Hydrothermal Alteration of the Ocean Crust and Patterns in Mineralization With Depth as Measured by Micro‐Imaging Infrared Spectroscopy

Abstract

Imaging spectroscopy efficiently and effectively mapped spatial patterns in hydrothermal alteration mineral occurrence in ocean crust core  Samail ophiolite upper ocean crust cores are dominated by chlorite, amphibole, and epidote, while deeper cores have more zeolite/prehnite  Hydrothermal alteration largely decreases with depth in the ocean crust but is locally intense in major fault zones, even in lower crust Accepted ArticleThis article has been accepted for publication and undergone full peer review but has not been through the copyediting, typesetting, pagination and proofreading process, which may lead to differences between this version and the Version of Record. Please cite this article as

Characterizing Hydration of the Ocean Crust Using Shortwave Infrared Microimaging Spectroscopy of ICDP Oman Drilling Project Cores

“…Higher abundances of zeolite and zeolite‐prehnite assemblages in Hole GT2A and GT1A may be driving their higher mean hydration values, and the lower frequency of these minerals in Hole GT3A may explain its lower predicted H 2 O values (Figures 7c and 7d). (We note that limitations in the mapping by Greenberger et al., 2021; prohibit identification of zeolites in pixels with the 1.48 μm overtone of OH that is diagnostic of prehnite, resulting in likely underestimation of zeolite proportion.) Thus, although hydration increases with increased alteration, the specific minerals formed as a result of alteration processes are important in affecting the overall amount of water sequestered at different depths of the crust.…”

“…Comparing mean hydration of each 1‐m length of core and the percentage of pixels within that meter that contained the mineral of interest from Greenberger et al. (2021) provides a means of understanding the carrier phases of hydration in the ocean crust. While overall hydration increases with alteration of primary igneous minerals, the specific phases of the alteration mineralogy appear to be one of the most important drivers of changes in degree of bulk hydration with depth (Figure 7).…”

“…This may be due to the overall abundance of chlorite and the role of accessory phases that are in mineral assemblages with chlorite. Prehnite and zeolite are more common spatially in Hole GT1A and Hole GT2A compared to Hole GT3A (Greenberger et al., 2021). Zeolite minerals contain on the order of ∼15 wt% H 2 O.…”

“…There are more very hydrated zones in GT1A compared to GT3A, driving the mean H 2 O of GT1A higher than that of GT3A. The larger amount of high H 2 O zones in GT1A is likely a result of the fact that Hole GT1A contains ∼twice as much high H 2 O content zeolite as Hole GT3A, likely due to the presence of relatively more low temperature fluid circulation (Greenberger et al., 2021), and has extensive mineralized fault zones (Kelemen et al., 2020).…”

“…The LOI measurements used in this study were published in Kelemen et al., (2020), and data are available from ICDP. The underlying imaging spectroscopy data set used is archived through CaltechDATA (Greenberger et al., 2021, http://dx.doi.org/10.22002/D1.2009). H 2 O maps of each core section are also available as PDF images (Crotteau et al., 2021a, http://dx.doi.org/10.22002/D1.2141) and .img files through CaltechDATA (Crotteau et al., 2021b, http://dx.doi.org/10.22002/D1.2142).…”