中更新世以来北天山的向北扩展

Northward spreading of the North Tian Shan since middle Pleistocene

利用深部地球物理结果与浅部地质调查结果进行对比,并基于DEM的地貌分析,研究了中更新世以来北天山向北扩展的造山过程.中更新世以来,北天山地壳中存在南倾的低角度滑脱面,滑脱面之上,逆断裂和褶皱带组成的山前活动构造带整体向北滑脱并缩短变形.中更新世早期,气候暖湿,基岩山脉剥蚀强烈,在山前形成了大规模的洪泛平原.中更新世中期以来,持续的构造活动一方面使山前盆地卷入变形,另一方面使盆地遭受分隔,天山北麓地壳以阶梯式的形式自南向北逐步抬升.中更新世中期约600ka以来,气候越来越干旱,山前盆地地表仅遭受了轻微剥蚀,地壳抬升全部转换为自南向北的地表隆起,隆起的北部向天山靠拢,隆起的南部逐渐成为山系,与天山相连,北天山得以向北扩展.中更新世以来的掀斜隆起造成山麓至盆地高差达1000多米的坡面,为30ka以来的河流下切提供了坡度条件,造成了深达300多米的河流强烈下切.

With the analysis of geophysical interpretation, field work and landform features based on the digital elevation model, we study northward spreading of the North Tian Shan since Mid- Pleistocene. Along the basal decollement which dips to south at a low angle in crust, upper layers which consist of active folds and thrusts were shortened and slipped to north. A flood plain was formed as a result of humid climate in early mid-Pleistocene. The surface of the basin was partitioned into several parts by thrusts and folds. At the same time, partitioned basins were distorted and the crust in the North Tian Shan uplifted and tilted from south to north. Since ~600 ka B.P. in mid-Pleistocene, the climate became increasingly drier in the North Tian Shan. The surface of the northern range front basin was slightly eroded with the low runoff. As a result of shortening, uplift of crust almost totally converted to uplift of the surface. The surface of range-front basin uplifted from south to north. The north part of the uplift was moving closer to the Tian Shan and the south part became a hill of the North Tian Shah. The North Tian Shan was continuing to spread to north due to rock uplift and slight erosion. On the other hand, relief of more than 1000 m induced by continuing uplift and dry climate at a timescale of 600 ka supportedlarge slope for incision of the rivers. Since 30 ka B. P. , the rivers on the north flank of the Tian Shan were intensely incised to about 300 m.