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| 东喜马拉雅构造结更新世两期抬升-剥露事件的裂变径迹证据 | |
| 引用本文： | 雷永良,钟大赉,季建清,贾承造,张进.东喜马拉雅构造结更新世两期抬升-剥露事件的裂变径迹证据[J].第四纪研究,2008,28(4):584-590. |
| 作者姓名： | 雷永良 钟大赉 季建清 贾承造 张进 |
| 作者单位： | 1. 中国石油勘探开发研究院,北京100083;中国科学院地质与地球物理研究所,北京100029 2. 中国科学院地质与地球物理研究所,北京,100029 3. 北京大学地球与空间科学学院,北京,100871 4. 中国石油天然气股份有限公司,北京,100010 5. 中国地震局地质研究所,北京,100029 |
| 基金项目： | 国家自然科学基金项目 , 中国科学院知识创新工程重要方向项目 |
| 摘 要： | 对出露在东喜马拉雅构造结南迦巴瓦地区那木拉峰的片麻岩进行了系统垂向上的磷灰石裂变径迹取样分析,在3393～4537m取样高程内的10个样品获得的磷灰石裂变径迹分析结果显示:中值年龄在0.64～1.58Ma之间,平均封闭径迹长度在14.0～15.2μm之间,标准偏差在1.0～3.5μm之间。其中,径迹长度数据为这一地区的首次报道,可以为数据分析的可靠性提供重要保证。通过利用裂变径迹的"香蕉图"模式分析,在这批年龄结果中进一步区分出了代表混合年龄的样品组分和代表事件年龄的样品组分。事件年龄揭示这一地区在更新世有两期抬升-剥露事件的记录,时间分别为1.10±0.24Ma和0.65±0.08Ma。而磷灰石裂变径迹年龄在剖面线上的空间分布显示山体内部的高海拔地区年龄较新,向边缘低海拔地区逐渐变老的趋势。这种分布特征与早期多雄拉-那木拉褶皱构造变形无关,是东喜马拉雅构造结地区正处于快速抬升-剥露过程中的一种指示。据地温梯度30～40℃/km推算的1Ma以来的平均视剥露速率约为2.43～3.24mm/a。而结合前人的研究成果分析,这一地区快速地抬升-剥露过程可能自3Ma已发生。东喜马拉雅构造结1.10Ma和0.65Ma的抬升-剥露事件可以与青藏高原隆起过程中周缘地区的"昆黄运动"、气候转型和沙漠化等同期响应事件在年代学上建立联系。青藏高原的周缘隆起在更新世时期表现出的活动响应具有准同时的特征。 |
| 关 键 词： | 磷灰石裂变径迹 抬升-剥露 东喜马拉雅构造结 南迦巴瓦 更新世 |
| 收稿时间： | 2008-03-02 |
| 修稿时间： | 2008-04-08 |
FISSION TRACK EVIDENCE FOR TWO PLEISTOCENE UPLIFT-EXHUMATION EVENTS IN THE EASTERN HIMALAYAN SYNTAXIS |
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| Lei Yongliang,Zhong Dalai,Ji Jianqing,Jia Chengzao,Zhang Jin.FISSION TRACK EVIDENCE FOR TWO PLEISTOCENE UPLIFT-EXHUMATION EVENTS IN THE EASTERN HIMALAYAN SYNTAXIS[J].Quaternary Sciences,2008,28(4):584-590. | |
| Authors: | Lei Yongliang Zhong Dalai Ji Jianqing Jia Chengzao Zhang Jin |
| Institution: | 1. Institute of Petroleum Exploration and Development, PetroChina, Beijing 100083; 2. Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029; 3. School of Earth and Space Sciences, Peking University, Beijing 100871; 4. PetroChina Company Limited, Beijing 100010; 5. Institute of Geology, China Earthquake Administration, Beijing 100029 |
| Abstract: | Located in the front edge of the India-Eurasia Collision,the Eastern Himalayan Syntaxis is an important eastern end hinge in the Himalayan orogenic Belt,with orogenic structures turn sharply.In this area,Mt.Namche Barwa(or Namjag Barwa)is up to 7782m with a minor peak in Nam-La,Mt.Giala Peri up to 7152m and the Yarlung Zangbo Great Canyon a deep-cutting gorge.In this paper,the ten gneiss samples collected from Nam-La vertical profile,Mt.Namche Barwa in the Eastern Himalayan Syntaxis have been analyzed by using apatite fission track(AFT)technique.The AFT analyses of these samples from 3393m to 4537m height show their central ages ranging from 0.64Ma to 1.58Ma,mean confined track lengths ranging from 14.0μm to 15.2μm,and length standard deviations ranging from 1.0μm to 3.5μm.And the track length data,which can help test the reliability of fission track ages,are reported for the first time in this region.Using boomerang pattern of AFT analysis,mixed ages and event ages are clearly distinguished from all datum results.The event ages are 1.10±0.24Ma and 0.65±0.08Ma,which indicate two uplift-exhumation events in Pleistocene.From the top to the bottom,the AFT ages of samples are gradually older and older.In the Eastern Himalayan Syntaxis,this characteristic may not link to the early fold deformations of Nam-La but the process of rapid uplift-exhumation in Late Cenozoic time.Assuming that the geothermal gradient is of 30～40℃/km,the mean exhumation rates calculated in the study area are ca.2.43～3.24mm/a since 1Ma.Combining with previous studies,however,the process of rapid uplift-exhumation may have occurred since 3Ma.In the eastern Himalayan Syntaxis,the uplifting-exhumation events in 1.10Ma and 0.65Ma may associate with the responses to the margin uplifting of the Tibetan Plateau,such as the"Kunlun-Huanghe movement",climatic shift,and desertification in China.All of these events in the Pleistocene are coeval to some extent. |
| Keywords: | apatite fission track(AFT) uplift-exhumation eastern Himalayan syntaxis Namche Barwa Pleistocene |
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