Petrogenesis and magma residence time of lavas from Tengchong volcanic field (China): Evidence from U series disequilibria and 40Ar/39Ar dating
Petrogenesis and magma residence time of lavas from Tengchong volcanic field (China): Evidence from U series disequilibria and 40Ar/39Ar dating
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DOI：
10.1029/2005gc001023
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发表时间：
2006-01
期刊：
影响因子：
3.7
通讯作者：
Fei Wang;Zi-cheng Peng;R. Zhu;Huaiyu He;Liekun Yang
中科院分区：
文献类型：
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作者：
Fei Wang;Zi-cheng Peng;R. Zhu;Huaiyu He;Liekun Yang
本文介绍了中国西南部印度-亚洲碰撞带附近腾冲火山区近20万年来喷发的火山岩的U-Th不平衡测量结果以及放射成因和微量元素数据。矿物分离物、基质和整个岩石分别通过质谱法分析230 Th-238 U不平衡。全岩以230 Th相对于238 U富集或亏损为特征。测定了3种矿物的内部~（230）Th等时线和CO_2激光~（40）Ar/~（39）Ar年龄。230 Th年龄与40 Ar/39 Ar年龄相差约40 ka，可解释为岩浆的停留时间。大的变化，Sr，Nd和Pb同位素组成和微量元素的比例表明TVF熔岩不止一个来源。高Th含量、Th/U比值和大离子亲石元素丰度以及它们的巨大变化可以归因于地幔的部分熔融，这些地幔先前被俯冲衍生组分交代。某些熔岩中铀-238的过量可能是另一个端元的特征，即源岩中的弧型熔体。熔体的快速提取可能导致观察到的化学不平衡。
We present U‐Th disequilibria measurements as well as radiogenic and trace element data for volcanic rocks erupted over the past ∼200,000 years at Tengchong volcano field (TVF), near the collisional belt of India‐Asia, southwestern China. Mineral separates, matrix, and whole rock were analyzed separately by mass spectrometry for 230Th‐238U disequilibria. Whole rocks are characterized by either 230Th enrichment or depletion relative to 238U. Three mineral internal 230Th age isochrons and a CO2 laser 40Ar/39Ar age were determined. A difference of ∼40 ka between the 230Th age and the 40Ar/39Ar age can be interpreted as the residence time of the associated magma. Large variations in Sr, Nd, and Pb isotopic compositions and trace element ratios suggest more than one source for the TVF lavas. High Th contents, Th/U ratios and LILE element abundances, as well as their large variations can be attributed to partial melting of mantle previously metasomatized by subduction‐derived components. Excesses of 238U in some lavas could be the feature of another end‐member, an arc‐type melt, in the source. Fast extraction of the melts may result in the observed chemical disequilibrium.