| 河砂岩屑磷灰石裂变径迹模拟流域热史——以藏东南察隅河为例 |
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| 引用本文： | 孙东霞,钟大赉,季建清,涂继耀.河砂岩屑磷灰石裂变径迹模拟流域热史——以藏东南察隅河为例[J].地球物理学报,2015,58(2):613-627. |
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| 作者姓名： | 孙东霞 钟大赉 季建清 涂继耀 |
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| 作者单位： | 1. 中国科学院地质与地球物理研究所, 北京 100029;
2. 北京大学地球与空间科学学院, 北京 100871 |
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| 基金项目： | 国家自然科学基金项目(40472100,40872149,41302280,41472175)资助 |
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| 摘 要： | 河砂岩屑热年代学被广泛应用于揭示造山带和流域范围内热演化历史.由于受到地貌特征、剥蚀速率的空间分布、年龄与高程关系等多种因素的影响,河砂岩屑热年代学年龄所代表的意义存在多解性.本文提出了一种利用地貌形态特征和实测河砂热年代学数据模拟流域热史的计算模型.该模型首先利用DEM数据计算流域高程分布特征,通过数据中各象元对应的坡度角大小定量计算剥蚀速率的空间分布,以确定不同高程区域对河砂岩屑样品组分的贡献量.然后根据区域地质特征建立多种可能的热史年龄-高程关系,并模拟计算出与设定的年龄-高程关系相对应的河砂年龄概率分布曲线.最后,通过对模拟河砂年龄概率分布曲线与实测分布曲线的匹配度进行卡方检验,选取最可能形成实测河砂年龄分布的年龄-高程关系,即代表了流域真实的热史演化.通过河砂岩屑磷灰石裂变径迹方法将该模型应用于藏东南地区察隅河两条支流桑曲和贡日嘎布曲流域,模拟计算结果表明两个地区的热史演化均具有多阶段的特征,桑曲流域在38~7Ma之间均匀冷却,对应的剥露速率约为0.14km/Ma,7 Ma以来剥露速率加快,达到1.62km/Ma;贡日嘎布曲的热史年龄记录比桑曲新,18~14 Ma的隆升速率为0.32km/Ma,14~8 Ma比较稳定;8 Ma以来隆升速率逐渐加快,8~5 Ma对应的隆升速率为0.21km/Ma,5~3 Ma为0.43km/Ma,3~1.1 Ma为0.83km/Ma.桑曲的模拟计算结果与前人利用该区域基岩年龄数据所揭示的热史演化特征及剥露速率基本吻合,表明该方法可以准确模拟河砂岩屑年龄所代表的流域热史特征.因此,在地形险峻或者冰川覆盖而无法获取基岩样品的野外地区,可以通过采集河砂样品替代基岩剖面模拟地质体热史特征.
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| 关 键 词： | 河砂岩屑 磷灰石裂变径迹 察隅河 年龄-高程关系 |
| 收稿时间： | 2014-05-12 |
Inversion model of drainage basins' tectono-thermal evolution through detrital AFT ages: A case study of Chayu River in southeastern Tibet |
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| SUN Dong-Xia;ZHONG Da-Lai;JI Jian-Qing;TU Ji-Yao.Inversion model of drainage basins' tectono-thermal evolution through detrital AFT ages: A case study of Chayu River in southeastern Tibet[J].Chinese Journal of Geophysics,2015,58(2):613-627. |
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| Authors: | SUN Dong-Xia;ZHONG Da-Lai;JI Jian-Qing;TU Ji-Yao |
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| Institution: | 1. Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029, China;
2. Key Laboratory of Orogenic Belt and Crustal Evolution, School of Earth and Space Sciences, Peking University, Beijing 100871, China |
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| Abstract: | Detrital thermochronology data is widely used in revealing the tectono-thermal evolution of drainage basins in orogen belts. Due to the impact of many factors, such as drainage topographic features, the spatial distribution of erosion, the age-elevation relationship and so on, multiple solutions exist for the significance of detrital thermochronology data. Among such factors, the assumption of uniform spatial erosion maybe not rigorous. An inversion model was suggested to compute the tectono-thermal evolution of drainage basins using landform data and observed detrital thermochronology data. In this model, the distribution of altitudes is calculated using DEM data of drainage basins; slope angles are used to quantify spatial erosion rates for different altitudes; then different elevations' relative sand contribution ratios to detrital sample are determined. The detrital ages was acquired through apatite-fission-track (AFT) analysis. A variety of possible age-elevation relationships are randomly set, and the density distribution curve of detrital ages is calculated according to the settled relationships. Through the Chi-square test of observed and calculated age density distribution curve, the most probable age-elevation relationship is chosen which represents actual tectono-thermal evolution of drainage basin.The inversion model was used to investigate the evolution of drainage basins of Sangqu River and Gongrigabu River, which are two tributaries of Chayu River in southeastern Tibet. Two modern river sand samples from the catchments were analyzed by AFT method. The cooling ages of Sample CY from Sangqu River ranges from 5.8 to 38.2 Ma. The age range for another sample GR which from Gongrigabu River is 1.1~18.2 Ma. Two age-elevation relationships derived from the catchments' inversion results show that tectono-thermal evolutions of two drainage basins are both divided into several phases. The different stage corresponds to different estimated exhumation rate. The drainage basin of Sangqu River was uniformly exhumed between 38 and 7 Ma, and the exhumation rate was about 0.14 km/Ma; from 7 Ma to present the basin was fast exhumed and the corresponding exhumation rate was about 1.62 km/Ma. The drainage basin of Gongrigabu River was uniformly exhumed between 18 and 14 Ma, and the exhumation rate was about 0.32 km/Ma; the basin was relatively stable afterward; since 8 Ma the exhumation rate increased to 0.21 km/Ma during 8~5 Ma, 0.43 km/Ma during 5~3 Ma and 0.83 km/Ma during 3~1.1 Ma respectively. The observations of AFT ages across two tributaries of Chayu River lead to different tectono-thermal evolution of this area. First, the catchment of Gongrigabu River record younger cooling histories than Sangqu River. Second, the model result for Sangqu River is consistent with the exhumation rates previously reported in the same region through bedrock sample ages. It demonstrates that the inversion model in this paper can accurately uncover the tectono-thermal evolution represented by detrital thermochronology data. Therefore, in areas with high relief or covered with glaciers where bedrock samples are difficult to be obtained, detrital samples can be good substitute in revealing regional tectono-thermal evolution. |
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| Keywords: | Detrital Apatite fission track Chayu River Age-elevation relationship |
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