皖赣两省地质公园造景花岗岩的岩石特征、形成时代及景观成因

Petrological and Geochronological Features of the Granites in Global and National Geoparks in Anhui and Jiangxi Province and Their Contributions to Landscape

皖赣两省气候宜人,旅游资源丰富.黄山、三清山、天柱山、九华山、牯牛降等地质公园更是以独特的花岗岩地貌景观闻名于世.通过对地质公园内造景花岗岩进行年代学、岩石学、地球化学等方面的研究,证明上述地质公园内的花岗岩集中形成于135～125 Ma,属于早白垩世强烈岩浆活动的产物.这些花岗岩高硅、富碱、过铝,轻重稀土分馏不明显,Eu强烈亏损,稀土配分曲线呈海鸥型;强烈亏损Ba、Sr、P、Ti,形成四个明显的凹槽,具有造山后铝质A型花岗岩的岩石地化特征,属于铝质A型花岗岩或者高分异花岗岩.上述花岗岩主要形成于造山后伸展的构造背景.该构造背景下产出的花岗岩以浅色矿物为主,暗色矿物含量稀少,抗风化蚀变能力更佳;并具有多组密集的原生节理,对花岗岩地貌景观的形成起着极其重要的控制作用.

There are pleasant climate and abundant tourism resources in Anhui and Jiangxi Provinces.Huangshan,Sanqingshan,Tianzhushan,Jiuhuashan and Guniujiang national geoparks are well known for their unique granitic geomorphologic landscapes.Geochronology,geochemistry,petrology study on these granites were conducted,and the result constrained their formation time to 135 ～ 125Ma,belonging to the product of intensive magmatic event happened in early Cretaceous.These granites are riched in SiO2 and alkali,peraluminous,without obvious fractionation between LREE and HREE,profoundly depleted in Eu that the REE pattern is in seagull form.They are tremendously depleted in Ba,Sr,P,Ti,featuring the post-collision aluminous A-type granite geochemistry characteristics,and should belong to aluminous A-type granites or high-differentiation granites.All granites mentioned above formed under a post-collisional extensional tectonic setting,where the granites are featured by high content of light-colored minerals but little dark minerals,with excellent weather resistance and several groups of primary joints,having great impact on the formation of granitic geomorphologic landscapes.