摘要
侏罗纪是中国东南部从特提斯构造域向太平洋构造域发生重大变化的转换期,该时期形成的沉积盆地以及至今保留完好的侏罗纪沉积序列是研究和发掘中生代构造演化信息的理想对象。根据地球动力学特征,将侏罗纪盆地分为后造山盆地(T3-J1)和伸展盆地(J2)2种类型,后者可再分为裂谷断陷和沉积断陷2种。发生在早、中三叠世期间华南与华北块体的碰撞以及华南与东南亚块体的碰撞,基本结束了特提斯洋在华南的历史,导致本区及其邻区先前的浅海盆地关闭,褶皱隆升,形成陆内造山带和山前盆地。岩石组合和古流向研究表明,晚三叠世—早侏罗世期间,水体携带碎屑物从北向南搬运,呈现北高南低的古地理格局;中侏罗世开始,区内古地理格局发生变化,武夷山开始抬升,导致原先北高南低的单向地貌格局变为南北两侧地形高、中间地形低的古地理环境。武夷山地区的沉积序列研究表明,下侏罗统由粗变细,反映水体由浅变深,沉积环境从山前河流→湖滨→湖泊演化,中侏罗统则由细变粗,反映水体变浅,地壳抬升,山体剥蚀,推测其挤压动力来自太平洋板块朝东亚陆缘的俯冲作用。另一方面,在武夷山西缘的闽西—赣南一带,则发生了中国东南部自寒武纪以来最强烈的一次火山喷发活动,形成东西向的陆内裂谷盆地带,盆内堆积双峰式火山岩、碱性—偏碱性玄武岩,并有双峰式侵入岩的形成。通过SHRIMP锆石U-Pb成分测定,获赣南东坑盆地中侏罗世火山岩剖面上部的流纹岩160Ma±1Ma的测年值。研究认为,发生在中侏罗世的地理格局改变、沉积环境变化、闽西—赣南裂谷型火山活动是太平洋板块开始影响华南的重要证据,也是构造转换事件(从挤压到伸展、从特提斯到太平洋)的直接标志。武夷山—南岭东段是中国东南部发生构造转换的重要区段,时间为中侏罗世。
Two types of the Jurassic basin were distinguished in Southeast China, according to their geodynamic features, namely the Late Triassic-Early Jurassic post-orogenic basin and the Middle Jurassic intra-continental extensional basin. The Early Jurassic se- quence in Mount Wuyishan showed that the accumulation was changed from coarse-to fine-grained and the depositional environment was gradually turned deeper, from submontane river to shore-lake and to deep lake. As a distinct contrast, the Middle Jurassic accumulation was changed from clay stone to conglomerate in Southeast China coastal area, indicating that a crustal uplift was underway. Mount Wuyishan was a paleo-geographical separating zone since Middle Jurassic. The Late Jurassic stratum was absent in the most parts of Southeast China. A large-scale bimodal volcanic eruption was taken place in Middle Jurassic, forming W-Fujian to S-Jiangxi intra-continental rift zone of 40km to 60km wide and 200kin long, which was likely the most intensive volcanism in Southeast China since Cambrian period. The concord age of 160Ma± 0.5 Ma was obtained by SHRIMP zircon U-Pb analysis on the rhyolite of Dongkeng basin, providing an upper limit of bimodal eruption time. Basin features indicated that a Middle-Late Triassic depositional environment change occurred from a shallow-sea to an intra-continent in Southeast China, as a tectonic response to the strong collision between the Yangtze and North China blocks. Sedimentary structures recorded a southward direction of Early Jurassic paleo-currents, reflecting their source areas were situated in the north side. The authors proposed that Mount Wuyishan was uplifted as early as Middle Jurassic, followed by a wide E-W trend depression and bimodal volcanism in the western foot of Mount Wuyishan. It was the uplift of the Mount Wuyishan domain that changed the Middle Jurassic paleo-geographic outline and formed the transformational tectonic regime from compression to extension, reflecting a strong tectonic response to the Pacific plate
出处
《地质学刊》
CAS
2011年第4期337-348,共12页
Journal of Geology
关键词
沉积特征
古地理格局
构造转换
火山岩定年
侏罗纪
中国东南部
Sedimentary features
Paleo-geographic framework
Transformation of tectonic regime
Volcanic rocks and age determina- tion
Jurassic period
Southeast China
