岷江上游坡断型裂点迁移速率与构造隆升历史研究

doi:10.13745/j.esf.sf.2023.11.60

摘要/Abstract

摘要：

基岩河道中坡断型裂点是构造活动和水力侵蚀共同作用的产物,根据其空间分布特征可以反演区域构造隆升历史和地貌演化过程。本文采用坡度-面积分析法和积分分析法识别出岷江上游坡断型裂点和裂点带,并结合河道纵剖面反演岷江上游的隆生历史和河口裂点形成时间,对坡断型裂点溯源迁移过程和速率进行模拟。研究结果表明:(1)岷江上游流域坡断型裂点有较明显的分层特征,干流及支流当前形成了海拔1 300、2 500和3 500 m的3条裂点带,其对应的河道信息说明岷江上游流域早更新世以来经历了3次较为强烈的构造运动;(2)构造隆升历史大致可分为4个时期,分别为缓慢隆升(20~12 Ma)、加速隆升(12~8 Ma)、稳定隆升(8~2 Ma)和强烈隆升(2 Ma以来),其中在2.0 Ma以来,岷江上游流域的隆升速率达到0.6 mm/a;(3)3 500 m裂点带对应的坡段型裂点水平迁移平均速率为38.0~127.9 km/Ma,其最小残差平方和最优拟合度均表明1.3 Ma是裂点最可能产生的时间,其溯源迁移速率为79.1 km/Ma。

关键词: 裂点, 河道纵剖面, 构造历史反演, 裂点迁移

Abstract:

The regional tectonic uplift history and landscape evolution can be simulated based on the spatial distribution characteristics of slope-break knickpoints in bedrock channels, which result from the combined action of tectonic activity and water erosion. This study identifies slope-break knickpoints and knickpoint belts in the upper reaches of the Minjiang River using slope-area analysis and integral analysis methods. It then simulates the uplift history, formation times of river mouth knickpoints, and headwater migration processes and rates of slope-break knickpoints, combined with longitudinal river profiles. The findings are as follows: (1) In the upper reaches of the Minjiang River, slope-break knickpoints exhibit distinct layered distribution characteristics, forming three knickpoint belts at 1300 m, 2500 m, and 3500 m in the main channel and tributaries. Data from these knickpoint belts suggest that the area has experienced three relatively intense tectonic movements since the Early Pleistocene. (2) The tectonic uplift history in this region can be divided into four periods: slow uplift (20-12 million years ago), accelerated uplift (12-8 million years ago), stable uplift (8-2 million years ago), and intense uplift (since 2 million years ago), with an uplift rate of 0.6 mm/a since 2 million years ago. (3) The average horizontal migration rate of the 3500 m slope-break knickpoint ranges from 38.0 to 127.9 km/Ma, likely forming around 1.3 million years ago with a migration rate of 79.1 km/Ma according to the minimum residual squares method and optimal fitting method.

Key words: knickpoint, longitudinal river profiles, tectonic history reconstruction, knickpoint migration

中图分类号:

P548

田述军, 温宇航, 伍文洽, 李凯. 岷江上游坡断型裂点迁移速率与构造隆升历史研究[J]. 地学前缘, 2024, 31(4): 314-325.

TIAN Shujun, WEN Yuhang, WU Wenqia, LI Kai. Study on the migration rate of the slope-break knickpoints and the tectonic uplift history in the Minjiang River[J]. Earth Science Frontiers, 2024, 31(4): 314-325.

图/表 12

图1 岷江上游构造与地形分布图

Fig.1 Tectonic and topographic distribution map of the upper Minjiang River

图2 岷江干流坡断型裂点及其上、下游地貌差异

Fig.2 Slope-break knickpoints on the main stream of the Minjiang River and the geomorphic differences between the upper and lower reaches

图3 裂点chi-plot和坡度-流域面积双对数图(据文献[12]补充修改)

Fig.3 Chi-plot and slope-area double logarithmic graph for identifying knickpoints. Modified after [12].

图4 岷江上游坡断型裂点分布图

Fig.4 Distribution of slope-break knickpoints in the upper reach of the Minjiang River

图5 岷江干流和主要支流河道纵剖面及裂点分布

Fig.5 Longitudinal profile and distribution of knickpoints in the main stream and major tributaries of the Minjiang River

图6 黑水河裂点的识别和分布情况 a—黑水河主干流域chi-plot和坡度-流域面积图;b—黑水河和支流河道纵剖面及裂点分布。

Fig.6 (a) Chi-plot and slope-basin area map of the main basin of the Heishui River; (b) Longitudinal profile and distribution of knickpoints in the Heishui River and its tributaries

图7 参考凹度和最佳chi值 a—凹度为0.45和chi间隔1.6时岷江上游所有河道chi-plot(红线代表研究区均值曲线):b—不同chi值间隔下河道chi-plot与实际河道的高程偏差。

Fig.7 (a) Reference concavity and optimal chi value when the concavity is 0.45 and the chi interval is 1.6, the chi-plot of all channels in the upper reaches of the Minjiang River (the red line represents the average curve of the study area); (b) The elevation deviation between the channel chi-plot and the actual channel under different chi value intervals

图8 构造隆升模拟结果 a—无量纲隆升历史(t*为图7b中的chi值);b—根据不同K值模拟的有量纲隆升历史。

Fig.8 (a) Dimensionless uplift history (t* represents the chi value in Fig. 7b); (b) Dimensioned uplift history simulated according to different K values

图9 最佳侵蚀系数和面积指数组合及时间间隔 a—黑水河20组中K和m的最佳组合(红色点代表K和m最佳组合);b—河口裂点不同形成时间假设下的最佳参数组合值。

Fig.9 Optimal combination of erosion coefficient and area index and time interval (a) The optimal combination of K and m in the 20 groups of Heishui river (red dots represent the optimal combination of K and m); (b) The optimal parameter combination values for knickpoints formed at different formation times at the estuary

图10 形成于不同时间的河口裂点模拟迁移速率

Fig.10 Simulated migration rate of knickpoints formed at different times

图11 黑水河流域拟合程度 a—河口裂点不同形成时间下的残差平方和;b—形成于1.3 Ma河口裂点实际位置与模拟位置拟合程度。

Fig.11 Fitting degree of the Heishui River Basin (a) Residual sum of squares under different formation times of knickpoints; (b) The fitting degree between the actual position and simulated position of knickpoints formed at 1.3 Ma estuary

图12 形成于1.3 Ma的河口裂点实际位置与模拟位置的空间分布图

Fig.12 Spatial distribution map of the actual and simulated positions of knickpoints formed at 1.3 Ma

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