Micro-Imaging Spectroscopy of ICDP Oman Drilling Project Cores: New Insights into Alteration of the Oceanic Crust
Abstract
The ICDP Oman Drilling Project cored 3.2 km of ocean crust, mantle, and metamorphic sole from 9 boreholes with ~100% core recovery in the Oman ophiolite to answer questions about the origin and modification of the oceanic crust and upper mantle. We use a novel measurement technique, infrared micro-imaging spectroscopy, to understand fluid-rock reactions within the oceanic crust.
All sections of the archive half of the core were scanned at ~250 μm/pixel with the Caltech Ehlmann laboratory visible-shortwave infrared imaging spectrometer to measure the reflectance of light at wavelengths 0.4-2.6 μm. Because different materials and minerals absorb and reflect light differently as a function of wavelength, we can use the spectral signatures of the core to determine mineralogy. In contrast to traditional core analysis techniques that rely on the accuracy of human core logging or x-ray and chemical measurements of a small subset of samples collected throughout the core, the infrared micro-imaging spectroscopy technique provides a measurement of the mineralogy of optically active phases at each 250x250 μm pixel. In the 3.2 km of core, we have ~3 billion measurements of mineralogy. Our initial work focused on the extent and character of the alteration of oceanic crust through analysis of ~1.2 km of core through sheeted dikes and gabbros of the ophiolite. First, we calculated basic indicators of the presence/absence and degree of alteration, including the depth of the 1.9 μm absorption feature due to mineral-bound H2O and the depth of the 2 μm feature that indicates the presence of pyroxene. The data show a decrease in hydration and slight increase in residual pyroxene identifications with depth in borehole GT2 (foliated and layered gabbros). Additionally, hydration values are higher in GT2 than in the deeper borehole GT1. We will present additional maps of specific alteration minerals that serve as indicators of the temperatures and fluid chemistries of the water-rock reactions and will examine the proximity to structural features and fault zones and changes in the primary igneous classifications. Mineral identifications will also be compared with those from visual description of these cores and with published analyses of IODP drill cores to assess the new insights into alteration of oceanic crust using this dataset.- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2019
- Bibcode:
- 2019AGUFM.V33C0245G
- Keywords:
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- 1009 Geochemical modeling;
- GEOCHEMISTRY;
- 1034 Hydrothermal systems;
- GEOCHEMISTRY;
- 1039 Alteration and weathering processes;
- GEOCHEMISTRY;
- 1090 Field relationships;
- GEOCHEMISTRY