Paleo-Permeability Structure of the Crustal Section of the Samail Ophiolite Based on Automated Detection of Veins in X-Ray CT Core Images From the Oman Drilling Project

To assess the paleo-permeability structure of oceanic crust, we used 3-D X-ray Computed Tomography (XCT) images to quantify the distribution and geometry of mineral veins in core samples from Oman Drilling Project Holes GT1A, GT2A, and GT3A, which correspond to the upper to lower crustal sections of the Samail ophiolite. We developed a new method that automatically detects veins in the XCT core images based on iterative adaption of the two-step Hough transform combined with multiscale Hessian filtering for identifying an elongate structure. Application of the developed method allowed us to identify the geometry and Computed Tomography number of more than 1500 veins with millimeter-scale apertures in core sections with a total length of & SIM;1,200 m. High-CT (HCT) veins in the drilled cores can be related to relatively high-temperature fluid circulation near the mid-ocean ridge, whereas Low-CT (LCT) veins can be related to subsequent low-temperature fluid circulation. Applying fracture fluid-flow models to the geometric information for the detected veins, we found that the HCT and LCT vein systems both yielded bulk permeability of 10(-13)-10(-9) m(2) for each hole. This indicates that millimeter-wide fractures can control crustal-scale permeability, even in the lower oceanic crust. However, these vein systems show different depth dependencies and anisotropies of permeability, possibly reflecting the different spatial variations of high- and low-temperature fluid circulation in oceanic crust.

Automated summary

To assess the paleo-permeability structure of the oceanic crust, 3-D X-ray Computed Tomography (XCT) images were used to quantify the distribution and geometry of mineral veins in core samples from Oman Drilling Project Holes GT1A, GT2A, and GT3A. A new method was developed to automatically detect veins in the XCT core images. The study found that high-temperature and low-temperature vein systems have different depth dependencies and anisotropies of permeability.