CENOZOIC FAULT ACTIVITY OF THE SOUTHERN SEGMENT OF THE LONGMENSHAN THRUST BELT：EVIDENCE FROM LOW-TEMPERATURE THERMOCHRONOLOGY DATA

doi:10.3969/j.issn.0253-4967.2013.03.005

Abstract

Abstract:

The Longmen Shan,located at the eastern margin of the Tibetan plateau,is a steep and high exhumation area. In recent years,the 2008 Wenchuan M_W7.9 earthquake and the 2013 Lushan M_S7.0 earthquake occurred,and researchers presented a lot of low-temperature thermochronology data of the Longmen Shan and adjacent area. In this paper,we provide 4 ZFT ages and 4 AFT ages for the southern segment of the Longmenshan Thrust Belt(LTB),where the low-temperature thermochronology data are still few. Combining with previous researches,we get the Cenozoic exhumation history of the Baoxing Massif,located at the southern segment of the LTB,and new knowledge about the Cenozoic activity of the southern segment of the LTB.The Baoxing Massif began quickly cooling in the early Cenozoic,with the cooling range exceeding 225℃,while the cooling range of the Pengguan Massif in the central segment of the Longmen Shan is between 185～225℃.The four AFT ages in the Baoxing Massif are between 2.7～5.0Ma,which are younger than that in the Pengguan Massif,and it indicates that the late-Cenozoic cooling rate of the Baoxing Massif is bigger than that of the Pengguan Massif. Under this assumption that the surface temperature is 15℃ and the paleo-geothermal gradient is 30℃/km,the average exhumation rate from 3～5Ma to present is about 0.63～1.17mm/yr. The low-temperature thermochronology data indicate that the differential exhumation is concentrated in the Beichuan-Yingxiu Fault and the Jiangyou-Guanxian Fault in the central segment of the LTB,while it is dispersed in a wider region along the two branches of the Shuangshi-Dachuan Fault and the faults and folds to the east,in the southern segment.

Key words: Lushan earthquake, Low-temperature thermochronology, eastern Tibet, Baoxing Massif, Longmen Shan

摘要：

龙门山位于青藏高原东边缘,地形陡变,剥蚀作用强烈。近年来先后经历了2008年汶川M_W7.9地震和2013年芦山M_S 7.0地震,多位学者对龙门山地区做了大量的低温热年代学研究。文中在研究程度相对薄弱的龙门山南段补充了4个锆石裂变径迹年龄和4个磷灰石裂变径迹年龄,结合前人的低温热年代学数据结果得出,宝兴杂岩从新生代早期开始快速冷却,降温幅度超过225℃,而龙门山中段的彭灌杂岩降温幅度为185～225℃。宝兴杂岩的4个裂变径迹年龄分布在2.7～5Ma,相对彭灌杂岩较年轻,表明晚新生代以来宝兴杂岩的冷却速率要高于彭灌杂岩。在地表温度为15℃和古地温梯度为30℃/km的假设下,宝兴杂岩距今3～5Ma以来的平均剥露速率为0.63 ～1.17mm/a。低温热年代学数据揭示出龙门山中段的差异剥蚀集中在北川-映秀断裂和江油-灌县断裂上,而南段的差异剥蚀分散在更宽范围内的双石-大川断裂(南、北2个分支)及其东侧的断层和褶皱。

关键词: 芦山地震, 低温热年代学, 青藏高原东缘, 宝兴杂岩, 龙门山

CLC Number:

P597

TAN Xi-bin, LEE Yuan-hsi, XU Xi-wei, CHEN Wen-yu, XU Chong, YU Gui-hua. CENOZOIC FAULT ACTIVITY OF THE SOUTHERN SEGMENT OF THE LONGMENSHAN THRUST BELT：EVIDENCE FROM LOW-TEMPERATURE THERMOCHRONOLOGY DATA[J]. SEISMOLOGY AND GEOLOGY, 2013, 35(3): 506-517.

谭锡斌, 李元希, 徐锡伟, 陈玟禹, 许冲, 于贵华. 低温热年代学数据对龙门山推覆构造带南段新生代构造活动的约束[J]. 地震地质, 2013, 35(3): 506-517.

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