Geological Analysis and FT Dating of Crustal Deformation in the Jianchuan Basin Since the Tertiary
Geological Analysis and FT Dating of Crustal Deformation in the Jianchuan Basin Since the Tertiary
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发表时间：
2009
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通讯作者：
W. Jinglin
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作者：
W. Jinglin
通过对地层、褶皱和断裂方式变化的分析，研究了滇西北剑川盆地第三纪以来的地壳形变史。结果表明，在早始新世，宝相寺群(EB)形成了一条近南北向的褶皱，沿NNE向盆缘主干断裂右行逆冲。中新世以来，双河群(N1S)褶皱在盆缘主干断裂转变为左行逆冲时走向北东。上新世(n2-q)以后，剑川地块经历了伸展裂谷作用，盆地边缘出现差异地壳抬升和正断层运动，上新世粗面岩通过裂隙侵入。裂变径迹测年结果表明，双河褶皱群(N1S)的年龄为15.8±1.8 Ma，盆缘主断裂的左旋逆冲年龄为5.4±1.1 Ma，后期断裂的年龄为1.6±0.7 Ma，隆升的剑川群(N2j)和上新世粗面岩的年龄为2.4±0.85 Ma~3.1±0.5 Ma。这些资料表明，盆地的近EW向挤压作用发生在15 Ma B.P.，NW向挤压运动发生在15~5.4 Ma B.P.，后期伸展和正断层作用开始于5.4 Ma B.P.，并在1.5~1.6 Ma B.P.达到顶峰，这意味着研究区地壳变形在始新世早期为近EW向挤压，中新世转变为NW向挤压，上新世以来转变为伸展裂谷。这种地壳形变过程可能与印度板块的推动、青藏高原的隆升和高原物质的东南向流动有关。
Crustal deformation history in the Jianchuan basin of northwestern Yunnan Province since the Tertiary is studied through analyses of strata, folding and variations of faulting modes. The result shows that a nearly NS trending fold formed in the Baoxiangsi group (Eb), with dextral thrust on the main fault along the NNE directed basin rim in the early Eocene. Since the Miocene, the fold in the Shuanghe group (N1s) stroke in NE when the main fault on the basin rim changed into sinistral thrust. After the Pliocene (N2-Q), the Jianchuan block experiences extension and rifting, with differential crust uplift and normal faulting on the basin rim, as well as intrusion of the upper Pliocene trachyte through fissures. The fission track (FT) dating indicates that the folded Shuanghe group (N1s) is of age15.8±1.8Ma, sinistral thrust on the main fault of the basin rim occurred at 5.4±1.1Ma, later faulting at 1.6±0.7Ma, and the ages of uplifted Jianchuan group (N2j) and upper Pliocene trachyte fall in 2.4±0.85Ma～3.1±.5Ma. These data suggest that the nearly EW directed compression on the basin was at 15Ma B.P, NW directed compressive motion occurred in 15～5.4Ma B.P., and the later extension and normal faulting began 5.4Ma B.P. and culminated in 1.5～1.6Ma B.P. It means that the crustal deformation of the study area was nearly EW directed compression in the early Eocene, changed into NW directed compression in the Miocene, and transformed into extension and rifting since the Pliocene. Such a process of crustal deformation is presumably associated the push of the Indian plate, uplift of the Tibetan plateau and southeastward flow of the plateau material.