ISOTOPIC COMPOSITION OF LEAD IN VOLCANIC ROCKS FROM CENTRAL HONSHU WITH REGARD TO BASALT GENESIS.
ISOTOPIC COMPOSITION OF LEAD IN VOLCANIC ROCKS FROM CENTRAL HONSHU WITH REGARD TO BASALT GENESIS.
复制标题
本州中部火山岩中铅的同位素组成与玄武岩成因有关。
DOI：
10.2343/geochemj.3.53
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发表时间：
1969
期刊：
影响因子：
--
通讯作者：
R. Knight
中科院分区：
文献类型：
--
作者：
M. Tatsumoto;R. Knight
在日本中部的拉斑玄武岩和高铝玄武岩及其钙碱性岩石系列中测定了铅的同位素组成和铅、铀、钍的浓度。高铝玄武岩的铅同位素组成与邻区拉斑玄武岩相似，但其钙碱性分异岩（钙碱性岩系）富含207 Pb和208 Pb。这被解释为地壳污染的结果。从太平洋一侧到日本海一侧，原始玄武岩中铅同位素组成的放射成因特征逐渐降低，而玄武岩中238 U/204 Pb和232 Th/238 U比值的放射成因特征则逐渐升高。这种反相关性可解释为上地幔在3.6b.y左右的分异作用。前，与拉斑玄武岩（太平洋一侧）从一个较浅的地带比碱性玄武岩（日本海一侧）。岩浆的生成与过去（源区多次分异）或岩浆生成阶段浅部Pb优先于U、Th，深部U、Th优先于Pb的过程有关。对这种反向相关的另一种解释是，洋底被冲到日本岛弧之下，同位素差异是由岛弧之下的地幔物质与冲断层物质的混合程度造成的。
The isotopic composition of lead and concentrations of lead, uranium, and thorium were determined in tholeiitic and high-alumina basalts, and their calc-alkali rock series, from central Japan. The isotopic composition of lead of high alumina basalts is similar to that of tholeiites from adjacent areas, whereas their silicic differentiates (calc-alkali rock series) are rich in 207Pb and 208Pb. This is interpreted as a result of crustal contamination. The isotopic composition of lead in the primary basalts gradually decreases in radiogenic character from the Pacific Ocean side to the Japan Sea side, whereas the observed 238U/204Pb and 232Th/238U ratios in the basalts increase in the same direction. This inverse correlation can be interpreted as resulting from differentiation of the upper mantle about 3.6b.y. ago, with tholeiite (Pacific side) generated from a shallower zone than the alkali basalt (Japan Sea side). The magma generation is associated with a process which extracts Pb preferentially to U and Th at shallower depth and U and Th preferentially to Pb at deeper depth in the past (multi differentiation for the source region) or at the magma generation stage. An alternative interpretation of this inverse correlation is that the ocean floor is being thrust under the Japanese Island arcs and the isotopic difference is produced by the degree of mixing of mantle material under the arcs with thrust material.