Highland Basalt Research Articles

Low-pressure crystallization of a volatile-rich lunar basalt: A means for producing local anorthosites?

The presence of anorthosite in the lunar highlands containing plagioclase that is compositionally less calcic than plagioclase in the ferroan anorthosites cannot be readily explained by the current lunar paradigm in which lunar anorthosite was produced as a floatation cumulate in the lunar magma ocean. Phase-equilibrium experiments were conducted to investigate whether such anorthosite could arise locally from crystallization of aluminous magma at shallow levels within the lunar crust. The experiments were conducted on a synthetic analog of Cl-, F-, and S-bearing aluminous highland basalt 14053 at pressures of approximately 1 bar and f O 2 at ~QIF. Pyroxene and plagioclase (An 93–89 ) saturation occurs early, and with continued crystallization, the residual liquid evolves to a silica-poor, halogen-, Fe-, and Ti-rich melt with a computed density of >3.1 g/mL. This liquid remains higher in density than the plagioclase over the crystallization interval, providing the possibility of plagioclase/melt separation by liquid draining. A model is proposed in which “alkali” anorthosite, consisting of sodic anorthite or bytownite, coupled with underlying pyroxenite (or harzburgite) is produced locally during crystallization of plagioclase from “Al-rich” magmas at or within roughly a kilometer of the lunar surface. In this model, segregation of plagioclase would be attained by settling of ferromagnesian minerals to the bottom of a shallow magma chamber, and draining of low-viscosity, low-silica, Fe-Ti-K-REE-P-enriched residual basaltic melt to deeper regions of the crust, or into topographic lows. Such residual melt may be represented by magma compositions similar to some of the intermediate- to high-Ti mare basalts. This model would provide a mechanism that can account for the more “alkali” anorthosite identified in widespread isolated locales on the Moon and allow for variable ages for such anorthosite that may extend to ages of the mare basalts.

Herbaceous biomass, species composition and soil properties of keygrazing patches in coastal forest thornveld and two grassland types of theEastern Cape province, South Africa

In spite of predictions of communal rangeland collapse due to continuous grazing and increased livestock populations, this grazing system remains prevalent in communal areas, suggesting animals utilise heterogeneity found in these areas. A study was conducted to compare biomass and herbaceous species composition in patches frequently grazed by cattle to randomly selected control sites in three communal areas located in Lesotho Highland Basalt Grassland (Magwiji), Bhisho Thornveld (Mnyameni) and Tsomo Grassland (Cala). The relationship of vegetation parameters in frequently selected patches to the corresponding soil properties, topography and human impact was also examined. Biomass of frequently selected patches was significantly (p < 0.05) higher in the dry season (June) at Magwiji (528 kg ha−1) than in less frequently selected patches (130 kg ha−1). There was an association between sites selected in winter and soil organic carbon, and these sites were dominated by Cynodon dactylon and Pennisetum clandestinum. The floristic patterns observed in Magwiji were associated with soil organic carbon content. Low-lying swampy patches had high soil pH in Cala, while mountain top soils in Magwiji had low electrical conductivity and these areas selected in winter were associated with grass species such as Eragrostis superba and Heteropogon contortus.

Physicochemical characteristics of communal rangeland soils along two defined toposequences in the Eastern Cape, South Africa

To proffer a sustainable solution to rangeland degradation, an understanding of the innate soil properties is vital. This study investigated the relative association of surface (0–20 cm) soil physicochemical properties, viz. electrical conductivity, cation exchange capacity (CEC), soil organic carbon, available phosphorus, particle size composition, soil aggregate stability and microbial respiration, along a toposequence in two vegetation types. The study sites and vegetation types were Magwiji (Lesotho Highland Basalt Grassland) and Upper Mnxe (Tsomo Grassland). In each site, we identified three experimental units along toposequence delineation, classified as crest, midslope and valley bottom. Vegetation type significantly (p < 0.05) affected sand fraction, aggregate stability under fast wetting, and mechanical disaggregation and CEC. Toposequence delineation significantly (p < 0.05) affected fast wetting, slow wetting, mechanical disaggregation, microbial respiration and CEC. There was significant variation and relationship between vegetation types, toposequence delineation and soil properties. The results suggest that toposequence delineation more than vegetation type influences soil property rangelands; therefore, in determining site-specific management techniques for communal rangelands it is important to consider the direction and magnitude of these relationships.

Compositional studies of the Orientale, Humorum, Nectaris, and Crisium lunar basins

We have used full‐resolution (250 m/pixel) Clementine images to map the compositions of ejecta from four multiring basins on the Moon: Orientale, Humorum, Nectaris, and Crisium. All basins have relatively feldspathic ejecta, with iron contents ranging from 2 to 6 wt% FeO. Some basins show remarkably homogeneous ejecta blankets (Orientale), while others display distinct compositional zoning within exterior sectors of the basin (Crisium); in some cases this zoning correlates with morphologically observed ejecta facies (Nectaris). The iron‐poor composition of most basin ejecta indicates that the crust of the Moon at these locations is feldspathic down to depths of at least several tens of kilometers, the likely sampling depth of basin‐forming impacts. The inner rings of all four basins display massifs and small crater floors of nearly pure anorthosite (FeO &lt;1 wt%), virtually the only such occurrences of this rock type on the Moon. Because basin rings are structurally emplaced topographic elements derived from depths of at least 10–20 km into the Moon, we postulate that basin inner rings are sampling a unique stratigraphic level in the Moon and at these depths, the primordial, pristine anorthositic crust of the Moon is largely preserved. Below this zone of anorthosite is the more mafic region of the lower crust, probably having “highland basalt” composition (FeO ∼ 10 wt%, Al2O3 ∼ 18–22 wt%). The petrologic nature of lower crustal levels remains uncertain but must at least in part include members of the mafic highland suite, such as norites and troctolites.

The lunar highland melt‐rock suite

Size can be used as a criterion to select 18 large (&gt; 1 cm) samples from among 148 melt‐rock fragments of all sizes. This selection provides a suite of large samples which represent the important chemical variants among highland melt rocks; each large sample has enough material for a number of sample‐destructive studies, as well as for future reference. Cluster analysis of the total data base of 148 highland melt rocks shows six distinct groups: anorthosite, gabbroic anorthosite, anorthositic gabbro (“highland basalt”), low‐K Fra Mauro, intermediate‐K Fra Mauro, and high‐K. Large samples are available for four of the melt‐rock groups (gabbroic anorthosite, anorthositic gabbro, low‐K Fra Mauro, and intermediate‐K Fra Mauro). This sample selection reveals two sub‐groups of anorthositic gabbro (one anorthite‐poor with negative Eu anomaly and one anorthite‐rich without Eu anomaly). There is a sharp distinction between those Apollo 16 melt rocks and glasses which have both been classified as “gabbroic anorthosite”.

Lunar glass compositions: Apollo 16 core sections 60002 and 60004

Approximately 500 glasses between 1 mm and 125 μm in size have been analyzed from fourteen samples from the Apollo 16 core sections 60002 and 60004. The majority of glasses have compositions comparable to those found in previous studies of lunar surface soils; however, two new and distinct glass compositions that are probably derived in part from mare material occur in the core samples. The major glass composition in all samples is that of Highland Basalt glass, but it also appears that high-K Fra Mauro Basalt (KREEP) glass is more common at the Apollo 16 site than was previously thought. The relative abundance of glasses within the core samples is random in distribution: each sample is characterized by a particular assemblage and distribution of the constituent glass compositions.

Experimental Petrology of Lunar Highland Basalt Composition and Applications to Models for the Lunar Interior: A Discussion

Previous articleNext article No AccessDiscussion and ReplyExperimental Petrology of Lunar Highland Basalt Composition and Applications to Models for the Lunar Interior: A DiscussionCurtis C. MasonCurtis C. Mason Search for more articles by this author PDFPDF PLUS Add to favoritesDownload CitationTrack CitationsPermissionsReprints Share onFacebookTwitterLinkedInRedditEmail SectionsMoreDetailsFiguresReferencesCited by The Journal of Geology Volume 83, Number 5Sep., 1975 Article DOIhttps://doi.org/10.1086/628149 Views: 1Total views on this site Citations: 1Citations are reported from Crossref Copyright 1975 University of ChicagoPDF download Crossref reports the following articles citing this article:J. J. Papike, A. E. Bence Planetary basalts: Chemistry and petrology, Reviews of Geophysics 17, no.77 (Jan 1979): 1612.https://doi.org/10.1029/RG017i007p01612

Experimental Petrology of Lunar Highland Basalt Composition and Applications to Models for the Lunar Interior: A Reply

Experimental Petrology of Lunar Highland Basalt Composition and Applications to Models for the Lunar Interior: A Reply

Experimental Petrology of Lunar Highland Basalt Composition and Applications to Models for the Lunar Interior

Lunar Highland Basalt (gabbroic anorthosite) composition transforms with increasing pressure through assemblages of spinel + clinopyroxene + anorthite, and garnet + clinopyroxene + anorthite ± quartz to eclogitic assemblages of garnet + clinopyroxene + kyanite + quartz (p = 3.51 - 3.52). Estimates of the lunar thermal gradient allow evaluation of the mineralogical variation with depth in the moon and thus allow calculation of mean lunar density and coefficient of moment of inertia for several models for the moon. These calculations show that the simplest models of Highland Basalt as the mean lunar composition and Highland Basalt as comprising the outer 250-270 km (formed as a partial melt from a Ca, Al-rich lunar interior) fail to meet the lunar density constraint but could do so if the hypotheses were modified towards more Fe-rich compositions. The geochemical constraints are much stronger and show that it is not possible for Highland Basalt to act as a source rock for mare basalt magmas under any conditions of melting in the lunar interior. It is further shown that Highland Basalt cannot be a partial melt from a mean lunar composition matching the Ca, Al-rich inclusions of the Allende meteorite (Anderson 1973) leaving the residual deep lunar interior of diopside + merwinite + spinel mineralogy.

Composition of the Descartes region, lunar highlands

Analytical data for 40 elements are reported for Apollo 16 soils 60601, 61181, 61501, 64801, 67701, 68501, 65701 and breccias 60015, 60017, 60018, 60315, 61016, 61175, 65015 and 66055. The soils are uniform except for the North Ray Crater rim sample which is richer in Al 2O 3. The breccia components show great diversity in composition. Low-K Fra Mauro basalt, Highland basalt (anorthositic gabbro) and plagioclase are important constituents. Medium-K Fra Mauro basalt is an important constituent of breccias 65015 and 60315. The breccias contain many meteorite fragments and high nickel contents, evidence of the early highland bombardment. Most of the refractory elements (REE, Th, U, Zr, Hf, Nb, Ba) show strong positive correlations, interpreted as resulting from mixing. The REE patterns of the breccias show extreme variation relative to chondrites. There is a good inverse correlation between REE and the europium anomaly ( Eu Eu x ). The La Yb ratio is constant at 3.1 except in plagioclase. Eu depletion or enrichment is interpreted as due to addition or removal of plagioclase. The Cayley and Descartes formations cannot be distinguished chemically and the differences in surface expression are not due to chemical distinctions. They are interpreted as structural differences, related to early highland cratering and mare basin formation. The complex soil and breccia compositions are related to mixing of four components. These are Low-K Fra Mauro basalt, Highland basalt (anorthositic gabbro) and subordinate plagioclase and Medium-K Fra Mauro basalt. These compositions have been used in a computer program (PETMIX III) to provide fits for the analytical data in terms of the end-members. An average highland composition is proposed, based on the Apollo 15 and 16 orbital data for Si, Al, Mg and Th. Abundances for most other elements are derived from the interelement relationships and correlations, and checked by the mixing program. The resulting composition consists of 69 per cent Highland basalt (anorthositic gabbro) and 31 per cent Low-K Fra Mauro basalt. There is no significant Eu anomaly. The abundances are: SiO 2: 45.2 per cent; TiO 2: 0.68 per cent; Al 2O 3: 24.9 per cent; FeO: 6.3 per cent; MgO: 8.5 per cent; CaO: 13.8 per cent; Na 2O: 0.4 per cent; K 2O: 0.11 per cent; Cr 2O 3: 0.11 per cent; Ba: 144 ppm; Th: 1.8 ppm; U: 0.46 ppm; Pb: 1.6 ppm; Zr: 156 ppm; Hf: 3.2 ppm; Nb: 10.8 ppm; Y: 32 ppm; ΣREE: 85 ppm.

Luna 20 soil: abundance and composition of phases in the 45–125 micron fraction

Glass compositions in the Luna 20 soil indicate a minor contribution of mare rocks and a major contribution of highly feldspathic highland material. Glasses with the composition of Highland basalt (anorthositic gabbro or norite) predominate in a range of highly aluminous glasses. The analyses of minerals in the soil show that the highland rocks have a unique assemblage of minerals that can readily be distinguished from the mineral assemblages of either mare or KREEP basalts. The soils are characterized by abundant anorthitic (An 92–99), low-Fe plagioclase. Highly magnesian orthopyroxenes, pigeonites and augites are the most prominent pyroxenes. Unlike mare basalt pyroxenes, clinopyroxenes with intermediate Ca values are not abundant, but extreme iron enrichment towards pyroxferroite does occur. Olivines are more abundant than at other sites and are Mg-rich, low in Ca and Cr. Spinels with compositions approaching MgAl 2O 4 predominate over pleonastes and chromites. Ilmenite and metal are present but not abundant. These data establish the unique nature of the minerals in the highland soils. The mineral compositions are consistent with derivation from a suite of highly feldspathic rocks in which Highland basalt compositions predominate. Some of the mineral data, particularly from the pyroxenes, are suggestive of surface or near-surface processes, rather than plutonic crystallization.

Major element chemistry of glasses in Apollo 14 soil 14156

Glasses in a soil sample (14156) from the middle layer of the trench at the Fra Mauro landing site show a wide range of compositions clustered around certain preferred compositions. Ninety per cent of the glasses are of two major types—Fra Mauro basalt (63 per cent) with high K and 17 weight per cent Al 2O 3 and Highland basalt or anorthositic gabbro (27 per cent) with low K and 25–26 weight per cent Al 2O 3. The glass population is almost identical with that of the comprehensive soil 14259 ( Apollo Soil Survey, 1971).

Geochemistry of the lunar highlands

The principal rock types in the highlands are highland basalt (gabbroic anorthosite) with 28% Al2O3 and low K Fra Mauro basalt with 18% Al2O3. The chemistry of the highland soils and breccias can be represented by simple mixing models involving these rock types as major constituents. The mixing occurred during the intense highland cratering. Layering observed at the Apennine Front is interpreted as produced the Serenitatis basin collision. The plains-forming Cayley Formation and the Descartes Formation are not volcanic, but are derived from pre-existing highland crust.

Major element composition of Luna 20 glasses

Ten percent of the 50–150 micron size fraction of Luna 20 soil is glass. A random suite of 270 of these glasses has been analyzed by electron microprobe techniques. The major glass type forms a strong cluster around a mean value corresponding to Highland basalt (anorthositic gabbro) with 70% normative feldspar. Minor glass groups have the compositions of mare basalts and of low-K Fra Mauro type basalts. The glass data indicate that Highland basalt is the major rock type in the highlands north of Mare Fecunditatis.

MAJOR ELEMENT COMPOSITION OF GLASSES IN THREE APOLLO 15 SOILS

Approximately 180 glasses in each of three Apollo 15 soils have been analyzed for nine elements. Cluster analysis techniques allow the recognition of preferred glass compositions that are equated with parent rock compositionsGreen glass rich in Fe and Mg, poor in Al and Ti may be derived from deep seated pyroxenitic material now present at the Apennine Front. Fra Mauro basalt (KREEP) is most abundant in the LM soil and is tentatively identified as ray material from the Aristillus‐Autolycus area. Highland basalt (anorthositic gabbro), believed to be derived from the lunar highlands, has the same composition as at other landing sites, but is less abundant. The Apennine Front is probably not true highland material but may contain a substantial amount of material with the composition of Fra Mauro basalt, but lacking the high‐K content. Glasses with mare basalt compositions are present in the soils and four subgroups are recognized, one of which is compositionally equivalent to the large Apollo 15 basalt samples

Nature of the Density Reversal Beneath the Lunar Maria

Research Article| December 01, 1972 Nature of the Density Reversal Beneath the Lunar Maria CURTIS C MASON CURTIS C MASON Associates for Planetary Research, 1910 Seakale Lane, Houston, Texas 77058 Search for other works by this author on: GSW Google Scholar Author and Article Information CURTIS C MASON Associates for Planetary Research, 1910 Seakale Lane, Houston, Texas 77058 Publisher: Geological Society of America Received: 10 May 1972 Revision Received: 26 Jul 1972 First Online: 02 Mar 2017 Online ISSN: 1943-2674 Print ISSN: 0016-7606 Copyright © 1972, The Geological Society of America, Inc. Copyright is not claimed on any material prepared by U.S. government employees within the scope of their employment. GSA Bulletin (1972) 83 (12): 3725–3730. https://doi.org/10.1130/0016-7606(1972)83[3725:NOTDRB]2.0.CO;2 Article history Received: 10 May 1972 Revision Received: 26 Jul 1972 First Online: 02 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation CURTIS C MASON; Nature of the Density Reversal Beneath the Lunar Maria. GSA Bulletin 1972;; 83 (12): 3725–3730. doi: https://doi.org/10.1130/0016-7606(1972)83[3725:NOTDRB]2.0.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGSA Bulletin Search Advanced Search Abstract The density of basalt samples from Mare Tranquillitatis and Oceanus Procellarum is 3.36 g/cm3. These basalts should undergo a phase change at a pressure of approximately 10 kbar (200 km lunar depth) that would increase the density to 3.74 g/cm3. This density is substantially higher than the average density of the moon; therefore, lunar maria must be surrounded by a lower density material. The gravity anomaly at Mare Serenitatis, the largest lunar mascon, is so small that only a slender neck of mare material can extend to a source region at depth. No large mass concentrations exist in Mare Tranquillitatis and Oceanus Procellarum; therefore, only a tenuous network of pipes or thin dikes, at most, can connect the vast expanses of basalt on the lunar near side to a source region at depth. A density reversal must be present beneath the maria and Oceanus Procellarum. A good candidate for highland material is a high-aluminum basalt, which has a mineralogical composition similar to that of anorthositic gabbro and a density of 3.0 g/cm3. In the pressure range from 4 to 10 kbar (80 to 200 km in depth on the moon), this highland basalt would undergo a phase transformation with a concomitant density increase to 3.4 g/cm3. With this phase change, a moon composed predominantly of this high-alumina basalt would have the correct density and moment of inertia. For the lunar model proposed in this paper, the maria are areas of 3.36-g/cm3-density material overlying a 3.0-g/cm3-density material that undergoes a gradual phase change to a density of 3.4 g/cm3. In previous work I have hypothesized a modified fission process that would result in the moon having the composition described in this paper. This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.