摘要:北山地区泥盆纪是古亚洲洋由板块体制向板内体制转变的关键时期，晚古生代旱山微大陆与塔里木板块发生碰撞造山作用，两个板块拼接在一起，形成统一大陆。沿红柳河—牛圈子—洗肠井一带形成古生代蛇绿岩，在蛇绿岩带南部为平头山推覆构造。作为这次碰撞的沉积响应，在墩墩山一带形成厚度巨大，横向变化极大的三个井组。通过对三个井组岩性特征和沉积建造的分析研究，认为三个井组整体属于磨拉石建造，其沉积盆地性质为周缘前陆盆地；岩性显示快速堆积的特征，物源区主要为北部逆冲推覆带；垂向层序由下向上表现为粗—细—粗的序列，代表了一个完整的前陆盆地沉降 —沉积构造旋回。结合前人的锆石U-Pb测年结果，三个井组的沉积时间应始于晚志留世，而早于晚泥盆世，由此表明北山地区晚古生代的造山作用始于晚志留世，至晚泥盆世，已经完成板块拼接。
关键词: 三个井组/
磨拉石/
碰撞/
造山/
前陆盆地/
甘肃北山
Abstract:Devonian of Beishan region was a critical period of the ancient Asian oceanic plate systemturned to the inner plate institution, Hanshan micro-continent collided with Tarim plate thenoccurred orogenesis in the Late Paleozoic, the two plates spliced together to form a unified continent.Paleozoic ophiolite formed along the Hongliuhe-Niujuanzi-Xichangjin, in the south of ophiolite beltwas the Pingtoushan nappe structures. As the depositional response of this collision, a hugethickness and lateral varying Sangejing Formation occurred in the Dundunshan region. Through theanalysis of the lithological characteristics and sedimentary construction of the Sangejing Formation,we considered that it belonged to Molasse entirely, and the nature of the sedimentary basin wasperipheral foreland basin; lithological characteristics showed a rapid accumulation, and the mainsource area was northern orogenic belt. Vertical sequence is coarse-fine-coarse sequence frombottom to top, which represented a complete foreland basin depression-sedimentary tectonic cycle.Combined with previous zircon U-Pb dating results, the deposition time of Sangejing Formationbegan in the Later Silurian, yet earlier than Later Devonian, which show that the Late Paleozoicorogenesis of Beishan began in Later Silurian, it has completed the plate splicing till the LateDevonian.
Key words:Sangejing Formation/
Molasse/
Collisional orogeny/
Foreland basin/
Gansu Beishan/
PDF全文下载地址:
http://www.dzkx.org/data/article/export-pdf?id=geology_11665
