东大别罗田地区纵弯式褶皱及其地质意义

THE BUCKLING FOLD AND ITS GEOLOGICAL SIGNIFICANCE IN LUOTIAN AREA OF EASTERN DABIE MOUNTAINS

野外调查研究发现,东大别罗田片麻岩区广泛发育了轴面倾向SE的纵弯式褶皱,这些褶皱近平行于片麻理。整个罗田地区的片麻理显示它在区域上是一个SE-NW方向上的倒转背斜。三维有限应变分析发现,罗田片麻岩区在核部、翼部的不同位置既有挤压、也有拉伸变形,显示为纵弯式褶皱的成因机制。石英C轴组构显示,罗田片麻岩区主要遭受SE-NW方向上的挤压作用,并在中等温度的中上地壳环境下形成了纵弯褶皱。由片麻理显示的轴面SE倾向的褶皱形成于罗田穹隆形成之后,表明自罗田穹隆开始形成后,罗田地区乃至整个东大别又发生了一次较深层次的挤压作用。这次挤压作用促进了穹隆在早白垩世中晚期的快速隆升。

In Luotian area, many bucking folds occur which are nearly parallel to the gneissosity direction, and the gneissosity shows that it is an overturned anticline striking to SE-NW. Strain analysis for the Luotian area indicates that compression deformation and extension deformation occur in the core and also in the limbs of the Luotian area. These data reflect that the gneiss in Luotian area has suffered buckling. Quartz C-axis fabrics, which usually develop high maxima parallel to the Z-axis, show that the gneiss also suffers SE-NW compression. The SE-NW compression results in the bulking fold in the middle-upper crust. These bulking folds, shaped after the Luotian dome, indicate that Luotian area has suffered a deeper compression after the formation of the Luotian dome. This compression serves to accelerate the uplifting of the Luotian dome during the earlier Cretaceous.