Characterizing Hydration of the Ocean Crust Using Shortwave Infrared Microimaging Spectroscopy of ICDP Oman Drilling Project Cores
Characterizing Hydration of the Ocean Crust Using Shortwave Infrared Microimaging Spectroscopy of ICDP Oman Drilling Project Cores
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DOI：
10.1029/2021jb022676
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发表时间：
2021-11
期刊：
影响因子：
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通讯作者：
Molly A. Crotteau;R. Greenberger;B. Ehlmann;G. Rossman;M. Harris;P. Kelemen;D. Teagle
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文献类型：
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作者：
Molly A. Crotteau;R. Greenberger;B. Ehlmann;G. Rossman;M. Harris;P. Kelemen;D. Teagle
尽管洋壳覆盖了地球表面的60%以上，但形成、冷却和改变洋壳的过程还没有完全被了解。我们利用国际大陆科学钻探计划的阿曼钻井项目取心的∼1.2公里岩石的短波红外显微成像光谱，量化了来自Samail蛇绿岩的玄武岩岩脉和辉长岩的水化作用随深度、矿物学和变形的变化。我们建立了∼1,350-1,650 nm OH/H2O吸收面积与样品点火损失测量之间的回归关系(R2=0.66)，并应用该关系为所有岩芯生成定量∼250μm/像素水合地图。蚀变程度最大的岩墙-辉长岩界面的平均水化程度最低(GT3a，H2O平均值=2.1±1.6wt%)，这与主要蚀变矿物角闪石和绿帘石的低H2O含量相一致。层状辉长岩中H2O含量最高(GT2a，H2O平均值=3.2±3.0wt%)和层状辉长岩(GT1a，H2O平均值=2.8±3.1wt%)。与浅层低wt%H2O角闪石相反，沸石蚀变随深度的增加而增加，以及与断裂带相关的强烈水化带(H2O平均值=5.7±4.0wt%)的出现，导致下洋壳的水化程度更高。这一新方法提供了这些岩芯中水化作用的客观量化，使人们能够更好地了解洋壳水化作用的数量和特征。它强调了特定阶段和断层作用在控制水化作用方面的重要性，这对洋壳冷却、流变性以及蚀变在全球生物地球化学循环中的作用都有影响。
Although ocean crust covers over 60% of Earth's surface, the processes that form, cool, and alter the ocean crust are not completely understood. We utilize shortwave infrared micro‐imaging spectroscopy of ∼1.2 km of rock cored by the International Continental Scientific Drilling Program's Oman Drilling Project to quantify hydration of basaltic dikes and gabbros from the Samail ophiolite as a function of depth, mineralogy and deformation. We develop a regression (R2 = 0.66) between area of the ∼1,350–1,650 nm OH/H2O absorption and measurements of loss on ignition of samples and apply this relationship to generate quantitative ∼250 μm/pixel hydration maps for all cores. The lowest mean hydration is observed in the most pervasively altered dike‐gabbro boundary (GT3A, H2Omean = 2.1 ± 1.6 wt%), consistent with the low H2O content of the dominant alteration minerals, amphibole and epidote. The highest H2O content occurs in deeper foliated and layered gabbros (GT2A, H2Omean = 3.2 ± 3.0 wt%) and layered gabbros (GT1A, H2Omean = 2.8 ± 3.1 wt%). The greater prevalence with depth of zeolite alteration as opposed to lower wt% H2O amphibole at shallow stratigraphic depths, as well as the occurrence of zones of intensive hydration associated with fault zones (H2Omean = 5.7 ± 4.0 wt%) lead to greater hydration of the lower ocean crust. This new approach provides an objective quantification of hydration in these cores, enabling an improved understanding of quantities and characteristics of ocean crust hydration. It highlights the importance of specific phases and faulting in controlling hydration, which has implications for ocean crust cooling, rheological properties, and the role of alteration in global biogeochemical cycling.