Belgrano Thomas M., Diamond Larryn W., Vogt Yves, Biedermann Andrea R., Gilgen Samuel A., Al-Tobi Khalid (2019), A revised map of volcanic units in the Oman ophiolite: insights into the architecture of an oceanic proto-arc volcanic sequence, in Solid Earth
, 10(4), 1181-1217.
Belgrano Thomas M., Diamond Larryn W. (2019), Subduction-zone contributions to axial volcanism in the Oman–U.A.E. ophiolite, in Lithosphere
, 11(3), 399-411.
Lava, dyke and volcanic glass samples from across the northern Semail ophiolite were collected to provide references for geological mapping of the Semail volcanic units. These samples were analysed by various geochemical means to assign them to a volcanic unit. In addition, the bulk rock magnetic properties of a subset of these samples were determined to aid interpretation of existing aeromagnetic data. The whole-rock major element and select trace element (Ba, Sr, Zr, Y, Zn, Cu, Ni, Cr, V, Sc) composition of the majority of these samples was determined by X-Ray fluorescence (XRF) at ETH Zürich using a PANalyticalTM Axios wavelength-dispersive instrument. Trace elements in a subset of these samples were further analysed by pressed-powder-pellet laser-ablation inductively-coupled plasma spectrometry (PPP-LA-ICP-MS) using a GeoLas-Pro 193 nm ArF Excimer™ laser system in combination with an ELAN DRC-e™ quadrupole mass spectrometer at the University of Bern. Where necessary for unit assignment, igneous clinopyroxenes in another subset of samples were measured by Electron microprobe (EMP) on a JeolTM JXA-8200 EMP at the University of Bern. A set of volcanic glasses were also analysed by EMP on the same instrument. Bulk magnetic susceptibility was determined by two methods: a handheld Exploranium KT-5 kappameter and a desktop Magnon kappameter at the Institute for Rock Magnetism (IRM), University of Minnesota. Duplicate analyses of the same samples with both instruments indicates good comparability between the two datasets. Natural remanent magnetization (NRM) was determined on a 2G Enterprises 760 RF TM SQUID superconducting rock magnetometer at the IRM.
This project is a direct continuation of an on-going SNF project with the same title. The planned research addresses water-rock interaction and mass redistribution in sub-seafloor hydrothermal systems within mafic oceanic crust. Among the features of these systems are extensive zones of rock alteration and associated volcanogenic massive sulphide (VMS) deposits, which are important metal resources for industry and which are targets of exploration worldwide. Current models of hydrothermal circulation in the oceanic crust suggest a direct genetic relationship between VMS deposits on the seafloor and deep, high-temperature hydrothermal reaction zones identified by epidote-rich rocks, "epidosites". However, this relationship remains untested and its basis is incompletely explained. We intend to clarify these issues by investigating the hydrothermal alteration in exposed oceanic crust in the Semail Ophiolite in northern Oman. Our on-going work in Oman has revealed abundant epidosites within the volcanic sequence and has laid the foundation for the present proposal. We solicit support from SNF to continue our project for a further 36 months by extending funding for 2 existing PhD candidates and 1 new PhD candidate, plus associated research and conference costs. One PhD candidate will continue to field mapping, interpreting satellite-SWIR imagery and analysing rock samples to produce lithological, structural and hydrothermal alteration maps of the extrusive sequence of the ophiolite and its underlying sheeted dike complex. This will enable reconstruction of the 3D geometry and hydraulic properties of hydrothermal flow paths at the equivalent depth of several km below the ocean floor. It will also provide a means to test for spatial correlations between deep footwall alteration and VMS deposits. A second PhD candidate will continue to analyse fluid inclusions in epidosites in order to characterize the physicochemical properties of the alteration fluids. This information will aid in reconstructing the chemical reactions that produce the mineral alteration, in tracing the origin of the fluids and in testing if they correlate chemically with fluids venting at the modern seafloor. Fluid inclusions in miarolitic cavities in tonalite intrusions will also be analysed to evaluate the extent to which magmatic fluids play a role in hydrothermal alteration of the oceanic crust and formation of VMS deposits. The third PhD candidate will use a reactive-transport code to conduct numerical simulations of the coupled thermal-hydraulic-chemical processes leading to the deep footwall alteration. The simulations will be constrained by input from the parallel field, geochemical and fluid inclusion studies in this project. This modelling is aimed at quantifying reaction mechanisms and fluxes of solutes and heat, providing a way to test scenarios for the origin of the input fluids and for their fate and relationship to VMS deposits once they exit the epidosites and migrate towards the seafloor.The products of this research project will be a series of conference presentations and publications in international, peer-reviewed, scientific journals. The results in these publications will be of practical significance to the exploration industry. In addition, the project we will have provided scientific training for the PhD candidates and several Master students.