张蕾^1,,
李海兵^1,,,
孙知明²,
周祐民³,
曹勇²,
王焕¹,
叶小舟²,
何祥丽¹
1. 自然资源部深地动力学重点实验室, 中国地质科学院地质研究所, 北京 100037
2. 自然资源部古地磁与古构造重建重点实验室, 中国地质科学院地质力学研究所, 北京 100081
3. 南方科技大学海洋科学与工程系, 广东深圳 518055

基金项目: 国家自然科学基金项目（41520104006，41330211，41602226）和中国地质科学院基本科研业务费项目（YYWF201601）联合资助


详细信息

作者简介: 张蕾, 女, 1988年出生, 博士, 主要从事地震断裂作用研究.E-mail:zhanglei881102@126.com

通讯作者: 李海兵, 男, 博士, 研究员, 博士生导师, 主要从事构造地质学及活动构造研究.E-mail:lihaibing06@163.com

中图分类号: P315

收稿日期:2018-03-14
修回日期:2018-04-12
上线日期:2018-05-05

Rock magnetic evidence for the seismogenic setting of large earthquakes in the Longmen Shan fault zone

ZHANG Lei^1,,
LI HaiBing^1,,,
SUN ZhiMing²,
CHOU YuMin³,
CAO Yong²,
WANG Huan¹,
YE XiaoZhou²,
HE XiangLi¹
1. Key Laboratory of Deep-Earth Dynamics of Ministry of Natural Resources, Institute of Geology, Chinese Academy of Geological Sciences, Beijing 100037, China
2. Key Laboratory of Paleomagnetism and Tectonic Reconstruction of Ministry of Natural Resources, Institute of Geomechanics, Chinese Academy of Geological Sciences, Beijing 100081, China
3. Department of Ocean Science and Engineering, South University of Science and Technology, Guangdong Shenzhen 518055, China


More Information

Corresponding author: LI HaiBing,E-mail:lihaibing06@163.com

MSC: P315

--> Received Date: 14 March 2018
Revised Date: 12 April 2018
Available Online: 05 May 2018


摘要
摘要:地震断裂带的孕震环境对于研究地震的发生至关重要.本文以汶川地震断裂带科学钻探2号（WFSD-2）钻孔岩心中的假玄武玻璃、碎裂岩及其围岩为研究对象，通过岩石磁学测试，并结合显微结构观察探讨龙门山断裂带大地震的孕震环境.WFSD-2岩心碎裂岩中的假玄武玻璃是龙门山断裂带曾经发生过大地震活动的岩石学证据，假玄武玻璃具有高磁化率特征，而碎裂岩的磁化率值与围岩相似，假玄武玻璃中的新生磁铁矿是其高磁化率值异常的重要原因之一.假玄武玻璃中较少量的新生磁铁矿暗示了假玄武玻璃的生成环境为含氧量较低的高温还原环境.大地震断裂的摩擦热是改变龙门山断裂带中假玄武玻璃岩石磁学特征的主导因素，流体作用较弱.无高磁化率异常的碎裂岩经历的温度小于300℃，推测假玄武玻璃的生成深度较深.WFSD-2岩心中20余层假玄武玻璃脉体证明映秀—北川断裂带是一条长期活跃的断裂带，龙门山断裂带上曾经发生了多次大地震断裂活动，这些大地震可能发生在深度较大、流体作用较弱的还原性孕震环境中.
关键词: 假玄武玻璃/
碎裂岩/
岩石磁学/
大地震活动/
龙门山断裂带

Abstract:The seismogenic setting of earthquake fault zones is important for seismological research. To investigate the seismogenic environment of earthquakes in the Longmen Shan fault zone, we carried out microstructural and rock-magnetic analyses of pseudotachylyte, cataclasite and its wall rocks within cores from the Wenchuan earthquake Fault Scientific Drilling borehole 2 (WFSD-2). Pseudotachylyte, observed in a cataclasite zone, attests to that large earthquakes have occurred in the Longmen Shan fault zone. It has higher magnetic susceptibility values than cataclasite, while cataclasite has similar values as its wall rocks. The newly-formed magnetite contributes to the higher values of magnetic susceptibility of pseudotachylyte. In addition, a little newly-formed magnetite in the pseudotachylyte indicates that pseudotachylyte was formed at high temperature and a reducing environment. Frictional heating is the main factor which changes the rock magnetic properties of pseudotachylytes in the Longmen Shan fault zone, while fluids play a minor role. The cataclasite has never been subjected to heating over 300 ℃ in nature, which implies that the pseudotachylye was formed at depth. More than 20 layers of pseudotachylytes demonstrate that the Yingxiu-Beichuan fault zone is a long-term active fault, and ancient powerful earthquakes have occurred repeatedly in the Longmen Shan fault zone. These earthquakes most likely occurred in deep seismogenic environment, with strong reducing and weak fluid activity.
Key words:Pseudotachylyte/
Cataclasite/
Rock magnetism/
Large earthquakes/
Longmen Shan thrust belt



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