Importance of the size and distribution of chemical heterogeneities in the mantle source to the variations of isotope ratios and trace element abundances in mid-ocean ridge basalts
Importance of the size and distribution of chemical heterogeneities in the mantle source to the variations of isotope ratios and trace element abundances in mid-ocean ridge basalts
复制标题
地幔源化学异质性的大小和分布对洋中脊玄武岩同位素比和微量元素丰度变化的重要性
DOI：
10.1016/j.gca.2019.10.013
复制
发表时间：
2020
影响因子：
5
通讯作者：
Liang, Yan
中科院分区：
文献类型：
--
作者：
Liu, Boda;Liang, Yan
地幔源化学非均质性的大小和分布影响地表喷发玄武岩的组成。为了了解非均质地幔源的大小和分布对洋中脊玄武岩同位素比值和不相容微量元素丰度变化的影响，我们建立了一个以截断三角形熔融区不平衡熔融和通道化熔体迁移为特征的时间依赖的双孔脊模型。我们对一个由贫地幔和富地幔组成的双组分地幔进行了数值模拟，这些富地幔包括一系列富成分和大小。富集地幔的体积分数在地幔源的10%以下变化，对汇集熔体有贡献的熔体生产区域的大小也被视为一个变量。结果表明，富集地幔中不相容微量元素丰度越高，富集团块尺寸越大，熔池面积越窄，熔池熔体同位素比值变化越大。我们建立了一个经验标度方程，将同位素比值的波动量化为元素丰度、源内富集非均质大小和平均间距以及熔池区宽度的函数。不受热点影响的143nd /144Nd、176Hf/177Hf、87Sr/86Sr和206pb /204Pb的双标准偏差可以通过熔融双组分地幔产生，其富集程度为5.2-8.2%，平均大小为5.1-6.7 km， Nd、Hf、Sr和Pb的丰度分别是贫地幔的7.0（±1.6）、5.3（±1.2）、2.0（±0.5）和9.8（±2.2）倍。岩石圈底部熔体的不完全混合可能是造成MORB中不相容微量元素变化的重要原因。在脊轴处爆发的熔体可以代表熔体池区中心汇集的熔体和远离脊轴的局部地区汇集的熔体的集合。本研究强调了地幔非均质大小和分布对玄武岩同位素比值和微量元素丰度解释的重要性。
The size and distribution of chemical heterogeneities in the mantle source affect compositions of basalts erupted on the surface. To understand the effect of size and distribution of heterogeneous mantle source on the variations of isotope ratios and incompatible trace element abundances in mid-ocean ridge basalts (MORB), we develop a time-dependent two-porosity ridge model that features disequilibrium melting and channelized melt migration in a truncated triangular melting region. We run numerical simulations for a two-component mantle that consists of the depleted mantle and enriched blobs spanning a range of enriched compositions and sizes. The volume fraction of enriched mantle varies under 10% of the mantle source and the size of the melt production area that contributes to the pooled melt is also treated as a variable. Results show that higher abundance of incompatible trace element in the enriched mantle, larger size of enriched blobs, and narrower melt pooling area produce larger variations of isotope ratios in the pooled melt. We develop an empirical scaling equation that quantifies the fluctuation of isotope ratios as a function of elemental abundance, size and average spacing of enriched heterogeneities in the source, and the width of melt pooling area. The two-standard deviation of143Nd/144Nd,176Hf/177Hf,87Sr/86Sr, and206Pb/204Pb in global MORB not affected by hotspots can be produced by melting a two-component mantle with 5.2–8.2% enriched heterogeneities of 5.1–6.7 km mean size and 7.0(±1.6), 5.3(±1.2), 2.0(±0.5), and 9.8(±2.2) times higher abundances of Nd, Hf, Sr, and Pb than the depleted mantle, respectively. Incomplete mixing of melts at the base of the lithosphere is likely important for producing the variation of incompatible trace elements in MORB. The melt erupted at the ridge axis may represent an ensemble of the melt pooled from the center of the melt pooling area and melts pooled from local areas away from the ridge axis. The present study underscores the importance of the size and distribution of mantle heterogeneities to the interpretation of isotope ratios and trace element abundances in basalts.
登录
查看更多内容
通过山脊轴上熔岩成分的分布揭示了熔体提取的时间尺度
DOI：
--
发表时间：
2010
期刊：
影响因子：
--
作者：
C. Cordier;M. Benoit;C. Hemond;J. Dyment;Bernard Le Gall;A. Briais;M. Kitazawa
通讯作者：
M. Kitazawa
上涌地幔中熔体迁移导致的化学不均匀性拉伸：基于时间依赖性批量和分数熔融模型的分析
影响因子：
5.3
作者：
Liang, Yan;Liu, Boda
通讯作者：
Liu, Boda
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：
--
发表时间：
1989
期刊：
The Journal of geology
影响因子：
--
作者：
M. Holness;F. Richter
通讯作者：
F. Richter
影响因子：
13.6
作者：
Liu B;Liang Y
通讯作者：
Liang Y
影响因子：
5
作者：
Weatherley S
通讯作者：
Weatherley S