Trace element partition coefficients for clinopyroxene and phlogopite in an alkaline lamprophyre from Newfoundland by LAM-ICP-MS
Trace element partition coefficients for clinopyroxene and phlogopite in an alkaline lamprophyre from Newfoundland by LAM-ICP-MS
复制标题
DOI：
10.1016/0016-7037(95)00422-x
复制
发表时间：
1996-02-01
影响因子：
5
通讯作者：
Jenner, GA
中科院分区：
文献类型：
--
作者：
Foley, SF;Jackson, SE;Jenner, GA
采用激光烧蚀微探针（LAM-ICP-MS）测定了加拿大纽芬兰中生代碱性煌斑岩中斜辉石（Cpx）和绿云母的矿物/岩石基质分配系数。由于稀土元素丰度低于检出限（远低于1ppm）， Cpx得到了21种元素的值，而绿云母只有11种元素的值。直径40-50 μ m的烧蚀坑可用于研究斑晶阶段的分带。一般来说，除了最外层的Cpx生长外，斑晶表现出很少的微量元素分带性。其中，许多微量元素丰度增加4到5倍与Ti和Al含量的增加密切相关，这与最近的实验研究一致。只有Li在云母中表现出明显的分带性，富集于边缘。将原位激光分析得到的分配系数与溶液ICP-MS分离得到的分配系数进行比较，发现对某些元素存在相当大的差异，例如D-Ba为0.0006与0.0255。这些差异可归因于富含微量元素的生长体、微量元素富集带和微包裹体的包裹体，以及在名义上干净的斜辉石矿物分离物中可能存在少量基质或玻璃（1-2%）。Cpx的分配系数低于大多数玄武岩的公布值，但与SIMS测定的玄武岩的实验值相当。与煌斑岩的实验值相比，低估了强烈的体积成分效应，因此与早期玄武岩值的差异可能归因于矿物分离问题，强调了使用原位微束方法进行高质量分配测定的必要性。绿云母数据大大扩展了已公布的范围；新值通常也低于已发表的值，尽管这里的差异可能是由于整体组成效应，因为许多已发表的值来自更多的硅系统。煌斑岩值在稀疏实验测定值的范围内。
Mineral/rock matrix partition coefficients have been determined for clinopyroxene (Cpx) and phlogopite from a Mesozoic alkaline lamprophyre from Newfoundland, Canada, by Laser Ablation Microprobe (LAM-ICP-MS). Values for twenty-one elements were obtained for Cpx, whereas only eleven were possible for phlogopite due to REE abundances below detection Limits (much less than 1 ppm). Ablation pits of 40-50 mu m diameter enabled investigation of zonation in phenocryst phases. In general, phenocrysts exhibit little trace element zonation except in the outermost overgrowths of Cpx. In these, a fourfold to fivefold increase in many trace element abundances correlates strongly with increasing Ti and Al contents, in agreement with recent experimental studies. Only Li shows appreciable zonation in phlogopite, being enriched in the rims. Comparison of the partition coefficients determined by in-situ laser analysis with those obtained from apparently pure mineral separates by solution ICP-MS indicates that, for several elements, considerable differences exist, e.g., D-Ba 0.0006 vs. 0.0255. These differences are attributable to the inclusion of trace element-rich overgrowths, and zones of trace element enrichment and micro-inclusions, in addition to the possibility of small amounts of matrix or glass (1-2%) in the nominally clean clinopyroxene mineral separates.Partition coefficients for Cpx are lower than most published values for basaltic rocks, but are comparable to experimental values for basalt determined by SIMS. Comparison with experimental values from lamproite discounts a strong bulk compositional effect, so that the discrepancy with earlier values for basalt should probably be attributed to problems with mineral separates, emphasizing the need for high quality partitioning determinations with in-situ microbeam methods. The phlogopite data extend considerably the published range; the new values are also generally lower than published values, although the discrepancy here may be due to bulk compositional effects, as many published values are from more silicic systems. The lamprophyre values are within the range of sparse experimentally determined values.