华南东段早古生代造山带研究

Early Paleozoic orogenic belt in the eastern segment of South China

对华南东段早古生代的沉积环境、火山岩、超镁铁岩—镁铁岩年代、韧性变形运动学、早古生代造山带特色等方面进行了研究。研究结果表明,震旦纪一奥陶纪期间(680-440Ma)的沉积岩以泥砂质碎屑岩为主体,岩层中浅海相沉积构造发育;缺乏鲍玛层序,不含火山熔岩和爆发火山碎屑岩;原定的一些玄武岩实为杂砂岩。结合沉积岩地球化学成果.认为本区早古生代为被动大陆边缘浅海一半深海沉积环境。对区内部分镁铁岩和火山岩作SHRIMP岩浆锆石U—pb定年,年龄集中在860-800Ma之间。韧性变形运动学研究表明,武夷山南东麓从北西向南东逆冲推覆,北麓从南向北逆冲推覆,剖面上呈花状构造样式。之后发生了韧性走滑剪切作用。对糜棱岩的云母矿物作40Ar-39Ar定年,年龄集中在430-390Ma之间。与国内外典型加里东期造山带相比,华南早古生代造山带具有鲜明的地域特色,造山机制大致可与西欧比利牛斯造山带相比。

The authors perfonned a systematic study of the Early Paleozoic belt in the eastern segment of South China, including its sedimentary environment, volcanic rocks, ages of mafic-ultramafic rocks, kinematic analysis of ductile deformation and orogenic mechanism. Results suggest that the Sinian-Ordovician sequence （680-440 Ma） consists chiefly of sandstone and mudstones. In the strata neritic sedimentary structure is well developed, without the Bouma sequence, volcanic lavas or explosive pyroclastic rocks. Some originally defined basalt is actually graywacke. Based on the aforesaid study, combined with the geocbenfical features of graywacke, the study area was a neritic-bathyal environment on the passive continental margins during the Early, Paleozoic. SHRIMP U-Pb zircon dating of some mafic rocks and volcanic rocks show that their ages cluster at 860-800 Ma. The kinematic pattern of ductile deformation indicates that the southeastern foot of the Wuyi Mountains was overthrust from northwest to southeast, while the northern foot was thrust from south to north, displaying a flower-shaped structural style in section. Slightly later, strike-slip shearing occurred. The ^40Ar-^39Ar dating of muscovite and biotite from mylonitic yielded ages in the range from 430 to 390 Ma. By comparing with the typical Caledonian orogens in the world, the Early Paleozoic South China orogenic belt shows distinct local features and the orogenic mechanism is similar to that of the Pyrenean orogenic belt of Western Europe.