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At least 19 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS1993

Estimation of age of Dali-Ganis rifting and associated volcanic activity, Venus

This paper deals with the estimation of age for the Dali and Ganis Chasma rift zones and their associated volcanism based on photogeologic analysis of stratigraphic relations of rift-associated features with impact craters which have associated features indicative of their age. The features are radar-dark and parabolic, and they are believed to be mantles of debris derived from fallout of the craters' ejecta. They are thought to be among the youngest features on the Venusian surface, so their 'parent' craters must also be very young, evidently among the youngest 10 percent of Venus' crater population. Dali Chasma and Ganis Chasma are a part of a system of rift zones contained within eastern Aphrodite and Atla Regio which is a significant component of Venus tectonics. The rifts of this system are fracture belts which dissect typical Venusian plains with rare islands of tessera terrain. The rift zone system consists of several segments following each other (Diane, Dali, Ganis) and forming the major rift zone line, about 10,000 km long, which has junctions with several other rift zones, including Parga Chasma Rift. The junctions are usually locations of rift-associated volcanism in the form of volcanic edifices (Maat and Ozza Montes) or plain-forming flows flooding some areas within the rift zones and the adjacent plains.

Basilevsky, A. T.↗
NASA NTRS2003

Cosmogenic Records in 18 Ordinary Chondrites from the Dar Al Gani Region, Libya: Noble Gases - 1

In the last decade thousands of meteorites have been recovered from hot deserts in the Sahara and Oman. One of the main meteorite concentration surfaces in the Sahara is the Dar al Gani plateau in Libya, which covers a total area of ~8000 km2. More than 1000 meteorites have been reported from this area. The geological setting, meteorite pairings and the meteorite density of the Dar al Gani (DaG) field are described in more detail in [1]. In this work we report concentrations of the noble gas isotopes of He, Ne, Ar as well as 84Kr and 132Xe in 18 DaG meteorites. In a separate paper we will report the cosmogenic radionuclides [2]. We discuss the thermal history and cosmic-ray exposure (CRE) history of these meteorites, and evaluate the effects of the hot desert environment on the noble gas record.

Schultz, L.↗
NASA NTRSDate not supplied

The Chemical and Isotopic Signatures of the Hibonite-rich FUN Inclusion "HIDALGO" in Dar al Gani 027 (CO3)

Refractory Ca-Al-rich Inclusions (CAIs) with FUN (Fractionation with Unidentified Nuclear effects) characteristics are peculiar samples among all high-temperature components in chondritic meteorites. They are generally characterized by strong mass-dependent isotopic fractionations in several elements (e.g., O, Mg, Ca, Ti), large (~5-20‰) enrichments or depletions in neutron-rich isotopes (e.g., 48 Ca, 50 Ti, 54 Cr), and low inferred abundances of 26 Al ( 26 Al/ 27 Al < 1×10 −5 ). Understanding the origins of these features in FUN CAIs can shed light on the astrophysical environment and chemical processes that took place in the early Solar System. A large fraction (slightly less than 50%) of the ~20 FUN CAIs discovered so far are hibonite-rich (such as HAL, SHAL and DH-H1, collectively called HAL-type inclusions hereafter). According to their elemental and isotopic signatures and the results of evaporation experiments, HAL-type inclusions are thought to have formed as a distillation residue. However, questions regarding the timing of the formation of HAL-type inclusions (or FUN inclusions in general) relative to those of regular CAIs and the decoupling between the 26 Al abundances and nucleosynthetic anomalies remain poorly understood. In 2021, we reported the discovery of a new HAL-type inclusion, HIDALGO (Hibonite in Dar al Gani CO3) in the CO3 chondrite Dar al Gani 027 (DaG027), based on its (fractionated) oxygen isotopic compositions and low inferred 26 Al/ 27 Al ratio of (1.50±0.02)×10 −5 . Since then, more work on other short-lived and stable isotope systems and trace element abundances has been conducted. Here we report these new results and discuss the implications for the possible formation history of HIDALGO and origins of shortlived radionuclides (SLRs).

Meteorite↗
NASA NTRS2003

Cosmogenic Records in 18 Ordinary Chondrites from the Dar Al Gani Region, Libya: Radionclides - 2

In the past decade more than 1000 meteorites have been recovered from the Dar al Gani (DaG) plateau in the Libyan part of the Sahara. The geological setting, meteorite pairings and density are described. So far, only a few terrestrial ages are known for DaG meteorites, e.g. 60+/- 20 kyr for the DaG 476 shergottite shower and 80+/- 20 kyr for the lunar meteorite DaG 262. However, from other desert areas, such as Oman, it is known that achondrites may survive much longer than chondritic meteorites, so the ages of these two achondrites may not be representative of the majority of the DaG meteorite collection, of which more than 90% are ordinary chondrites. In this work we report concentrations of the cosmogenic radionuclides, 14C (half-life = 5,730 yr), 41Ca (1.04x10 superscript 5 yr), Cl-36 (3.01x10 superscript 5 yr), Al-26 (7.05x10 superscript 5 yr) and 10Be (1.5x10 superscript 6 yr) to determine the terrestrial ages of DaG meteorites and constrain their pre-atmospheric size and exposure history.

Welten, K. C.↗
NASA NTRS2024

Supra-Chondritic 7Li/6Li in the Hibonite-Rich Fun Inclusion “HIDALGO” in Dar al Gani 027 (CO3): A Hint for the Former Presence of Beryllium-7?

HIDALGO, a ~300×300 μm, hexagonally shaped, chemically and mineralogically simple hibonite crystal residing in the matrix of the CO3 chondrite Dar al Gani 027 (DaG027), is the newest member in the FUN-hibonite family. Based on the mass-dependent fractionations in O, Ca, and Ti isotopes, large negative anomalies in δ 48 Ca (= −30‰) and δ 50 Ti (= −20‰), and the abundances of short-lived radioisotopes of 10 Be, 26 Al, 41 Ca, which have all been reported previously, we have inferred that HIDALGO evolved from a condensate that most likely formed before 26 Al was built up and homogenized to 26 Al/ 27 Al = 5.2×10 −5 in the solar system. This precursor also incorporated 10 Be at the level of 10 Be/ 9 Be = 7.5×10 −4 , possibly through local irradiation of gas and/or dust or inheritance from the molecular cloud, but the amount of 41 Ca present at that time and location is uncertain. Strong heating of the precursor occurred ~0.5 Myr after the initial condensation, leading to total melting accompanied by extensive distillation (losing Mg, Si, and other moderately volatile elements) resulting in a stoichiometrically pure hibonite crystal with strongly mass fractionated O, Ca, and Ti isotope compositions and an extreme Ce depletion relative to other REEs. Here we report the results of Li isotope analyses of HIDALGO and discuss the irradiation history of this inclusion.

Meteorite↗
NASA NTRS2002

Dar Al Gani 872: Yet Another Eucrite, Yet Another Lesson to Learn?

We present chemical and mineralogical data on a new monomict basaltic eucrite recovered from Libya. In contrast to most other eucrites, it exhibits high shock features, unusually heterogeneous exsolution of pigeonite, and interesting melt pockets. Additional information is contained in the original extended abstract.

Patzer, A.↗
NASA NTRS1993

Geologic mapping of Northern Atla Regio on Venus: Preliminary data

The Northern part of Atla Regio within the frame of C1-formate Magellan photo map 15N197 was mapped geologically at scale 1:8,000,000. This is a part of Russia's contribution into C1 geologic mapping efforts. The map is reproduced here being reduced about twice. The map shows that the Northern Atla area is predominantly a volcanic plain with numerous volcanic features: shield volcanoes, domes and hills with various morphology, corona-like constructions, radar bright and dark spots often with flow-like outlines. Relatively small areas of tessera occurred in the area are mainly semi-flooded with the plain material. Tesserae are considered to be the oldest terrains within the map sheet. There are many lineated terrains in the region. They are interpreted as the old, almost-buried tesserae (those with crossed lineaments) or partly buried ridge belts (those with parallel lineaments). These lineated terrains have an intermediate age between the young volcanic plains and the old tessera areas. Two prominent high volcanic shields are located within the region - Ozza Mons and Sapas Mona. The most prominent structure in Northern Atla is Ganis Chasma rift. The rift cuts volcanic plain and is considered to be under formation during approximately the same time with Ozza Mons shield. Ganis Chasma rift valley is highly fractured and bounded with fault scarps. Rift shoulder uplifts are typical for Ganis Chasma. There are few relatively young volcanic features inside the rift valley. The analysis of fracturing and rift valley geometry shows the rift originated due to 5-10 percent crustal extention followed by the crustal subsidence. The age sequence summary for the main terrain types in the region is (from older to younger ones): tesserae; lineated terrains with crossed lineaments; lineated terrains with parallel lineaments; volcanic plains; and prominent volcanic shields and Ganis Chasma rift valley. The geologic structure of Atla Regio as it appeared now with the Magellan high resolution images is very close to that of Beta Regio. Such conclusion coincide with the earlier ones based on the coarser data.

Nikishin, A. M.↗
NASA NTRS1992

Venus: Preliminary geologic mapping of northern Atla Regio

A preliminary geologic map of C1 sheet 15N197 was compiled according to Magellan data. Northern Atla Regio is dominantly a volcanic plain with numerous volcanic features: radar-bright and -dark flows and spots, shield volcanos, volcanic domes and hills with varied morphology, and coronalike constructions. Tesserae are the oldest terrains semiflooded by plain materials. There are many lineated terrains on this territory. They are interpreted as old, partly buried ridge belts. Lineated terrains have intermediate age between young plains and old tesserae. Ozza Mons and Sapas Mons are the high shield volcanos. The prominent structure of northern Atla Regio is Ganis Chasma rift. The rift dissected the volcanic plain and evolved nearly contemporaneously with Ozza Mons shield volcano. Ganis Chasma rift valley is highly fractured and bounded by fault scarps. There are a few relatively young volcanic features in the rift valley. The rift originated due to 5-10 percent crustal extension and crustal subsidence according to analysis of fracturing and rift valley geometry. Ganis Chasma is characterized by rift shoulder uplifts. Geological structures of Alta Regio and Beta Regio are very similar as assumed earlier.

Nikishin, A. M.↗
NASA NTRS1999

Workshop on Extraterrestrial Materials from Cold and Hot Deserts

The workshop was held July 6-8, 1999 before the Meteoritical Society meeting in Johannesburg, South Africa. The venue was Kwa Maritane Resort in the Pilanesburg Game Reserve. Conveners were Ludolf Schultz (Chair, MPI fur Chemie), Ian Franchi (Open University), Arch Reid (University of Houston), and Mike Zolensky (NASA JSC). Extended abstracts will be published as an LPI Technical Report. In the first session, Marvin discussed three African iron meteorites: Cape of Good Hope, Gibeon, and Hoba. Grady presented a statistical analysis of meteorites from hot and cold deserts. Wasson discussed types of Antarctic iron meteorites. Several presentations characterized populations of meteorites from individual desert areas: Libyan Desert (Weber et al.), Nullarbor Region (Bevan et al.), and Mojave Desert (Kring et al. and Verish et al). Pairing among EET87503-group howardites was discussed by Buchanan et al. Based on 14C terrestrial ages of Allan Hills ordinary chondrites, Bland et al. suggested that ice flow may be the principal sink for Antarctic meteorites. The effects of preterrestrial and terrestrial alteration were considered in the second session. Nakamura et al. and Lipschutz discussed asteroidal metamorphism of carbonaceous chondrites. Zolensky presented evidence for preterrestrial halide and sulfide in meteorites. Crozaz and Wadhwa described terrestrial alteration of Dar al Gani 476. Welten and Nishiizumi discussed terrestrial weathering of chondrites from Frontier Mountain, Antarctica. Most of the third session dealt with terrestrial meteorite ages. Based on 14C-10Be ages, Jull et al. discussed the exponential decay in numbers of meteorites with increased age. Nishiizumi et al. concluded that some Allan Hills meteorites have much older terrestrial ages than any meteorites from Lewis Cliffs. Welten et al. discussed terrestrial ages determined by 41Ca/36CI of metal separates from hot desert meteorites. Based on a comparison with large IDPs, Flynn et al. suggested that polar micrometeorites, lost a water-soluble sulfate phase by terrestrial alteration. Nyquist suggested that Type I cosmic spheres from deep sea sediments and polar ice were derived from carbonaceous chondrite-like asteroidal sources. The final session considered noble gases, cosmic ray effects, and thermoluminescence. Calculations presented by Reedy indicate that cosmic ray-produced nuclides are more likely to be preserved in small objects than in larger objects. Murty and Mohapatra. reported that trapped gas in Dar al Gani 476 includes a Martian atmospheric component. Wieler et al. and Scherer et al. reported noble gas abundances in different types of desert meteorites. Patzer and Schultz discussed the influence of terrestrial weathering on cosmic ray exposure ages of enstatite chondrites. Franchi et al. suggested that it is difficult to discriminate whether differences in gas release profiles of lunar meteorites from hot deserts and returned lunar samples are the result of terrestrial weathering or shock metamorphism. Benoit and Sears surveyed natural and induced thermoluminescence of Antarctic ordinary chondrites. Merchel et al. analyzed Saharan meteorites with short or complex exposure histories.

Buchanan, Paul C.↗
NASA NTRS2003

Microfossils in CI and CO Carbonaceous Meteorites

Secondary and backscatter electron images and x-ray spectral data of selected CI (Alais, Orgueil, and Tagish Lake) and CO3 (Rainbow and Dar a1 Gani 749) carbonaceous meteorites have recently been obtained using Field Emission and Environmental Scanning Electron Microscopes These studies indicate the presence of a large assemblage of biomarkers and complex lithified and carbonized remains of bodies that we interpret as indigenous microfossils. We discuss the meteorites, provide images of many of the biogenic forms found embedded in the freshly fractured meteorite surfaces.

Hoover, Richard B.↗
NASA NTRS2007

Rb-Sr and Sm-Nd Isotopic Studies of Martian Depleted Shergottes SaU 094/005

Sayh al Uhaymir (SaU) 094 and SaU 005 are olivine-phyric shergottites from the Oman desert and are considered as pairs. [e.g., 1]. They are very similar to the Libyan desert shergottite Dar al Gani (DaG) 476 in petrology, chemistry and ejection age [2-6]. This group of shergottites, also recognized as depleted shergottites [e.g. 7] has been strongly shocked and contains very low abundances of light rare earth elements (REE). In addition, terrestrial contaminants are commonly present in meteorites found in desert environments. Age-dating these samples is very challenging, but lower calcite contents in the SaU meteorites suggest that they have been subjected to less severe desert weathering than their DaG counterparts [3-4]. In this report, we present Rb-Sr and Sm-Nd isotopic results for SaU 094 and SaU 005, discuss the correlation of their ages with those of other similar shergottites, and discuss their petrogenesis.

Shih, C.-Y.↗
NASA NTRS2001

Highly Siderophile Element Abundances in Martian Meteorites

Critical evaluation of new and literature data for highly siderophile elements (HSE) in Martian (SNC) meteorites allows several first order conclusions to be drawn. (i) Re concentrations in SNC meteorites are nearly constant (within a factor of two) and do not correlate with rock type. Exceptions to this rule are Chassigny and Dar al Gani (DaG) 476, both of which are inferred to have experienced terrestrial Re contamination. (ii) Fractionations between Rh and Pd are small. Excluding Shergotty, the Rh/Pd ratio of the SNC suite is 0.22\pm0.05. (iii) Os and Ir contents vary by about four orders of magnitude; and positive correlations with MgO, Cr, and Ni suggest that these variations are not controlled by sulfide fractionation. A possible exception is the orthopyroxenite ALH84001, whose HSE's (including Ni, which is compatible in opx) are very low. (iv) Zagami, Shergotty, and Nakhla have nearly identical HSE signatures. Shergotty and Zagami have experienced assimilation-fractional crystallization (AFC) and have "crustal" Sr and Nd isotopic signatures. Conversely, the Nakhla parent was a small degree partial melt of a depleted mantle that interacted little with the Martian crust. These observations suggest that "evolved" HSE signatures can be produced by either fractional crystallization or small degrees of partial melting. (v) Chassigny and other mafic SNC's have HSE signatures that are very distinct from those of Nakhla-Zagami-Shergotty. The HSE elemental ratios of mafic SNC's approach chondritic, implying that the Martian mantle has nearly chondritic relative abundances of the HSE's. (vi) This chondritic HSE signature is observed in SNC's of various ages, suggesting that this is an ancient feature that has not evolved over time. (vii) No correlation is observed between HSE's and signatures of crustal contamination (e.g., Sr isotopes), indicating that the HSE signatures of the SNC suite are not derived from the crust. (vii) The Ru/Pd for the SNC suite ratio is about 0.5 chondritic. We attribute this depletion of Ru to the presence of spinel in the SNC source regions. (viii) Assignment of this depletion of Ru to spinel seems to also imply that spinel is not the cause of Os and Ir fractionations, requiring some other mafic phase to account for the observed variations. -----.

Jones, J. H.↗
NASA NTRS2011

Almahata Sitta and Brecciated Ureilites: Insights into the Heterogeneity of Asteroids and Implications for Sample Return

Analysis of samples returned to terrestrial laboratories enables more precise measurements and a wider range of techniques to be utilized than can be achieved with either remote sensing or rover instruments. Furthermore, returning samples to Earth allows them to be stored and re-examined with future technology. Following the success of the Hayabusa mission, returning samples from asteroids should be a high priority for understanding of early solar system evolution, planetary formation and differentiation. Meteorite falls provide us with materials and insight into asteroidal compositions. Almahata Sitta (AS) was the first meteorite fall from a tracked asteroid (2008 TC3) [1] providing a rare opportunity to compare direct geochemical observations with remote sensing data. Although AS is predominantly ureilitic, multiple chondritic fragments have been associated with this fall [2,3]. This is not unique, with chondritic fragments being found in many howardite samples (as described in a companion abstract [4]) and in brecciated ureilites, some of which are known to represent ureilitic regolith [5-7]. The heterogeneity of ureilite samples, which are thought to all originate from a single asteroidal ureilite parent body (UPB) [5], gives us information about both internal and external asteroidal variations. This has implications both for the planning of potential sample return missions and the interpretation of material returned to Earth. This abstract focuses on multiple fragments of two meteorites: Almahata Sitta (AS); and Dar al Gani (DaG) 1047 (a highly brecciated ureilite, likely representative of ureilite asteroidal regolith).

Ross, A. J.↗
NASA NTRS2013

Mesosiderites on Vesta: A Hyperspectral VIS-NIR Investigation

The discussion about the mesosiderite origin is an open issue since several years. Mesosiderites are mixtures of silicate mineral fragments or clasts, embedded in a FeNi metal matrix. Silicates are very similar in mineralogy and texture to howardites [1]. This led some scientists to conclude that mesosiderites could come from the same parent parent asteroid of the howardite, eucrite and diogenite (HED) meteorites [2, 3]. Other studies found a number of differences between HEDs and mesosiderite silicates that could be explained only by separate parent asteroids [4]. Recently, high precision oxygen isotope measurements of m esosiderites silicate fraction were found to be isotopically identical to the HEDs, requiring common parent body, i.e. 4 Vesta [5]. Another important element in favor of a common origin was given by the identification of a centimeter-sized mesosiderite clast in a howardite (Dar al Gani 779): a metal-rich inclusion with fragments of olivine, anorthite, and orthopyroxene plus minor amounts of chromite, tridymite, and troilite [6]. The Dawn mission with its instruments, the Infrared Mapping Spectrometer (VIR) [7], the Framing Camera [8] and the Gamma-Ray and Neutron Detector (GRaND) [9] confirmed that Vesta has a composition fully compatible with HED meteorites [10]. We investigate here the possibility to discern mesosiderite rich locations on the surface of Vesta by means of hyperspectral IR images.

Palomba, E.↗
NASA NTRS2017

A New Type of Foreign Clast in A Polymict Ureilite: A CAI or AL-Rich Chondrule

Introduction: Polymict ureilites are breccias interpreted to represent regolith formed on a ureilitic asteroid [1-3]. They consist of approximately 90-95% clasts of various ureilite types (olivine-pyroxene rocks with Fo 75-95), a few % indigenous feldspathic clasts, and a few % foreign clasts [4-20]. The foreign clasts are diverse, including fragments of H, L, LL and R chondrites, angrites, other achondrites, and dark clasts similar to CC [6,7,9-19]. We report a new type of foreign clast in polymict ureilite DaG 999. Methods: Clast 8 in Dar al Gani (DaG) 999/1 (Museum fur Naturkunde) was discovered during a survey of feldspathic clasts in polymict ureilites [19,20]. It was studied by BEI, EMPA, and X-ray mapping on the JEOL 8530F electron microprobe at ARES, JSC. Petrography and Mineral Compositions: Clast 8 is sub-rounded to irregular in shape, approximately 85 micrometers in diameter, and consists of approximately 68% pyroxene and 32% mesostasis (by area). Part of the pyroxene (top half of clast in Fig. 1a and 2) shows a coarse dendritic morphology; the rest appears massive. Mesostasis may be glassy and contains fine needles/grains of pyroxene. The pyroxene has very high CaO (23.5 wt.%) and Al2O3 (19.7 wt.%), with the formula: (Ca(0.91)Mg(0.63)Fe(0.01)Al(sup VI) (0.38)Cr(0.01)Ti(0.05)1.99 Si2O6. The bulk mesostasis also has very high Al2O3 (approximately 26 wt.%). A bulk composition for the clast was obtained by combining modal abundances with phase compositions (Table 1, Fig. 3). Discussion: The pyroxene in clast 8 has a Ca-Al-(Ti)- rich (fassaitic) composition that is clearly distinct from compositions of pyroxenes in main group ureilites [22] or indigenous feldspathic clasts in polymict ureilites [4-8]. It also has significantly higher Al than fassaite in angrites (up to approximately 12 wt.% [23]), which occur as xenoliths in polymict ureilites. Ca-Al-Ti rich pyroxenes are most commonly found in CAIs, Al-rich chondrules and other types of refractory inclusions in chondrites [21,24-31]. However, the clast 8 pyroxene matches only the most Al-Ca-rich of these, e.g., pyroxenes in type B CAIs in CV3 chondrites [25,30,31], a pyroxene-hibonite spherule and a pyroxene-anorthitespinel fragment from unique CC Acfer 094 [29], and one Al-rich chondrule from Chainpur (LL3.4) [21]. The mineralogy of clast 8 is not consistent with the mineral assemblages of any of these objects (since it lacks hibonite, spinel and/or anorthite), which suggests that it is unrepresentatively sectioned or is a fragment of a more mineralogically diverse object. Its bulk composition (Table 1; Fig. 3) is similar to bulk compositions of some Al-rich chondrules, as well as those of Type C CAIs (which plot in the sp+An+L field in Fig. 3), although it is enriched in silica relative to type C CAIs [e.g., 31]. This suggests a more likely affinity to Al-rich chondrules, although most Al-rich chondrules have less Al-Ca-rich pyroxene [21,26,27]. These bulk compositional comparisons may not be definitive, however, if the clast is unrepresentatively sampled. One of eleven Al-rich chondrules from UOCs described by [21] has textural and compositional characteristics that make it a possible progenitor type for clast 8. This chondrule (Chainpur 1251-14-2) is anorthiteporphyritic, with an interstitial dendritic intergrowth of pyroxene (similar in composition to that in clast 8) and plagioclase [21]. Clast 8 is conceivably a fragment from the interstitial area of such an object. The occurrence of glassy mesostasis (in clast 8) rather than plagioclase may not be a significant difference; it could result from a difference only in cooling rate. Al-rich chondrules with glassy mesostasis are rare, and known occurrences are Ca-poor [26], unlike clast 8. Polymict ureilites are known to contain xenoliths of various chondrites (including OC, R and CC) as well as individual ferromagnesian and silica-pyroxene chondrules probably derived from OC or RC [6,9,15,16,18]. This is the first report of an individual chondritic refractory inclusion as a xenolith in a polymict ureilite. An RC-like sample from anomalous polymict ureilite Almahata Sitta contains CAIs, but they are spinel-rich and not similar to clast 8 [13,14]. Further studies of this clast (which, unfortunately, may not be possible), or the discovery of additional (more representative?) materials of this type would be needed to determine the exact nature of this xenolith and the type of chondrite from which it is derived.

Goodrich, C. A.↗