大巴山前陆北西向褶皱的厘定及其意义

NW Folding distinguished in the Northwestern Daba Mountains,Central China,and It's Tectonic Significances

大巴山位于南秦岭造山带与上扬子前陆交接部位,其西北缘地区发育规模大、方向各异、叠加特征明显的褶皱构造体系。通过关键地区的褶皱及其叠加变形的几何学、运动学及时空序列的研究鉴别出至少是三期褶皱构造,包括北东—近东西向、近南北—北北西向和北西向褶皱。本文详细介绍北西向褶皱的厘定依据和空间构造要素,研究其对晚侏罗世形成的大巴山弧形褶皱带的叠加改造及过程。根据区域变形的特征分析,以及下白垩统地层卷入北西向褶皱变形的事实,推测这组褶皱形成与早白垩世晚期或其后的收缩变形事件有关,但其地球动力学背景仍需进一步探讨。大巴山地区北西—南东向褶皱的厘定有助于完善和深化大巴山西缘地区构造演化及地壳变形历史的认识。

The Daba mountain is located in complex geological area where the linkage between southern Qinling orogenic belt and Upper Yangtze foreland occurs. Its northwest side shows very conspicuous and spectacular examples of differently-trending system of folds and buckle superposition. Detailed analyses of the kinematic, geometric and spatial relationships between all of the structural generations in the key areas of the northwestern Dabashan support development of the polyphase deformational history with at least three folding phases deformation. These are the NE-near EW trending folds（F,）, near SN--NNW trending folds（Fz） and NW trending folds（F3）. In this paper, the evidence for NW folding deformation as well as the corresponding spatial structural elements are showed. And NW folds（F3） how to reprint and superpose on the late Jurassic Daba arcuate fold belt（F2） is also discussed. Combination of the regional deformation analysis and the fact that Cretaceous red bed were involved, it is thought that the NW folding forming may relate to the contractile deformation during or after the late of the early Cretaceous. The question concerning the cause or driving mechanism of NW trending folds（F3）, however, deserve further attention. To distinguish NW folds in this areas may be significant to understand the tectonic evolution history in the western Dabashan Mountains.