黄山花岗岩节理及对地貌发育的控制

黄山在印支-早燕山陆内造山之后,由于岩石圈的加厚,重力失稳,燕山晚期(早白垩世中晚期)发生岩石圈拆沉、岩石圈减薄,软流圈上涌,后造山伸展发育,地表浅部伸展、断陷盆地发育。早白垩世中期主要发育中酸性的岩浆活动;规模较小,多呈近东西向展布;早白垩世晚期,由于拆沉作用的加强,大规模的岩浆活动发育,以酸性花岗岩为主,规模大,多为岩基状,同时地表浅部断陷盆地内火山喷溢活动发育。区域构造应力场研究成果表明:发育于燕山晚期-早喜马拉雅期的伸展作用所计算的应力场特征则明显的表现为NW-SE的伸展,应力场主要表现为σ1NW-SE的伸展,σ2和σ3近于水平,为典型的伸展应力场;喜马拉雅运动使黄山不断抬升,同时经受风化剥蚀,在第四纪期间,新构造运动使黄山地区发生三次幅度不等的抬升,尤其是距今约200万年的更新世初期,影响了黄山山体更为急剧的上升和沿节理或断裂发育的沟谷强烈侵蚀下切,形成了高逾千米、翘首云天的花岗岩峰林。

THE GRANITE JOINTS AND THEIR CONTROL OVER LANDFORMS IN HUANGSHAN

Lithospheric delamination, lithospheric thinning, asthenospheric uprush, post-orogen extensional development, shallow surface extension and rifted basin development occurred in Huangshan in the late Yanshanian period （mid- and late-Early Cretaceous time） after the Indosinian-early Yanshanian intra=continental orogen, as a result of lithospheric thickening and gravitational instability. In the middle Early Cretaceous, intermediate-acid magmatic activities dominated, but on small scales, mostly and roughly in EW direction; in late Early Cretaceous, owing to intensifying delamination, widespread magmatism mainly formed acid granites, mostly in the form of extensive batholith, meanwhile, volcanic eruptions frequented the shallow-surface rifted basins. Based on regional structural stress field research, calculated stress field feature of the extension developed in late Yanshanian to early Himalayanian period was evidently of a NW-SE extension. The stress field shows NW- SE signature for o~ and sub-horizontality for 02 and 03, thus is a typical extensional kind. The Hymalayanian movement kept uplifting Huangshan, and exposed it to weathering erosion. In the Quaternary, neotectonic movement triggered three times of elevation of Huangshan to different degrees, especially, the early Pleistocene event about 2 Ma ago made the Huangshan mountain body go up abruptly, leading to violent downward cutting of the valleys already developed along joints or rifts, forming up to a thousand meters high granite forests looking up in the sky.