Annama H chondrite—Mineralogy, physical properties, cosmic ray exposure, and parent body history

Abstract

The fall of the Annama meteorite occurred early morning (local time) on April 19, 2014 on the Kola Peninsula (Russia). Based on mineralogy and physical properties, Annama is a typical H chondri te. It has a high Ar-Ar age of 4.4 Ga. Its cosmic ray exposure history is atypical as it is not part of the large group of H chondrites with a prominent 7 -8 Ma peak in the exposure age histograms. Instead, its exposure age is within uncertainty of a smal ler peak at 30 ±4 Ma. The results from short-lived radionuclides are compatible with an atmosperic pre-entry radius of 30 -40 cm. However, based on noble gas and cosmogenic radionuclide data, Annama must have been part of a larger body (radius >65 cm) for a large part of its cosmic ray exposure history. The 10 Be concentration indicates a recent (3 -5 Ma) breakup which may be responsible for the Annama parent body size reduction to 30 -35 cm pre-entry radius.

Spinels in Meteorites: Observation Using Mössbauer Spectroscopy

“…This temperature range is in agreement with the range for Curie temperature of 40-80 K for the chromite ferrimagnetic-paramagnetic phase transition in various ordinary chondrites obtained in [20]. [12].…”

“…Additionally, the fusion crust from Chelyabinsk LL5 fragment No 1a and the massive troilite inclusion from the Sikhote-Alin iron meteorite were removed and prepared as a powder for the study. Details of different samples preparation and characterization were described in [9][10][11][12][13][14][15].…”

“…Mössbauer spectra were measured using an automated precision Mössbauer spectrometric system built on the base of the SM-2201 spectrometer with a saw-tooth shape velocity reference signal formed by the digital-analog converter using discretization of 2 12 (quantification of the velocity reference signal using 4096 steps) and a liquid nitrogen cryostat with moving absorber. The high level of the velocity scale discretization provides much better adjustment to resonance, and significantly increases the spectra quality and analytical possibilities of Mössbauer spectroscopy.…”

“…The Mössbauer spectra were measured in transmission geometry with moving absorber in the cryostat and recorded in 4096 channels. To increase the signal-to-noise ratio in the complex spectra with the minor components, they were converted into 1024 channels by consequent summation of four neighboring channels to reach higher statistics and larger signal-to-noise ratio (details for each sample study are given in [9][10][11][12][13][14][15]).…”

“…Two representative Mössbauer spectra of non-weathered LL ordinary chondrites are shown in Figure 4. [12].…”