下花园地区下马岭组第三段中尖棱褶皱特征及地质意义

Characteristics and Geological Importance of hevron Folds in Third Segment of the Xiamaling CFormation at Xiahuayuan,Hebei Province

尖棱褶皱是在下列特定地质条件下形成的:构造变动比较强烈的地区;构成尖棱褶皱的介质是以层理发育的薄层脆性岩层为主,间夹塑性较大的薄层页岩,尖棱褶皱的底部和上部要有较厚的塑性较大的页岩层;形成尖棱褶皱的应力方式为主压应力平行或近于平行层理。此外,①尖棱褶皱的空间分布反映较大规模的构造型式。②各部位尖棱褶皱的轴面走向和枢纽延伸方向与所在部位的大褶皱的轴面走向和枢纽延伸方向,以及逆断层的走向基本一致,尖棱褶皱与所在部位大规模同形褶皱的枢纽倾伏方向也近似一致.③各部位尖棱褶皱的变动强度,膝折带的应变大小及小断层的发育情况,反映了所在部位的较大规模构造变动的强烈程度.④在同样构造力的作用下,薄的脆性岩层比厚的脆性岩层更易形成尖棱褶皱和膝折褶皱。尖棱褶皱、膝折褶皱和共轭褶皱常共生在一起,说明它们的形成机制是相同的,箱状褶皱的共轭膝折面所夹钝角在110°—120°之间,其平分线方位与同期形成的大规模构造受力方向是一致的.⑤膝折带不仅能在低温高压地质条件下形成,在低温低压的地质条件下也能形成.

The special conditions by which the chevron folds were formed are as follows:the area where the folds took place was strongly tectonic deformed,the media constructing chevron folds were mainly stratification well-developed,thinner and brittler rock beds intercalated with more pla- stic thin-beded shales,there must been thicker and more plastic shale beds at the basal and the top parts of the chervon folds,and in addition the stress pattern was marked by that the principle compressive stress was parallel or nearly parallel to the stratification. Moreover,there are other reatures,firstly the spartial distribution of the chervon folds reflected the tectonic pattern in rather larger scale; secondarilythe strike of axial plane and the streching direction of the hinge in various parts of the chervon folds were basically consistent with both those of the dependent huger folds and the strike of the reversed fault,also the chervon folds were nearly consistent with the plunging di- rection of the hinge of the depen tent large folds in identical style;third- ly the intensity of deformation all the chervon folds,the strain dimens- ions of the kink-bands and the developement of the minor faults reflect- ed the intensity of all the dependent larger tectonic deformation;fourthly under the same tectonic force,the thinner and brittler beds were more easier to form chervon folds and knee folds than the thicker and brittler beds, the common close association of the chervon folds,knee folds and conjuga- ted folds suggested that their mechanisms of formation were identical,the obtuse angle formed by the conjugated kind-plants of the box folds varied between 110° to 120° and the bisector direction of this angle was consistent with the direction of force exerting on the synchronous dependent larg scale tectonics;and finally the kink-bands could be formed at the geologicai condition not only under low temperature and high pressure but also under low temperature and low pressure.