Petrography and shock‐related remagnetization of pyrrhotite in drill cores from the Bosumtwi Impact Crater Drilling Project, Ghana
Petrography and shock‐related remagnetization of pyrrhotite in drill cores from the Bosumtwi Impact Crater Drilling Project, Ghana
复制标题
加纳博苏姆特维撞击坑钻探项目钻芯中磁黄铁矿的岩相学和与冲击相关的重磁化
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发表时间：
2007
期刊：
影响因子：
--
通讯作者：
Jochen Zolk
中科院分区：
文献类型：
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作者：
A. Kontny;T. Elbra;J. Just;L. Pesonen;A. Schleicher;Jochen Zolk
摘要：岩石磁性和磁性矿物学数据来自国际大陆科学钻探计划 (ICDP) Bosumtwi 冲击构造的 LB-07A 和 LB-08A 岩心，以便了解冲击和目标岩性的磁性行为及其与冲击相关的再磁化机制。提供了用于解释磁异常模式和磁钻孔测量以及新磁建模的基本数据。磁化率 (150–500 × 10−6 SI) 和自然剩磁 (10−3−10−1 A/m) 通常较弱，但局部较高值高达 10.6 × 10−3 SI 和 43 A/m。 63% 的研究岩石样本显示 Q 值高于 1，表明剩磁明显超过感应磁化强度，这是冲击结构的典型特征。亚铁磁性磁黄铁矿是主要磁铁矿相，除了少量磁铁矿和居里温度在 330 至 350 °C 之间的磁性相外，也存在，解释为异常磁黄铁矿。矫顽力在 20 到 40 mT 之间。磁黄铁矿的角砾化和断裂是确认其撞击前起源的共同特征。磁黄铁矿的晶粒尺寸表现出很大的变化，但通过透射电子显微镜（TEM）观察到的大量应力诱导的纳米结构被认为表现为单域晶粒。我们认为，钻孔岩石在冲击事件期间失去了冲击前的剩磁记忆，并在冲击引起的晶粒尺寸减小期间获得了新的、稳定的剩磁。观察到的脆性微观结构表明温度不高于 250 °C，低于亚铁磁性磁黄铁矿的居里温度 (310 °C)。
Abstract— Rock magnetic and magnetic mineralogy data are presented from the International Continental Scientific Drilling Program (ICDP) drill cores LB‐07A and LB‐08A of the Bosumtwi impact structure in order to understand the magnetic behavior of impact and target lithologies and their impact‐related remagnetization mechanism. Basic data for the interpretation of the magnetic anomaly patterns and the magnetic borehole measurements as well as for new magnetic modeling are provided. Magnetic susceptibility (150–500 × 10−6 SI) and natural remanent magnetization (10−3−10−1 A/m) are generally weak, but locally higher values up to 10.6 × 10−3 SI and 43 A/m occur. Sixty‐three percent of the investigated rock specimens show Q values above 1 indicating that remanence clearly dominates over induced magnetization, which is a typical feature of impact structures. Ferrimagnetic pyrrhotite is the main magnetite phase, which occurs besides minor magnetite and a magnetic phase with a Curie temperature between 330 and 350 °C, interpreted as anomalous pyrrhotite. Coercive forces are between 20 and 40 mT. Brecciation and fracturing of pyrrhotite is a common feature confirming its pre‐impact origin. Grain sizes of pyrrhotite show a large variation but the numerous stress‐induced nanostructures observable by transmission electron microscopy (TEM) are assumed to behave as single‐domain grains. We suggest that the drilled rocks lost their pre‐shock remanence memory during the shock event and acquired a new, stable remanence during shock‐induced grain size reduction. The observed brittle microstructures indicate temperatures not higher than 250 °C, which is below the Curie temperature of ferrimagnetic pyrrhotite (310 °C).
ICDP 博苏姆特维湖撞击坑科学钻探项目（加纳）：核心 LBâ08A 岩石、相关喷射物和冲击恢复实验
影响因子：
2.2
作者：
Deutsch;Luetke;Heinrich
通讯作者：
Heinrich