Origin Of The Lunar Highlands Mg-Suite: An Integrated Petrology, Geochemistry, Chronology, And Remote Sensing Perspective
Origin Of The Lunar Highlands Mg-Suite: An Integrated Petrology, Geochemistry, Chronology, And Remote Sensing Perspective
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DOI：
10.2138/am-2015-4817
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发表时间：
2015
影响因子：
3.1
通讯作者：
C. Shearer;S. Elardo;N. Petro;L. Borg;F. McCubbin
中科院分区：
文献类型：
--
作者：
C. Shearer;S. Elardo;N. Petro;L. Borg;F. McCubbin
摘要镁岩套代表了月球高地岩浆活动的一段神秘插曲，可能代表了原始分异后地壳建造的第一阶段。本文对这套高地深成岩的矿物学、地球化学、岩石学、年代学和行星尺度分布进行了研究，提出了它们的成因模式，研究了它们与其他高地岩的岩石成因关系，并探索了这种岩浆作用与月球早期分异阶段之间的联系。在考虑镁系列母岩浆起源的模型中，这些数据最适合于这样一个过程：在堆积堆倾覆过程中，早期月球岩浆的热(≥2 GPa1600~1800°C)和密度较低(ρ~3100 kg/m~3)的岩浆堆积上升到地壳底部。会发生一些减压熔融，但将热的堆积层置于富斜长石的原始地壳和富含Kreep的岩性(温度为1300°C)附近，将导致这些不同的原始岩性的混合，产生镁套母岩浆。由于urKREEP(原始Kreep)不是这种类型岩浆作用的“岩石学驱动因素”，在Procellarum Kreep Terrane(PKT)之外，镁系列岩浆不需要有Kreep签名。对这段高地演化年代学的评价表明，镁系列岩浆作用是在原始分异(<；10英里)之后不久开始的。或者，与地幔翻转有关的热事件可能已经扰乱了用于测定原始地壳年龄的计时器。镁岩套与其他高地岩套(如碱性岩套和镁质斜长麻粒岩)的岩石成因关系既符合分离结晶过程，也符合明显不同混合源的熔融作用。
Abstract The Mg-suite represents an enigmatic episode of lunar highlands magmatism that presumably represents the first stage of crustal building following primordial differentiation. This review examines the mineralogy, geochemistry, petrology, chronology, and the planetary-scale distribution of this suite of highlands plutonic rocks, presents models for their origin, examines petrogenetic relationships to other highlands rocks, and explores the link between this style of magmatism and early stages of lunar differentiation. Of the models considered for the origin of the parent magmas for the Mg-suite, the data best fit a process in which hot (solidus temperature at ≥2 GPa = 1600 to 1800 °C) and less dense (ρ ~3100 kg/m3) early lunar magma ocean cumulates rise to the base of the crust during cumulate pile overturn. Some decompressional melting would occur, but placing a hot cumulate horizon adjacent to the plagioclase-rich primordial crust and KREEP-rich lithologies (at temperatures of <1300 °C) would result in the hybridization of these divergent primordial lithologies, producing Mg-suite parent magmas. As urKREEP (primeval KREEP) is not the “petrologic driver” of this style of magmatism, outside of the Procellarum KREEP Terrane (PKT), Mg-suite magmas are not required to have a KREEP signature. Evaluation of the chronology of this episode of highlands evolution indicates that Mg-suite magmatism was initiated soon after primordial differentiation (<10 m.y.). Alternatively, the thermal event associated with the mantle overturn may have disrupted the chronometers utilized to date the primordial crust. Petrogenetic relationships between the Mg-suite and other highlands suites (e.g., alkali-suite and magnesian anorthositic granulites) are consistent with both fractional crystallization processes and melting of distinctly different hybrid sources.