¹Walter Goetz et al. (>10)
Journal of Geophysical Research (Planets) (in Press) Link to Article [https://doi.org/10.1029/2021JE007101]
¹Max-Planck-Institut für Sonnensystemforschung (MPS), D-37077 Göttingen, Germany
Published by arrangement with John Wiley & Sons

Laser-Induced Breakdown Spectroscopy, as utilized by the ChemCam instrument onboard the Curiosity rover, detected enhanced abundances of the element copper. Since landing in Gale crater (August 6, 2012) 10 enhancements in copper abundance were observed during 3007 Martian days (sols) of rover operations and 24 km of driving (as of January 20, 2021). The most prominent ones were found in the Kimberley area on the crater floor (Aeolis Palus) and in Glen Torridon on the lower flanks of Aeolis Mons (Mt. Sharp). Enhancements in copper record the former existence of modestly acidic and oxidizing fluids, which were more oxidizing in Kimberley than in Glen Torridon. Of the two main types of bedrock in the lowest part of Glen Torridon, Mg-rich ‘coherent’ and K-rich ‘rubbly’ (named based on their outcrop expression), copper was only detected in coherent, not in rubbly bedrock. The difference between these two types of bedrock may be due to difference in provenance. Alternatively, based on a recently developed lacustrine-groundwater mixing model, we suggest that rubbly bedrock was altered by modestly acidic, shallow-subsurface lake water that leached out both copper and manganese, while coherent bedrock was affected by dominantly alkaline fluids which would be consistent with its mineralogical composition (including siderite) as returned by the CheMin instrument onboard the rover. Higher up in Glen Torridon, ChemCam data indicated significant gradients in copper concentration in coherent bedrock on a local scale of only few meters, which suggests a different alteration style and possibly different types of diagenetic fluids.

¹Yuki Masuda,¹Tetsuya Yokoyama
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2023.01.024]
¹Department of Earth and Planetary Sciences, Tokyo Institute of Technology, Meguro, Tokyo 152-8551, Japan
Copyright Elsevier

Calcium-aluminum-rich inclusions (CAIs) in chondrite meteorites are the oldest rocks in the Solar System and were formed by condensation from nebular gas. Recent mass spectrometric measurements have revealed that CAIs possess nucleosynthetic isotopic compositions different from those of terrestrial materials for various elements, indicating a heterogeneous distribution of nuclides from various stellar sources in the early Solar System. CAIs are classified into coarse-grained (CGs) and fine-grained (FGs) inclusions. The former have experienced secondary melting through thermal events after their formation, while the latter evidently avoided the remelting. Thus, FGs are considered to be direct condensates from a high-temperature gas, making them ideal for investigation of the origin and formation process of CAIs. In this study, the elemental abundances and Sr isotopic compositions in eight FGs from a carbonaceous chondrite Allende were analyzed by utilizing a micromilling technique. These FG samples were found to have rare-earth element (REE) patterns reflecting various degrees of elemental fractionation and variable µ84Sr values ranging from 61 to 844 ppm. It cannot be ruled out that matrix contamination during micromilling or secondary alteration on the Allende parent body has affected the elemental abundances and µ84Sr values observed in FGs to some extent; however, the large variation in µ84Sr values could reflect the variability in the FG formation processes. Importantly, REE-fractionated FGs, which were depleted in heavy REEs relative to light REEs, had relatively high µ84Sr values. This suggests that the formation of REE-fractionated FGs was triggered by rapid heating events, such as FU Orionis that occurred periodically in the early Solar System, and that at least two different heating events probably formed FGs with two different µ84Sr values.