Igneous zircon: trace element composition as an indicator of source rock type
Igneous zircon: trace element composition as an indicator of source rock type
复制标题
DOI：
10.1007/s00410-002-0364-7
复制
发表时间：
2002-08-01
影响因子：
3.5
通讯作者：
Fisher, NI
中科院分区：
文献类型：
--
作者：
Belousova, EA;Griffin, WL;Fisher, NI
由电子微探针和激光燃烧微探针ICPMS分析确定，火成岩锆石中的痕量元素丰度被证明对源岩石类型和结晶环境很敏感。已经确定了来自各种不同岩石类型的锆石的26个痕量元素的浓度，并揭示了特定岩石类型的独特元素丰度和软骨差的痕量元素模式。从超镁铁质到镁铁质到花岗岩岩石的锆石的痕量元素丰度增加的一般趋势。 REE的平均含量通常在金伯利岩锆石中少于50 ppm，碳酸盐和兰普罗尼特锆石的平均含量最高为600-700 ppm，而来自镁铁质岩石的锆石中的平均含量可以达到2,000 ppm，并且可以从花岗岩和pegmatites的锆石中达到锆石的百分比。相对平坦的软骨差异REE模式具有30至30的软骨均衡的Yb/SM比率，其特征在于金伯利岩和碳酸盐的锆石，但是pegmatites的锆石中通常超过100个。 TH/U比通常在0.1到1范围内，但在某些碳酸盐和奈皮线岩岩岩岩中的锆石中可以为100-1000。在双变量判别图中可以识别出锆石的地球化学特征，但是多变量统计分析对于从大多数岩石类型的锆石歧视至关重要。基于递归分区技术的分类树提供了将父岩类型与锆石跟踪元素分析联系起来的快速方法；来自许多岩石类型的锆石可以以75％或以上的置信度来区分。这些树木可以识别出重矿物浓缩物的碎屑锆石的出处，并显着提高了锆石在区域地壳研究中的实用性，并作为矿物勘探的指标矿物质。
Trace element abundances in igneous zircons, as determined by electron microprobe and laser-ablation microprobe ICPMS analysis, are shown to be sensitive to source rock type and crystallisation environment. The concentrations of 26 trace elements have been determined for zircons from a wide range of different rock types and reveal distinctive elemental abundances and chondrite-normalised trace element patterns for specific rock types. There is a general trend of increasing trace element abundance in zircons from ultramafic through mafic to granitic rocks. The average content of REE is typically less than 50 ppm in kimberlitic zircons, up to 600-700 ppm in carbonatitic and lamproitic zircons and 2,000 ppm in zircons from mafic rocks, and can reach per cent levels in zircons from granitoids and pegmatites. Relatively flat chondrite-normalised REE patterns with chondrite-normalised Yb/Sm ratios from 3 to 30 characterise zircons from kimberlites and carbonatites, but Yb/Sm is commonly over 100 in zircons from pegmatites. Th/U ratios typically range from 0.1 to 1, but can be 100-1000 in zircons from some carbonatites and nepheline syenite pegmatites. The geochemical signatures characteristic of zircon from some rock types can be recognised in bivariate discriminant diagrams, but multivariate statistical analysis is essential for the discrimination of zircons from most rock types. Classification trees based on recursive partitioning techniques provide a rapid means of relating parent rock type to zircon trace element analysis; zircons from many rock types can be discriminated at confidence levels of 75% or more. These trees allow recognition of the provenance of detrital zircons from heavy mineral concentrates, and significantly enhance the usefulness of zircon in regional crustal studies and as an indicator mineral in mineral exploration.