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Thermal histories of IVA stony-iron and iron meteorites; evidence for asteroid fragmentation and reaccretion

, : Thermal histories of IVA stony-iron and iron meteorites; evidence for asteroid fragmentation and reaccretion. Geochimica et Cosmochimica Acta 60(16): 0-3113

We have investigated the thermal history of the IVA iron and stony-iron meteorites to help resolve the apparent conflict between their metallographic cooling rates, which are highly diverse, and their chemical trends, which favor crystallization in a single core. Transmission electron microscopy of the disordered clinobronzite in the stony-iron, Steinbach, using electron diffraction and high resolution imaging techniques indicates that this meteorite was rapidly cooled at 100°C/hr through 1200°C. The IVA irons cooled much slower in the range 1200–1000°C: absence of dendrites in large troilite nodules indicate cooling rates of <300°C/y. We infer that the parent asteroid was catastrophically fragmented and reaccreted when the core had cooled to 1200°C and was 95% crystallized. We argue that radiative heat losses from the debris cloud would have been minor due to its high opacity, small size (only a few asteroid diameters), and short reaccretion times ( a few hours). We calculate that global heating effects were also minor (T < 300°C for a body with a diameter of < 400 km) and that the mean temperature of the IVA parent body before and after the impact was 450–700°C. We infer that Steinbach cooled rapidly from 1200°C at the edge of a core fragment by thermal equilibration with cooler silicates during and after reaccretion. Metallographic cooling rates of IVA irons and stony-irons for the temperature range 600–350°C (Rasmussen et al., 1995) strongly support this model and indicate that the IVA meteorites are derived from only a few core fragments. The large range of these cooling rates (20–3000°C/My) and the decrease in the metallographic cooling rates of high-Ni IVA irons with falling temperature probably reflect the diversity of thermal environments in the reaccreted asteroid, the low thermal conductivity of fragmental silicates, and the limited sintering of this fragmental material.


DOI: 10.1016/0016-7037(96)00139-1

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Everson, Leroy, 1949: Preliminary studies to establish laboratory methods for the germination of weed seed. Germinative methods for 23 kinds of weed seeds were studied and recommended procedures for laboratory germination are presented. Wide alternation of temperatures was found to break the dormancy of certain smartweeds satisfactorily. Hardseededness...

Keydel F., 1969: Rationalization of cultivation harvesting and later operations in cereal breeding by means of a newly developed mechanized series. Zeitschrift Fuer Pflanzenzuechtung: 252-261

Kopecky, M., 1961: Otitis externa and a new method for its treatment. Ceskoslovenska Otolaryngologie 10: 27-37

Rasmussen, S.J., 1992: Reflections on Tamazai, a Tuareg idiom of suffering. In this essay, I explore ways in which the theatrical and the medical are inextricably mixed and affect each other, in the Nigerien Tuareg idiom of tamazai. Tamazai is locally-described as "an illness of the heart and soul, not curable by Kor...

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Anonymous, 1968: Structure and origin of sandstone nodules in the Liassic alpha 1 (Hettangian) of Helmstedt. Calcareous fine-grained sandstone nodules, early diagenetic origin, Jurassic stratigraphic sequence, Germany.

Lebedeva, K.S.; Alekseev, K.P., 1968: Study of different starters in Cheddar cheese manufacture. In manufacture of Cheddar cheese by customary procedures, 1% normal starter (mesophilic lactic streptococci) was used alone or with 0.5% thermo-philic Streptococcus or 0.5 or 1.0% Lactobacillus bulgancus starter. The additions shortened ched-darin...

Volkovich, Mg, 1984: A new genus of Acmaeoderini from Southeast Asia and the systematic position of Acmaeodera philipinensis Obenberger (Coleoptera, Buprestidae). Entomological reviewt 63(3): 124-128

Sachse, H.H., 1959: On the question of the specificity of hemagglutination reactions of the Middlebrook-Dubos type. Beitrage Zur Klinik der Tuberkulose und Spezifischen Tuberkulose-Forschung 121: 148-151

Houdée, G.; Lamouliatte, H.; Quinton, A.; Texier, L., 1985: Erythema multiforme premonitory for acute hepatitis B. Gastroenterologie Clinique et Biologique 9(2): 186-186