The oxygen isotope composition, petrology and geochemistry of mare basalts: Evidence for large-scale compositional variation in the lunar mantle
The oxygen isotope composition, petrology and geochemistry of mare basalts: Evidence for large-scale compositional variation in the lunar mantle
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DOI：
10.1016/j.gca.2010.09.023
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发表时间：
2010-12-01
影响因子：
5
通讯作者：
Russell, S. S.
中科院分区：
文献类型：
--
作者：
Hallis, L. J.;Anand, M.;Russell, S. S.
为了研究月球地幔和地壳的形成和早期演化，我们分析了一套月球玄武岩的氧同位素组成，钛含量和模式矿物学。我们的样品集包括来自阿波罗12号和15号集合的8个低钛玄武岩，以及来自阿波罗11号和17号集合的12个高钛玄武岩。此外，我们还测定了阿波罗15号KREEP（K -钾，REE -稀土元素和P -磷）玄武岩（样品15386）和阿波罗14号月海玄武岩（样品14053）的氧同位素组成。我们的数据显示大块岩石Delta O-18值的连续性，从最富钛样本中的相对较低值到贫钛样本中的较高值，阿波罗11号样本组部分弥补了这一差距。计算散装岩石三角洲O-18值，使用以前公布的氧同位素数据的月球玄武岩矿物分离，和模态矿物学（在这项研究中确定）相结合，与测量散装岩石三角洲O-18值相匹配。这表明，矿物模式组合的差异产生的差异月海玄武岩三角洲O-18块岩石值。低钛和高钛月海玄武岩之间的差异似乎在很大程度上反映了地幔源的不均匀性，特别是在月球地幔中钛铁矿的高度可变的分布。大块三角洲O-18变化在月海玄武岩也控制了一些关键矿物相的分步结晶。因此，钛铁矿分馏是重要的情况下，高钛阿波罗17号样品，而橄榄石起着更主导的作用，低钛阿波罗12号samples.Consistent与以前的研究结果，我们的数据显示，没有可检测到的差异之间的三角洲O-17地球和月球。氧三同位素研究无法以如此高的精度检测到可测量的差异，这一事实加强了对目前提出的巨大撞击假说的怀疑。版权所有（C）2010由爱思唯尔有限公司出版。保留所有权利。
To investigate the formation and early evolution of the lunar mantle and crust we have analysed the oxygen isotopic composition, titanium content and modal mineralogy of a suite of lunar basalts. Our sample set included eight low-Ti basalts from the Apollo 12 and 15 collections, and 12 high-Ti basalts from Apollo 11 and 17 collections. In addition, we have determined the oxygen isotopic composition of an Apollo 15 KREEP (K - potassium, REE - Rare Earth Element, and P - phosphorus) basalt (sample 15386) and an Apollo 14 feldspathic mare basalt (sample 14053). Our data display a continuum in bulk-rock delta O-18 values, from relatively low values in the most Ti-rich samples to higher values in the Ti-poor samples, with the Apollo 11 sample suite partially bridging the gap. Calculation of bulk-rock delta O-18 values, using a combination of previously published oxygen isotope data on mineral separates from lunar basalts, and modal mineralogy (determined in this study), match with the measured bulk-rock delta O-18 values. This demonstrates that differences in mineral modal assemblage produce differences in mare basalt delta O-18 bulk-rock values. Differences between the low- and high-Ti mare basalts appear to be largely a reflection of mantle-source heterogeneities, and in particular, the highly variable distribution of ilmenite within the lunar mantle. Bulk delta O-18 variation in mare basalts is also controlled by fractional crystallisation of a few key mineral phases. Thus, ilmenite fractionation is important in the case of high-Ti Apollo 17 samples, whereas olivine plays a more dominant role for the low-Ti Apollo 12 samples.Consistent with the results of previous studies, our data reveal no detectable difference between the Delta O-17 of the Earth and Moon. The fact that oxygen three-isotope studies have been unable to detect a measurable difference at such high precisions reinforces doubts about the giant impact hypothesis as presently formulated. Crown copyright (C) 2010 Published by Elsevier Ltd. All rights reserved.