四川盆地东部弧形构造控制的地形和水系发育

利用构造地貌学的研究方法,基于数字高程模型(DEM)数据对四川盆地东部大巴山和川东-湘鄂西弧形带的地形特征和水系样式进行深入剖析,结果表明: 1)弧形构造变形机制控制了大尺度地形特征。在大巴山弧形带的逆冲推覆机制作用下形成高海拔-高起伏地形,而在川东-湘鄂西弧形带的拆离滑脱机制作用下形成高海拔-低起伏地形。2)弧形构造扩展模式控制了水系样式。大巴山弧形带"推土机"式扩展模式导致山脉前缘发育横向水系,而川东-湘鄂西弧形带则表现为"三维"构造扩展,即在垂直构造走向递进式扩展的同时,还伴随有平行构造走向从中央向两侧的扩展,此种模式导致弧形带发育由中央分水岭分隔的纵向水系。弧形构造控制的地形和水系发育规律还暗示了长江三峡的成因。长江三峡很可能是在川东-湘鄂西弧形构造变形阶段首先发育先成河,而后由于构造叠加作用伴随河流下切而形成的深切峡谷。

STRUCTURAL CONTROL ON TOPOGRAPHY AND DRAINAGE DEVELOPMENT IN ARCUATE FOLD-THRUST BELTS IN EASTERN SICHUAN BASIN

Based on DEM(Digital Elevation Model),the topography characters and drainage patterns are analyzed in two arcuate fold-thrust belts in eastern Sichuan basin,the Dabashan fold-thrust belt and the eastern Sichuan-western Hubei and Hunan fold-thrust belt.They are both formed as thin-skinned fold-thrust belts during Late Jurassic to Cretaceous,and involved the Paleozoic platform sequence and Late Triassic-Jurassic foreland sequence.Our results indicate that 1)the ancient structural deformation control the distribution of the large-scale topography today in the two arcuate fold-thrust belts.The high-elevation,high-relief topography in Dabashan fold-thrust belt is dominantly related to the SW oriented thrusting structures established during Late Jurassic to Early Cretaceous.In contrast,the high-elevation,low-relief topography in eastern Sichuan-western Hubei and Hunan fold-thrust belt is highly related to the NW oriented thin-skinned folding structures established during Late Cretaceous|2)the kinematics of thrusting and folding propagation control the present-day drainage pattern in the two arcuate fold-thrust belts.The Dabashan fold-thrust belt is dominated by range-parallel rivers developed during SW oriented thrusting propagation,while the eastern Sichuan-western Hubei and Hunan fold-thrust belt is dominated by range-transverse rivers developed during lateral propagation of the fold-thrust belt.Such kinematic of lateral propagation caused the along-strike uplift first occurring on the "midline" of the eastern Sichuan-western Hubei and Hunan fold-thrust belt,leading to a "midline" drainage divide between the SW-flowing and NE-flowing range-parallel rivers.Our results also provide new clues for Yangtze River evolution in the Three Gorges regions.We interpret this segment of Yangtze River to be an antecedent range-parallel river that was formed during Early Cretaceous E-W trending deformation.The Gorges could not have been cut across until the late stage NE trending deformation occurred and superposed onto the early stage E-W folds during Late Cretaceous or later.