湖南炎陵印支期隔槽式褶皱形成机制

Forming Mechanism of Indosinian Trough-Like Folds in Yanling Region,Hunan

为查明湘东南印支期褶皱特征及形成机制,对炎陵地区进行了详细的地质填图和野外观察。调查表明,泥盆纪跳马涧组与前泥盆纪褶皱基底间不整合界面在空间上组成背、向斜,表明褶皱基底参与了印支期褶皱作用。平面上,向斜出露宽度及延伸规模明显较背斜小,向斜转折端表现清楚且狭窄尖长,而背斜转折端没有清楚显示;剖面上,不整合界面靠近向斜核部产状陡,向两翼方向迅速变缓。反映出背斜平缓开阔、向斜紧闭狭窄且侧翼呈上拱尖棱状的隔槽式褶皱特征。印支期褶皱呈北北东向,横跨在前泥盆纪褶皱基底中加里东期北西向褶皱之上,但未对加里东期褶皱造成明显地叠加改造效应,说明前泥盆纪地层在印支运动中没有发生明显地弯滑褶皱作用。露头显示,褶皱过程中盖层未沿不整合界面产生明显滑脱。因此,认为炎陵地区隔槽式褶皱形成于基底(厚皮式)横向收缩与压扁作用,并从理论上论证了其隔槽式褶皱不可能是盖层沿基底滑脱的产物,纠正了前人的薄皮式观点。

This paper carried out regional geological survey in Yarding area in order to study the characteristics and forming mechanism of the Indosinian folds in southeast Hunan. The survey declared that the uncomformity surface between Devonian Tiaomajian Formation and Predevonian basement make up anticlines and synclines, which indicate that the folded basement participated in Indosinian folding. On surface, the synclines have less width and less extending size than the anticlines; the hinge ends of synclines are clear, narrow and sharp, while the hinge ends of anticlines aren＇t distinct. At section plane, the uncomformity surface is steep near the syncline core, and become gentle toward two limbs. Above features show pattern of trough like folds with gentle and wide anticlines as well and narrow close clinoriums. The NNE- directed Indosinian folds stride across the Caledonian NW-directed folds in the predevonian basement, and didn＇t transform the Caledonian folds evidently. Outcrops show that the cover did not detach along the uneomformity surface. The trough like folds in Yarding region were formed during the transverse shrinking and flattening of the basement （thickskin）, the trough like folds were not the production of cover detachment along basement, so the former standpoint of thin skin about it was corrected.