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

Molly A. Crotteau1,2, Rebecca N. Greenberger1, Bethany L. Ehlmann1, George R. Rossman1, Michelle Harris3, Peter B. Kelemen4, Damon A.H. Teagle5, The Oman Drilling Project Phase 1 Science Party6

1 Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, California 91125, United States

2 Now at Department of Earth Science, University of California Santa Barbara

3 School of Geography, Earth and Environmental Sciences, Plymouth University, Plymouth, PL4 8AA, UK

4 Department of Earth & Environmental Sciences, Columbia University, Lamont–Doherty Earth Observatory, Palisades, NY 10964, USA

5 School of Ocean and Earth Science, National Oceanography Centre Southampton, University of Southampton, European Way, Southampton, SO14 3ZH, UK

6 See Apendix A


ABSTRACT

Although ocean crust covers over 60% of Earth’s surface, the processes that form, cool, and alter the ocean crust are not completely understood. We utilize shortwave infrared micro-imaging spectroscopy of ~1.2km of rock cored by the International Continental Scientific Drilling Program’s Oman Drilling Project to quantify hydration of basalts/gabbros from the Samail ophiolite as a function of depth, mineralogy, and deformation. We develop a regression (R2=0.66) between area of the ~1350-1650nm OH/H2O absorption and measurements of loss on ignition of samples and apply this relationship to generate quantitative ~250 µm/pixel hydration maps for all cores. The lowest mean hydration is observed in the most pervasively altered dike-gabbro boundary (GT3A, H2Omean=2.1 wt%), consistent with the fact that a dominant alteration mineral, amphibole, has low H2O. The highest H2O occurs in deeper foliated and layered gabbros (GT2A, H2Omean=3.2 wt%) and layered gabbros (GT1A, H2Omean=2.8 wt%). The greater prevalence with depth of zeolite alteration phases as opposed to lower wt% H2O amphibole at shallow stratigraphic depths, as well as the occurrence of zones of intensive hydration associated with fault zones (H2Omean=5.7 wt%) lead to greater hydration of the lower ocean crust. While unlikely, some hydration may be related to obduction. This new approach provides an objective quantification of hydration in these cores, enabling an improved understanding of quantities and characteristics of ocean crust hydration. It highlights the importance of specific phases and faulting in controlling hydration, which has implications for ocean crust cooling, rheological properties, and the role of alteration in global biogeochemical cycling.