Multispectral discrimination of spectrally similar hydrothermal minerals in mafic crust: A 5000 km2 ASTER alteration map of the Oman–UAE ophiolite

Rock‐Matrix Porosity and Permeability of the Hydrothermally Altered, Upper Oceanic Crust, Oman Ophiolite

“…Measurements at the drill‐core (∼15 cm 3 ) scale are corrected for post‐alteration effects, and upscaled values for entire pillow stacks at the 10 4 m 3 scale are obtained from the weighted volumetric contributions of their constituent rock types. Our findings quantify the porosity and permeability that led to the huge volumes of pervasive prehnite–pumpellyite to greenschist facies alteration in the Semail upper crust (Belgrano et al., 2022). The values also explain visible patterns of alteration intensity in epidosite zones and they demonstrate the importance of interpillow hyaloclastites as permeable conduits through the volcanic sequence.…”

“…Labeled literature permeability ranges are from various locations but are overlain on the Semail axial setting and summarize: bulk permeability from MOR in situ hydraulic tests (k in situ ), rock-matrix permeability (k matrix ) from MOR, Troodos and Semail ophiolites, permeability modeled using ophiolite fracture maps (k frac ) from Semail and Troodos ophiolites, and permeability invoked for heat and fluid flux models (k model ) from: 1 Johnson (1980b), 2 Jarrard et al (2003), 3 Anderson et al (1985), 4 Becker (1989), 5 Becker and Fisher (2000), 6 Fisher (1998), 7 Becker and Davis (2003), 8 Davis and Becker (2002), 9 Brett-Adams et al ( 2021) 10 van Everdingen (1995), 11 Nehlig (1994), 12 Coelho et al (2015), 13 Hasenclever et al (2014), 14 Price et al (2022) Weakly altered dikes are rare (Miyashita et al, 2003). The Geotimes and Lasail lavas are also pervasively altered to spilite assemblages throughout the ophiolite, characterized by albite + chlorite ± actinolite ± relict augite (Alabaster & Pearce, 1985;Alabaster et al, 1982;Belgrano et al, 2022), with glass preserved only very rarely (Kusano et al, 2017). The above alteration is estimated to have occurred at temperatures of ∼200-440°C at near-hydrostatic fluid pressures of >31-54 MPa (taking into account a seafloor depth of ∼3,100-3,500 m b.s.l.…”

“…Pervasive epidosite alteration makes up just a few percent of the exposed area of the Semail upper crust (Belgrano et al., 2022). Individual bodies reach up to 1 km 2 in outcrop extent, replacing earlier spilite alteration in the SDC and in all overlying lavas, most commonly in the Geotimes and Lasail units (Gilgen et al., 2016).…”

“…Weakly altered dikes are rare (Miyashita et al., 2003). The Geotimes and Lasail lavas are also pervasively altered to spilite assemblages throughout the ophiolite, characterized by albite + chlorite ± actinolite ± relict augite (Alabaster & Pearce, 1985; Alabaster et al., 1982; Belgrano et al., 2022), with glass preserved only very rarely (Kusano et al., 2017). The above alteration is estimated to have occurred at temperatures of ∼200–440°C at near‐hydrostatic fluid pressures of >31–54 MPa (taking into account a seafloor depth of ∼3,100–3,500 m b.s.l.…”

“…The Semail SDC is regionally altered to albite + actinolite + chlorite spilite assemblages (Belgrano et al., 2022; Nehlig et al., 1994), with most dikes showing pervasive alteration in which augite is the only igneous relict. Weakly altered dikes are rare (Miyashita et al., 2003).…”