of delamination of lithosphere and extension of the thickened crust. During the period of 40-32 Ma,large-scale potassium rich alkaline magmatism occurred in this area. The porphyry metallogenesis is related to the magmatic activities in this period.
基金the National Natural Science Foundation of China (Nos. 41772057, 41702064)the Fundamental Research Funds for the Central Universities (Nos. 2652018118, PA2018GDQT0020)。
文摘Unlike the typical large igneous provinces(LIPs) that are dominated by mafic-ultramafic rocks, the Tarim large igneous province(TLIP) is characterized by a high proportion of felsic rocks, based on which the TLIP is classified as a transitional LIP. In this study, we focus on the trachydacite from the TLIP in which we report the characteristics of hisingerite employing a variety of techniques such as EMPA, LA-ICPMS, CCD single crystal diffraction, and bulk-rock oxygen isotopes. The hisingerite in this rock is associated with plagioclase, amphibole, apatite and ilmenite. These minerals occur as aggregates of fine curled fibers in micron-scale and display heavy rare earth elements(HREE) enriched signature with significant negative Eu anomalies. In the primitive mantle-normalized trace element spider diagrams, they show pronounced Th and U spikes and Nb, Zr, Hf troughs. Petrological observation and mineralogical study reveal a closely genetic relationship between hisingerite and amphibole, indicating that the hisingerite might have been derived from the breakdown of amphibole during the magma ascent. The formation of hisingerite requires excess water from the surrounding melts, suggesting a hydrous parental magma. The hisingerite and amphibole assign a hydrous crustal source for the rock, and extensive crustal melting accounts for the voluminous felsic rocks in the TLIP.
基金funded by the National Key R&D Program of China (Nos.2016YFC0600407 and 2020YFA0714804)the National Natural Science Foundation of China (Nos.42173048 and 41863005)+1 种基金the Second Tibetan Plateau Scientific Expedition and Research Program (STEP)(No.2019QZKK0703)the Innovation Project of Guangxi Graduate Education (No.YCBZ2022119)
文摘The Lhasa terrane records voluminous magmatism related to the subduction of the Neo-Tethyan oceanic lithosphere,the study of which constrains the tectonomagmatic evolution of the region.We report zircon U-Pb ages,whole-rock compositions and Sr-Nd isotopic data from volcanic rocks in the Bangba district within the central Lhasa subterrane to constrain their magmatic source and petrogenesis.Zircon U-Pb dating of two volcanic rock samples yields End Cretaceous ages of 70.0±0.8 and 74.3±1.2 Ma.The rocks have high SiO_(2)(65.41 wt.%-68.45 wt.%),Al_(2)O_(3)(16.16 wt.%-16.59 wt.%)and K_(2)O(5.00 wt.%-6.73 wt.%)contents,and low TFe2O3(2.33 wt.%-2.79 wt.%),MgO(0.64 wt.%-1.44 wt.%)and TiO_(2)(0.61 wt.%-0.65 wt.%)contents,with aluminium saturation indices(A/CNK)of 0.99-1.06.The major-and trace-element compositions of the rocks show they are metaluminous to slightly peraluminous high-K calc-alkaline trachydacite.The relatively high SiO2 and Sr-Nd isotopic compositions((^(87)Sr/^(86)Sr)_(i)=0.722654,0.722038 and 0.725787 andε_(Nd)(t)=-12.27,-12.36 and-6.09,respectively)indicate that the trachydacites formed by partial melting of crustal material.The trachydacites are relatively enriched in light rare earth elements,depleted in heavy rare earth elements,have high(La/Yb)_(N) and(Gd/Yb)_(N) ratios(>61 and>6,respectively),and low Y(<18 ppm)and Yb(<18 ppm)contents,indicating they most likely formed from partial melting of lower crust in the garnet stability field.Considering the geodynamic setting of the region during this period,partial melting of the ancient Lhasa crust was likely triggered by underplating mafic magmas during rollback of the Neo-Tethyan slab.
