The X-ray fluorescence(XRF)core-scanned Rb/Sr ratios of lake sediments have been widely used as a proxy for chemical weathering intensity and past climate change.However,some factors could affect Rb/Sr ratios,causing ...The X-ray fluorescence(XRF)core-scanned Rb/Sr ratios of lake sediments have been widely used as a proxy for chemical weathering intensity and past climate change.However,some factors could affect Rb/Sr ratios,causing misinterpretation and limiting its application.In this study,we present a high-resolution XRF core-scanned Rb/Sr record of core ZB13-C1 from the Zoige Basin in the eastern Tibetan Plateau.To validate its application,we correlated this record with the chemical index of alteration(CIA)and other paleoclimatic proxies.Our results showed that(1)the core-scanned Rb/Sr ratios and CIA were reliable proxies of chemical weathering intensity in fine-grained sedimentary sequences;(2)the low values of corescanned Rb/Sr ratios and CIA were significantly correlated with high total organic carbon content,arboreal pollen content,carbonate content,and C/N ratios,confirming its reliability as a proxy for the Asian summer monsoon intensity;(3)the corescanned Rb/Sr ratios at core depths of 25–0.3 and 56–47 m were unable to reliably reflect chemical weathering intensity due to both the grain-size effect and the low test accuracy.Our study highlights the need for mutual verification of multiple indicators before accurately applying Rb/Sr as a paleoclimatic proxy in other similar study areas.展开更多
The Rb/Sr ratios for samples from six loess-paleosol sections on the Chinese Loess Plateau during the last glacial-interglacial cycle, and for samples from 18 modern surface soils, have been analyzed. The six sections...The Rb/Sr ratios for samples from six loess-paleosol sections on the Chinese Loess Plateau during the last glacial-interglacial cycle, and for samples from 18 modern surface soils, have been analyzed. The six sections are along north-south and west-east transects respectively. The results show that the spatial distribution of Rb/Sr is characterized by a remarkable increase from north to south while Rb/Sr ratio changes little from west to east, whose latitude indicates shift of summer monsoon intensity. A regression equation between Rb/Sr ratios and mean annual pre-cipitation (MAP) has been constructed through statistical analysis for the modern surface soils. Paleorainfall during the last 130 ka is estimated for the six sections based on the regression equa-tion. It is evident that precipitation increased remarkably during marine isotope stages 3 and 5, exhibiting the high and similar gradients of variation with latitude. This demonstrates that the envi-ronmental effect is more prominent in the south of the Loess Plateau than in the north during the dominance of summer monsoon.展开更多
The Tiegelongnan deposit is a newly discovered super-large porphyry-epithermal Cu-（Au） deposit in the western part of the Bangong Co-Nujiang metallogenic belt, Tibet（China）. Field geology and geochronology indicat...The Tiegelongnan deposit is a newly discovered super-large porphyry-epithermal Cu-（Au） deposit in the western part of the Bangong Co-Nujiang metallogenic belt, Tibet（China）. Field geology and geochronology indicate that the porphyry mineralization was closely related to the Early Cretaceous intermediate-felsic intrusions（ca. 123–120 Ma）. Various epithermal ore and gangue mineral types were discovered in the middle-shallow part of the orebody, indicating the presence of epithermal mineralization at Tiegelongnan. Potassic, propylitic, phyllic and advanced argillic alteration zones were identified. 40Ar/39Ar dating of hydrothermal biotite（potassic zone）, sericite（phyllic zone）, and alunite（advanced argillic zone） in/around the ore-bearing granodiorite porphyry yielded 121.1±0.6 Ma（1σ）, 120.8±0.7 Ma（1σ） and 117.9±1.6 Ma（1σ）, respectively. Five hydrothermal mineralization stages were identified, of which the Stage IV pyrite was Rb-Sr dated to be 117.5±1.8 Ma（2σ）, representing the end of epithermal mineralization. Field geology and geochronology suggest that both the epithermal and porphyry mineralization belong to the same magmatic-hydrothermal system. The Tiegelongnan super-large Cu-（Au） deposit may have undergone a prolonged magmatichydrothermal evolution, with the major mineralization event occurring at ca.120–117Ma.展开更多
基金supported by the Strategic Priority Research Program of Chinese Academy of Sciences(Grant No.XDA20070101)the National Natural Science Foundation of China(Grant Nos.41690113&41888101)the National Key Research and Development Program of China(Grant No.2016YFA0600501)。
文摘The X-ray fluorescence(XRF)core-scanned Rb/Sr ratios of lake sediments have been widely used as a proxy for chemical weathering intensity and past climate change.However,some factors could affect Rb/Sr ratios,causing misinterpretation and limiting its application.In this study,we present a high-resolution XRF core-scanned Rb/Sr record of core ZB13-C1 from the Zoige Basin in the eastern Tibetan Plateau.To validate its application,we correlated this record with the chemical index of alteration(CIA)and other paleoclimatic proxies.Our results showed that(1)the core-scanned Rb/Sr ratios and CIA were reliable proxies of chemical weathering intensity in fine-grained sedimentary sequences;(2)the low values of corescanned Rb/Sr ratios and CIA were significantly correlated with high total organic carbon content,arboreal pollen content,carbonate content,and C/N ratios,confirming its reliability as a proxy for the Asian summer monsoon intensity;(3)the corescanned Rb/Sr ratios at core depths of 25–0.3 and 56–47 m were unable to reliably reflect chemical weathering intensity due to both the grain-size effect and the low test accuracy.Our study highlights the need for mutual verification of multiple indicators before accurately applying Rb/Sr as a paleoclimatic proxy in other similar study areas.
基金NKBRSF(Grant No.1999043401) the National Natural Science Foundation of China(Grant Nos.49894170,40173003).
文摘The Rb/Sr ratios for samples from six loess-paleosol sections on the Chinese Loess Plateau during the last glacial-interglacial cycle, and for samples from 18 modern surface soils, have been analyzed. The six sections are along north-south and west-east transects respectively. The results show that the spatial distribution of Rb/Sr is characterized by a remarkable increase from north to south while Rb/Sr ratio changes little from west to east, whose latitude indicates shift of summer monsoon intensity. A regression equation between Rb/Sr ratios and mean annual pre-cipitation (MAP) has been constructed through statistical analysis for the modern surface soils. Paleorainfall during the last 130 ka is estimated for the six sections based on the regression equa-tion. It is evident that precipitation increased remarkably during marine isotope stages 3 and 5, exhibiting the high and similar gradients of variation with latitude. This demonstrates that the envi-ronmental effect is more prominent in the south of the Loess Plateau than in the north during the dominance of summer monsoon.
基金jointly sponsored by the Public Science and Technology Research Funds Projects,Ministry of Land Resources of the People’s Republic of China(project No.201511017 and 201511022-02)the Basic Research Fund of the Chinese Academy of Geological Sciences(Grant No.YYWF201608)+3 种基金the National Natural Science Foundation of China(Grant No.41402178)Geological Survey Project of the China Geological Survey(project 1212011405040)Golden Dragon Mining Co.Ltd.(project XZJL-2013-JS03)China Scholarship Council
文摘The Tiegelongnan deposit is a newly discovered super-large porphyry-epithermal Cu-（Au） deposit in the western part of the Bangong Co-Nujiang metallogenic belt, Tibet（China）. Field geology and geochronology indicate that the porphyry mineralization was closely related to the Early Cretaceous intermediate-felsic intrusions（ca. 123–120 Ma）. Various epithermal ore and gangue mineral types were discovered in the middle-shallow part of the orebody, indicating the presence of epithermal mineralization at Tiegelongnan. Potassic, propylitic, phyllic and advanced argillic alteration zones were identified. 40Ar/39Ar dating of hydrothermal biotite（potassic zone）, sericite（phyllic zone）, and alunite（advanced argillic zone） in/around the ore-bearing granodiorite porphyry yielded 121.1±0.6 Ma（1σ）, 120.8±0.7 Ma（1σ） and 117.9±1.6 Ma（1σ）, respectively. Five hydrothermal mineralization stages were identified, of which the Stage IV pyrite was Rb-Sr dated to be 117.5±1.8 Ma（2σ）, representing the end of epithermal mineralization. Field geology and geochronology suggest that both the epithermal and porphyry mineralization belong to the same magmatic-hydrothermal system. The Tiegelongnan super-large Cu-（Au） deposit may have undergone a prolonged magmatichydrothermal evolution, with the major mineralization event occurring at ca.120–117Ma.
