Fluorine and chlorine abundances in lunar apatite: Implications for heterogeneous distributions of magmatic volatiles in the lunar interior
Fluorine and chlorine abundances in lunar apatite: Implications for heterogeneous distributions of magmatic volatiles in the lunar interior
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DOI：
10.1016/j.gca.2011.06.017
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发表时间：
2011-09
影响因子：
5
通讯作者：
F. McCubbin;B. Jolliff;H. Nekvasil;P. K. Carpenter;R. Zeigler;A. Steele;S. Elardo;D. Lindsley
中科院分区：
文献类型：
--
作者：
F. McCubbin;B. Jolliff;H. Nekvasil;P. K. Carpenter;R. Zeigler;A. Steele;S. Elardo;D. Lindsley
使用专门为磷灰石开发的电子探针微量分析程序，从玛雷玄武岩、镁系列、碱性系列和富含Kreep的冲击熔岩中分析了磷灰石。我们确定，所有被分析的月球磷灰石颗粒主要是富氟的；然而，它们也含有不同浓度的氯和缺失的结构成分，在排除其他可能性后，我们将其归因于OH。母质玄武岩中的磷灰石颗粒在成分上不同于镁系列、碱性系列和富克里普冲击熔岩中的磷灰石颗粒，它们的磷灰石成分都很相似。马雷玄武岩中的磷灰石颗粒缺乏氯，许多分析颗粒的化学计量表明存在显著的OH组分(即-gt；0.08结构式单元)，而镁系列、碱性系列和富Kreep冲击熔体中的磷灰石颗粒富含氯，通常不存在可归因于OH−的缺失结构成分(在0.08sfu的检测下限内)。根据这些数据，我们推测在磷灰石结晶时，母质玄武岩中的残余液体相对于氯是富含H2O和氟的，而在镁系列、碱性系列和富Kreep冲击熔体中的残余液体在磷灰石结晶时相对于H2O和氟来说是富氯的。我们测定的母质玄武岩的相对挥发性丰度与之前测定的月球苦味玻璃的相对挥发丰度是相同的。这一结果表明苦橄榄玻璃源区的相对挥发分丰度特征与母质玄武岩源区相同。镁系列、碱性系列和富克里普冲击熔岩可能反映了一种挥发分来源，其挥发分丰度与母质火山岩的来源不同。此外，镁质岩套、碱性岩套和富Kreep冲击熔岩可能揭示了岩浆海洋残余熔体urKREEP的相对挥发性丰度。岩浆挥发分丰度在所研究的岩性群之间的差异不能用单一来源成分(相对于岩浆挥发分)去气来解释。对成分差异最合理的解释是月球岩浆源区相对挥发性丰度的差异。因此，我们得出结论，月球内部岩浆挥发分的分布是不均匀的，在月球地幔部分熔融产生的岩浆和受到Kreep组分严重污染的岩浆之间存在化学分界(相对于岩浆挥发分)。
Apatite has been analyzed from mare basalts, the magnesian-suite, the alkali-suite, and KREEP-rich impact-melt rocks using an electron probe microanalysis routine developed specifically for apatite. We determined that all the lunar apatite grains analyzed are predominantly fluorine rich; however, they also contain varying concentrations of chlorine and a missing structural component that, after ruling out other possibilities, we attribute to OH. Apatite grains from mare basalts are compositionally distinct from the apatite grains in the magnesian-suite, the alkali-suite, and KREEP-rich impact-melt rocks, which all had similar apatite compositions. Apatite grains in mare basalts are depleted in chlorine, and many of the analyzed grains have stoichiometry that suggests a significant OH component (i.e., >0.08 structural formula units), whereas apatite grains in the magnesian suite, alkali suite, and KREEP-rich impact melts are enriched in chlorine and do not typically have a missing structural component that could be attributed to OH−(within the detection limit of 0.08sfu). From these data, we infer that residual liquids in the mare basalts were enriched in H2O and fluorine relative to chlorine at the time of apatite crystallization, whereas residual liquids in magnesian-suite, alkali-suite, and KREEP-rich impact melts were enriched in chlorine relative to H2O and fluorine at the time of apatite crystallization. The relative volatile abundance that we determined for the mare basalts is identical to the previously determined relative volatile abundance for the lunar picritic glasses. This result indicates that the observed relative volatile abundance signature of the picritic glass source is the same as that in the mare basalt source regions. The magnesian-suite, alkali-suite, and KREEP-rich impact-melt rocks likely reflect a volatile source with different volatile abundances than the sources of mare volcanics. Moreover, the magnesian-suite, alkali-suite, and KREEP-rich impact-melt rocks may reveal the relative volatile abundance of urKREEP, the residual melt of the magma ocean. This difference in relative magmatic volatile abundance among the lithologic groups investigated cannot be explained by degassing of a single source composition (relative to magmatic volatiles). The most reasonable explanation for the compositional disparity is a difference in the relative volatile abundances in the magmatic source regions of the Moon. Therefore, we conclude that the Moon has a heterogeneous distribution of magmatic volatiles within its interior, with a chemical divide (with respect to magmatic volatiles) existing between magmas that arise by partial melting of the lunar mantle and magmas that have seen significant contamination by a KREEP component.