Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “polymict diogenite”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 19 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS1984

Processes and subdivisions in diogenites, a multivariate statistical analysis

Multivariate statistical techniques used on diogenite orthopyroxene analyses show the relationships that occur within diogenites and the two orthopyroxenite components (class I and II) in the polymict diogenite Garland. Cluster analysis shows that only Peckelsheim is similar to Garland class I (Fe-rich) and the other diogenites resemble Garland class II. The unique diogenite Y 75032 may be related to type I by fractionation. Factor analysis confirms the subdivision and shows that Fe does not correlate with the weakly incompatible elements across the entire pyroxene composition range, indicating that igneous fractionation is not the process controlling total diogenite composition variation. The occurrence of two groups of diogenites is interpreted as the result of sampling or mixing of two main sequences of orthopyroxene cumulates with slightly different compositions.

Harriott, T. A.↗
NASA NTRS2012

Composition and Petrology of HED Polymict Breccias: The Regolith of (4) Vesta

The polymict breccias of the howardite, eucrite and diogenite (HED) clan of meteorites preserve records of regolith processes that occur on Vesta, their putative home world. These breccias -- howardites, polymict eucrites and polymict diogenites -- are impact-engendered mixtures of diogenites and eucrites. The compositions of polymict breccias can be used to constrain the lithologic diversity of the vestan crust and the excavation depths of these materials. We have done petrological and compositional studies of multiple samples of 5 polymict eucrites and 28 howardites to investigate these issues. Older analyses were done on samples of approx 0.5 gram mass by INAA; newer analyses on samples of approx 5 gram mass by XRF and ICP-MS. We estimate the percentage of eucritic material (POEM) of polymict breccias by comparing their Al and/or Ca contents to those of average basaltic eucrite and diogenite. Our samples have POEM ranging from 28 to 98; adding two polymict diogenites from extends the range to POEM 10. One hypothesis is that ancient, well-mixed vestan regolith has POEM approx 67 and has a higher content of admixed impactor material. Several of our howardites have POEM of 59-74 (Al and/or Ca contents +/- 10% of POEM 67); about a third have Ni contents >300 micro g/g suggesting they contain >2% chondritic material (CM and/or CR). These may be regolithic howardites. Only one (LEW 85313) contains Ne dominated by a solar wind (SW) component. PCA 02066 is dominated by impact-melt material of polymict parentage and petrologically appears to be a mature regolith breccia, yet it does not contain SW-Ne. GRO 95602 falls within the POEM window, contains SW-Ne], yet has a Ni content of 193 micro g/g. Its petrologic characteristics suggest it was formed from immature regolith (no polymict breccia clasts; no glass). Trace element characteristics of the polymict breccias demonstrate the dominance of main-group eucrites as the basaltic component. Mixing diagrams of Zr, Nb, Ba, Hf and Ta with Al show no evidence for a significant contribution from Stannern-trend eucrites. An exception is polymict eucrite LEW 86001 (POEM 92), which is dominated by Stannern-trend basaltic debris. Howardite LAP 04838 (POEM 84) has higher incompatible trace concentrations than other polymict breccias (excluding LEW 86001), and either contains a Stannern-trend basaltic component, or has a significant contributions from evolved eucrites like Nuevo Laredo.

Mittlefehldt, David W.↗
NASA NTRS2021

Mesosiderite Silicates vs. HED Polymict Breccias

The silicate portions of mesosiderites are broadly like howardites [1], and this has led to persistent interpretations that mesosiderites and howardites are derived from the same parent asteroid [2]. Yet, when examined carefully, one finds that there are substantial petrological and compositional differences between these polymict breccias. These differences indicate that separate parent asteroids are more probable [3, 4]. I will document the distinctions between these groups based on my data and literature information [5] and discuss their origins.

mesosiderite↗
NASA NTRS1983

The nomenclature of polymict basaltic achondrites

The system of nomenclature for basaltic achondrite meteorites is discussed, and new classification criteria are proposed. Under the new system, all achondrites are divided intno the broad groupings 'monomict' and 'polymict' by the number of lithologies present. The monomicts are classified structurally as brecciated or unbreccciated and as eucrites, diogenites, or cumulate eucrites. The polymicts are classified using an arbitrary mineral-chemical standard based on the percentage content of diogenite (magnesium orthopyroxenite): diogenites have more than 90 percent, eucrites have less than 10 percent, and all other polymicts area howardites. Tables listing all known achondrites by classification are provided.

Delaney, J. S.↗
NASA NTRS2012

In the Pursuit of Regolithic Howardites

The HED (Howardite, Eucrite and Diogenite) meteorite clan likely originate from the asteroid 4-Vesta [1]. Howardites (polymict breccias of eucritic and diogenitic material) are believed to originate from the vestan surface, and many contain regolith-like features (impact and/or melt clasts, fragmental breccia clasts, carbonaceous chondrite fragments), which may relate to regolith-formation processes. Noble gas analysis can help determine true regolithic nature, as Solar Wind (SW) is im-planted into grains at the upper-surfaces of solar system bodies lacking an atmosphere or magnetic field. Howardites from Ves-ta s true regolith would thus show evidence for SW components. Thus far, we have identified 5 regolithic howardites: LEW 85313; MET 00423; PRA 04401; SCO 06040 and EET 87513; based on our noble gas analyses, with the latter 3 showing some evidence for a planetary(+SW) component, likely related to CM-like material present in the assemblage [2-5]. However, we did not find a good correlation between SW content and other petro-logic regolithic features. Nor did we find an obvious correlation between SW and high siderophile element contents (Ni greater than 300 micrograms/gram), or an Al2O3 range of 8-9 wt% and eucrite/diogenite (E/D) ratio of 2:1 as suggested by [6] to be further regolith indicators. Here, we report our latest noble gas data for two howardites GRO 95535, GRO 95602 and a polymict eucrite EET 87518 in continuing research aimed at better understanding the vestan regolith. Results: Noble gas analysis was performed on an MAP 215-50 noble gas mass spectrometer using furnace step-heating. Our results, shown in Table 1, are compared with SW- (LEW 85313) and planetary-dominated (PRA 04401 ~60% CM) howardites [2]. EET 87518 is dominated by cosmogenic components. By comparison, both howardites show strong evidence for SW, with total Ne-20/Ne-22 ~8.7-8.8 (SW: Ne-20/Ne-22 13.78 [7]), and identical release patterns to our other CM-poor SW-rich samples. This suggests that these samples are from the vestan regolith. As they have lower Ni contents than suggested by [6], this further illustrates that these parameters may show some bias [2].

Cartwright, J. A.↗
NASA NTRS1987

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.↗
NASA NTRS2011

Investigation of Orthopyroxene Diversity in Howardite Meteorites

The howardite, eucrite and diogenite (HED) family of meteorites is considered to originate from the asteroid 4-Vesta [1]. Howardites are polymict breccias made mostly of diogenitic and eucritic debris [2], and have recently been divided into two types: regolithic and fragmental [3]. Regolithic howardites have higher noble gas contents due to solar wind exposure, have a greater abundance of impact-produced glass, are richer in siderophile elements, e.g. Ni, and may preferentially have a mixing ratio of eucrite to diogenite of approx.2:1 [3]. The hypothesis is that these characteristics are a result of originating from an ancient, well-mixed regolith [3]. Fragmental howardites, by contract, show less evidence of regolithic processing and are suggested to have originated in more recently formed impact ejecta [3]. Our work aims to evaluate this hypothesis. We have examined the compositional variations of orthopyroxene (diogenite) clasts within eight howardites. We posited that because regolithic howardites sampled a wider range of the asteroid surface, they would contain orthopyroxene fragments with wider ranges in incompatible element contents than would fragmental howardites that sampled fewer diogenitic source rocks. One purpose of developing an additional method to differentiate regolithic and fragmental howardites is to aid in interpretation of data expected from the Dawn mission to 4-Vesta. The Dawn analyses will be of the regolith layers, making an understanding of regolithic meteorites and the processes by which they were formed an important constraint on understanding Dawn data.

Johnson, Kristin N.↗
NASA NTRS2010

Petrology and Composition of HED Polymict Breccias

The howardite, eucrite and diogenite (HED) clan of meteorites forms the largest suite of achondrites with over 900 named members. The HEDs are igneous rocks and breccias of igneous rocks from a differentiated asteroid [1]. The consensus view is that these rocks hail from the asteroid 4 Vesta, which will be the first target of NASA's Dawn mission. When Dawn arrives at Vesta, she will begin remote imagery and spectroscopy of the surface. The surface she will observe will be dominated by rocks and soils mixed through impact gardening. To help with the interpretation of the remotely sensed data, we have begun a project on the petrologic and compositional study of a suite of HED polymict breccias. Here we report on the preliminary findings of this project.

Mittlefehldt, David W.↗
NASA NTRS1981

A preliminary report on the achondrite meteorites in the 1979 U.S. Antarctic meteorite collection

Seventy-three meteorite samples were collected in Antarctica during the austral summer of 1979-80. A description is presented of the seven achondrites found among the meteorite samples. The achondrites described include an ALHA79017-polymict eucrite, an EETA79001-shergottite, an EETA79002-diogenite, an EETA79004-eucrite, an EETA79005-polymict eucrite, an EETA79006-howardite, and an EETA79011-polymict eucrite. The most exciting single aspect of the 1979 collection is undoubtedly the discovery of a new member of the shergottite group of meteorites. Sample EETA79001 is just under 8 kg and should thus provide ample material for detailed studies. In addition to the achondrites, a unique iron meteorite with abundant silicate (orthopyroxene) inclusions and a large diogenite is also discussed.

Reid, A. M.↗
NASA NTRS2011

Howardite Noble Gases as Indicators of Asteroid Surface Processing

The HED (Howardite, Eucrite and Diogenite) group meteorites likely or iginate from the Asteroid 4 Vesta - one of two asteroid targets of NA SA's Dawn mission. Whilst Howardites are polymict breccias of eucriti c and diogenitic material that often contain "regolithic" petrologica l features, neither their exact regolithic nature nor their formation processes are well defined. As the Solar Wind (SW) noble gas compon ent is implanted onto surfaces of solar system bodies, noble gas anal yses of Howardites provides a key indicator of regolithic origin. In addition to SW, previous work by suggested that restricted Ni (300-12 00 micro g/g) and Al2O3 (8-9 wt%) contents may indicate an ancient we ll-mixed regolith. Our research combines petrological, compositional and noble gas analyses to help improve understanding of asteroid reg olith formation processes, which will play an intergral part in the i nterpretation of Dawn mission data. Following compositional and petrological analyses, we developed a regolith grading scheme for our sampl e set of 30 Howardites and polymict Eucrites. In order to test the r egolith indicators suggested by, our 8 selected samples exhibited a r ange of Ni, Al2O3 contents and regolithic grades. Noble gas analyses were performed using furnace stepheating on our MAP 215-50 noble gas mass spectrometer. Of our 8 howardites, only 3 showed evidence of SW noble gases (e.g approaching Ne-20/Ne-22 approximately equals 13.75, Ne-21/Ne-22 approximately equals 0.033). As these samples display low regolithic grades and a range of Ni and Al2O3 contents, so far we are unable to find any correlation between these indicators and "regolit hic" origin. These results have a number of implications for both Ho wardite and Vesta formation, and may suggest complex surface stratigr aphies and surface-gardening processes.

Cartwright, J. A.↗
NASA NTRS2010

The Search for Truly "Regolithic" Howardites

The howardite meteorites are polymict breccias of eucrite (basaltic) and diogenite (orthopyroxenitic) material [1] that likely originate from the asteroid 4 Vesta [2]. The true regolithic nature of the suite is not well defined, with previous research suggesting correlations between Ni and solar wind noble gas contents, and minimal variation in Al2O3 content [3]. Through combined petrological, compositional and noble gas analyses, we aim to better understand howardite petrological diversity, regolith formation processes on the parent asteroid, and to establish what defines a truly "regolithic" howardite. Our petrological study of 30 polymict eucrites and howardites has identified regolithic features (e.g. melt clasts, chondrite fragments), used to develop a regolith grading scheme. Bulk major element com-positional data have been collected [4], and both trace-element and noble gas analyses are underway. We expect those howardites with regolithic petrological and chemical features to have high abundances of implanted solar wind noble gases.

Cartwright, J. A.↗
NASA NTRS2011

Noble Gas Analysis in the Quest to Find "Regolithic" Howardites

The howardite meteorites consist of approximately 200 polymict breccias of eucrite (basaltic) and diogenite (orthopyroxenitic) material (collectively, the HED group) that originate from the asteroid belt. Infrared reflectance spectroscopy of asteroids and laboratory studies of HEDs have indicated that the asteroid 4-Vesta is the likely parent body, and the partially-demolished south pole may be the source region. Asteroid regolith formation processes may be responsible for a number of observed petrological features including impact melt clasts, reworked clasts and mosaisicm. We have identified such features in a study of 30 howardites and polymict eucrites, and developed a regolith grading scheme based on petrology. However, the true regolithic nature of the howardite suite is not well defined, and previous research has suggested correlations between Ni contents of 300 - 1200 micron / g, a minimal variation in Al2O3 content around 8-9 wt% and the presence of solar wind noble gases are key hallmarks of an ancient regolith on Vesta . Through combined petrological, compositional and noble gas research, we aim to better understand howardite petrological diversity, regolith formation processes on parent asteroids, and to establish what defines a truly "regolithic" howardite. Our research will play an integral part in the interpretation of data gathered by the Dawn mission. Here we report the preliminary results from our noble gas analyses of four howardites: LEW 85313, EET 99408, MET 96500 and PCA 02066. Bulk major element compositional data have been collected, further petrological data for the HED group are reported by our colleagues, whilst trace-element analyses are underway. Our work will investigate the extent of whether previously described Ni, Al2O3 and noble gas characteristics are in fact indicative of a "regolithic" howardite.

Cartwright, Julia A.↗
NASA NTRS2015

Impact History on Vesta: Petrographic, Compositional and Future Chronological Studies of Melt Clasts in Howardites

Howardite meteorites are polymict breccias composed mainly of eucritic and diogenitic material that likely originate from the surface of the Asteroid 4 Vesta. They can be separated into two subtypes: Regolithic, which represent the lithified remains of the active vestan regolith; Fragmental, which represent simpler polymict breccias. Amongst the regolithic features observed in the former, melt clasts are particularly striking for their appearance and compositional variability. They range from glassy spherules to finely crystalline (i.e., devitrified) clasts, and clasts containing only relict mineral grains to those containing only phenocrysts. Glasses can be separated into compositional sub-types including those with low FeO/MgO ratios (less than 5) -low alkali glasses, K-rich (K2O greater than 0.2 wt.%), Na-rich (Na2O greater than 0.6 wt.%) and CaO-rich, and those with high FeO/MgO ratios (greater than 10). There is also a distinction to be made between primary volcanic melt clasts and those produced by impacts. While suggested that a lack of chemical homogeneity among their studied melt clasts ruled out a primary volcanic origin, the low siderophile element contents observed in such clasts suggest less compositional influence from impactors than commonly assumed. Studying the chronology of the impact melt clasts in howardites can help us to better determine the timing of impact events on Vesta and the asteroid belt. In this research, we are launching an investigation into the petrology, composition (major/trace element and noble gas) and chronology of melt clasts in howardites. We have selected a set of howardites known to contain large quantities of melt clasts, and have begun the petrological and compositional studies of these materials. Once the melt clasts have been fully classified, we aim to perform chronological studies of individual clasts using both the Ar-40/Ar-39 and Pb-Pb chronometers, as well as determine the noble gas components present. Of particular note, the study will take advantage of the laser ablation techniques associated with the noble gas facilities at ASU, which will allow high-resolution, in-situ analysis of individual clasts. The broader aim of this work is to ascertain whether the impact flux in the region of the asteroid belt was similar to that on the Moon. Our understanding of impact events in the inner Solar System relies heavily on our analyses of lunar meteorites and returned samples, and there is currently some debate regarding whether there was a "Lunar Cataclysm" event around approx. 3.9 Ga, or the end of an epoch of "Late Heavy Bombardment" (LHB) at this time. New and more comprehensive constraints on howardite melt clast ages may help determine whether the asteroid belt experienced such a cataclysm or LHB.

Cartwright, J. A.↗
NASA NTRS2014

Experimental Constraints on a Vesta Magma Ocean

A magma ocean model was devised to relate eucrites (basalts) and diogenites (orthopyroxenites), which are found mixed together as clasts in a suite of polymict breccias known as howardites. The intimate association of eucritic and diogenitic clasts in howardites argues strongly that these three classes of achondritic meteorites all originated from the same planetoid. Reflectance spectral evidence (including that from the DAWN mission) has long suggested that Vesta is indeed the Eucrite Parent Body. Specifically, the magma ocean model was generated as follows: (i) the bulk Vesta composition was taken to be 0.3 CV chondrite + 0.7 L chondrite but using only 10% of the Na2O from this mixture; (ii) this composition is allowed to crystallize at 500 bar until approx. 80% of the system is solid olivine + low-Ca pyroxene; (iii) the remaining 20% liquid crystallizes at one bar from 1250C to 1110C, a temperature slightly above the eucrite solidus. All crystallization calculations were performed using MELTS. In this model, diogenites are produced by cocrystallization of olivine and pyroxene in the >1250C temperature regime, with Main Group eucrite liquids being generated in the 1300-1250C temperature interval. Low-Ca pyroxene reappears at 1210C in the one-bar calculations and fractionates the residual liquid to produce evolved eucrite compositions (Stannern Trend). We have attempted to experimentally reproduce the <1250C portion of the MELTS Vesta magma ocean. In the MELTS calculation, the change from 500 bar to one bar results in a shift of the olivine:low-Ca pyroxene boundary so that the 1250C liquid is now in the olivine field and, consequently, olivine should be the first-crystallizing phase, followed by low-Ca pyroxene at 1210C, and plagioclase at 1170C. Because at one bar the olivine:low-Ca pyroxene boundary is a peritectic, fractional crystallization of the 1210C liquid proceeds with only pyroxene crystallization until plagioclase appears. Thus, the predictions of the MELTS calculation are clear and straightforward.

Hoff, C.↗
NASA NTRS1988

Petrology and pairing of mesosiderites from Victoria Land, Antarctica

Petrological data on mesosiderites from Reckling Peak (RKP) and Allan Hills (ALH), Antarctica, are presented. The results suggest that the Allan Hills mesosiderites A77219, A81059, and A81098 are probably paired (being of similar texture, modes, and mineral composition), and ALHA 81208 is, most likely, a clast from one of these mesosiderites. RKPA 80258 is a weakly poikilitic plagioclase-poor mesosiderite, completely different from ALHA 77219, 81059, and 81098. On the other hand, RKPA 79015, 80229, 80246, and 80263 are very similar, belonging to subgroup C diogenitic mesosiderites. These mesosiderites contain orthopyroxene and recrystallized orthopyroxenite clasts in a metal-troilite matrix. The silicate fraction of mesosiderites ranged from diogenitic (RKPA 79015) to analogous to polymict eurcrite (Dyarrl Island). On the basis of petrologic data, the mesosiderite subdivision scheme was amended, making it possible to classify the formerly 'anomalous' RKPA 79015.

Hewins, Roger H.↗
NASA NTRS2011

A Howardite-Eucrite-Diogenite (HED) Meteorite Compendium: Summarizing Samples of ASteroid 4 Vesta in Preparation for the Dawn Mission

The Howardite-Eucrite-Diogenite (HED) suite of achondritic meteorites, thought to originate from asteroid 4 Vesta, has recently been summarized into a meteorite compendium. This compendium will serve as a guide for researchers interested in further analysis of HEDs, and we expect that interest in these samples will greatly increase with the planned arrival of the Dawn Mission at Vesta in August 2011. The focus of this abstract/poster is to (1) introduce and describe HED samples from both historical falls and Antarctic finds, and (2) provide information on unique HED samples available for study from the Antarctic Meteorite Collection at JSC, including the vesicular eucrite PCA91007, the olivine diogenite EETA79002, and the paired ALH polymict eucrites.

Garber, J. M.↗
NASA NTRS2012

The Continuing Quest for "Regolithic" Howardites

The howardite, eucrite and diogenite (HED) meteorites likely originate from asteroid 4-Vesta, the first of two asteroids targeted by NASA's Dawn mission]. Howardites are polymict breccias dominantly composed of basaltic (eucrite) and orthopyroxenitic (diogenite) material. They are believed to originate from the surface of Vesta, and may represent the regolithic surface layer. Many howardites contain "regolith"-like features including fragmental breccias clasts, carbonaceous chondrite fragments and melt clasts (impact and volcanic). Though such features may relate to asteroid regolith formation processes, the exact regolithic nature of the howardite suite is not well defined.

Cartwright, J. A.↗
NASA NTRS1971

A re-examination of relationships among pyroxene-plagioclase achondrites.

In light of the new data of Jerome (1970), a brief discussion of genetic relationships between eucrites, howardites and diogenites is presented. Howardites are not direct products of magmatic crystallization, as has sometimes been postulated, but instead are interpreted as polymict breccias resulting from the mechanical mixture of eucrites and diogenites. Testing of this model by means of chemical arguments is made complicated however by the probable presence of a chondritic component in howardites and by a sequence analogous to terrestrial differentiation series, among the eucrites themselves.

Jerome, D. Y.↗