Basaltic magmatism on the Moon: A perspective from volcanic picritic glass beads

It is widely accepted that basaltic magmas are products of partial fusion of periodotite within planetary mantles. As such, they provide valuable insights into the composition, structure, and processes of planetary interiors. Those compositions which approach primary melt compositions provide the most direct information about planetary interiors and serve as a starting point to understand basaltic evolution. Within the collection of lunar samples returned by the Apollo and Luna missions are homogeneous, picritic glass beads of volcanic origin. These picritic glasses are our closest approximations to primary magmas. As such, these glass beads provide a unique perspective concerning the origin of mare basalts, the characteristics of the lunar interior, and processes in the early differentiation of the Moon. We have obtained trace element data for these picritic glasses using SIMS techniques. These data and literature isotopic and experimental data on the picritic glasses are placed within the framework of mare basaltic magmatism.The volcanic glasses are very diverse in their trace element characteristics, for example, they have a wide range of REE pattern shapes and concentrations. Like the crystalline mare basalts, all picritic glasses have a negative Eu anomaly. Unlike the crystalline mare basalts, there is little correlation between the size of the Eu anomaly and overall REE concentrations. Trace element differences among the various glasses suggests that a KREEP component was incorporated into their mantle source. This implies large scale mixing of the “Lunar Magma Ocean”-derived cumulate pile. Subtle differences among glasses suggest that local mixing of sources may also have been an important process. Preservation of subtle chemical differences in the picritic glasses and crystalline basalts may be interpreted as indicating that they were produced by small to moderate degrees of partial melting and that the lunar mantle did not experience extensive melting during episodes of mare volcanism.Several lines of evidence are consistent with the view that the picritic glasses were derived from mantle sources that were compositionally distinct from the sources for crystalline mare basalts. These are parallel, but no common, liquid lines of descent; chemical differences between picritic glasses and the more primitive crystalline mare basalts; experimental studies indicating that the picritic glasses are multiply saturated at depths greater than that of the mare basalts; differences in lead isotopic data; and the mode of eruption (i.e., fire fountaining for glass beads). These data also provide circumstantial evidence that suggests that the picritic glasses were derived from a source somewhat more volatile-rich than that of the mare basalts.Several petrogenetic models are suggested by the trace element characteristics of the picritic glasses:

• 1.(1) Partial melting of heterogeneous lunar mantle at depths greater than 300 km to produce the parental magmas (picritic) for both the mare basalts and picritic glasses. Picritic magmas represented by glass beads were erupted to the surface with small degrees of fractional crystallization while mare basalts were produced by larger degrees of fractional crystallization (15–30%) of similar (but not identical) picritic magmas.
• 2.(2) Picritic magmas represented by the glass beads were generated at depths greater than 400 km in a volatile-enriched (relative to the mare basalt source) heterogeneous mantle while mare basalts are fractional crystallization products of picritic magmas generated at depths of less than 400 km.
• 3.(3) The picritic magmas represented by the glass beads represent polybaric melting that initiated at depths of at least 1000 km. A primitive mantle component or less processed cumulate mantle components may have been involved in the generation of the picritic glasses in any of these models.

     

The Moon

Recent geochemical and geophysical data from the Moon enable a revision of earlier interpretations regarding lunar origin, structure and bulk composition. Earth and Moon show many similarities among their isotopic compositions, but they have evolved in totally dissimilar ways, probably related to the deficiency of water and volatile elements in the Moon as well as the vast differences in size and internal pressure. Some global geochemical differences from the Earth such as volatile depletion based on K/U ratios have been established. However, all current lunar samples come from differentiated regions, making the establishment of a bulk composition more reliant on bulk geophysical properties or isotopic similarities; it remains unclear how the latter arose or relate to whole Moon composition. The lack of fractionation effects among the refractory and super-refractory elements indicates that the proto-lunar material seems unlikely to have been vaporized while the presence of volatile elements may place lower limits on proto-lunar temperatures. The apparent lack of geochemical evidence of an impacting body enables other possible impactors, such as comets, to be considered. Although the origin of the Moon remains currently unknown, it is generally believed that the Moon originated as the result of a giant impact on the Earth.     

月球的化学演化

月球是一个发生了化学分异的星球,它由月壳、月幔±一个小的金属月核组成。大量观察事实显示月球曾经有过岩浆洋,岩浆洋的结晶分异主导了月球的化学演化。目前主流观点认为,月球是在太阳系演化的早期,至少45亿年前,一个火星大小的星球,与即将完成原始吸积的地球胚胎发生偏心撞击,造成地球的熔融,形成岩浆洋,飞溅出来的物质迅速吸积形成绕地球运动的月球,并且在月球上形成了全球规模的岩浆洋,进而发生了结晶分异。,由于月球上没有海洋和板块俯冲,岩浆洋分异是其化学演化的主要途径。月球岩浆洋的80％～85％在大撞击后的100Ma内已经固化,这可能是由于月球体积小、表面没有大气包裹所致。月球极贫水,因此在岩浆结晶过程中斜长石首先结晶。斜长石由于密度小于玄武质岩浆而漂浮在岩浆洋的表层,橄榄石等密度大的矿物则堆积在岩浆洋的底部。随着结晶分异的进行,残余岩浆不断富集不相容元素,包括K、U等放射性元素;与此同时,密度较大的钛铁矿开始结晶,造成高钛堆晶岩密度大于其下的橄榄石堆晶岩的不稳定结构,进而发生月幔翻转,引发一系列岩浆活动,进而形成月球上特有的镁质系列、碱质系列等岩石。由于月球氧逸度较低,Eu主要以＋2价形式存在,因此斜长石高度富集Eu,相应地除高地斜长岩外,其他岩石均表现为Eu高度亏损的特点。与此同时,Re在低氧逸度下表现为强亲铁元素的特点,Re／Os在月球岩浆过程中不发生分异。月球的体积远小于地球,因而其演化时间远远短于地球,很多原始的分异被完整地保留下来。因此月球的化学演化是类地行星早期演化过程的“化石”,尽管与现代的地球存在较大差异,但是对于认识地球早期演化具有借鉴意义。     

The Physical Surface of the Moon: A Digital Model Based on Satellite Altimetry

Astronomy Reports - Investigations of the Solar System with space missions yielded a significant volume of data on geophysical and morphological properties of planets. On this basis, a new research...     

The spatiality of multifunctional agriculture: A human geography perspective

Based on reconceptualisations of multifunctional agriculture as a normative spectrum of decision-making (strong to weak multifunctionality) bounded by productivist and non-productivist action and thought [Hollander, G.M., 2004. Agricultural trade liberalization, multifunctionality, and sugar in the south Florida landscape. Geoforum 35, 299-312; Holmes, J., 2006. Impulses towards a multifunctional transition in rural Australia: gaps in the research agenda. Journal of Rural Studies 22, 142-160; Wilson, G.A., 2007. Multifunctional Agriculture: A Transition Theory Perspective. CAB International, Wallingford], this paper argues that there is currently insufficient research into the geography of multifunctionality. Building on current human geography debates about issues of scale, the paper suggests that we should conceive of multifunctionality as a spatially complex nested hierarchy comprising different interlinked ’layers’ of multifunctional decision-making ranging from the farm level to the national and global levels. It suggests that the notion of multifunctional agriculture only makes sense if it is applied at the farm level as the most important spatial scale for the implementation of multifunctional action ‘on the ground’. Multifunctionality can be interpreted as having ’direct’ expression only at the ’lower’ geographical scales (i.e. farm, community and regional levels in particular) while the regional, national and global levels show ’indirect’ expressions of multifunctionality that are mediated by local level actors in order to find tangible expression on the ground. The notion of global-level multifunctionality is the most challenging, as this level lacks political and ideological coherence about the required directions necessary for implementation of strong multifunctionality pathways. The paper concludes by arguing that much work still awaits those investigating the spatiality of multifunctionality, in particular with regard to the question whether global-level strong multifunctionality is possible, or whether strong multifunctionality in one territory is predicated on weak multifunctionality in others.     

月球上的水：探测历程与新的证据

最早提出月球上可能有水的设想是在20世纪60年代初,但一直停留在理论阶段,即使60～70年代阿波罗计划采集的月球样品在地面实验室的精细分析也认为月球上没有任何形式的水.美国1994年发射的克莱门汀号和1998年发射的月球勘探者号虽然获得月球上可能有水的一些间接证据,但其探测数据的解释一直存在质疑和争论.2008年以来,...     

The Moon as a piece of Mercury

The giant impact on Earth proposed by some to generate the Moon could not have happened because the amount of carbonate rock and organic carbon present on Earth closely approximates the amount of CO₂ predicted for the Earth's early atmosphere by comparison with the present atmosphere of Venus. It is suggested that the Moon may have fissioned from Mercury more than 4.4 billion years ago and may have been captured by the Earth no later than 3.2 billion years ago.A model for the origin of the Earth-Moon system that has been gaining favor recently visualizes a Marssize body impacting Earth and excavating enough material from the Earth to form the Moon (Newsome &Taylor, 1989). This giant impact not only would have sterilized the planet (Maher &Stevenson, 1988), obliterating any form of life that might have existed at the time, but also would have blown off the Earth's atmosphere (Kaula, 1990). As the story goes, Venus suffered no giant impact and conserved its CO₂ atmosphere, whereas the loss of her CO₂ atmosphere cooled the Earth's surface allowing the oceans to rain out (Kaula, 1990). It is widely believed that the different histories in the early evolution of their atmospheres set markedly different courses for the subsequent evolution of the two planets. I agree with this conclusion but disagree with the cause for the difference.If the giant impact really happened, it must have taken place not only after the Earth's accumulation was practically completed but also after a substantial core had formed (to account for the lesser density of the Moon).Venus has approximately 89 kg/cm² of CO₂ for a total of 4.110²⁰kg. The Earth with a mass 1.226 greater than Venus, should have had 5.010²⁰ kg of CO₂. If entirely precipitated as carbonate, the Earth should now have 1.110²¹ kg of carbonate. A recent estimate (Hay, 1985) gives the total volume of carbonate rock on Earth as 276.110⁶ km³ which, for an average density of 2.83, corresponds to a mass of 7.810²⁰ kg. This figure and the ratio limestone/shale/sandstone of 15/74/11 (Garrels &Mackenzie, 1971) leads to the carbonate inventory shown in Table 1.     

月球南极艾特肯盆地的地质特征:探索月球深部的窗口

月球南极艾特肯盆地(South Pole-Aitken Basin,简称SPA盆地)是月球上规模最大、最古老的撞击盆地,形成于43~39亿年前的前酒海纪。巨大的撞击可能挖掘出下月壳甚至月幔的物质,因此,它是探索月球深部物质组成的重要窗口。本文通过对SPA盆地形貌和构造特征、物质组成及其分布特征,以及形成机制等方面的分析,综述了艾特肯盆地的地质特征,探讨了SPA盆地对探索早期月球形成演化历史的意义。     

The Pachuca obsidian source,Hidalgo, Mexico: A geoarchaeological perspective

Sierra Las Navajas, known to archaeologists as “the Pachuca obsidian source,” has been a major source of obsidian to Mesoamerican societies for more than 3000 years, producing a fine green obsidian unique in Middle America. It was the primary source of the obsidian that formed the economic backbone of the major sociopolitical centers of Classic period Teotihuacán, epi‐Classic Toltec Tula, and Aztec Tenochtitlán. In this paper, the obsidian of Sierra Las Navajas is discussed in the following contexts: (1) geologically, because the extraordinary quality of the Pachuca obsidian, its ease of extraction, and its distinctive color and chemistry are a direct result of its geologic emplacement; (2) locally, as the different mining localities within Sierra Las Navajas reflect the varying needs of the cultures working them; and (3) globally, as the obsidians of Las Navajas were used in concert with obsidians from other sources, and were traded great distances across Mesoamerica. © 2004 Wiley Periodicals, Inc.     

Statehood: A politico-geographic and legal perspective

The political geographical literature of focuses on the State yet little attention has been placed on the basic criteria and attributes of statehood. This paper presents a linked politico-geographic and legal perspective on statehood. The criteria and attributes identified and discussed are: a particular defined territory; a permanent resident population; a constituted effective government; independence; sovereignty; recognition; permanence; the capacity to enter into relations with other States; a State apparatus; a circulation system; and an organized economy. Certain conceptualizations and the importance of discourse are discussed.     

The Clementine mission —A 10-year perspective

Clementine was a technology demonstration mission jointly sponsored by the Department of Defense (DOD) and NASA that was launched on January 25th, 1994. Its principal objective was to use the Moon, a near-Earth asteroid, and the spacecraft’s Interstage Adapter as targets to demonstrate lightweight sensor performance and several innovative spacecraft systems and technologies. The design, development, and operation of the Clementine spacecraft and ground system was performed by the Naval Research Laboratory. For over two months Clementine mapped the Moon, producing the first multispectral global digital map of the Moon, the first global topographic map, and contributing several other important scientific discoveries, including the possibility of ice at the lunar South Pole. New experiments or schedule modifications were made with minimal constraints, maximizing science return, thus creating a new paradigm for mission operations. Clementine was the first mission known to conduct an in-flight autonomous operations experiment. After leaving the Moon, Clementine suffered an onboard failure that caused cancellation of the asteroid rendezvous. Despite this setback, NASA and the DOD applied the lessons learned from the Clementine mission to later missions. Clementine set the standard against which new small spacecraft missions are commonly measured. More than any other mission, Clementine has the most influence (scientifically, technically, and operationally) on the lunar missions being planned for the next decade.     

月球上的"水"

在地球科学的各个领域中,在行星演化学和太空探索中,水都是不可缺少的元素。长久以来,我们一直认为月球是干燥的。然而最新的研究成果推翻了这个观点。近期的遥感探测和撞月实验表明,月球表面不仅含有结构水(OH和H₂O), 而且还有固态冰的存在。对月球火山玻璃和玄武岩的磷灰石重新分析也发现了这些玻璃中的OH,揭示了月球内部有水的存在。这个发现,意味着我们可能需要重新审视现有的月球火山活动和演化的模式。月表水和内部水的存在,还为未来以月球为跳板进行太空探索,提供了重要的资源。这里,我们对月表水和内部水的研究作一总结,并就这些发现的意义展开讨论。     

Physical Libration of the Moon: An Extended Problem

Astronomy Reports - The work is devoted to the study of the physical libration of the Moon. Interest in the traditional topic related to the rotation of the Moon is stirred up by the activity of...     

The silent articulation of private land rights in Soviet Estonia: A geographical perspective

With an explicit focus on the spatial articulation of landownership, this paper explores various ways in which pre-Soviet land rights were expressed in rural Estonia during the Soviet period (1940-1941, 1944-1991). Drawing on cartographical analyses and interviews made in the rural district of Muhu, the paper demonstrates that people who owned land before the Soviet occupation kept track of the officially annulled pre-Soviet land rights, by relating to inertial landscape elements as memory-aids. To local inhabitants the landscape, in which past and present structures always merge, provided substantial evidence in support of the idea of legal continuity of pre-Soviet land rights. Hence, the post-Soviet land restitution reform often implied a re-discovery or re-expression of property rights that had been silenced, but not lost.