کد مقاله | کد نشریه | سال انتشار | مقاله انگلیسی | نسخه تمام متن |
---|---|---|---|---|
4744251 | 1641850 | 2011 | 7 صفحه PDF | دانلود رایگان |
In a massive siliceous mudstone at the site of the Horonobe Underground Research Laboratory in Hokkaido, Japan, a “hard part”, having a very high unconfined compressive strength, occurs at the top of siliceous mudstone (opal-CT zone) at the boundary with the overlying diatomaceous mudstone (opal-A zone). Bulk chemical data does not indicate additional silica cementation or differences in mineralogy in the “hard part” compared with the remainder of the siliceous mudstone. The “hard part” corresponds to a transition zone between opal-A and opal-CT, where the two phases coexist. SEM images show that microcrystalline opal-CT precipitates within pore spaces in the pre-existing, intricate diatom-supported framework of the transition zone. Below this zone, the framework is replaced by aggregations of relatively fine and equigranular opal-CT. The strength of the “hard part” probably reflects the strong framework/cementation due to the coexistence of opal-A and opal-CT. Consequently, the transition zone between opal-A and opal-CT is generally strong and brittle, and if it tectonically deformed it could act as a fluid conduit.
► Strength of an opal-A to opal-CT transition zone in siliceous rocks was tested.
► Unconfined compressive strengths of the transition zone showed higher values.
► Bulk chemistry and SEM images imply it results from usual burial diagenesis.
► The transition zone, where opal-A and opal-CT coexist, is generally strong.
Journal: Engineering Geology - Volume 122, Issues 3–4, 10 October 2011, Pages 215–221