Influence of Early Low‐Temperature and Later High‐Temperature Diagenesis on Magnetic Mineral Assemblages in Marine Sediments From the Nankai Trough
Influence of Early Low‐Temperature and Later High‐Temperature Diagenesis on Magnetic Mineral Assemblages in Marine Sediments From the Nankai Trough
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DOI：
10.1029/2021gc010133
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发表时间：
2021-10
期刊：
影响因子：
3.7
通讯作者：
M. Kars;M. Köster;S. Henkel;R. Stein;F. Schubotz;Xiang Zhao;S. Bowden;A. Roberts;K. Kodama
中科院分区：
文献类型：
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作者：
M. Kars;M. Köster;S. Henkel;R. Stein;F. Schubotz;Xiang Zhao;S. Bowden;A. Roberts;K. Kodama
成岩作用对沉积矿物学有重要影响。原生磁性矿物组合在成岩作用早期或晚期可因溶解作用或新磁性矿物的形成而发生明显的变化。在国际海洋发现计划C0023站点，该站点在日本四国岛近海的南海海槽的原逆冲带中进行了钻探，非稳态条件产生了复杂的磁性叠加序列。详细的岩石磁性测量，其特征磁性矿物组合的丰度，粒度和成分，进行评估磁性矿物蚀变和成岩叠加。根据岩石磁性变化，在海底以下200米至1,100米的岩芯中确定了四个磁性区（MZ）。MZ 1是一个高磁场强度区，含有亚铁磁云英岩，形成于较浅的深度，由于快速沉积而保存下来。MZ 2和MZ 4为低磁场强度区，磁性矿物较少，主要为粗粒（钛）磁铁矿和赤铁矿。这个磁性矿物组合是一个更复杂的组合，是在沉积后几百万年，当该网站进入南海海槽成岩蚀变的残余。MZ 3是MZ 2和MZ 4之间的高磁场强度区。它含有自生单畴磁性粒子，可能是由通过增生棱镜中断层循环的流体形成的。不同的沉积物供应和有机质输入，通过时间，埋藏温度和构造流体循环是磁性矿物组合变化的主要驱动力。
Diagenesis can have a major impact on sedimentary mineralogy. Primary magnetic mineral assemblages can be modified significantly by dissolution or by formation of new magnetic minerals during early or late diagenesis. At International Ocean Discovery Program Site C0023, which was drilled in the protothrust zone of the Nankai Trough during Expedition 370, offshore of Shikoku Island, Japan, non‐steady state conditions have produced a complex sequence of magnetic overprints. Detailed rock magnetic measurements, which characterize magnetic mineral assemblages in terms of abundance, grain size, and composition, were conducted to assess magnetic mineral alteration and diagenetic overprinting. Four magnetic zones (MZs) are identified down‐core from ∼200 to 1,100 m below sea floor based on rock magnetic variations. MZ 1 is a high magnetic intensity zone that contains ferrimagnetic greigite, which formed at shallow depths and is preserved because of rapid sedimentation. MZs 2 and 4 are low magnetic intensity zones with fewer magnetic minerals, mainly coarse‐grained (titano‐)magnetite and hematite. This magnetic mineral assemblage is a remnant of a more complex assemblage that was altered diagenetically a few million years after deposition when the site entered the Nankai Trough. MZ 3 is a high magnetic intensity zone between MZs 2 and 4. It contains authigenic single‐domain magnetic particles that probably formed from fluids that circulated through faults in the accretionary prism. Varying sediment supply and organic matter input through time, burial temperature, and tectonic fluid circulation are the primary drivers of magnetic mineral assemblage variations.