Potash-rich volcanic rocks and lamprophyres in western Shandong Province: 40Ar-39Ar dating and source tracing |
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Authors: | Jiansheng Qiu Xisheng Xu Ching-Hua Lo |
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Institution: | (1) State Key Laboratory of Mineral Deposit Research of Nanjing University, 210093 Nanjing, China;(2) Department of Earth Sciences, Nanjing University, 210093 Nanjing, China;(3) Department of Geology, Taiwan University, 106-17 Taibei, China |
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Abstract: | Highly precise 40Ar-39Ar dating results demonstrate that the ages of potash-rich volcanic rocks in western Shandong Province are 114.7–124.3 Ma,
and that of the lamprophyres is 119.6 Ma. The potash-rich volcanic rocks have relatively high (87Sr÷86Sr)i ratios (0.708715–0.711418) and distinctly negative εnd values (−11.47–−17.54), and are enriched in radiogenic lead (206Pb÷204Pb=17.341−17.622, 207Pb÷204Pb=15.525−15.538, 208Pb÷204Pb = 37.563−37.684). Similarly, the lamprophyres also have quite low εnd values (−11.57–−19.64). Based on the fact that the Sr, Nd and Pb isotopic compositions of potash-rich volcanic rocks are
very consistent with that of the clinopyroxene separates, and by integrating comprehensive analyses of their tectonic settings,
and extensive comparisons of the Sr, Nd isotopic compositions with that of the related simultaneous rocks, it is concluded
that the potash-rich volcanic rocks and lamprophyres in western Shandong Province were most possibly derived from the partial
melting of enriched mantle which was caused by source contamination and metasomatism of subducted continental crustal materials. |
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Keywords: | potash-rich volcanic rocks lamprophyres 40Ar-39Ar dating Sr-Nd-Pb isotope tracing western Shandong Province |
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