我所2016年发表论文欣赏-第二十期

地球所研究生会 · 公众号 · · 2017-05-15 10:22

正文

题目

Seismic heating signatures in the Japan Trench subduction plate-boundary fault zone: evidence from a preliminary rock magnetic ‘geothermometer’

作者

Tao Yang, 1,2 Mark J. Dekkers 2 and Bo Zhang 1

发表刊物

《Geophysical Journal International》

摘要

Frictional heating during earthquake rupture reveals important information on earthquake mechanisms and energy dissipation. The amount of annealing varies widely and is, as yet,poorly constrained. Here we use magnetic susceptibility versus temperature measurements during cycling to increasingly elevated temperatures to constrain the maximum temperature
a slip zone has experienced. The case study comprises sheared clay cored from the Japan Trench subduction plate-boundary fault zone (décollement), which accommodated the large slip of the 2011 M w 9.0 Tohoku-oki earthquake. The décollement was cored during the Integrated Ocean Drilling Program (IODP) Expedition 343, the Japan Trench Fast Drilling Project (JFAST). Heating signatures with estimated maximum temperatures ranging from∼300 to over 500 ◦ C are determined close to the multiple slip surfaces within the décollement. Since it is impossible to tie a specific slip surface to a certain earthquake, thermal evidence for the cumulative effect of several earthquakes is unveiled. This as yet preliminary rock magnetic ‘geothermometer’wouldbeausefultooltodetectseismicheatingalongfaultsthatexperienced medium temperature rise, a range which is difficult to assess with other approaches.

题目

Rock magnetic expression of fluid infiltration in the
Yingxiu-Beichuan fault (Longmen Shan thrust belt, China)

作者

Tao Yang 1,2 , Xiaosong Yang 3 , Qingbao Duan 3 , Jianye Chen 3,4 , and Mark J. Dekkers 2

发表刊物

《Geochemistry, Geophysics, Geosystems》

摘要

Fluid infiltration within fault zones is an important process in earthquake rupture. Magnetic properties of fault rocks convey essential clues pertaining to physicochemical processes in fault zones. In 2011, two shallow holes (134 and 54 m depth, respectively) were drilled into the Yingxiu-Beichuan fault (Longmen Shan thrust belt, China), which accommodated most of the displacement of the 2008 Mw 7.9 Wenchuan earthquake. Fifty-eight drill core samples, including granitic host rock and various fault rocks, were analyzed rock-magnetically, mineralogically, and geochemically. The magnetic behavior of fault rocks appears to be dominated by paramagnetic clay minerals. Magnetite in trace amounts is identified as the predominant ferrimagnetic fraction in all samples, decreasing from the host rock, via fault breccia to (proto-)cataclasite. Significant mass-losses (10.7–45.6%) are determined for the latter two with the ‘‘isocon’’ method. Volatile contents and alteration products (i.e., chlorite) are enriched toward the fault core relative to the host rocks. These observations suggest that magnetite depletion occurred in these fault rocks—exhumed from the shallow crust—plumbed by fluid-assisted processes. Chlorite, interpreted to result from hydrothermal activity, occurs throughout almost the entire fault core and shows high coefficients of deter-mination (R 2 >0.6) with both low and high-field magnetic susceptibility. Close relationships, with R 2 >0.70, are also observed between both low and high-field magnetic susceptibility and the immobile elements (e.g., TiO 2 , P 2 O 5 , MnO), H 2 O 1 , and the calculated mass-losses of fault rocks. Hence, magnetic properties of fault rocks can serve as proxy indicators of fluid infiltration within shallow fault zones.

感谢人才资源部狄传芝老师、第四研究室张盛峰提供论文目录及原文
编辑：贾源源、刘翰林
审阅：杜柠、陈婷、李佳威