The history of the Tissint meteorite, from its crystallization on Mars to its exposure in space: New geochemical, isotopic, and cosmogenic nuclide data

摘要

The Tissint meteorite fell on July 18, 2011 in Morocco and was quickly recovered, allowing the investigation of a new unaltered sample from Mars. We report new high-field strength and highly siderophile element (HSE) data, Sr-Nd-Hf-W-Os isotope analyses, and data for cosmogenic nuclides in order to examine the history of the Tissint meteorite, from its source composition and crystallization to its irradiation history. We present high-field strength element compositions that are typical for depleted Martian basalts (0.174 ppm Nb, 17.4 ppm Zr, 0.7352 ppm Hf, and 0.0444 ppm W), and, together with an extended literature data set for shergottites, help to reevaluate Mars' tectonic evolution in comparison to that of the early Earth. HSE contents (0.07 ppb Re, 0.92 ppb Os, 2.55 ppb Ir, and 7.87 ppb Pt) vary significantly in comparison to literature data, reflecting significant sample inhomogeneity. Isotope data for Os and W (Os-187/Os-188 = 0.1289 +/- 15 and an epsilon W-182 = +1.41 +/- 0.46) are both indistinguishable from literature data. An internal Lu-Hf isochron for Tissint defines a crystallization age of 665 +/- 74 Ma. Considering only Sm-Nd and Lu-Hf chronometry, we obtain, using our and literature values, a best estimate for the age of Tissint of 582 +/- 18 Ma (MSWD = 3.2). Cosmogenic radionuclides analyzed in the Tissint meteorite are typical for a recent fall. Tissint's pre-atmospheric radius was estimated to be 22 +/- 2 cm, resulting in an estimated total mass of 130 +/- 40 kg. Our cosmic-ray exposure age of 0.9 +/- 0.2 Ma is consistent with earlier estimations and exposure ages for other shergottites in general.