Edward R. D. Scott

• University of Hawaiʻi at Mānoa

A unique 2 mm‐wide clast of fine‐grained garnet–omphacite peridotite with chondritic chemistry was reported from the CR2 chondrite Northwest Africa 801 by Hiyagon et al. (2016, Geochimica et Cosmochimica Acta , 186, 32–48). Those authors described the clast as eclogitic and inferred from its mineral compositions that the rock formed quickly, during...

Metallographic cooling rates of 10–20 K Myr⁻¹ were obtained for four IAB iron meteorites from electron probe analyses of taenite and models simulating kamacite growth. Cooling rates were also determined for 21 irons in the IAB complex from the size of tetrataenite particles in the cloudy zone and a calibration curve using data for the four IAB iron...

The remarkable complementary isotopic relationship in the Allende chondrite between chondrules (depleted in s‐process molybdenum and tungsten) and matrix (enriched in these nuclides) has been interpreted as evidence that the anomalies were established during chondrule formation, and that chondrules were, therefore, not made by planetesimal collisio...

Cambridge Core - Planetary Science and Astrobiology - Chondrules - edited by Sara S. Russell

Whole rock Δ¹⁷O and nucleosynthetic isotopic variations for chromium, titanium, nickel, and molybdenum in meteorites define two isotopically distinct populations: carbonaceous chondrites (CCs) and some achondrites, pallasites, and irons in one and all other chondrites and differentiated meteorites in the other. Since differentiated bodies accreted...

Ureilite meteorites are abundant, carbon-rich, primitive achondrites made of coarse-grained, equilibrated olivine and pyroxene (usually pigeonite). They probably sample the baked, heterogeneous, melt-depleted mantle of a large, once-chondritic parent body that was broken up catastrophically while still young and hot. Heterogeneity in the parent bod...

Processes governing the evolution of planetesimals are critical to understanding how rocky planets are formed, how water is delivered to them, the origin of planetary atmospheres, how cores and magnetic dynamos develop, and ultimately, which planets have the potential to be habitable. Theoretical advances and new data from asteroid and meteorite ob...

Carbon concentrations in kamacite, taenite, and plessite (kamacite-taenite intergrowths) were measured in 18 iron meteorites and 2 mesosiderites using the Cameca ims 1280 ion microprobe at the University of Hawai‘i with a 5–7 μm beam and a detection limit of <1 ppm. Our goal was to investigate the effects of carbon on the microstructure of iron met...

Ordinary chondrites (OCs) are by far the most abundant meteorites (80% of all falls). Their origin has long been the matter of a heated debate. About thirty years ago (e.g., Pellas 1988), it was proposed that OCs should originate from S-type bodies (the most abundant asteroid spectral types in the inner part of the asteroid belt), but the apparent...

The origin of silicate-bearing irons, especially those in groups IAB, IIICD, and IIE, is poorly understood as silicate should have separated rapidly from molten metal. Here we report the results of high precision oxygen isotope analysis of silicate inclusions in eleven group IIE meteorites and a petrological study of silicate inclusions in ten IIE...

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...

The inner solar system's biggest and most recent known collision was the Moon-forming giant impact between a large protoplanet and proto-Earth. Not only did it create a disk near Earth that formed the Moon, it also ejected several percent of an Earth mass out of the Earth-Moon system. Here, we argue that numerous kilometer-sized ejecta fragments fr...

Differentiated asteroids and igneous meteorites present numerous challenges to our understanding of the impact and dynamical evolution of asteroids and meteorite parent bodies. Igneous meteorites, including irons, achondrites, and stony-iron meteorites, testify to the prior existence of ~100 differentiated bodies. Destruction of these bodies by hyp...

Ordinary chondrites (OCs) are by far the most abundant meteorites (80% of all falls). Their origin has long been the matter of a heated debate. About thirty years ago (e.g., Pellas 1988), it was proposed that OCs should originate from S-type bodies (the most abundant asteroid spectral types in the inner part of the asteroid belt), but the apparent...

Introduction: The pyroxene dominated matrix of the ALH84001 meteorite contains both plagioclase glass and various carbonates [1]. The carbonates can be divided into three types: Mg-Fe-Ca zoned discs, carbonate globules within plagioclase glass and irregular carbonates in crush zones [2]. Here we have sought to understand better the mode of carbonat...

Introduction: The pyroxene dominated matrix of the ALH84001 meteorite contains both plagioclase glass and various carbonates [1]. The carbonates can be divided into three types: Mg-Fe-Ca zoned discs, carbonate globules within plagioclase glass and irregular carbonates in crush zones [2]. Here we have sought to understand better the mode of carbonat...

Analyses and modeling of Ni zoning in taenite in differentiated meteorites provide metallographic cooling rates at ∼500 °C that are inconsistent with conventional formation models. Group IVA iron meteorites have very diverse cooling rates of 100–6600 °C/Myr indicating that they cooled inside a large metallic body with little or no silicate mantle (...

The authors review the composition of chondrites and conclude that compositions of grains and planetesimals in the central layer or midplane of the nebula did not vary simply with heliocentric distance. Instead they believe that there was considerable local chemical heterogeneity in the nebular midplane and that the extent of planetesimal transport...

We have studied cloudy taenite, metallographic cooling rates, and shock effects in 30 H3-6 chondrites to elucidate the thermal and early impact history of the H chondrite parent body. We focused on H chondrites with Ar-Ar ages greater than 4.4 Gyr and unshocked and mildly shocked H chondrites, as strongly shocked chondrites with such old ages are v...

Mysterious hematite spherules, also known as "blueberries", observed at Meridiani Planum on Mars have been widely accepted as concretions which formed by precipitation of aqueous fluids. One of the biggest mysteries is that all observed Martian blueberries are limited in size with maximum diameter of 6.2 mm. In contrast, terrestrial concretions are...

Pyroxene equilibration temperatures and inferred cooling rates, for H5-6 chondrites, provide more evidence for fast cooling to 700°C due to parent body disruption.

A study of the inclusions located some of the IIE iron meteorites has produced a formation mechanism dependent on the cooling rates within a impact melt pool.

Scattered ejecta from the Moon-forming impact hit asteroids and made ancient Ar-Ar reset ages. They suggest the Moon formed 100 ± 30 Ma after CAIs.

Conventional ideas about the origins of differentiated meteorites must be modified to include catastrophic effects of early impacts on differentiated asteroids.

Mesosiderites may have formed beneath HEDs on Vesta following early impact of a molten metallic body and were then cooled slowly through 3.8 Ga.

Olivine from the Eagle Station pallasite contains minute magnetic inclusions capable of recording ambient magnetic fields during parent body cooling.

Accretion of high ∆17O ice to the cold ureilite parent body may have led to the otherwise enigmatic correlation between ∆17O and Fe/Mg in ureilite olivine.

Tishomingo is a chemically and structurally unique iron with 32.5 wt.% Ni that contains 20% residual taenite and 80% martensite plates, which formed on cooling to between −75 and −200 °C, probably the lowest temperature recorded by any meteorite. Our studies using transmission (TEM) and scanning electron microscopy (SEM), X-ray microanalysis (AEM)...

In this chapter, we review current classification of meteorites, which is based on several primary classification parameters the whole-rock chemical compositions, oxygen isotopic compositions, carbon and nitrogen abundances and isotopic compositions, stable-isotope anomalies, mineralogy and petrography. Secondary classification parameters - petrolo...

High precision oxygen isotope measurements of chromites from IIIAB irons indicate a common origin with the silicates from main group pallasites. Cape York has an anomalous isotopic composition that challenges current understanding of IIIABs.

The validity of the kamacite/taenite interface method to obtain relative metallorgaphic cooling rates was reinvestigated. Strong support is found for the 50 fold variation in cooling rate across the IVA chemical group.

Positively correlated Fe# and ∆^17O in ureilites remains puzzling. We suggest it might be a legacy of the hydrothermal oxidation of metal by high ∆^17O ice long before the onset of partial melting in the parent body.

Metallographic cooling rates, cloudy taenite particle sizes, and Ar/Ar ages of H chondrites require early extensive impact scrambling of the parent body; subsequent quiescent cooling reestablished a radial thermal gradient prior to cooling to 300°C .

Taiban is a heavily shocked L6 chondrite showing opaque melt veins. Raman spectroscopy was used to characterize the high-pressure silicate assemblages in a thin section crossed by a shock-created 4 mm wide melt vein. Raman spectra using different excitation wavelengths allowed identification of mineral phases such as olivine, wadsleyite, ringwoodit...

Cooling rate measurements and the link with winonaites suggest that IAB complex irons cooled at depth at different locations in one or more silicate-rich bodies.

Metallographic cooling rates of H3 chondrites and cloudy taenite studies are incompatible with the onion-shell model and require impact mixing during cooling.

Similar-sized collisions lead to a great diversity of planetary composition, and can produce iron-rich cores by mantle stripping.

High-precision oxygen-isotope analysis provides new evidence for the origin and evolution of pallasites, mesosiderites, HEDs and anomalous eucrites.

We investigate the hypothesis that many chondrules are frozen droplets of spray from impact plumes launched when thin-shelled, largely molten planetesimals collided at low speed during accretion. This scenario, here dubbed "splashing," stems from evidence that such planetesimals, intensely heated by 26Al, were abundant in the protoplanetary disk wh...

Magnetic Pallasites The origin of pallasite meteorites seems to defy explanation because their main constituents—iron and olivine—should have segregated into layers inside their parent body. The generally accepted model suggests that they formed at the coremantle boundary of an asteroid. Tarduno et al. (p. 939 ; see the Perspective by Weiss ) measu...

Parent bodies of magmatic iron meteorites, pallasites, mesosiderites, and angrites were not gradually eroded by impacts over Gyr but were fragmented by low velocity grazing impacts during accretion. Vesta was the only survivor from this destructive era.

Metallographic cooling rates and cloudy taenite dimensions for 17 and 23 H3-6 chondrites show that the H parent body did not retain an onion-shell structure as it cooled. Impacts excavated and mixed material and may have heated surficial material.

The C content and C distrubution between phases in 17 irons were measured with the ion microprobe. These data provide information about the effect of C on the formation of the Widmanstatten pattern, cloudy zone, and carbides during cooling.

The relative cooling rates of IVA and IIIAB irons obtained recently by Wasson and Hoppe must be treated with much caution as they were obtained with inadequate spatial resloution and a flowed phase diagram and methodology.

Chondrule formation and chondrite accretion ~2 Myr after CAIs is shown to be an inevitable consequence of ongoing collisions and mergers between planetesimals heated strongly by 26Al and still substantially molten at that time.

To understand the effects of carbon on phase growth in iron meteorites, we measured the C distribution between kamacite, taenite, and plessite regions. Carbon concentrations were systematically lower in meteorites lacking graphite and carbides.

The scanning electron microscope was used to measure the size of the high-Ni island phase in 10 members of groups IAB and IIICD iron meteorites. These size measurements were used to determine the relative cooling rates of these meteorites.

Petrographic and isotopic analysis have shown three distinct relationships exist between the ordinary chondrites and IIE silicates, expanding our concept of the parent body and the thermal history it encountered.

Oxygen isotope analyses for 122 HED samples are used to examine whether Vesta is a viable source for the HEDs. The levels of isotopic heterogeneity within the HED parent body are assessed and the origin of anomalous HED meteorites re-examined.

Two carbides—cohenite Fe_3C and haxonite Fe_2_3C_6 — and graphite are abundant in groups IAB and IIICD, and totally absent in groups IVA and IVB reflecting nebular conditions during the formation of chondritic precursors.

In their model for the origin of the parent bodies of iron meteorites, Bottke et al. proposed differentiated planetesimals, formed in 1-2 AU during the first 1.5 Myr, as the parent bodies, and suggested that these objects and their fragments were scattered into the asteroid belt as a result of interactions with planetary embryos. Although viable, t...

Eucrites, which are probably from 4 Vesta, and angrites are the two largest groups of basaltic meteorites from the asteroid belt. The parent body of the angrites is not known but it was probably comparable in size to Vesta, or perhaps even larger, as it retained basalts and had a core dynamo. Both bodies were melted early by 26 Al and formed basalt...

Abstract– The microstructures of six reheated iron meteorites—two IVA irons, Maria Elena (1935), Fuzzy Creek; one IVB iron, Ternera; and three ungrouped irons, Hammond, Babb’s Mill (Blake’s Iron), and Babb’s Mill (Troost’s Iron)—were characterized using scanning and transmission electron microscopy, electron-probe microanalysis, and electron backsc...

From TEM studies of six reheated irons and diverse shock and thermal constraints, we divide IVA irons into four progressive stages of shock and reheating probably caused by destruction of their metallic parent body within 10-20 Ma of CAI formation.

Meteorites come from numerous parent bodies with a wide variety of geological histories. A few (∼0.5%) come from Mars or the Moon; the rest are impact debris from collisions between asteroids orbiting between Mars and Jupiter. Unlike terrestrial, Martian, and lunar rocks, the asteroidal meteorites contain minerals that formed before the Sun and the...

The extraordinary number of different parent bodies of iron meteorite, and the dearth of asteroids and meteorites derived from the silicate mantles and crusts of these objects is better understood if these bodies accreted at 1-2 AU during the first 2 Myr when 26Al melted all ice-free planetesimals larger than 20-km. It has been suggested that plane...

New oxygen isotopic measurements of IIEs and H chondrites are indistinguishable --- strengthening a possible common origin for these groups. Combining oxygen results with mineralogy, the nature of their parent body or bodies can be explored.

We have determined metallographic cooling rates below 975 K for eight main group (MG) pallasites from Ni profiles across taenite lamellae of known crystallographic orientation in metallic regions with Widmanstätten patterns. Comparison with profiles generated by modeling kamacite growth gave cooling rates ranging from 2.5 to 18 K/Myr. Relative cool...

We have determined metallographic cooling rates of 9 IVB irons by measuring Ni gradients 3 μm or less in length at kamacite–taenite boundaries with the analytical transmission electron microscope and by comparing these Ni gradients with those derived by modeling kamacite growth. Cooling rates at 600–400 °C vary from 475 K/Myr at the low-Ni end of g...

Preliminary analysis of the oxygen isotopic composition of the solar wind recorded by the Genesis spacecraft suggests that the Sun is 16O-rich compared to most chondrules, fine-grained chondrite matrices, and bulk compositions of chondrites, achondrites, and terrestrial planets (Δ17O = –26.5‰ ± 5.6‰ and –33‰ ± 8‰ (2σ) versus Δ17O ~ ±5‰). The inferr...

Cooling rates of H3-6 chondrites inferred from the dimensions of cloudy taenite intergrowths are consistent with published metallographic cooling rates and suggest that H chondrites cooled in a concentrically layered body that was modified by impact.

This research shows why some metallic core of asteroids crystallized inside-out and others outside-in and meteorite evidence is given.

Abstract— Primary minerals in calcium-aluminum-rich inclusions (CAIs), Al-rich and ferromagnesian chondrules in each chondrite group have δ18O values that typically range from −50 to +5%0. Neglecting effects due to minor mass fractionations, the oxygen isotopic data for each chondrite group and for micrometeorites define lines on the three-isotope...

Abstract— We have studied a unique impact-melt rock, the Ramsdorf L chondrite, using optical and scanning microscopy and electron microprobe analysis. Ramsdorf contains not only clast-poor impact melt (Begemann and Wlotzka, 1969) but also a chondritic portion (>60 g) with what appears at low magnification to be a normal, well-defined chondritic tex...

Abstract— The enstatite chondrite reckling peak (rkp) a80259 contains feldspathic glass, kamacite, troilite, and unusual sets of parallel fine-grained enstatite prisms that formed by rapid cooling of shock melts. Metallic Fe,Ni and troilite occur as spherical inclusions in feldspathic glass, reflecting the immiscible Fe-Ni-S and feldspathic melts g...

Abstract— We studied the petrography, mineralogy, bulk chemical, I-Xe, and O-isotopic compositions of three dark inclusions (E39, E53, and E80) in the reduced CV3 chondrite Efremovka. They consist of chondrules, calcium-aluminum-rich inclusions (CAIs), and fine-grained matrix. Primary minerals in chondrules and CAIs are pseudomorphed to various deg...

Abstract— Imaging of asteroids Gaspra and Ida and laboratory studies of asteroidal meteorites show that impacts undoubtedly played an important role in the histories of asteroids and resulted in shock metamorphism and the formation of breccias and melt rocks. However, in recent years, impact has also been called upon by numerous authors as the heat...

Abstract— We have studied carbonate and associated oxides and glasses in a demountable section of Allan Hills 84001 (ALH 84001) using optical, scanning, and transmission electron microscopy (TEM) to elucidate their origins and the shock history of the rock. Massive, fracture-zone, and fracture-filling carbonates in typical locations were characteri...

Abstract— Microstructures in the Allan Hills 84001 meteorite were studied using optical and electron microscopy, putting emphasis on shock effects, which are widespread. Some orthopyroxene exhibits only (100) slip, but more typical grains suffered extensive slip, microfracturing, and frequently contain (100) clino-inversion lamellae. In fracture zo...

We review the crystallization of the iron meteorite chemical groups, the thermal history of the irons as revealed by the metallographic cooling rates, the ages of the iron meteorites and their relationships with other meteorite types, and the formation of the iron meteorite parent bodies. Within most iron meteorite groups, chemical trends are broad...

A few eucrites have anomalous oxygen isotopic compositions. To help understand their origin and identify additional samples, we have analyzed the oxygen isotopic compositions of 18 eucrites and four diogenites. Except for five eucrites, these meteorites have Δ17O values that lie within 2σ of their mean value viz., −0.242 ± 0.016‰, consistent with i...

Mineralogical observations, chemical and oxygen–isotope compositions, absolute 207Pb–206Pb ages and short-lived isotope systematics (7Be–7Li, 10Be–10B, 26Al–26Mg, 36Cl–36S, 41Ca–41K, 53Mn–53Cr, 60Fe–60Ni, 182Hf–182W) of refractory inclusions [Ca,Al-rich inclusions (CAIs) and amoeboid olivine aggregates (AOAs)], chondrules and matrices from primitiv...

An excellent 53 Mn– 53 Cr isochron for bulk CI, CM, CO, CV, CB, and ungrouped C3 chondrites seems to suggest that each carbonaceous chondrite group acquired its Mn/Cr ratio 4568 ± 1 Myr ago. This age is indistinguishable from the age of Ca– Al-rich inclusions (CAIs), which is considered to be the start of the solar system (t 0). However, carbonaceo...

We have measured the size of the high-Ni particles in the cloudy zone and the width of the outer taenite rim in eight low shocked and eight moderately to heavily shocked IVA irons using a transmission electron microscope (TEM). Thin sections for TEM analysis were produced by a focused ion beam instrument. Use of the TEM allowed us to avoid potentia...