Hyperspectral mapping of a kilometer of mantle rock core: insight into active serpentinization systems&#160;
Authors: Mandon Lucia , Ehlmann Bethany L. , Greenberger Rebecca N. , Ellison Eric T. , Mayhew Lisa E. , Templeton Alexis S. ,   Oman Drilling Project Science Team
Published: March 2024

Serpentinization is one of the major processes of silicate alteration in the solar system. Associated reactions are drivers for redox disequilibria and sources of H2, which are favorable to habitability. Minerals formed are responsible for crustal density and magnetization changes, and a significant amount of water can be sequestered. Released gases are expected to affect climate and have been proposed as potentially responsible for warming early Mars [1]. However, depending on protolith and geochemical conditions, a diversity of mineral assemblages exist, and the full spectrum of serpentinization is not well understood. In addition, some products are not well characterized, reducing our ability to assess serpentinization in the solar system.

The Oman Drilling Project [2] is a multi-national collaboration to characterize the Samail ophiolite in Oman, which consists of altered oceanic crust. About 3.2 km of core were recovered and characterized with bulk rock and vein description, thin section photos, rock chemistry and mineralogy, microbial cell abundance, and borehole water properties, performed at regular intervals [2]. In addition, rock cores were analyzed using a hyperspectral imager covering the 0.4&#8211;2.6 &#181;m range at a submillimeter spatial resolution (Fig. 1; [2]), allowing fine-scale characterization of the whole cores (as opposed to specific depth intervals), with tracking of most minerals of interest, hydration and Fe redox &#8211; of particular interest in understanding the fate of Fe in serpentinized systems and production of H2. This spectroscopy technique is also widely used in planetary exploration to assess composition of surfaces (e.g., [3]); collection of spectra of materials present in the cores will aid in the detection and characterization of serpentinization on Earth, Mars, asteroids and ocean worlds.

Our ongoing study builds on previous hyperspectral analysis of the gabbroic section [4, 5], and focuses on the mantle section, some of which may be actively weathering. We will present our approach to automatically map minerals, hydration and serpentine redox on ~1 km of core from three boreholes, allowing us to investigate how these parameters vary with depth (e.g., what is the extent of carbonation and hydration in the oceanic crust/mantle?) and with variables that influence serpentinization processes (e.g., rock chemistry, faults, biology or fluid chemistry). This approach allows us to better understand serpentinization processes and products and their impacts on planetary crusts.
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Figure 1. Spectral mapping of a portion of the Oman mantle core at a depth of 370 m (left: color composite from data in the visible; right: classification based on SWIR data).&#160;

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[1] Ramirez et al. (2014), Nat. Geo. 7(1)

[2] Kelemen et al. (2020), Proceedings of the Oman Drilling Project

[3] Carter et al. (2023), Icarus 389

[4] Greenberger et al. (2021), JGR: Solid Earth 126(8)

[5] Crotteau et al. (2021), JGR: Solid Earth 126(11)