MAGNETIC PROPERTIES AND OXIDATION OF IRON-TITANIUM OXIDE MINERALS IN ALAE AND MAKAOPUHI LAVALAKES, HAWAII
MAGNETIC PROPERTIES AND OXIDATION OF IRON-TITANIUM OXIDE MINERALS IN ALAE AND MAKAOPUHI LAVALAKES, HAWAII
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DOI：
10.1029/jb074i022p05277
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发表时间：
1969-01-01
影响因子：
--
通讯作者：
PECK, DL
中科院分区：
文献类型：
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作者：
GROMME, CS;WRIGHT, TL;PECK, DL
对夏威夷基拉韦厄火山阿拉湖和马考普希熔岩湖的48个拉斑玄武岩钻芯样品进行了−温度范围内强磁场磁化强度的测量。这些样品最初是在50°到1020°C的温度范围内获得的，几乎所有的样品都含有丰富的铁铁矿，居里温度在−100°到−160°C之间。高温(800°到1000°C)的样品由于未氧化钛磁铁矿而具有150°到290°C的第二居里温度，而在较低温度(50°C到400°到700°C)下获得的样品的第二居里温度在500°到580°C之间。原始钛磁铁矿氧化成含钛铁矿片层的贫钛磁铁矿是导致居里温度升高的原因。氧化物矿物的组成与Sato和Wright的氧逸度数据以及Buddington和Lindsley的平衡反应数据的对比表明，氧逸度主要受氧化物矿物的缓冲作用控制，因此钛磁铁矿被氧化，而较丰富的赤铁矿在熔岩冷却时变化不大。这种氧化作用在远低于平衡的温度下发生，两者之间的差异一般在100℃左右，但高达400℃。我们得出结论，在某些玄武岩熔岩中，磁性矿物可能是在远低于其最终居里温度的温度下通过固相反应形成的。在这种熔岩中，自然剩余磁化是热剩余磁化和高温化学剩余磁化的混合。
Measurements of strong‐field magnetization over the temperature range −196° to 700°C have been made on forty‐eight drill core samples of tholeiitic basalt from Alae and Makaopuhi lava lakes, Kilauea volcano, Hawaii. These samples were originally obtained at temperatures ranging from 50° to 1020°C. Nearly all samples contain abundant hemoilmenite with Curie temperatures in the range −100° to −160°C. Samples quenched from high temperatures (800° to 1000°C) have second Curie temperatures ranging from 150° to 290°C, due to unoxidized titanomagnetite, and samples obtained at lower temperatures (50° to between 400° and 700°C) have second Curie temperatures ranging from 500° to 580°C. This transition from medium to high Curie temperatures occurs between 850° and 300°C, varying from one drill hole to another, and is accompanied by a marked increase in the strong‐field magnetization at room temperature. Oxidation of original titanomagnetite to Ti‐poor titanomagnetite containing ilmenite lamellas is the cause of the increase in Curie temperature. Comparison of the compositions of the oxide minerals with the oxygen fugacity data of Sato and Wright and the equilibrium reaction data of Buddington and Lindsley shows that oxygen fugacity was controlled largely by the buffering action of the oxide minerals; hence titanomagnetite was oxidized, whereas the more abundant hemoilmenite was little changed as the lava cooled. This oxidation occurred at temperatures well below equilibrium, the difference being generally of the order of 100°C but as much as 400°C. We conclude that in some basaltic lavas the magnetic minerals may form through subsolidus reactions at temperatures well below their final Curie temperatures. In such lavas the natural remanent magnetization is a mixture of thermoremanent magnetization and high‐temperature chemical remanent magnetization.