河流纵剖面陡峭指数对庐山构造抬升的指示

doi:10.11821/dlxb201509013

摘要/Abstract

摘要：

庐山是位于江南造山带北缘的断块山,其抬升过程对于认识本区的构造演化至关重要。利用河流纵剖面的形态参数可以定量估算相对的构造抬升速率。基于5 m分辨率的DEM提取了庐山9条主要河流的纵剖面,依据坡度—面积图确定了裂点类型,结合地质图判别出裂点成因,并利用河流水力侵蚀模型计算了稳定态河段的陡峭指数以及凹曲度。结果显示,庐山的河流基本呈过渡态,以发育数量不等的裂点为标志;垂阶型裂点的形成主要与岩石强度不均一有关,而坡断型裂点是侵蚀基准面下降产生的。坡断型裂点以下的基岩河段具有较大的陡峭指数,表明庐山经历了从早期低抬升速率到晚期高抬升速率的转变。庐山受快速抬升影响的河段,陡峭指数具有南高北低的特点,主要是由于庐山整体抬升过程中南部、北部的抬升速率存在一定差异,亦可能是岩性不同造成的。

关键词: 庐山, 河流水力侵蚀模型, 陡峭指数, 构造抬升, 裂点

Abstract:

In this study, we extracted nine river profiles from a 5-m DEM of the Mt. Lushan region. Knickpoints of two types, namely the vertical-step knickpoint and the slope-break knickpoint, are recognized, and are compared with the geological settings to determine their origins. At the same time, we calculated the channel steepness index (k_sn) and concavity (θ) of separated parts of these rivers, using the stream-power incision model. The results show that these rivers are almost in a transient state represented by the occurrence of knickpoints. The vertical-step knickpoints are related to inhomogeneous substrates and the slope-break knickpoints are ascribed to the lowering of the base level due to rapid mountain uplift. The parts of the rivers below the slope-break knickpoint have a relatively large k_sn, which probably indicates a shift from low rate at early uplift to a later high rate. The steepness index in the south of the mountain is larger than that in the north, which might be induced by different uplift rates or substrates.

Key words: Lushan, stream-power incision model, normalized channel steepness index, tectonic uplift, knickpoint

王乃瑞, 韩志勇, 李徐生, 陈刚, 王先彦, 鹿化煜. 河流纵剖面陡峭指数对庐山构造抬升的指示[J]. 地理学报, 2015, 70(9): 1516-1525.

Nairui WANG, Zhiyong HAN, Xusheng LI, Gang CHEN, Xianyan WANG, Huayu LU. Tectonic uplift of Mt. Lushan indicated by the steepness indices of the river longitudinal profiles[J]. Acta Geographica Sinica, 2015, 70(9): 1516-1525.

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流域编号	流域名称	河流长度(km)	流域面积(km²)	拟合河段	k_sn(m^0.9）	凹曲度
R1	庐山垄	14	38	S1	27	0.42
R1	庐山垄	14	38	S2	168	0.55
R2	青玉峡	5	5	-	-	-
R3	三峡涧	12	42	S1	9	0.37
R3	三峡涧	12	42	S2	169	0.51
R4	七里冲	11	19	-	-	-
R5	白沙河	10	29	S1	9	0.20
R5	白沙河	10	29	S2	117	0.24
R6	定慧寺	9	20	S1	93	0.19
R7	剪刀峡	10	14	S1	15	0.49
R7	剪刀峡	10	14	S2	143	0.42
R8	石门涧	13	30	-	-	-
R9	黄龙庵	8	13	-	-	-