南天山洋古地理及构造演化:西南天山放射虫硅质岩与地层记录的再认识

Palaeogeographic and tectonic evolution of South Tianshan Ocean:Re-examination of radiolarian cherts and stratigraphic record of southwestern Tianshan

泥盆纪—石炭纪放射虫硅质岩在西南天山广泛分布,从东部的独库公路沿线到西部的阿合奇中—吉边境构成一条深水沉积带。独库公路沿线已发现中泥盆世晚期至早石炭世维宪早期的放射虫硅质岩,可用"库勒湖组"统称。从志留系顶统科克铁克达坂组经下泥盆统阿尔腾柯斯组到库勒湖组的生物地层和沉积相研究表明了南天山洋从浅海到深水洋盆的演化过程。南天山洋是塔里木北缘浅海陆架裂解产生的小洋盆。构造古地理和生物古地理研究表明,南天山洋是古特提斯的分支洋盆,不属古亚洲洋范围。塔里木以南的古特提斯分支洋盆,在早石炭世及之后的继续扩张,使塔里木北移,导致南天山洋和准噶尔—北天山区的古亚洲洋在早石炭世晚期和晚石炭世相继消亡。

Devonian-Carboniferous radiolarian cherts are widely distributed in southwestern Tians- ban, and formed a deep-water sedimentary belt from the Dushanzi-Kuqa highway on the east to the Aheqi area on the west. The radiolarian cherts ranging from the late Middle Devonian to early Visean of Early Carboniferous were found along the Dushanzi-Kuqa highway, and may be used the name ＂Kulehu Forma- tion＂. Studies of the biostratigraphy and sedimentary facies on the succession from the Pridolian Keke- tiekedaban Formation through the Lower Devonian Artengkesi Formation to the Kulehu Formation indicate the evolution of South Tianshan Ocean from shallow marine to deep oceanic basin. The South Tianshan O- cean was a small oceanic basin caused by rifting of the continental shelf on north Tarim margin. Tectono- palaeogeographic and palaeobiogeographic studies indicate that the South Tianshan Ocean was a branch ofthe Palaeo-Tethys and not belongs to the scope of the Palaeo-Asian Ocean. The spreading of branches of the Palaeo-Tethys on the south to Tarim in the Early Carboniferous and afterwards led the drifting northward of Tarim and the closing of the South Tianshan Ocean and the Palaeo-Asian Ocean in Junggar and north Tianshan region.