闽西武夷山建宁—泰宁地区白垩纪火山-沉积序列:对华南东部晚中生代构造演化的制约

Cretaceous volcano-sedimentary sequences in the Jianing-Taining region of Mts Wuyi,western Fujian:constraint on Late Mesozoic tectonic evolution of SE China

闽西武夷山建宁—泰宁地区发育2套白垩纪火山-沉积序列,构成2个火山-沉积旋回,每套序列由下部火山岩和上部沉积岩地层组成。锆石U-Pb年代学和地球化学分析显示,早期中酸性火山岩喷发时代为早白垩世141~135 Ma,具有陆缘火山弧的地球化学亲缘性,并富集Hf同位素(-20.2~1.9);而晚期火山岩活动集中在早、晚白垩世之交(105~97 Ma),呈现弧后伸展特征并相对亏损Hf同位素(-16.1~10.2)。通过这两套白垩纪火山-沉积序列区域对比,发现早、晚两套火山活动之间的岩浆活动宁静期呈现自南西向北东逐渐消减的趋势,于120 Ma前后基本结束,这个时期在华南东部陆缘加积了一套河湖相沉积地层,并遭受不同程度的挤压变形。晚期火山-沉积序列受到伸展断陷盆地的控制,其中加积了一套含膏盐红层沉积。研究认为,华南东部陆缘白垩纪2套火山-沉积序列记录了该陆缘2个显著不同的构造演化阶段,从早期陆缘火山弧及其挤压变形到晚期的弧后伸展和断陷湖盆的发展历程。

Two Cretaceous volcano-sedimentary sequences were identified in the Jianning-Taining region of Mts Wuyi in Fujian,each consisting of volcanic rocks overlain by clastic sedimentary deposits.Zircon U-Pb dating results and geochemistry analysis show that the lower volcanic rock series erupted in Early Cretaceous between 141 to 135 Ma,with the affinity of volcanic arc in a continental margin,and enriched Hf isotope(-20.2~1.9).The upper volcanic rock series erupted at 105~97 Ma,with the affinity of back-arc extensional setting and relatively depleted Hf isotope(-16.1~10.2).These two Cretaceous volcano-sedimentary sequences can be correlated with those in other regions of SE China.It is found that the magmatism lull between these two volcanisms displays a tendency to vanish in an array from SW to NE,with cessation at 120 Ma.During this magmatic quiescent period in SE China,a package of fluvial-lacustrine facie swas deposited and subsequently deformed by a compressional event.The upper Late Cretaceous volcano-sedimentary series seems to be controlled by extensional faulted basins,in which thick,gypsum-bearing red beds accumulated.These two Cretaceous volcano-sedimentary sequences recorded two tectonic stages in SE China with distinct features that marks the change from Early Cretaceous volcanic arc and associated compressional deformation to Late Cretaceous back-arc extension and the generation of faulted basins.