剑川盆地第三纪以来地壳变形的地质分析与FT测年  

Geological Analysis and FT Dating of Crustal Deformation in the Jianchuan Basin Since the Tertiary

作　　者：向宏发[1] 张秉良[1] 张晚霞[1] 虢顺民[1] 万景林[1] 

机构地区：[1]中国地震局地质研究所,北京100029

出　　处：《地质学报》2009年第2期230-238,共9页Acta Geologica Sinica

基　　金：国家自然科学基金(编号40272087;40572127)资助的成果

摘　　要：通过地层沉积、褶皱变形、断裂活动性质转化等分析可以看出:始新世早期,剑川盆地的宝相寺组(Eb)构成轴向近南北向的褶皱和与之相伴的NNE向盆缘主断裂右旋逆推运动;中新世以来,双河组(N1s)地层的褶皱走向为NE向,此期间盆缘主断裂变为左旋逆推性质;上新世以后(N2-Q)剑川地壳块体以伸展裂陷为主,伴随地壳的差异隆升,盆缘断裂以正断裂为主,同时有晚上新世粗面岩沿裂隙侵位。裂变径迹测年(简称FT测年,下同)表明:遭褶皱变形的双河组(N1s)地层年龄为(15.8±1.8)Ma;盆缘主断裂的左旋逆推运动发生在(5.4±1.1)Ma,后期正断裂运动发生在(1.6±0.7)Ma;被断裂抬升的剑川组(N2j)和晚上新世(τ6)粗面岩的FT年龄介于(2.4±0.85～3.1±0.5)Ma。上述资料揭示:盆地近EW向挤压作用发生在15Ma.BP,而区内NW向挤压运动发生在(15～5.4)Ma.BP间,后期正断引张运动开始于距今5.4Ma前,强烈活动于(1.5～1.6)Ma.BP。也即区内地壳变形由早期(E3)近EW向挤压经中新世(N2)NW向挤压至上新世(N2)后,则以引张裂陷作用为主。该变形过程可能与印度洋板块推挤、青藏高原隆升及高原物质作SE向流展的地壳动力学过程有关。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 traehyte 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.

关 键 词：地质分析 FT测年 地壳变形 第三纪以来 剑川盆地 

分 类 号：P542[天文地球—构造地质学]