57 Fe Mössbauer spectroscopy studies of chondritic meteorites from the Atacama Desert, Chile: Implications for weathering processes

Abstract

Some terrestrial areas have climatic and geomorphologic features that favor the preservation, and therefore, accumulation of meteorites. The Atacama Desert in Chile is among the most important of such areas, known as dense collection areas. This desert is the driest on Earth, one of the most arid, uninhabitable locals with semi-arid, arid and hyper-arid conditions. The meteorites studied here were collected from within the dense collection area of San Juan at the Central Depression and Coastal Range of Atacama Desert.57 Fe Mössbauer spectroscopy was used for quantitative analysis of the degree of weathering of the meteorites, through the determination of the proportions of the various Fe-bearing phases and in particular the amount of oxidized iron in the terrestrial alteration products. The abundance of ferric ions in weathered chondrites can be related to specific precursor compositions and to the level of terrestrial weathering. The aim of the study was the identification, quantification and differentiation of the weathering products in the ordinary chondrites found in the San Juan area of Atacama Desert.

Artificial weathering of an ordinary chondrite: Recommendations for the curation of Antarctic meteorites

“…Drilled powder of samples MET-1 and MET-2 containing weathering material was analyzed using M€ ossbauer spectroscopy. This technique is extensively used to study the alteration of meteorites as it allows determining the degree of ferric oxidation of primary ironbearing phases resulting for terrestrial weathering (Bland et al, 1998(Bland et al, , 2006Munayco et al, 2013Munayco et al, , 2014. The aim of these analyses was to determine whether the relative amounts of Fe 0 , Fe 2+ , and Fe 3+ in MET-2 were different from the control sample, MET-1.…”

Applications of Mössbauer Spectroscopy in Meteoritical and Planetary Science, Part I: Undifferentiated Meteorites

“…(ii) δ = 0.62 mm/s, H eff = 285 kOe, A = 16% (goethite), δ = 0.33 mm/s, H eff = 498 kOe, A = 8% (maghemite) and δ = 0.27 mm/s, H eff = 478 kOe, A = 9% (maghemite) for Gunnadorah 002 L5; and (iii) δ = 0.311 mm/s, H eff =~501 kOe, A =~7% (hematite), δ = 0.239 mm/s, H eff =~491 kOe, A =~13% (magnetite, (A) sites), δ = 0.671 mm/s, H eff = 460 kOe, A =~4% (magnetite, [B] sites), δ = 0.174 mm/s, H eff =~477 kOe, A =~3% (unknown Fe 3+ compound 1) and δ = 0.288 mm/s, H eff =~421 kOe, A =~4% (unknown Fe 3+ compound 2) for Gandom Beryan 008 H5. However, to determine ferric compounds exactly, the low temperature measurements are required because paramagnetic compounds undergone magnetic phase transitions as well as distinguishing of the different ferric compounds in the magnetic states is better due to different behavior (see, e.g., [64,118,[126][127][128][129]). [118,123,124].…”

“…In this case, for instant, the weathering of different meteorites recovered at the same desert may be considered as occurred within the same conditions. For example, the Mössbauer spectra of two ordinary chondrites San Juan 013 L3 and San Juan 025 H5 with different weathering grade recovered in the San Juan area of the Atacama Desert, Chile, are shown in Figure 48 for comparison (see [127]). These spectra show the presence of (i) one paramagnetic ferric component in San Juan 013 L3 with A = 13% and (ii) one paramagnetic and two magnetic ferric components in San Juan 025 H5 with A =~58%.…”

“…Mössbauer received a Nobel Prize in physics for this discovery. Then, the Mössbauer effect was observed on a number of isotopes, so-called Mössbauer isotopes, such as 57 Fe, 119m Sn, 121 Sb, 125 Te, 127 I, 197 Au, 151 Eu, etc. This phenomenon results from the nuclear resonant transitions between the ground and excited states of the Mössbauer nuclei.…”

57Fe Mössbauer Analysis of Meteorites and Tektites

“…Other Fe-bearing phases, like kamacite, can be present and masked in the maghemite envelope, but most probably Fe-containing minerals within this meteorite are affected by weathering, which is observed to be very strong. This kind of weathering is common in chondrites found in hot deserts [46,47]. The presence of troilite, together with a fusion crust, is evidence that this may indeed be a meteorite.…”