Magnetic Mineral Diagenesis in a High Temperature and Deep Methanic Zone in Izu Rear Arc Marine Sediments, Northwest Pacific Ocean
Magnetic Mineral Diagenesis in a High Temperature and Deep Methanic Zone in Izu Rear Arc Marine Sediments, Northwest Pacific Ocean
复制标题
DOI：
10.1029/2018jb015861
复制
发表时间：
2018-10
期刊：
影响因子：
--
通讯作者：
M. Kars;R. Musgrave;T. Hoshino;A. Jonas;T. Bauersachs;F. Inagaki;K. Kodama
中科院分区：
文献类型：
--
作者：
M. Kars;R. Musgrave;T. Hoshino;A. Jonas;T. Bauersachs;F. Inagaki;K. Kodama
磁性矿物成岩作用是沉积物中的一个重要过程，它部分或全部破坏了地球磁场变化的记录，并在铁、硫循环中起着重要作用。在伊豆小笠原后弧的国际海洋发现计划第350次考察地点U1437进行了一项岩石磁性研究，以调查海底以下~775至~1 002米深埋沉积物中磁性矿物的成岩作用，埋藏温度为~67至85 ° C。非稳态地球化学环境发生在一个不寻常的深甲烷区（低于850 mbsf），因为硫酸盐的释放低于浅硫酸盐还原区。磁化率和剩磁急剧下降，观察到在~850 mbsf由于亚铁磁性氧化铁含量的减少。（钛）磁铁矿的还原和黄铁矿化发生在推断的深部硫酸盐-甲烷过渡带。低于~850 mbsf，较低的磁性矿物含量与进一步的甲烷释放相一致。地球化学分析支持氧化还原条件的变化以及富甲烷区铁硫化物和碳酸盐的二次沉淀。磁性矿物蚀变在甲烷聚集在低孔隙度间隔下的区域增强，这些间隔起到密封作用。虽然地球化学过程，由于甲烷的发生可能是占主导地位的，一个以上的机制，可能涉及微生物的活动，可能是负责所观察到的磁性矿物组合的变化。
Magnetic mineral diagenesis is an important process in sediments that is responsible for the partial or total destruction of records of Earth's magnetic field variations and also plays an important part in iron and sulfur cycling. A rock magnetic study has been carried out at International Ocean Discovery Program Expedition 350 Site U1437 in the Izu Bonin rear arc to investigate magnetic mineral diagenesis in deeply buried sediments from ~775 to ~1,002 m below sea floor (mbsf) with burial temperatures ranging from ~67 to 85 °C. Nonsteady state geochemical environments occur within an unusual deep methanic zone (below 850 mbsf) because of a release of sulfate below the shallow sulfate reduction zone. A drastic decline in magnetic susceptibility and remanence is observed at ~850 mbsf due to a decrease in ferrimagnetic iron oxide contents. Reduction of (titano)‐magnetite and pyritization occur at this inferred deep sulfate‐methane transition zone. Below ~850 mbsf, lower magnetic mineral contents coincide with further methane release. Geochemical analyses support a change in redox conditions and secondary precipitation of iron sulfides and carbonates in the methane‐rich zone. Magnetic mineral alteration is enhanced in zones where methane accumulates underneath low porosity intervals that act as seals. Although geochemical processes due to methane occurrence are likely dominant, more than one mechanism, possibly involving microbial activity, is probably responsible for the observed magnetic mineral assemblage changes.