Presentation Information
[R5P-07]Goethite chronometry - developing an age estimation tool based on the mineral alteration structures in NWA11469 carbonaceous chondrites
*Sena Toyonaga1, Balazs Bradak1, Tatsuki Yamamoto1, Yusuke Seto2, Akos Kereszturi3 (1. Faculuty of Oceanology, Kobe University, 2. Osaka Met. Univ. Sci., 3. Konkoly Astron. Inst., RCAES, Hungary)
Keywords:
Carbonaceous chondrite,Goethite,Terrestrial age,Scanning electron microscopy (SEM)
The fall of most discovered meteorites was not observed, and there are only a few attempts to estimate their time on Earth. It is known that Fe-Ni metals and sulfides in meteorites that have reached Earth’s environment are transformed into secondary minerals such as akaganite and goethite through chemical weathering (reactions with atmospheric oxygen and water). Based on this statement, we theorized that the degree of transformation into oxidized and hydrated iron oxide minerals may reflect the duration of the meteorite’s stay on Earth. Despite its importance, there has been very little research quantifying the extent of transformation and applying it to estimate the duration of stay on Earth. The subject of this study, NWA11469, is a CO3-type carbonaceous chondrite discovered in Algeria in 2016. While this meteorite retains a relatively primitive texture, XRD analysis of its bulk mineral composition indicates approximately 23.9 vol% goethite, a high content even by comparison with other Saharan carbonaceous chondrites. Despite its uniqueness, the meteorite's formation, structure, and alteration have not been investigated in detail. To address this gap, we examined the occurrence of goethite using SEM/EDS and used QGIS to quantify the degree and timing of alteration in the rims surrounding the chondrules and in iron grains partially replaced by goethite. Furthermore, we used Al Haggounia 001, a Western Saharan enstatite chondrite, to develop the goethite chronometric method. With known terrestrial age (approximately 23 ± 2 kyr) and various secondary goethite morphologies, it provided an excellent candidate for defining goethite alteration rate and estimating the terrestrial age of NWA11469, which has been exposed to similar environmental conditions and developed similar goethite alteration features. This study is a preliminary investigation that quantitatively evaluates the range of alteration in oxidized and hydrated iron oxide minerals formed within meteorites and examines their potential application for estimating terrestrial ages using the newly developed “goethite chronometry method”.