A recently published study delved deep into the Hawaiian subsurface by using several spectroscopy techniques, including long-wave infrared (LWIR) spectroscopy, scanning electron microscopy with energy-dispersive spectroscopy (SEM-EDS), and bulk X-ray fluorescence (XRF) geochemistry, to learn more about the mineralogy of Hawaii’s PTA-2 drill core (1,2). This study, which was published in the Journal of Volcanology and Geothermal Research, revealed new information about the mineralogical and geochemical transformations preserved in the PTA-2 drill core (1).
The Big Island's Kohala Coast with the dormant volcano of Hualalai in the distance | Image Credit: © Kyo46 - stock.adobe.com
The lead author of this study is Pooja Sheevam, who conducted this study as part of her Ph.D. thesis. Sheevam now works as a Research Associate at the New Mexico Bureau of Geology and Mineral Resources in Albuquerque, New Mexico. Below is a text transcript of Part I of our interview with Sheevam. You can watch Part 1 of our conversation with Sheevam here.
Will Wetzel: What motivated the use of both long-wave infrared (LWIR) and short-wave IR (SWIR) spectroscopy in analyzing the PTA-2 drill core, and how do the two techniques complement each other?
Pooja Sheevam: Our motivation for using both long-wave infrared (LWIR) and short-wave IR (SWIR) spectroscopy is really twofold. First, we wanted to adopt a non-destructive analytical approach. And second, we wanted to maximize the data output and the information that we can get, especially in terms of geological information. When I entered this project with the PTA-2 drill core, we had a very limited set of samples remaining. So either we fly all the way to Hawaii, go to the core shed, grab samples and fly back, which is actually very expensive, or see how much further we could utilize spectroscopy to characterize the samples that we had left, which is what we decided to do.
Therefore, so rather than pursuing new sample collection again, which would require a lot more time, effort, and money, we focused on preserving the samples that we already have and get more data out of them. In this project, when I started, one of the major gaps that I identified was we didn't really well characterize the extent of hydrothermal alteration, and it hasn't been fully mapped, so in particularly relation to the mafic mineralogy so long wave was employed in the study to capture that sort of, you know, three-to-20-micron range. And it's particularly well suited for characterizing mafic and primary silicate phases, so things like basalts, pyroxenes, and feldspars olivines. Understanding how they're altering out of the system or declining in abundance gives us an idea to the extent of alteration, whereas previous studies use shortwave, which is around one to 2.5, but we went from visible near-infrared to shortwave, which is about 0.3 to 2.5 microns, and those are more sensitive to the clay minerals, sulfates, carbonates, things like that. So, by combining both techniques, we were able to get a broader view of the whole rock mineralogy, which was really awesome.
We also captured not just the secondary alteration minerals, but primary mineral assemblages which were affected by water and potentially pH and temperature. It really pushed our ability to understand the history of the systems that we were looking at, and it also adds to our understanding of the mineralogy of the core as well.
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