Possible Effects of Spreading Rate on Morb Isotopic and Rare Earth Composition Arising from Melting of a Heterogeneous Source
Possible Effects of Spreading Rate on Morb Isotopic and Rare Earth Composition Arising from Melting of a Heterogeneous Source
复制标题
扩散速率对非均质源熔化引起的 Morb 同位素和稀土成分的可能影响
DOI：
--
复制
发表时间：
1989
期刊：
影响因子：
--
通讯作者：
F. Richter
中科院分区：
文献类型：
--
作者：
M. Holness;F. Richter
太平洋和大西洋MORB的Sr和Nd同位素比值以及La/Sm比值的曲线图显示，随着扩张速率的增加，变化性减小，Sr同位素比值和La/Sm比值的平均值减小，平均Nd同位素比值增加。铅同位素比值没有表现出类似的相关性。在模拟这些数据，我们假设地幔源MORB是异质的浓度，同位素比，并在一个规模远远小于该地区的熔体绘制熔融。从更大的尺度上看，地幔源在固定分布的不均匀物质上取平均值，看起来是均匀的。锶同位素组成的熔体来自这样的来源，使用一个简单的亚脊熔融和偏析模型计算。如果越来越不完全提取的子脊熔体与扩展速率的增加，这个模型产生的Sr同位素的变化类似的MORB数据集中看到的。这表明熔体提取过程可能会显着改变地幔同位素特征，这对于决定MORB中同位素和REE比率的变化是否应归因于过程（即，熔体萃取）或地幔源。
Plots of Sr and Nd isotopic ratios, and La/Sm ratios of MORB from the Pacific and Atlantic oceans show a decrease in variability with increasing spreading rate, a decrease in the average value of the Sr isotopic ratio and La/Sm ratio, and an increase in the average Nd isotopic ratio. Pb isotopic ratios do not exhibit a similar correlation. In modeling this data we assume a mantle source for MORB that is heterogeneous in concentration, isotope ratios, and melting on a scale much smaller than the region from which melts are drawn. Viewed on a larger scale the mantle source would appear homogeneous by averaging over a fixed distribution of heterogeneous material. The Sr isotopic composition of melt derived from such a source is calculated using a simple sub-ridge melting and segregation model. If increasingly incomplete extraction of sub-ridge melt correlates with an increase in spreading rate, this model generates Sr isotopic variations similar to those seen in the MORB data set. This illustrates that melt extraction processes may well significantly modify mantle isotopic signatures, which has important implications for deciding whether isotope and REE ratios seen to vary in MORB should be attributed to process (i.e., melt extraction) or to the mantle source.