Petrology and hydrothermal mineralogy of U.S. geological survey Newberry: 2. Drill core from Newberry Caldera, Oregon
Petrology and hydrothermal mineralogy of U.S. geological survey Newberry: 2. Drill core from Newberry Caldera, Oregon
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美国纽伯里地质调查局的岩石学和热液矿物学：2.来自俄勒冈州纽伯里火山口的钻芯
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发表时间：
1988
期刊：
影响因子：
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通讯作者：
K. Bargar
中科院分区：
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作者：
T. Keith;K. Bargar
美国地质调查局纽伯里 2 号钻探深度为纽伯里破火山口 932 m。 265°C 的井底温度是美国喀斯喀特地区所有钻孔报告的最高温度。 Newberry 2 穿透的地层剖面的上部由火山口填充物组成，下面是越来越多的镁铁质熔岩，范围从 501 m 的流纹英安岩到 932 m 的玄武岩。 300 m以下的测得温度低于35°C，岩石蚀变包括玻璃水化和玄武质凝灰岩的局部长菱形岩化。 300 至 500 m 的整个浮石岩凝灰岩中都发生了早期沸石化以及灰和浮石的部分蒙皂石替代。凝灰岩在较高温度下转变为绿泥石和丝光沸石发生在 460-470 m 的流英安岩岩台附近；岩基内的蚀变矿物包括磁黄铁矿、黄铁矿、石英、方解石和菱铁矿。在 697 m 以下，岩石随深度变化逐渐加大，主要是因为沿传导梯度温度升高，从 697 m 处的 100°C 升至 930 m 处的 265°C。石英和方解石中的流体包裹体表明过去的温度高于现在，这很可能是由于不可渗透的熔岩流之间的局部围压造成的。无论成分如何，流角砾岩比邻近的致密大量熔岩流变化更大，因为它们的渗透性要高得多。该区热液矿物主要为绿泥石-蒙脱石混层、石英、方解石、黄铁矿等。绿泥石变得比孔底部附近的混合层粘土更加丰富。在最低的两条熔岩流中，局部出现绿帘石、硬石膏和稀有的赤铁矿。基底 2 m 的蚀变和淋滤是独特的，并导致了主要由蒸汽和 CO2 组成的局部两相流体区域的假设。纽伯里2号热液系统是一个与纽伯里火山演化相关的简单演化系统。只有少数局部高度蚀变层段发生压裂控制流体进入岩心。没有横切裂缝表明存在多个热液系统。对蚀变岩石和同等新鲜岩石的化学分析表明，几乎没有发生化学迁移。
U.S. Geological Survey Newberry 2 was drilled to a depth of 932 m within Newberry caldera. The bottom-hole temperature of 265°C is the highest reported temperature of any drill hole in the Cascades region of the United States. The upper part of the stratigraphic section penetrated by Newberry 2 consists of caldera fill below which are increasingly more mafic lavas ranging from rhyodacite at 501 m to basalt at 932 m. Measured temperatures shallower than 300 m are less than 35°C, and rock alteration consists of hydration of glass and local palagonitization of basaltic tuffs. Incipient zeolitization and partial smectite replacement of ash and pumice occurred throughout the pumiceous lithic tuffs from 300 to 500 m. Higher-temperature alteration of the tuffs to chlorite and mordenite occurs adjacent to a rhyodacite sill at 460–470 m; alteration minerals within the sill consist of pyrrhotite, pyrite, quartz, calcite, and siderite. Below 697 m the rocks are progressively more altered with depth mainly because of increased temperature along a conductive gradient from 100°C at 697 m to 265°C at 930 m. Fluid inclusions in quartz and calcite indicate that temperatures in the past have been higher than at present, most likely due to local confining pressures between impermeable lava flows. Flow breccias are more altered than the adjacent dense massive lava flows, regardless of composition, because of their much higher permeability. Hydrothermal minerals in this zone are mainly mixed-layer chlorite-smectite, quartz, calcite, and pyrite. Chlorite becomes more abundant than mixed-layer clays near the bottom of the hole. In the lowest two lava flows, epidote, anhydrite, and scarce hematite occur locally. Alteration and leaching in the basal 2 m are unique and have led to the postulation of a localized two-phase fluid zone consisting mainly of steam and CO2. The hydrothermal system of Newberry 2 is a simple evolving system associated with the evolution of Newberry Volcano. Only a few localized highly altered intervals where fracturing controlled fluid access occur in the core. There are no crosscutting fractures to indicate multiple hydrothermal systems. Chemical analyses of altered rocks and equivalent fresh rocks indicate that little chemical migration has taken place.