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At least 109 records · Page 6

Trace element composition of Luna 24 Crisium VLT basalt

The origins of the individual particles analyzed from the Luna 24 core and the information they provide on the trace-element composition of Mare Crisium basalt are considered. Previous analyses of several Luna 24 soil fragments are reviewed. It is concluded that: (1) the average trace-element concentrations for 12 VLT basalt fragments are the best available estimates for bulk samples of Crisium VLT basalt; (2) there is weak evidence that the average Crisium basalt might have a small positive Eu anomaly relative to chondritic matter; (3) the soils contain components from sources other than the Crisium VLT basalt; and (4) there is no convincing information in concentrations of rare-earth elements, Co, Sc, FeO, or Na2O among the analyzed fragments to indicate more than one parent basalt.

Haskin, L. A.↗

Petrogenesis of Luna 16 aluminous mare basalts

Bulk compositions, petrology and mineralogy of Luna 16 aluminous mare basalt particles of less than 0.5 mm are described. The data rule out any close genetic relationships between Luna 16 and other major types of lunar mare basalts. Compared to high-Ti mare basalts, the Luna 16 basalts contain lower TiO2 and Ta and higher Al2O3 and REE abundances, suggesting that the Luna 16 source rocks crystallized later than (i.e. stratigraphically above) the ilmenite-bearing high-Ti basalt cumulate source rocks. The REE pattern for the Luna 16 basalts requires that the source material from which they were derived crystallized from a light REE enriched magma.

Ma, M.-S.↗

Basaltic volcanism - The importance of planet size

The volumetrically abundant basalts on the earth, its moon, and the eucrite parent planet all have chemical compositions that are controlled to a large extent by dry, low-pressure, crystal-liquid equilibria. Since this generalization is valid for these three planetary bodies, we infer that it may also apply to the other unsampled terrestrial planets. Other characteristics of basaltic volcanism show variations which appear to be related to planet size: the eruption temperatures, degrees of fractionation, and chemical variety of basalts and the endurance of basaltic volcanism all increase with planet size. Although the processes responsible for chemical differences between basalt suites are known, no simple systematization of the chemical differences between basalts from planet to planet has emerged.

Walker, D.↗

Hotspots, basalts, and the evolution of the mantle

It is noted that the trace element concentration patterns of continental and ocean island basalts and of mid-ocean ridge basalts are complementary. Estimates of the relative sizes of the source regions for these fundamentally different basalt types can be arrived at from the trace element enrichment-depletion patterns. Their combined volume occupies the greater part of the mantle above the 670 km discontinuity. It is pointed out that the source regions separated as a result of early mantle differentiation and crystal fractionation from the resulting melt. The mid-ocean ridge basalts source evolved from an eclogite cumulate that gave up its late-stage enriched fluids at various times to the shallower mantle and continental crust. The mid-ocean ridge basalts source is rich in garnet and clinopyroxene, while the continental and ocean island basalt source is a garnet peridotite that has experienced secondary enrichment. These relationships are found to be consistent with the evolution of a terrestrial magma ocean.

Anderson, D. L.↗

Lu-Hf and Sm-Nd evolution in lunar mare basalts

Existing cumulate remelting models for mare basalt genesis are evaluated in light of Lu-Hf, Rb-Sr, Sm-Nd data and overall REE characteristics in order to determine the simplest model that can account for these data. A data base for comparing Lu-Hf evolution in the lunar mantle as inferred from Lu-Hf analyses of oceanic basalts is presented along with a preliminary comparison of Lu-Hf and Sm-Nd evolution betwee mare basalts and terrestrial oceanic basalts. It is found that Lu/Hf characteristics of mare basalts cannot be explained in terms of modal melting of cumulate sources formed from a magma ocean with chondritic Lu/Hf. The data are consistent with a model in which the cumulate sources formed from a light REE + HF-enriched magma ocean. Nonmodal melting of ilmenite in the sources is also required. The Lu-Hf data suggest that even the high-Ti basalt sources contained no more than about 3 percent ilmenite.

Unruh, D. M.↗

A potpourri of pristine moon rocks, including a VHK mare basalt and a unique, augite-rich Apollo 17 anorthosite

The anorthosite fragment, 76504,18, the first of the Apollo 17's pristine anorthosites, was found to have: (1) a higher ratio of high-Ca pyroxine to low-Ca pyroxene, (2) higher Na in its plagioclase, (3) higher contents of incompatible elements, and (4) a higher Eu/Al ratio in comparison to ferroan anorthosites. With a parent melt having a negative Eu anomaly, 76504,18 closely resembles a typical mare basalt. This anorthosite was among the latest to be formed by plagioclase flotation above a primordial magmasphere; typical mare basalt regions accumulated at about the same time or even earlier. Another fragment 14181c, a very high potassium basalt, was studied and found to be similar to typical Apollo 14 mare basalt though it has a K/La ratio of 1050. It is suggested that this lithology formed after a normal Apollo 14 mare basaltic melt partially assimilated granite. New data for siderphile elements in Apollo 12 mare basalts indicate that only the lowest of earlier data are trustworthy as being free of laboratory contamination.

Warren, P. H.↗

Volatile degassing of basaltic achondrite parent bodies Evidence from alkali elements and phosphorus

The Na, K, Rb, Cs, and P abundances in eucrites, diogenites, basaltic clasts from polymict eucrite, howardites, and mesosiderites are examined, and compared with an average of highly incompatible refractory (AHIR) elements normalized to cosmic abundances. It is observed that basaltic eucrites and basaltic clasts show a positive correlation between K, Rb, and Cs, and alkali element/AHIR ratios; the volatile loss of the alkali elements from the basalt affects the parent body inventory of volatile elements. The data reveal that for diogenites, the alkali /AHIR ratios are 1.4-2 times greater than in basaltic eucrites and are more variable; and the negative relation between K, Rb, Cs, and the alkali/AHIR ratio correlate with progressive alkali loss through volatile outgassing during crystallization of one or more magmas resulting in a greater than 90 percent loss of the volatile element inventory from the parent body. It is also detected that P displays volatile loss from the basaltic eucrites and elevated P/AHIR ratios in diogenites.

Mittlefehldt, David W.↗

Flood basalts and mass extinctions

There appears to be a correlation between the times of flood basalts and mass-extinction events. There is a correlation of flood basalts and hotspot tracks--flood basalts appear to mark the beginning of a new hotspot. Perhaps there is an initial instability in the mantle that bursts forth as a flood basalt but then becomes a steady trickle that persists for many tens of millions of years. Suppose that flood basalts and not impacts cause the environmental changes that lead to mass-extinctions. This is a very testable hypothesis: it predicts that the ages of the flows should agree exactly with the times of extinctions. The Deccan and K-T ages agree with this hypothesis; An iridium anomaly at extinction boundaries apparently can be explained by a scaled-up eruption of the Hawaiian type; the occurrence of shocked-quartz is more of a problem. However if the flood basalts are all well dated and their ages indeed agree with extinction times, then surely some mechanism to appropriately produce shocked-quartz will be found.

Morgan, W. Jason↗

Germanium abundances in lunar basalts - Evidence of mantle metasomatism?

To fill in gaps in the present Ge database, mare basalts were analyzed for Ge and other elements by RNAA and INAA. Mare basalts from Apollo 11, 12, 15, and 17 landing sites are rather uniform in Ge abundance, but Apollo 14 aluminous mare basalts and KREEP are enriched in Ge by factors of up to 300 compared to typical mare basalts. These Ge enrichments are not associated with other siderophile element enrichments and thus are not due to differences in the amount of metal segregated during core formation. Based on crystal-chemical and interelement variations, it does not appear that the observed Ge enrichments are due to silicate liquid immiscibility. KREEP basalt source regions may have been metasomatized, and Apollo 14 aluminous mare basalt magmas may have become enriched in Ge by interacting with these metasomatized areas. The presence of volatile- and Ge-rich regions in the moon suggest that the moon was never totally molten.

Dickinson, T.↗

Preliminary results of an experimental study of the interactions of basalt glass and a water vapor atmosphere: Implications for weathering on Mars

Models of weathering processes on the surface of Mars invoke hydrothermal alteration as the primary mechanism responsible for clay formation. Previous experimental studies of basalt glass interactions with water under hydrothermal conditions demonstrate that phyllosilicates and zeolites are the primary alteration minerals. Gas-solid weathering is thought to be less thermodynamically favorable and relatively unimportant, however, the experimental alteration of basalt glass under vapor ion conditions (large SA/V) can result in the formation of clay minerals, zeolites, and hydrated calcium silicates. We have undertaken a study of the reacted layers formed on basalt glasses experimentally altered under vapor hydration conditions to resolve this issue. High SA/V ratios promote reaction product buildup in solution and promote alteration mineral formation. It was previously shown that these reaction conditions promote weathering processes similar to those found in nature for tektite glasses, rhyolitic glasses, and basalt glasses. The hydration of basalt glass is described for 100 percent relative humidity experiments at temperatures of 150, 175, and 200 C for up to 400 days. Preliminary characterization of the alteration layers with analytical electron and scanning microscopy suggest that the reaction mechanism includes precipitation of a smectite clay on the outermost surface of the glass. Between the clay and the unreacted glass is an amorphous gel-like phase (palagonite). Our results provide an experimental basis for proposing that basalt glass interactions with vapor atmospheres can be an important source of clay minerals.

Mazer, J. J.↗

A dynamic melting model for the origin of Apollo 15 olivine-normative and quartz-normative mare basalts

Early studies of mare basalts from the Apollo 15 site established that two distinct groups are represented: the olivine-normative basalts (ONB) and the quartz-normative basalts (QNB). The ONB and QNB suites are distinguished petrographically by their phenocryst assemblages (the ONB's are olivine-phyric, the QNB's are generally pyroxene-phyric) and chemically by their major element compositions: the QNB's are higher in SiO2 and MgO/FeO, and lower in FeO and TiO2 than ONB's with similar MgO contents. Experimental data show that the QNB suite is derived from a more magnesian, olivine-normative parent magma, a conclusion which is supported by the recent discovery of high-SiO2 olivine-normative basalt clasts in breccia 15498. The high-SiO2 ONB's fall on olivine control lines with primitive QNB's, and least-squares mixing calculations are consistent with the high-SiO2 ONB's being parental to the more evolved QNB suite. These high-SiO2 ONB's are included as part of the 'QNB suite'. Our major element modeling results also are consistent with the conclusions of earlier studies which showed that the ONB and QNB suites cannot be related to one another by low pressure crystal fractionation. The combination of high Mg#, high SiO2, and low TiO2 in the QNB suite precludes a relationship to the ONB suite by simple removal of liquidus minerals (olivine and pigeonite). Despite these significant differences in petrography and major element composition, both groups have nearly identical trace element concentrations and chondrite-normalized abundance patterns. The major question to be addressed by any petrogenetic model for Apollo 15 mare basalts is how to form mare basalt suites with distinctly different major element characteristics but nearly identical trace element compositions. The similarity in trace element concentrations imply compositionally similar source regions and similar percent melting, but these conclusions are not easily reconciled with the observed differences in major element compositions, which require sources with distinct mineralogies or large differences in percent melt.

Vetter, Scott K.↗

Ambient Effects on Basalt and Rhyolite Lavas under Venusian, Subaerial, and Subaqueous Conditions

Both subaerial and subaqueous environments have been used as analog settings for Venus volcanism. To assess the merits of this, the effects of ambient conditions on the physical properties of lava on Venus, the seafloor, and land on Earth are evaluated. Rhyolites on Venus and on the surface of Earth solidify before basalts do because of their lower eruption temperatures. Rhyolite crust is thinner than basalt crust at times less than about an hour, especially on Venus. At later times, rhyolite crust is thicker because of its lower latent heat relative to basalt. The high pressure on the seafloor and Venus inhibits the exsolution of volatiles in lavas. Vesicularity and bulk density are proportional, so that lavas of the same composition should be more dense on the seafloor and less dense on land. Because viscosity depends partly upon the fraction of unvesiculated water in a melt, basalts with the same initial volatile abundance will be least viscous on the seafloor and most viscous on land. Assuming the same preeruptive H2O contents, molten rhyolites on Venus will have viscosities approx. 10% that of rhyolites on land. Despite lower expected viscosities, under-water flows are more buoyant and should have heights like subaerial and Venusian lavas of the same composition and extrusive history. In cases where the influence of crust is insignificant, a volume of rhyolite will have a higher aspect ratio than the same volume of basalt, no matter what the environment. If flow rheology is dominated by the presence of strong crust, aspect ratios differ little among environments or between compositions. These analyses support a rhyolitic interpretation for the composition of Venusian festooned flows and a basaltic interpretation for the composition of Venusian steep-sided domes. Although ambient effects are significant, extrusion rate and eruption history must also be considered to explain analogous volcanic landforms on Earth and Venus.

Bridges, Nathan T.↗

Oxygen Fugacity of Mare Basalts and the Lunar Mantle Application of a New Microscale Oxybarometer Based on the Valence State of Vanadium

The ability to estimate oxygen fugacities for mare basalts and to extend these observations to the lunar mantle is limited using bulk analysis techniques based on buffering assemblages or the valence state of iron. These limitations are due to reequilibration of mineral assemblages at subsolidus conditions, deviations of mineral compositions from thermodynamic ideality, size requirements, and the limits of the iron valence at very low fO2. Still, these approaches have been helpful and indicate that mare basalts crystallized at fO2 between the iron-w stite buffer (IW) and the ilmenite breakdown reaction (ilmenite = rutile + iron). It has also been inferred from these estimates that the lunar mantle is also highly reduced lying at conditions below IW. Generally, these data cannot be used to determine if the mare basalts become increasingly reduced during transport from their mantle source and eruption at the lunar surface and if there are differences in fO2 among mare basalts or mantle sources. One promising approach to determining the fO2 of mare basalts is using the mean valence of vanadium (2+, 3+, 4+, 5+) determined on spots of a few micrometers in diameter using synchrotron x-ray absorption fine structure (XAFS) spectroscopy. The average valence state of V in basaltic glasses is a function of fO2, temperature, V coordination, and melt composition. Here, we report the initial results of this approach applied to lunar pyroclastic glasses.

Shearer, C. K.↗

Aqueous Alteration of Basalts: Earth, Moon, and Mars

The geologic processes responsible for aqueous alteration of basaltic materials on Mars are modeled beginning with our knowledge of analog processes on Earth, i.e., characterization of elemental and mineralogical compositions of terrestrial environments where the alteration and weathering pathways related to aqueous activity are better understood. A key ingredient to successful modeling of aqueous processes on Mars is identification of phases that have formed by those processes. The purpose of this paper is to describe what is known about the elemental and mineralogical composition of aqueous alteration products of basaltic materials on Mars and their implications for specific aqueous environments based upon our knowledge of terrestrial systems. Although aqueous alteration has not occurred on the Moon, it is crucial to understand the behaviors of basaltic materials exposed to aqueous environments in support of human exploration to the Moon over the next two decades. Several methods or indices have been used to evaluate the extent of basalt alteration/weathering based upon measurements made at Mars by the Mars Exploration Rover (MER) Moessbauer and Alpha Particle X-Ray Spectrometers. The Mineralogical Alteration Index (MAI) is based upon the percentage of total Fe (Fe(sub T)) present as Fe(3+) in alteration products (Morris et al., 2006). A second method is the evaluation of compositional trends to determine the extent to which elements have been removed from the host rock and the likely formation of secondary phases (Nesbitt and Young, 1992; Ming et al., 2007). Most of the basalts that have been altered by aqueous processes at the two MER landing sites in Gusev crater and on Meridiani Planum have not undergone extensive leaching in an open hydrolytic system with the exception of an outcrop in the Columbia Hills. The extent of aqueous alteration however ranges from relatively unaltered to pervasively altered materials. Several experimental studies have focused upon the aqueous alteration of lunar materials and simulants (e.g., Keller and Huang, 1971; Eick et al., 1996). Lunar basalts are void of water and highly reduced, hence, these materials are initially very reactive when exposed to water under oxidizing conditions.

Ming, Douglas W.↗

Testing the Origins of Basalt Fragments fro Apollo 16

Several 2-4 mm regolith fragments of basalt from the Apollo 16 site were recently described by [1]. These included a high-Ti vitrophyric basalts (60603,10-16) and one very-low-titanium (VLT) crystalline basalt (65703,9-13). As Apollo 16 was the only highlands sample return mission distant from the maria, identification of basaltic samples at the site indicates input from remote sites via impact processes [1]. However, distinguishing between impact melt and pristine basalt can be notoriously difficult and requires significant sample material [2-6]. The crystal stratigraphy method utilizes essentially non-destructive methods to make these distinctions [7,8]. Crystal stratigraphy combines quantitative petrography in the form of crystal size distributions (CSDs) coupled with mineral geochemistry to reveal the petrogenetic history of samples. The classic CSD plot of crystal size versus population density can reveal insights on growth/cooling rates, residence times, and magma history which in turn can be used to evaluate basaltic vs impact melt origin [7-9]. Electron microprobe (EMP) and laser ablation (LA)-ICP-MS analyses of mineral phases complement textural investigations. Trace element variations document subtle changes occurring during the formation of the samples, and are key in the interpretation and preservation of this rare lunar sample collection.

Donohue, P. H.↗

Alteration of Basaltic Glass to Mg/Fe-Smectite under Acidic Conditions: A Potential Smectite Formation Mechanism on Mars

Phyllosilicates of the smectite group including Mg- and Fe-saponite and Fe(III)-rich nontronite have been identified on Mars. Smectites are believed to be formed under neutral to alkaline conditions that prevailed on early Mars. This hypothesis is supported by the observation of smectite and carbonate deposits in Noachian terrain on Mars. However, smectite may have formed under mildly acidic conditions. Abundant smectite formations have been detected as layered deposits hundreds of meters thick in intracrater depositional fans and plains sediments, while no large deposits of carbonates are found. Development of mildly acidic conditions at early Mars might allow formation of smectite but inhibit widespread carbonate precipitation. Little is known regarding the mechanisms of smectite formation from basaltic glass under acidic conditions. The objective of this study was to test a hypothesis that Mars-analogue basaltic glass alters to smectite minerals under acidic conditions (pH 4). The effects of Mg and Fe concentrations and temperature on smectite formation from basaltic glass were evaluated. Phyllosilicate synthesis was performed in batch reactors (Parr acid digestion vessel) under reducing hydrothermal conditions at 200 C and 100 C. Synthetic basaltic glass with a composition similar to that of the Gusev crater rock Adirondack (Ground surface APXS measurement) was used in these experiments. Basaltic glass was prepared by melting and quenching procedures. X-ray diffraction (XRD) analysis indicated that the synthesized glass was composed of olivine, magnetite and X-ray amorphous phase. Samples were prepared by mixing 250 mg Adirondack with 0.1 M acetic acid (final pH 4). In order to study influence of Mg concentration on smectite formation, experiments were performed with addition of 0, 1 and 10 mM MgCl2. After 1, 7 and 14 day incubations the solution composition was analyzed by Inductively Coupled Plasma Mass Spectrometry (ICP-MS) and the altered glass and formed phyllosilicates were examined by XRD analysis. Mineralogical changes were significant in Adirondack incubated with 10 mM MgCl2 at pH 4 and heated at 200 C. X-ray diffraction analysis revealed formation of phyllosilicate during 14 day incubation (Figure 1). Smectite was confirmed as the phyllosilicate after treatments with glycerol and KCl and heating to 550 C. The position of 02l (4.60 A) and 060 (1.54 A) diffraction bands were indicative of trioctahedral smectite such as saponite. Analysis of solution composition demonstrated that aqueous concentration of Mg decreased from 10 mM to approx.4 mM after 7 day incubation likely due to saponite formation. Smectite also formed in Adirondack incubated with 0 mM MgCl2 at pH 4 and heated at 200 C. However, diffraction peak positions of 02l (4.52 A) and 060 (1.51 A) suggested formation of dioctahedral nontronite. The 100degC Mg and Fe(II) treated basaltic glass experiments are ongoing and results will be presented.

Peretyazhko, Tanya↗

Additive Construction using Basalt Regolith Fines

Planetary surfaces are often covered in regolith (crushed rock), whose geologic origin is largely basalt. The lunar surface is made of small-particulate regolith and areas of boulders located in the vicinity of craters. Regolith composition also varies with location, reflecting the local bedrock geology and the nature and efficiency of the micrometeorite-impact processes. In the lowland mare areas (suitable for habitation), the regolith is composed of small granules (20 - 100 microns average size) of mare basalt and volcanic glass. Impacting micrometeorites may cause local melting, and the formation of larger glassy particles, and this regolith may contain 10-80% glass. Studies of lunar regolith are traditionally conducted with lunar regolith simulant (reconstructed soil with compositions patterned after the lunar samples returned by Apollo). The NASA Kennedy Space Center (KSC) Granular Mechanics & Regolith Operations (GMRO) lab has identified a low fidelity but economical geo-technical simulant designated as Black Point-1 (BP-1). It was found at the site of the Arizona Desert Research and Technology Studies (RATS) analog field test site at the Black Point lava flow in adjacent basalt quarry spoil mounds. This paper summarizes activities at KSC regarding the utilization of BP-1 basalt regolith and comparative work with lunar basalt simulant JSC-1A as a building material for robotic additive construction of large structures. In an effort to reduce the import or in-situ fabrication of binder additives, we focused this work on in-situ processing of regolith for construction in a single-step process after its excavation. High-temperature melting of regolith involves techniques used in glassmaking and casting (with melts of lower density and higher viscosity than those of metals), producing basaltic glass with high durability and low abrasive wear. Most Lunar simulants melt at temperatures above 1100 C, although melt processing of terrestrial regolith at 1500 C is not uncommon. These temperatures are achievable by laser heating or by using solar concentrators. Similar to volcanic magma, the cooling rate determines the crystallite size - slower cooling develops larger crystals, and rapid quenching can result in fully amorphous glass.

Additive↗

Using XRD to Characterize Sediment Sorting in a Mars Analog Glacio-Fluvio-Eolian Basaltic Sedimentary System in Iceland

The martian surface has a primarily basaltic composition and is dominated by sedimentary deposits. Ancient layered sedimentary rocks have been identified across the planet from orbit, have been studied in situ by the Mars Exploration Rovers and the Mars Science Laboratory rover, and will be studied by the Mars 2020 rover. These ancient sedimentary rocks were deposited in fluvial, lacustrine, and eolian environments during a warmer and wetter era on Mars. It is important to study the composition of sediments in Mars analog environments to characterize how minerals in basaltic sedimentary systems are sorted and/or aqueously altered. This information can help us better interpret sedimentary processes from similar deposits on Mars and derive information about the igneous source rocks. Sediment sorting has been studied extensively on Earth, but not typically in basaltic environments. Previous work has addressed sorting of basaltic sediments through experimental techniques and in modern eolian basaltic systems and aqueous alteration in subglacial and proglacial environments. We add to this body of research by studying sediment sorting and aqueous alteration in a glacio-fluvio-eolian basaltic system in southwest Iceland.

Rampe, E. B.↗