5:15 PM - 6:30 PM
[SCG51-P02] A new method for large number of core sample CT scanning and preliminary results of Nankai Trough DSDP and ODP core samples
Keywords:Nankai Trough, Hydrothermal alternation, X-ray CT
X-ray CT scan (hereafter referred to as CT) can obtain the three-dimensional internal structure of an object with non-destructive and high spatial resolution by using the difference in the degree of X-ray absorption depending on the density and/or element. Since it is highly valuable as basic information for geological core samples, geological core samples drilled by D/V Chikyu are taken CT data on board. However, other core samples are basically not collected CT data. One of the issues when collecting CT data for a large number of core samples is working time, and we report a new method for acquiring efficiently CT data at Kochi Core Center, Japan (hereafter referred to as KCC).
At KCC, core samples are usually scanned one by one using CT scanner. In the reporting method, 12 core samples were scanned at one time and divided into CT data for each core using an image processing program. With these improvements, work efficiency has increased about 10 times. For example, CT data can be acquired in about 1 or 2 days for core samples from one site of ODP or IODP (several hundred meters long). The spatial resolution of the CT image from the new method is about 0.5 mm/pixel, which is slightly inferior to the resolution of 0.2 mm/pixel when taken with a one by one image. Nevertheless, they can be fully utilized for analysis of geological structure, crack distribution, or downhole profiles of mean CT values of core samples.
As a preliminary study, the method of this study was applied to some DSDP and ODP core samples around the Nankai Trough. In the Nankai Trough, a hydrothermal mineralization was reported from the drilling core at Site C0023 of IODP Expedition 370 located at the toe of the Nankai accretionary complex (Tsang et al., 2020). In order to clarify the scale and origin of the hydrothermal mineralization, CT data of other sites excavated around the Nankai Trough are considered to be effective, and mainly the Nankai Trough off the coast of Ashizuri, Kochi Prefecture. CT data were obtained for the core samples from seven sites. As a result, sections showing high CT values were confirmed at multiple intervals. In particular, high CT value intervals were found in the lower part of the Shikoku Basin sediments at site 1177. At least in some of these high CT value intervals, no corresponding description or physical property data was confirmed by previous studies using the same samples. Thus, it is considered that there is a possibility that new geological information of core samples can be extracted by acquiring a large amount of CT data.
At KCC, core samples are usually scanned one by one using CT scanner. In the reporting method, 12 core samples were scanned at one time and divided into CT data for each core using an image processing program. With these improvements, work efficiency has increased about 10 times. For example, CT data can be acquired in about 1 or 2 days for core samples from one site of ODP or IODP (several hundred meters long). The spatial resolution of the CT image from the new method is about 0.5 mm/pixel, which is slightly inferior to the resolution of 0.2 mm/pixel when taken with a one by one image. Nevertheless, they can be fully utilized for analysis of geological structure, crack distribution, or downhole profiles of mean CT values of core samples.
As a preliminary study, the method of this study was applied to some DSDP and ODP core samples around the Nankai Trough. In the Nankai Trough, a hydrothermal mineralization was reported from the drilling core at Site C0023 of IODP Expedition 370 located at the toe of the Nankai accretionary complex (Tsang et al., 2020). In order to clarify the scale and origin of the hydrothermal mineralization, CT data of other sites excavated around the Nankai Trough are considered to be effective, and mainly the Nankai Trough off the coast of Ashizuri, Kochi Prefecture. CT data were obtained for the core samples from seven sites. As a result, sections showing high CT values were confirmed at multiple intervals. In particular, high CT value intervals were found in the lower part of the Shikoku Basin sediments at site 1177. At least in some of these high CT value intervals, no corresponding description or physical property data was confirmed by previous studies using the same samples. Thus, it is considered that there is a possibility that new geological information of core samples can be extracted by acquiring a large amount of CT data.