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8. Revised onset age of magnetochron M0r: Chronostratigraphic and geologic implications

Author

Li, Youjuan, primary, Qin, Huafeng, additional, Jicha, Brian R., additional, Huyskens, Magdalena H., additional, Wall, Corey J., additional, Trayler, Robin B., additional, Yin, Qing-Zhu, additional, Schmitz, Mark, additional, Pan, Yongxin, additional, Deng, Chenglong, additional, Singer, Brad S., additional, He, Huaiyu, additional, and Zhu, Rixiang, additional

Published
2023
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10. Expanded geographic distribution and dietary strategies of the earliest Oldowan hominins and Paranthropus

Author

Plummer, Thomas W., primary, Oliver, James S., additional, Finestone, Emma M., additional, Ditchfield, Peter W., additional, Bishop, Laura C., additional, Blumenthal, Scott A., additional, Lemorini, Cristina, additional, Caricola, Isabella, additional, Bailey, Shara E., additional, Herries, Andy I. R., additional, Parkinson, Jennifer A., additional, Whitfield, Elizabeth, additional, Hertel, Fritz, additional, Kinyanjui, Rahab N., additional, Vincent, Thomas H., additional, Li, Youjuan, additional, Louys, Julien, additional, Frost, Stephen R., additional, Braun, David R., additional, Reeves, Jonathan S., additional, Early, Emily D. G., additional, Onyango, Blasto, additional, Lamela-Lopez, Raquel, additional, Forrest, Frances L., additional, He, Huaiyu, additional, Lane, Timothy P., additional, Frouin, Marine, additional, Nomade, Sébastien, additional, Wilson, Evan P., additional, Bartilol, Simion K., additional, Rotich, Nelson Kiprono, additional, and Potts, Richard, additional

Published
2023
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11. Initial Characterisation of SK01 Sanidine: A Candidate 40Ar/39Ar Reference Material.

Author

Li, Youjuan, Jicha, Brian R., Zhang, Wanfeng, Chen, Wen, Singer, Brad S., Zheng, Dewen, and He, Huaiyu

Subjects
*URANIUM-lead dating, *REFERENCE sources, *DETERIORATION of materials
Abstract

The precision and accuracy of 40Ar/39Ar dates are ultimately linked to co‐irradiated reference materials of known age. Here we provide new data from the SK01 sanidine, which was analysed in three different laboratories to evaluate it as a 40Ar/39Ar reference material. Aliquots of 5 mg, incrementally heated in two laboratories, yielded indistinguishable results with a weighted mean age of 27.58 ± 0.06 Ma (95% confidence level). Single‐crystal step heating and single‐crystal total fusion analyses of SK01 sanidine were undertaken in the third laboratory to further test the intracrystalline homogeneity. For the seven step‐heating analyses, six crystals yielded nearly concordant age spectra with 40Ar/39Ar ages ranging from 26.853 ± 0.094 Ma to 26.963 ± 0.067 Ma, whereas one crystal gave an older age of 27.774 ± 0.071 Ma with a slightly discordant age spectrum. Twenty‐three single‐crystal total fusion analyses yielded 40Ar/39Ar ages ranging from 27.070 ± 0.108 Ma to 27.736 ± 0.062 Ma with a dispersion of ~ 3.8%. The older ages from single‐crystal total fusion dates are interpreted to reflect an inherited or excess argon component in some crystals. This is an initial characterisation of the SK01 sanidine, and additional work needs to be conducted to further evaluate the age dispersion so that it can be utilised as a 40Ar/39Ar reference material. [ABSTRACT FROM AUTHOR]

Published
2023
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15. Supporting Information from Catalyst-free decarboxylation of 4-hydroxycinnamic acids: efficient synthesis of 4-vinylphenols

Author

Yang, Qian, Li, Youjuan, Liu, Huanhuan, Wang, Enhua, Peng, Mei, Deng, Tingfei, Pan, Xiong, Luo, Zhongsheng, Yan, Yanfang, Yang, Lishou, and Yang, Xiaosheng

Abstract

We report herein an efficient protocol for the synthesis of 4-vinylphenols by a catalyst-free decarboxylation of trans-4-hydroxycinnamic acids. A variety of 4-vinylphenols has been synthesized in moderate to excellent yields. This protocol also features no polymerization.

Published
2022
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19. Topographic growth of the northeastern Tibetan Plateau during the middle‐late Miocene: Insights from integrated provenance analysis in the NE Qaidam Basin

Author

Li, Chaopeng, primary, Zheng, Dewen, additional, Zhou, Renjie, additional, Wang, Weitao, additional, Yu, Jingxing, additional, Liu, Caicai, additional, Wang, Yizhou, additional, Pang, Jianzhang, additional, Ma, Yan, additional, Hao, Yuqi, additional, Li, Youjuan, additional, and Wang, Xueye, additional

Published
2021
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26. Timing of Secondary Hydrothermal Alteration of the Luobusa Chromitites Constrained by Ar/Ar Dating of Chrome Chlorites

Author

Li Youjuan, Fei Su, Rixiang Zhu, Xiu-Juan Bai, Wei Guo, Yan Liu, and Huaiyu He

Subjects
Isochron, Luobusa chromitites, geography, Plateau, geography.geographical_feature_category, lcsh:Mineralogy, lcsh:QE351-399.2, 010504 meteorology & atmospheric sciences, Pluton, Ar/Ar dating, Geochemistry, Geology, chrome chlorite, 010502 geochemistry & geophysics, Geotechnical Engineering and Engineering Geology, 01 natural sciences, Plutonism, Hydrothermal circulation, Ultramafic rock, Chromite, Mafic, hydrothermal alteration, 0105 earth and related environmental sciences
Abstract

Chrome chlorites are usually found as secondary phases formed by hydrothermal alteration of chromite deposits and associated mafic/ultramafic rocks. Here, we report the 40Ar/39Ar age of chrome chlorites separated from the Luobusa massive chromitites which have undergone secondary alteration by CO2-rich hydrothermal fluids. The dating results reveal that the intermediate heating steps (from 4 to 10) of sample L7 generate an age plateau of 29.88 &plusmn, 0.42 Ma (MSWD = 0.12, plateau 39Ar = 74.6%), and the plateau data points define a concordant inverse isochron age of 30.15 &plusmn, 1.05 Ma (MSWD = 0.08, initial 40Ar/36Ar = 295.8 &plusmn, 9.7). The Ar release pattern shows no evidence of later degassing or inherited radiogenic component indicated by an atmospheric intercept, thus representing the age of the hydrothermal activity. Based on the agreement of this hydrothermal age with the ~30 Ma adakitic plutons exposed in nearby regions (the Zedong area, tens of kilometers west Luobusa) and the extensive late Oligocene plutonism distributed along the southeastern Gangdese magmatic belt, it is suggested that the hydrothermal fluids are likely related to the ~30 Ma magmatism. The hydrothermal fluid circulation could be launched either by remote plutons (such as the Sangri granodiorite, the nearest ~30 Ma pluton west Luobusa) or by a similar coeval pluton in the local Luobusa area (inferred, not found or reported so far). Our results provide important clues for when the listwanites in Luobusa were formed.

Published
2018

32. 40Ar/39Ar age of the onset of high-Ti phase of the Emeishan volcanism strengthens the link with the end-Guadalupian mass extinction.

Author

Li, Youjuan, He, Huaiyu, Ivanov, Alexei V., Demonterova, Elena I., Pan, Yongxin, Deng, Chenglong, Zheng, Dewen, and Zhu, Rixiang

Subjects
*IGNEOUS provinces, *MASS extinctions, *PHENOCRYSTS, *GEOCHRONOMETRY, *VOLCANISM
Abstract

Precise time constraints of the main extrusive phase of the Emeishan large igneous province (ELIP) remain unresolved because basalts commonly do not contain suitable minerals for U-Pb dating, whereas previous 40Ar/39Ar studies on basalts yielded tectonothermal overprint ages. The timing for the ELIP was deduced from indirect dating of minor intrusions of ultramafic/mafic and felsic compositions by geochronological methods and geological correlations. The extrusive part of the ELIP consists of an older low-Ti and younger high-Ti basalt phases. We have found fresh samples of plagioclase-phyric rocks at the lower Qiaojia extrusive section (the Yunnan province of China), which belong to the ELIP unit of the high-Ti basalt series. 40Ar/39Ar dating on plagioclase from two samples conducted at two different laboratories using different age standards yielded statistically indistinguishable results with the weighted mean age of 260.1 ± 1.2 Ma for five individual measurements. This provides the direct constraints on the onset of the ELIP high-Ti basalt extrusive phase. The obtained age is within the error or slightly older than the age of the Guadalupian-Lopingian boundary and felsic ignimbrite capping the ELIP lava succession (both dated at 259.1 ± 0.5 Ma). Our new data are strengthening the short duration of the, at least, high-Ti phase of the ELIP volcanism and its temporal link with the end-Guadalupian mass extinction. Estimation of the total duration of the ELIP volcanism awaits finding of suitable for dating low-Ti basalts. [ABSTRACT FROM AUTHOR]

Published
2018
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34. Efficient computation and model selection for regularized quantile regression.

Author

Li, Youjuan

Subjects
Computation, Efficient, Kernel Quantile Regression, L-norms, Model, Regularized, Selection
Abstract

Quantile regression extends the statistical analysis of the response models beyond conditional means. We consider regularized quantile regression models. In particular, we consider two types of regularization, the L2-norm and the L1-norm. The L2-norm regularization leads to the quantile regression in reproducing kernel Hilbert spaces, which we refer to as the kernel quantile regression (KQR). The L1-norm regularization uses the sum of the absolute values of the regression coefficients as the penalty. We derive efficient algorithms that compute exact entire solution paths for both the KQR model and the L1-norm quantile regression (L1-norm QR) model. The solution path, ranging from the least regularized model to the most regularized model, is achieved with a computational cost essentially same as fitting a single model for a specified regularization parameter. We also derive an estimate for the effective dimension of the proposed model, which allows convenient selection of the regularization parameter. Both simulation and real world data are used to demonstrate the KQR and the L1-norm QR models.

Published
2007

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