The black shales of the Lower Cambrian Niutitang Formation in Weng＇an, on the Yangtze platform of south China, contain voluminous polymetallic sulfide deposits. A comprehensive geochemical investigation of trace, rar...The black shales of the Lower Cambrian Niutitang Formation in Weng＇an, on the Yangtze platform of south China, contain voluminous polymetallic sulfide deposits. A comprehensive geochemical investigation of trace, rare earth, and platinum group elements （PGE） has been undertaken in order to discuss its ore genesis and correlation with the tectono-depositional setting. The ore-bearing layers enrich molybdenum （Mo）, nickel （Ni）, vanadium （V）, lead （Pb）, strontium （Sr）, barium （Ba）, uranium （U）, arsenic （As）, and rare earth elements （REE） in abundance. High uranium/ thorium （U/Th） ratios （U/Th〉I） indicated that mineralization was mainly influenced by the hydrothermal process. The 8U value was above 1.9, showing a reducing sedimentary condition. The REE patterns showed high enrichment in light rare earth elements （LREE） （heavy rare earth elements （HREE） （LREE/HREE=5-17）, slightly negative europium （Eu） and cerium （Ce） anomalies （δEu=0.81- 0.93）, and positive Ce anomalies （δCe=0.76-1.12）. PGE abundance was characterized by the PGE-type distribution patterns, enriching platinum （Pt）, palladium （Pd）, ruthenium （Ru） and osmium （Os）. The Pt/Pd ratio was 0.8, which is close to the ratios of seawater and ultramafic rocks. All of these geochemical features suggest that the mineralization was triggered by hydrothermal activity in an extensional setting in the context of break-up of the Rodinian supercontinent.展开更多
Limited Devonian magmatic record in northern West Junggar leads to contrasting models on its tectonic evolution.In this study,we conducted LA-ICP-MS U-Pb dating on detrital zircons of two sandstones from the Hebukesai...Limited Devonian magmatic record in northern West Junggar leads to contrasting models on its tectonic evolution.In this study,we conducted LA-ICP-MS U-Pb dating on detrital zircons of two sandstones from the Hebukesaier Formation in the Shaerbuerti Mountains.Detrital zircons with oscillatory zoning are characterized by high Th/U(>0.3)and low La/Yb(<0.15),indicating their magmatic origin.The youngest zircon ages of two samples are 402±2 Ma and 406±2 Ma,respectively,suggesting that the Hebukesaier Formation was deposited at the Early Devonian.Detrital zircon age patterns show single peaks(at ca.424 Ma,n=157),which indicates that these clastics were likely proximal accumulation after short distance transportation.Provenance of the Hebukesaier Formation was the Xiemisitai and Shaerbuerti Mountains.Detrital zircon ages range from 481 Ma to 395 Ma,which indicates that there was relatively continuous Early Paleozoic magmatism in the Xiemisitai and Shaerbuerti Mountains since the Early Ordovician.Age spectrums of sampled detrital zircons are distinct from those of Lower Devonian strata either in southern West Junggar or in East Junggar,which implies for individual tectonic evolution of northern West Junggar.We favor that Lower Devonian Hebukesaier Formation was developed in a fore–arc setting due to the northward subduction of the Junggar–Balkhash Ocean.展开更多
基金supported by grants from the Key Projectof Chinese Ministry of Education(no.:104004)the National Natural Science Foundation of China(no.:40839907)
文摘The black shales of the Lower Cambrian Niutitang Formation in Weng＇an, on the Yangtze platform of south China, contain voluminous polymetallic sulfide deposits. A comprehensive geochemical investigation of trace, rare earth, and platinum group elements （PGE） has been undertaken in order to discuss its ore genesis and correlation with the tectono-depositional setting. The ore-bearing layers enrich molybdenum （Mo）, nickel （Ni）, vanadium （V）, lead （Pb）, strontium （Sr）, barium （Ba）, uranium （U）, arsenic （As）, and rare earth elements （REE） in abundance. High uranium/ thorium （U/Th） ratios （U/Th〉I） indicated that mineralization was mainly influenced by the hydrothermal process. The 8U value was above 1.9, showing a reducing sedimentary condition. The REE patterns showed high enrichment in light rare earth elements （LREE） （heavy rare earth elements （HREE） （LREE/HREE=5-17）, slightly negative europium （Eu） and cerium （Ce） anomalies （δEu=0.81- 0.93）, and positive Ce anomalies （δCe=0.76-1.12）. PGE abundance was characterized by the PGE-type distribution patterns, enriching platinum （Pt）, palladium （Pd）, ruthenium （Ru） and osmium （Os）. The Pt/Pd ratio was 0.8, which is close to the ratios of seawater and ultramafic rocks. All of these geochemical features suggest that the mineralization was triggered by hydrothermal activity in an extensional setting in the context of break-up of the Rodinian supercontinent.
基金supported by the National Science Foundation of China(grants 41672217)the Fundamental Research Funds for the Central Universities(grants N2001004 and N2001021)State Scholarship Fund(grants 201806085034)。
文摘Limited Devonian magmatic record in northern West Junggar leads to contrasting models on its tectonic evolution.In this study,we conducted LA-ICP-MS U-Pb dating on detrital zircons of two sandstones from the Hebukesaier Formation in the Shaerbuerti Mountains.Detrital zircons with oscillatory zoning are characterized by high Th/U(>0.3)and low La/Yb(<0.15),indicating their magmatic origin.The youngest zircon ages of two samples are 402±2 Ma and 406±2 Ma,respectively,suggesting that the Hebukesaier Formation was deposited at the Early Devonian.Detrital zircon age patterns show single peaks(at ca.424 Ma,n=157),which indicates that these clastics were likely proximal accumulation after short distance transportation.Provenance of the Hebukesaier Formation was the Xiemisitai and Shaerbuerti Mountains.Detrital zircon ages range from 481 Ma to 395 Ma,which indicates that there was relatively continuous Early Paleozoic magmatism in the Xiemisitai and Shaerbuerti Mountains since the Early Ordovician.Age spectrums of sampled detrital zircons are distinct from those of Lower Devonian strata either in southern West Junggar or in East Junggar,which implies for individual tectonic evolution of northern West Junggar.We favor that Lower Devonian Hebukesaier Formation was developed in a fore–arc setting due to the northward subduction of the Junggar–Balkhash Ocean.
