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Major Mineral Fraction and Physical Properties of Carbonated Peridotite (Listvenite) From ICDP Oman Drilling Project Hole BT1B Inferred From X-Ray CT Core Images
Journal of Geophysical Research: Solid Earth ( IF 3.9 ) Pub Date : 2021-11-05 , DOI: 10.1029/2021jb022719
Keishi Okazaki 1 , Katsuyoshi Michibayashi 2, 3 , Kohei Hatakeyama 4, 5 , Natsue Abe 6, 7 , Kevin T.M. Johnson 8, 9 , Peter B. Kelemen 10 ,
Affiliation  

We quantified mineral proportions in listvenite (completely carbonated peridotite) in Hole BT1B drilled across the basal thrust of the Samail ophiolite by the International Continental Scientific Drilling Project Oman Drilling Project using 3D X-ray Computed Tomography (XCT). We analyzed >250,000 XCT images from a continuous ∼200 m listvenite core. Histograms of the intensity of X-ray attenuation of each XCT core-slice image were fitted assuming that the listvenites are composed of magnesite, quartz, and dolomite. The XCT mineral peaks were confirmed by comparison with chemical mapping data obtained using an X-ray fluorescence (XRF) core scanner. Listvenite matrix is composed almost entirely of magnesite and quartz, consistent with discrete XRD and XRF data. Veins are composed mostly of dolomite. The mean abundance of dolomite in listvenite from BT1B is 11 vol.%, whereas that in core sections within 15 m of the basal thrust is >50 vol.%, suggesting the basal thrust acted as a source of Ca- and CO2-rich fluids. The SiO2:MgO:CaO molar ratio in the entire core from BT1B is 42:52:6, similar to that of onboard XRF data for discrete samples (41:54:5), whereas average Oman peridotites have ratios of (39:60:1), indicating Ca addition perhaps during carbonation. P- and S-wave velocities and density of listvenite are close to those of peridotite and are higher than those of serpentinites. These results suggest that limited material transfer during carbonation and hydration of the Samail ophiolite, except for Ca, CO2, and H2O. Listvenites formed in the mantle wedge above subduction zones may be an overlooked reservoir for carbon in the Earth's interior.

中文翻译:

从 ICDP 阿曼钻探项目孔 BT1B 从 X 射线 CT 岩心图像推断出的碳酸橄榄岩(李斯特文岩)的主要矿物成分和物理性质

我们使用 3D X 射线计算机断层扫描 (XCT) 量化了国际大陆科学钻探项目阿曼钻探项目在 Samail 蛇绿岩基底冲断层上钻出的 BT1B 孔中的 listvenite(完全碳酸化橄榄岩)中的矿物比例。我们分析了 250,000 多张来自连续约 200 m listvenite 岩心的 XCT 图像。假设listvenite由菱镁矿、石英和白云石组成,拟合每个XCT核心切片图像的X射线衰减强度的直方图。XCT 矿物峰通过与使用 X 射线荧光 (XRF) 岩心扫描仪获得的化学映射数据进行比较来确认。Listvenite 矩阵几乎完全由菱镁矿和石英组成,与离散的 XRD 和 XRF 数据一致。脉主要由白云石组成。2-丰富的流体。来自 BT1B 的整个岩心的 SiO 2 :MgO:CaO 摩尔比为 42:52:6,类似于离散样品的机载 XRF 数据 (41:54:5),而阿曼橄榄岩的平均摩尔比为 (39:54:5)。 60:1),表明可能在碳酸化过程中添加了 Ca。利斯特文岩的P波和S波速度和密度接近橄榄岩,高于蛇纹岩。这些结果表明,除了 Ca、CO 2和 H 2 O之外,在 Samail 蛇绿岩碳化和水化过程中有限的物质转移。在俯冲带上方的地幔楔中形成的 Listvenite 可能是地球内部被忽视的碳储层。
更新日期:2021-11-27
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