Shock experiments up to 30 GPa and their consequences on microstructures and magnetic properties in pyrrhotite
Shock experiments up to 30 GPa and their consequences on microstructures and magnetic properties in pyrrhotite
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DOI：
10.1029/2012gc004242
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发表时间：
2013-01
期刊：
影响因子：
3.7
通讯作者：
C. Mang;A. Kontny;J. Fritz;R. Schneider
中科院分区：
文献类型：
--
作者：
C. Mang;A. Kontny;J. Fritz;R. Schneider
在3 ~ 30 GPa压力范围内对六方和单斜磁黄铁矿混合组合进行了冲击实验。研究了所有样品在高温和低温下的特殊冲击诱导微观结构和磁性能。高达8 GPa，在冲击磁黄铁矿的微观结构的特点是机械变形产生的晶体结构的损伤。在20 GPa及以上的压力下，非晶化和机械孪生是冲击引起的主要结构特征。在较低压力范围内，磁化率、饱和等温剩磁和剩磁磁化率随着冲击压力的增加而增加，与更类似单畴（SD）的行为一致。同时，六方磁黄铁矿的λ峰降低，单斜磁黄铁矿的34 K转变变宽并被抑制。磁硬化是由晶粒尺寸减小引发的，但也由离散多畴晶粒内SD的形成引发。平面变形特征将这种多畴晶粒细分为平均尺寸在SD范围内的板条状畴。平面变形特征在20 GPa下消失，取而代之的是不规则的纳米尺寸的“非晶畴”。压力从30 GPa释放最终触发磁黄铁矿的部分熔融。熔融和结晶磁黄铁矿之间的尖锐界面记录了热条件的快速变化。在熔融的磁黄铁矿中，会出现淬冷的铁晶体。天然铁的存在强烈影响磁性，这取决于所研究样品中的特定量，并可能影响地球和地外物质上撞击岩石的磁性。
Shock experiments with pressures ranging from 3 to 30 GPa have been conducted on a mixed assemblage of hexagonal and monoclinic pyrrhotite. All samples were studied with respect to their particular shock‐induced microstructures and magnetic properties at high and low temperatures. Up to 8 GPa, microstructures in shocked pyrrhotite are characterized by mechanical deformation producing a damage of the crystal structure. At pressures of 20 GPa and upward, amorphization and mechanical twinning are the dominant structural features induced by shock. Within the lower‐pressure range coercivity, saturation isothermal remanent magnetization and coercivity of remanence increase with shock pressures, in agreement with more single‐domain (SD)‐like behavior. Simultaneously, the λ‐peak of hexagonal pyrrhotite decreases and the 34 K transition of monoclinic pyrrhotite broadens and is depressed. Magnetic hardening is triggered by grain‐size reduction, but also by the formation of SD within discrete multidomain grains. Planar deformation features subdivide such multidomain grains into lath‐shaped domains with average sizes lying in the SD range. The planar deformation features disappear at 20 GPa and irregular, nanometer‐sized “amorphous domains” occur instead. Pressure release from 30 GPa finally triggers partial melting of pyrrhotite. The sharp interfaces between molten and crystalline pyrrhotite document a rapid change of thermal conditions. Within molten pyrrhotite, quenched iron crystals occur. The presence of native iron strongly influences the magnetic properties, depending on the particular amount in the studied sample and likely affects the magnetic properties of impact lithologies on Earth and extraterrestrial material.