地震地质 ›› 2024, Vol. 46 ›› Issue (1): 81-100.DOI: 10.3969/j.issn.0253-4967.2024.01.006

• 研究论文 • 上一篇    下一篇

断裂带方解石脉ESR定年研究及其对龙蟠-乔后断裂剑川段活动性的指示

姬昊1)(), 刘春茹1),*(), 魏传义1), 杨会丽1), 尹功明1), 常祖峰2)   

  1. 1) 中国地震局地质研究所, 地震动力学国家重点实验室, 北京 100029
    2) 云南省地震局, 昆明 650216
  • 收稿日期:2023-10-16 修回日期:2023-12-01 出版日期:2024-02-20 发布日期:2024-03-22
  • 通讯作者: *刘春茹, 女, 1980年生, 研究员, 主要研究方向为新构造年代学, E-mail: liuchunru0821@126.com
  • 作者简介:

    姬昊, 男, 1996年生, 现为中国地震局地质研究所构造地质学专业在读博士研究生, 主要研究方向为断层带演化及年代学, E-mail:

  • 基金资助:
    国家重点研发计划项目(2021YFC3000601); 国家自然科学基金(42172211); 国家自然科学基金(U1939201)

ESR DATING OF CALCITE VEINS AND IMPLICATIONS FOR THE ACTIVITY OF THE JIANCHUAN SECTION OF THE LONGPAN-QIAOHOU FAULT ZONE

JI Hao1)(), LIU Chun-ru1),*(), WEI Chuan-yi1), YANG Hui-li1), YIN Gong-ming1), CHANG Zu-feng2)   

  1. 1) State Key Laboratory of Earthquake Dynamics, Institute of Geology, China Earthquake Administration, Beijing 100029, China
    2) Yunnan Earthquake Agency, Kunming 650224, China
  • Received:2023-10-16 Revised:2023-12-01 Online:2024-02-20 Published:2024-03-22

摘要:

龙蟠-乔后断裂带作为川滇菱形块体的一条大型边界断裂, 构造运动强烈, 地震活动频繁, 发生多次5级以上地震, 造成了重大的财产损失和人员伤亡, 因此十分有必要加强对该断裂带的活动性研究, 并评估其地震危险性。龙蟠-乔后断裂剑川段河南村断层剖面发育厚层方解石脉, 为断层定年提供了十分宝贵的材料。文中利用ESR法对该剖面的方解石脉开展了测年研究, 得到4件方解石脉样品(HNC-ESR01、 HNC-ESR02、 HNC-ESR03、 HNC-ESR04)的年龄分别为(7.1±0.8)ka、 (7.1±0.9)ka、 (7.3±1.7)ka、 (6.9±1.5)ka, 年龄数据集中, 平均年龄为(7.1±1.3)ka, 指示该断层在不晚于距今(7.1±1.3)ka的时间段内发生过活动。年龄结果与该地区探槽工作揭示的古地震事件发生时间((6 130±30)~(6 320±40)a BP)在误差范围内吻合, 表明断裂带方解石脉ESR定年是活动断裂和古地震研究的一种有效的年代学方法。但需要注意的是, ESR年龄仍存在误差较大的问题, 在后续工作中需要进一步完善。另外, 文中采用了5种拟合函数(LIN、 SSE、 DSE、 EXP+LIN、 Dgamma)计算方解石脉样品的等效剂量值, 结果表明, SSE函数提供了最佳的拟合效果。

关键词: 川滇菱形块体, 龙蟠-乔后断裂, 方解石脉, ESR定年, 古地震

Abstract:

The Sichuan-Yunnan region is located in the southeastern part of the Qinghai-Tibet Plateau. Because of the compression and collision dynamics of the Indian Plate and the Eurasian Plate, the tectonic deformation is strong and seismic activities occur frequently. There have been many earthquakes above magnitude 7.0 in history. A series of active fault zones have developed in the region, among which the Sichuan-Yunnan rhombus block bounded by multiple active faults has attracted great research interests in recent years. The Longpan-Qiaohou fault zone is a boundary fault of the Sichuan-Yunnan rhombus block. The fault zone starts from Longpan in the north, passes through Jiuhe, Jianchuan, and Shaxi in the south, and ends at Qiaohou. It is about 120km long and the fault trend is 15°~20°. This fault zone is large in scale and highly active, with frequent seismic activity, complex mechanical properties, and variable movement patterns. The Mesozoic movement was intense. In the early Cenozoic, compression-thrust movement was dominant, and in the late Cenozoic, tension-strike movement was dominant. Since the Holocene, the fault zone has been characterized by left-lateral strike-slip movement with normal faulting properties, and earthquakes of magnitude 5 or above have occurred many times. Therefore, studying the activity of this fault zone is of great significance for the prediction and evaluation of regional strong earthquake risk. Thick calcite veins are well developed on the Henancun Fault of the Jianchuan section of the Longpan-Qiaohou fault zone, providing very valuable materials for fault dating. Calcite veins are coseismic rapid precipitation formed during seismic activity or syntectonic precipitation that filled along fractures after seismic activity. Therefore, their ages represent the latest time at which seismic activity occurred. Previous studies have shown that tensional fissures formed during coseismic events can close in a short period of time(days to months), suggesting that the filling of calcite veins within fault fissures is a relatively rapid process. This paper uses the ESR method to conduct dating study on the calcite veins in the study area. The results show that the ages of the four calcite veins(HNC-ESR01, HNC-ESR02, HNC-ESR03 and HNC-ESR04) are: (7.1±0.8)ka, (7.1±0.9)ka, (7.3±1.7)ka and (6.9±1.5)ka, respectively. The age results are concentrated, and the average age is(7.1±1.3)ka, indicating that the fault was active no later than(7.1±1.3)ka. The age results are consistent within the error range with the second paleoseismic event time revealed by trenching work in the area(between(6 130±30)a BP and(6 320±40)a BP), indicating that the dating of ESR in the fault zone is an effective dating method for the study of active tectonics and paleo-earthquakes. It is an effective chronological method for research, but it can be seen that compared with 14C and luminescence dating, the error of ESR results is relatively large. For faults with short earthquake recurrence intervals, it is still very challenging to accurately judge their activity. In the follow-up work, it is necessary to further improve the experimental process and reduce experimental errors, including refinement of sample pretreatment, accurate monitoring of irradiation dose, and accurate calculation of dose rate. In addition, by using five fitting functions(LIN, SSE, DSE, EXP+LIN and Dgamma)to calculate the equivalent dose values of calcite vein samples in this study, we found that the SSE function is capable of providing the best fitting effect.

Key words: Sichuan-Yunnan rhombus block, the Longpan-Qiaohou Fault, Calcite vein, ESR dating, paleo-earthquakes