Micro-Imaging Spectroscopy of the Oman Drilling Project Phase 1 and 2 Drill Cores
Abstract
The ICDP Oman Drilling Project recovered 3.2 km of diamond drill core in a series of boreholes at different levels of the Samail Ophiolite in Oman, sampling intrusive sections of the ocean crust, the upper mantle, and metamorphic sole. We scanned the full length of core at sub-mm spatial resolution with the Caltech Ehlmann Laboratory imaging spectrometer on board the JAMSTEC D/V Chikyu during the core description campaigns in 2017-2018. The technique measures light reflected off surfaces at 100's of wavelengths between 0.4 and 2.6 μm to provide information about mineral composition using absorption features at different wavelengths.
Many science questions can be addressed with this dataset. Our investigation focuses on tracing chemical fluxes during (a) hydrothermal alteration of the ocean crust, (b) mass transfer from subducting metabasalts/metasediments into the overlying mantle wedge, and (c) serpentinization and carbonation of peridotite during ongoing weathering. For example, imaging spectroscopy can identify high temperature amphiboles in the lower gabbros that would indicate early high-temperature hydrothermal circulation and thus support models in which high temperature alteration and rapid cooling extend into the lower crust near oceanic spreading ridges. Spectral identification of more prehnite in the gabbro and sheeted dike cores than was recorded during visual core description constrains chemical conditions of some stages of alteration. The extent to which listvenite (fully carbonated peridotite) forms in open vs closed systems is a key question; mapping of minerals such as dolomite and kaolinite in Hole BT1B suggests that alteration was not isochemical and there was input of elements such as Ca and Al from the subducting slab. Imaging spectroscopy also helped identify a carbonate- and talc-rich zone at the base of peridotite Hole CM2B. The raw dataset is nearly 31 TB and will be processed to produce high resolution mineral maps of the full core for eventual public release. Validation of the mineral identifications will leverage shipboard measurements (especially XRD) from the core description as well as our own sample analyses. We will present preliminary analyses of the micro-imaging spectroscopy measurements of the Oman Drilling Project cores, highlighting the most exciting results thus far.- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2018
- Bibcode:
- 2018AGUFM.V13E0153G
- Keywords:
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- 0456 Life in extreme environments;
- BIOGEOSCIENCESDE: 8140 Ophiolites;
- TECTONOPHYSICSDE: 8416 Mid-oceanic ridge processes;
- VOLCANOLOGYDE: 8424 Hydrothermal systems;
- VOLCANOLOGY