Fouad A. Hasan

Thermoluminescence and the shock and reheating history of meteorites. IV - The induced TL properties of type 4-6 ordinary chondrites

Abstract The induced thermoluminescence (TL) properties of 121 equilibrated ordinary chondrites have been measured. The samples were 74 H and 47 L chondrites, of which 33 H and 32 L were from Antarctica. The distribution of TL sensitivities for non-Antarctic L chondrites differs from that of non-Antarctic H chondrites, consistent with a greater proportion of the former class suffering post-metamorphic shock. Data on the effect of laboratory annealing on TL sensitivity, and step-wise Ar release measurements, enable the meteorites to be sorted into three shock-related temperature groups (

The type three ordinary chondrities: A review

The ordinary chondrites are the largest group of meteorites, and the type 3 ordinary chondrites are those which experienced only very mild parent metamorphism; their study provides a unique means of studying the first solid material to from in the early solar system which is either free from the effects of mild metamorphism, or in which the effects of mild metamorphism can be distinguished from primary, nebular effects. In this paper we list all known type 3 ordinary chondrites and references to their study, their compositional data and data relating to the metamorphic history. We review current theories on their formation and the effects of metamorphism, with emphasis on quantitative considerations. Studies on the thermoluminescence properties of these meteorites, which have provided many new insights into their metamorphic history, are reviewed. Some of the least metamorphosed meteorites show evidence for aqueous alteration, which provides a link between the type 3 ordinary chondrites and objects containing water in various forms the carbonaceous chondrites, comets and planets with ‘wet’ mantles.

Cumberland Falls chondritic inclusions: III. Consortium study of relationship to inclusions in Allan Hills 78113 aubrite

Abstract We describe the mineralogy and report contents of Ag, Au, Bi, Cd, Co, Cs, Ga, In, Rb, Sb, Se, Te, Tl, U and Zn determined by RNAA in three primitive chondritic inclusions from the ALH A78113 aubrite. Comparison of these data with those for large, petrologic type 3 chondritic clasts from the Cumberland Falls aubrite and the discovery of small clasts in it like those in ALH A78113 indicate that all constitute a single chondritic suite. We also report thermoluminescence data for Cumberland Falls chondritic inclusions and achondritic host. These results, together with mineralogie, major, minor and trace element information, demonstrate that aubrite inclusions represent a different sort of type 3 chondrite, not an LL3 chondrite altered during equilibration with aubrite host. Instead, the aubrite inclusions represent a distinct chondrite class. These inclusions reflect nebular condensation/accretion over a broad redox range and at temperatures relatively high compared with those at which other type 3 chondrites formed. Limited metamorphism and reduction occurred during condensation/accretion, prior to incorporation into aubrite host. During the impact of the chondritic parent body with the aubrite parent body, chondrite fragments were strongly shocked and cooled rapidly. They then mixed with aubrite host, possibly in a regolith, so that these aubrites now represent impact breccias.

Anomalous fading of thermoluminescence in meteorites

Abstract Anomalous fading in meteorites of diverse origin and history has been studied. The meteorites included the four known members of the shergottite class, Shergotty, Allan Hills A77005, Zagami and Elephant Moraine A79001, the type 3 ordinary chondrite Dhajala and the howardite Kapoeta. After irradiation and 15 days storage at room temperature, considerable fading of the TL of the Kapoeta meteorite and two of the shergottites (Shergotty and 77005) was observed, while the TL of the other shergottites and Dhajala remained constant. Mineral separation experiments and energy-dispersive X-ray analyses indicate that the phosphor responsible for the TL is located in the low-density feldspar rich fraction in the Dhajala meteorite and the shergottites and this is probably also true of Kapoeta. Despite the diverse history of the samples and major differences in composition, it is only the samples in which feldspar is thought to be present in the low-temperature form which display anomalous fading. It is argued that the present data are most consistent with the mechanism for anomalous fading involving overlap between the wavefunctions for the excited and ground state electrons. Fortunately, most meteorites contain feldspar in the high-temperature form and large scale studies of their natural TL should not be hampered by anomalous fading.

Thermoluminescence and the shock and reheating history of meteorites. III - The shergottites

Abstract The thermoluminescence (TL) sensitivities of the four shergottites are extremely low and display a 10-fold range (values are 0.15 to 1.8, where Dhajala = 1000), with the TL sensitivity decreasing with increasing peak temperature (from about 140 to 180°C) and peak width (from about 100 to 150°C). A mineral separation experiment indicates that the mineral producing the TL is associated with the maskelynite, presumably nanogram per gram quantities of crystalline feldspar are present in the maskelynite. Samples of Shergotty, Allan Hills A77005 and Elephant Moraine A79001 were annealed at 400–900°C for 24–98 h. For Shergotty, the peak increased in width and moved to higher temperatures in the glow-curve, while for Allan Hills A77005 and Elephant Moraine A79001, whose TL peaks were already broad and at high temperatures, remained unchanged. All samples showed a significant increase in TL sensitivity when annealed at >600–700°C. Apparently, the feldspar is present in varying proportions of high to low-temperature form and in amounts which vary from meteorite to meteorite. We conclude that the shergottites underwent post-shock recrystallization at a variety of cooling rates and that the order of increasing cooling rate was Shergotty, Allan Hills A77005, Zagami and Elephant Moraine A79001. The presence of a high-temperature phase implies peak post-shock cooling temperatures >600°C and that the size of the ejecta was

Thermoluminescence and the origin of the dark matrix of Fayetteville and similar meteorites

Abstract The induced thermoluminescence properties and carbon contents of the dark matrix and light clasts of 6 regolith breccias have been measured. The TL sensitivity of the matrix (normalized to that of the clasts) decreases from ~0.8 to ~0.3 with increasing inert gas content, increasing abundances of highly volatile elements and carbon, and decreasing amounts of interstitial, grain-boundary glass. For meteorites with the highest inert-gas contents (Fayetteville and Leighton), the matrix samples have broader TL peaks (by ~ 10°C) and lower peak temperatures (by ~ 10°C) than the light clasts, whereas meteorites with low inert-gas contents (e.g. Pantar) do not show this difference in the TL properties of the two lithologies. It is argued that the data are consistent with the formation of the dark matrix by comminution of the light clasts with the addition of a component, perhaps CM-like chondrites, with TL properties distinct from those of ordinary chondrites. The present data are inconsistent with the matrix being a new “primitive” material akin to type 3 ordinary chondrites, or with the dark matrix being related to the clasts by purely thermal processes.

Comment on “Update on terrestrial ages of Antarctic meteorites” by K. Nishiizumi, D. Elmore and P.W. Kubik

Comment and reply on the paper of K. Nishiizumi, D. Elmore et P.W. Kubik (1989) - Earth Planet. Sci. Lett. 93, 299-313

Structural state and anomalous fading of thermoluminescence of oligoclase

Abstract Anomalous fading of thermoluminescence was measured in four samples of oligoclase from Muskwa Lake, Canada. Two samples were annealed below the order/disorder transformation temperature and two were annealed at higher temperatures; X-ray diffraction measurements confirmed that the first two samples were fully ordered, while the others underwent appreciable, but not complete, disordering. After β-irradiation and a 15-day storage at room temperature, all samples showed anomalous fading in the high temperature regions (>400°C) of the glow curve, but the amount of fading was less for the partially disordered samples than for the fully ordered samples. We suggest that these data are consistent with the suggestion that the structural state of feldspars plays an important part in determining their anomalous fading properties.