Evaluating chemical weathering degree of basalts using laser-induced breakdown spectroscopy (LIBS) and its implications for Mars

Like Earth, Mars is also modified by chemical weathering processes. It is significant to understand the geological history and climate change of Mars by identifying weathering products and the chemical weathering degree. Laser-induced breakdown spectroscopy (LIBS), carried by rovers such as Curiosity, Perseverance, and Zhurong, has done an excellent job in the in-situ characterization of rocks and soil on the Martian surface. This technique offers advantages such as fast signal acquisition, remote sensing capabilities, and no need for sample preparation. Herein, we acquired and analyzed LIBS spectra from a series of weathered samples collected from a basaltic chemical weathering profile in Hainan Island, China, serving as a Martian analogue, under Martian conditions. We derived the major elemental concentrations (Si, Ti, Al, Fe, Mg, Ca, Na, K) from LIBS data and discussed the influence of weathering degree on quantitative results. Then the weathering degree was calculated using both conventional approaches (utilizing elemental abundance derived from LIBS data) and our proposed partial least squares (PLS) models (which describe the relationship between weathering degree indexes and LIBS data). The weathering degrees derived from our models were more accurate than the traditional approach because our PLS models identified the potential weathering information in LIBS data. The elemental correlation and the behaviors of elements with depth derived from LIBS data were also calculated and compared with the XRF results. Our results showed that LIBS is a powerful tool for evaluating the chemical weathering degree and identifying chemical weathering sequences on Mars.