P. C. Buchanan

Kilgore College · Geology/Chemistry

Asteroid 4 Vesta is typically thought to be the parent body of the HED (howardite, eucrite, and diogenite) meteorites due to spectral similarities. The discovery of asteroids far from Vesta with HED‐like spectra like (1459) Magnya and HED‐like meteorites (e.g., NWA 011) with anomalous oxygen isotopic values compared to typical HEDs is evidence that...

Bulk pyroxene compositions were calculated for a number of V-type asteroid spectra using formulae derived by Burbine et al. These formulae were derived by analyzing HED (howardite, eucrite, and diogenite) meteorites and calculate bulk Fs (mol%) and Wo (mol%) contents using derived band centers. Using HEDs with known bulk pyroxene compositions, the...

We compare methods for determining the pyroxene mineralogies of V-type near-Earth asteroids from their reflectance spectra. We evaluate whether band centers derived from the spectra of synthetic pyroxenes can be used to achieve greater analytical accuracy than is achieved through the use of band centers derived from the spectra of basaltic achondri...

Evidence from iron meteorites indicates that a large number of differentiated planetesimals formed early in Solar System history. These bodies should have had well-developed olivine-rich mantles and consequentially such materials ought to be abundant both as asteroids and meteorites, which they are not. To investigate this “Great Dunite Shortage” w...

This study examines the reflectance spectra of mixtures of varying proportions of a howardite and glass derived by melting a bulk sample of that howardite.

The mineralogy of NWA 6704 is retrieved from spectral data. Its band parameters are compared to the S-asteroid subtypes in the search for a possible parent asteroid.

New oxygen-isotope data provides additional constraints on the relationship between CO and CM chondrites. Both may be derived from a single asteroidal source.

We focused on surface and cumulate eucrites that were not affected by annealing, in order to estimate whether the deep crust was a relatively more oxidized environment.

Geochemistry of impact melts suggests that some of them formed from targets unlike HEDs.

We have done bulk rock compositional analyses (INAA, ICP-MS) and petrologic study of a suite of diogenite meteorites. Most contain orthopyroxenes with mg#s of 70.6-79.0. Meteorite Hills (MET) 00425 is magnesian (mg# of 83.9). Lewis Cliff (LEW) 88011 contains orthopyroxene grains of varying mg# (76.3-68.6). Queen Alexandra Range (QUE) 93009 (orthopy...

We analyzed plagioclase in four eucrites --- ALHA76005, EETA87520, Petersburg, and Piplia Kalan --- by Fe-XANES. We found that EETA87520 plagioclase had high Fe3+ ratio compared to others, and discussed its origin related to their crystallization on Vesta.

O-type asteroids 3628 Boznemcová and 7472 Kumakiri have absorption bands similar to pyroxenes but with band minima that are not typically found for terrestrial pyroxenes and known pyroxene-dominated meteorite assemblages.

We will discuss how we can possibly determine constraints on the mechanisms for forming Vesta's crust using Dawn reflectance spectra.

Abstract— Spectra of asteroid 4 Vesta and 21 small (estimated diameters less than 10 km) asteroids with Vesta-like spectral properties (Vestoids) were measured at visible and near-infrared wavelengths (∼0.44 to ∼1.65 μm). All of the measured small asteroids (except for 2579 Spartacus) have reflectance spectra consistent with surface compositions si...

Abstract— Piplia Kalan is an equilibrated eucrite consisting of 60–80 vol% lithic clasts in a subordinate brecciated matrix. Ophitic/subophitic clasts fall into two groups: finer-grained lithology A and coarser-grained lithology B. Very fine-grained clasts with equigranular textures (lithology C) also occur and originally were hypocrystalline in te...

Abstract— The Marquez Dome, Leon County, Texas represents a 13 km diameter Paleocene/Eocene impact structure formed in largely unconsolidated sediments in a near-shore environment. The present study is an analysis of samples from cores taken from boreholes drilled separately on the edge of the central uplift and in the surrounding annular basin. Th...

Abstract— We have calculated pyroxene mineralogies of seven near-Earth asteroids (NEAs) with reflectance spectra similar to HEDs (howardites, eucrites, and diogenites). Two different sets of formulas (Gaffey et al. 2002; Burbine et al. 2007) are used to calculate the pyroxene mineralogies of the NEAs from their Band I and II centers. The band cente...

Abstract— The Vredefort Granophyre represents impact melt that was injected downward into fractures in the floor of the Vredefort impact structure, South Africa. This unit contains inclusions of country rock that were derived from different locations within the impact structure and are predominantly composed of quartzite, feldspathic quartzite, ark...

As part of an investigation into the olivine-rich material in mesosiderites we have looked in detail at a clast from Vaca Muerta which may represent preserved mantle material.

In this study, near-infrared spectra of two of middle- and outer-belt Vestoids, 1459 Magnya and 21238 1995 WV7, are analyzed. Our goal is to determine whether the average pyroxene mineralogies of these objects are consistent with HEDs.

Oxygen isotopic data argues that HEDs and mesosiderites may be from the same parent body. A spectral survey of mesosiderites was done to determine their spectral properties in the visible and near-infrared and compare to HEDs.

We use high-resolution HED spectra and detailed compositional analyses to derive formulas for determining their average pyroxene mineralogies.

Immediately following the formation of the Solar System, small planetary bodies accreted, some of which melted to produce igneous rocks. Over a longer timescale (15-33 Myr), the inner planets grew by incorporation of these smaller objects through collisions. Processes operating on such asteroids strongly influenced the final composition of these pl...

The Rooiberg Group is a 6-km-thick sequence of mostly volcanic rocks, which represent the first phase of magmatic activity associated with the Bushveld Complex. These strata include, in ascending stratigraphic order, the Dullstroom, Damwal, Kwaggasnek, and Schrikkloof Formations. Units of the lower Dullstroom Formation range from basalts to andesit...

Abstract— On July 21, 2002, a meteorite fall occurred over the Thuathe plateau of western Lesotho. The well-defined strewn field covers an area of 1.9 times 7.4 km. Many of the recovered specimens display a brecciated texture with leucocratic, angular to subrounded clasts in a somewhat darker groundmass. Mineralogical and chemical data, as well as...

Fragments of diogenitic orthopyroxene in the Petersburg polymict eucrite have edges that are altered to more Fe-rich compositions. These alteration rims are consistent with heating of the breccia for 1000 10000 years by contact metamorphism.

The unequilibrated eucrite Yamato 82202 (Y82202) contains a network of glass veins, which are relatively thick (up to 1 mm in width) and are not devitrified. The host of the meteorite represents volcanic rock that crystallized >4.3 Gyr ago, probably as a lava flow on the surface of 4 Vesta. The impact event that formed the glass veins occurred at a...

This article provides a first report of the fall of a meteorite over the Thuathe plateau of western Lesotho, approximately 9 km east of the capital Maseru, on 21 July 2002. The strewn field has been mapped, and the characteristics of stones recovered from various sectors in the strewn field are compared. Initial mineralogical investigations have es...

Buchanan et al. and Zolensky et al. described carbonaceous chondrite fragments in a variety of howardites and concluded that the majority are CM2 and CR2 materials. Gounelle et al. also described similar, but very small, fragments in these meteorites. These clasts are important because they represent materials that were in orbital proximity to the...

The volcanic Rooiberg Group represents the earliest phase of Bushveld-related magmatism and comprises, in some areas, the floor and roof rocks of the mafic-ultramafic intrusive units of the Bushveld Complex. The lower to middle Dullstroom Formation is composed of two interbedded series of low Ti and high Ti volcanic strata, which are predominantly...

The Vredefort Granophyre represents impact melt that was injected downward into fractures in the floor of the Vredefort impact structure, South Africa. This unit contains inclusions of country rock that were derived from different locations within the impact structure and are predominantly composed of quartzite, feldspathic quartzite, arkose, and g...

The South African L6 chondrite Jackalsfontein contains enigmatic melt veins. The textures of these veins suggest formation associated with local cataclastic processes.

Spectra of asteroid 4 Vesta and 21 small (estimated diameters less than 10 km) asteroids with Vesta-like spectral properties (Vestoids) were measured at visible and near-infrared wavelengths (similar to0.44 to similar to1.65 mum). All of the measured small asteroids (except for 2579 Spartacus) have reflectance spectra consistent with surface compos...

Some lithic clasts in the Vredefort Granophyre contain quartz grains with multiple sets of PDFs. Some of these clasts contain melt pockets composed of microlites in a glassy groundmass. Analysis of these features confirms extreme amounts of mixing.

Flow differentiation of rock and mineral fragments in a relatively wide melt vein in the Antarctic L6 ordinary chondrite PCA82528 suggests that melt moved significant distances from the source area.

Near-infrared spectra were obtained for 196 asteroids as part of SMASSIR. SMASSIR focused on observing asteroids assumed to be one of the following: (1) olivine-rich, (2) objects with "Vesta-like spectra" (the "Vestoids"), and (3) postulated meteorite parent bodies.

New clasts were analyzed from the paired howardites EET87503 and EET87513. These clasts show a wide variety of textures and compositions.

Additional petrogenetic modeling of the Dullstroom Formation volcanic rocks suggests that low-Ti and high-Ti suites are the result of long-term compositional variations in the subcontinental lithosphere of southern Africa.

We report our meteorite search, discovery, and classification of the Lea County 003 (H4) from the deflation basin in Lea County, New Mexico, USA. We also compare this meteorite with Lea County 001 and 002 that were found in the same area.

The polymict eucrite Macibini is a fragmental breccia, predominantly composed of eucritic materials with minor proportions (maximum 2 vol%) of diogenitic material. Hence, it is intermediate between the Yamato‐74159‐type polymict eucrites, which contain negligible amounts of magnesian orthopyroxene, and the howardites. The present study provides min...

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...

The Precambrian Dullstroom Formation of South Africa, which is predominantly composed of basaltic andesites interbedded with subordinate sedimentary and felsic volcanic strata, represents the first phase of an extended period of magmatism that was responsible for the Bushveld Magmatic Province, including the extrusive Rooiberg Group and the intrusi...

The Dullstroom Formation was the first phase of a magmatic episode culminating in the formation of the Bushveld Complex. This study models available geochemical data to determine whether impact or endogenic terrestrial processes were responsible.

Nonporous silicate rims around type B and some type A/B dark inclusions may be formed by diffusion of aqueous fluids out of these xenoliths into hot, dry Allende matrix.

The ten HED polymict breccias EET82600, EET87503, EET87509, EET87510, EET87512, EET87513, EET87518, EET87528, EET87531, and EET92022 were found over a broad area in the Elephant Moraine collecting region of Antarctica. Locations are scattered among the Main (Elephant Moraine), Meteorite City, and Texas Bowl icefields and the Northern Ice Patch. It...

It has been suggested that the Bushveld Complex of South Africa could be the result of multiple large meteorite or comet impacts. According to this hypothesis, part of the lower Rooiberg Group, which forms the roof of the Complex, represents a sheet of impact melt breccia and other impact breccias. The present study is an attempt to test the viabil...

Lake Tana, the largest lake in Ethiopia, is a circular basin 70 km in diameter, set in Quaternary volcanic rocks. At least two types of volcanic rocks cover the area south of Lake Tana, including the Bahir Dar, Tiss Abay, and Gimjabet-Kosober regions. The rocks east of Lake Tana are subalkaline rhyodacites displaying evidence of chemical differenti...

Bulk compositions acquired by neutron activation analysis are reported for eight Allende dark inclusions (DIs) and compared with compositions of five DIs previously reported in the literature. Enrichments of the elements Na, K, Br, Ba, Au, and As are generally correlated with increased proportions of porous aggregates predominantly composed of fine...

The texture and mineralogy of the Pipliya meteorite are reported. The meteorite is a brecciated eucrite and is distinctive because of its high proportion of lithic clasts compared to the amount of brecciate matrix and because lithology A (fine-grained and containing pyroxenes similar in composition to those in 'main group' eucrites) and lithology B...

Based partly on its lobate shape, previous workers have suggested that the Bushveld Complex of South Africa and associated rocks are the result of multiple meteorite impacts. According to this interpretation, parts of the lower Rooiberg Group, rocks forming the roof of the Complex, represent a sheet of impact melt breccia. However, extensive field...

Petrographic and geochemical characteristics are studied for 29 samples from the Libyan BP impact structure and the Oasis impact structure, with a view to their association with the occurrence of Libyan Desert Glass (LDG). The enigmatic natural material, LDG, was most likely formed from rocks whose compositions were close to those found at the two...

The majority of the carbonaceous chondrite clasts found in howardites, eucrites and diogenites are CM2 material, a lesser proportion is CR2 material, and other rare types are present. A single clast that was found on the Moon and called the Bench Crater meteorite is apparently shocked CM1 material. The CM2 clasts are matrix supported mixtures of ol...

We provide compositional and mineralogical characterization of a type C dark inclusion in Vigarano, and one matrix lump in Sharps. These inclusions are apparently unrelated to each other as well as the type A to B dark inclusions described from CV3 chondrites.

Deformation lamellae are found in quartz grains throughout the Rooiberg Group, Transvaal Sequence of the Bushveld Complex, a proposed impact structure. Occurrence of these lamellae in the Rooiberg felsites indicates formation after crystallization of this unit and precludes generation at the same time as a hypothesized impact melt represented by th...

Since carbonaceous chondrite planetesimals are attractive candidates for the progenitors of HED asteroid(s), we have performed a survey of HED meteorites in order to locate and characterize the mineralogy, chemistry, and petrography of the oft-reported carbonaceous chondrite clasts by microprobe, SEM-EDX. and TEM techniques. We examined samples of...

The polymict eucrite Petersburg contains eucritic and diogenitic materials which span a broad range of compositions. The present study focuses on four eucritic clasts for which bulk compositions and mineralogical data were acquired; the broad compositional range of these clasts documents the diversity of the parent regolith. Clast A is REE-rich (~2...

Fruland et al. described dark inclusions found in the meteorite Allende as "black to light gray lithic inclusions (xenoliths) that have been found to be different from the bulk meteorite, both petrographically and chemically." Similar dark inclusions have been described from other CV3 meteorites (e.g., Leoville and Vigarano). Most authors have conc...

Enchanted Rock batholith in central Texas is a granitic pluton of ~250 km^2 area [1]. The batholith intrudes Precambrian metamorphic rocks and is dated by Rb-Sr at 1,048+/-34 m.y. [2]. Plutonic rocks are exposed in a series of exfoliation domes located along the southeastern edge of the batholith. Numerous subvertical fractures occur along the oute...

The polymict eucrite Petersburg is a regolith breccia containing significant proportions of matrix pyroxenes with compositions intermediate between those found in diogenites and noncumulate eucrites. Possible sources of these intermediate-composition pyroxenes are given. Abundant eucritic clasts in Petersburg allow examination of material from whic...

Twenty-two carbonaceous chondrite clasts from the two howardites Bholghati and EET87513 were analyzed. Clast N from EET87513 is a fragment classified as CM2 material on the basis of texture, bulk composition, mineralogy, and bulk O isotopic composition. Carbonaceous chondrite clasts from Bholghati, for which less data are available because of their...

Xenoliths of material resembling carbonaceous chondrites have been found in several HED polymict breccias. Most workers concluded that these clasts are related to CM2 meteorites on the basis of texture, bulk composition, and mineralogy. Data on clast N, a carbonaceous chondrite fragment from the howardite EET87513 large enough (approximately 4x5mm...

Pseudotachylite is known to occur in a variety of geologic settings including thrust belts (e.g., the Alps and the Himalayas) and impact craters such as Roter Kamm, Namibia. Controversy exists, however, as to whether pseudotachylite can be produced by shock brecciation as well as by tectonic frictional melting. Also open to debate is the question o...

Roter Kamm is a relatively young 2.5-km-diameter impact crater located in the southern Namib desert. The rocks of the crater rim are fractured and cut by numerous fine-grained, clast-rich veins and dykes that closely resemble pseudotachylytes in the field. Most veins closely match their host rocks in bulk composition and have formed by localized ca...

Thesis (M.S.)--University of Houston, 1991. Degree granted by Dept. of Geosciences. Includes bibliographical references (leaves 66-67).

A 10 g sample of the Bholghati howardite was disaggregated in order to separate two eucrite clasts, several small carbonaceous clasts, fragments of diogenitic pyroxene, and bulk matrix. The eucrite clasts show evidence of moderately rapid cooling from a melt, followed by prolonged subsolidus annealing. The carbonaceous clasts mostly resemble CM2 ca...

The present study compares texture, mineralogy, and composition of eucrite clast A/B from the meteorite