关键词: 亚肯背斜, 褶皱活动, 晚更新世, 天山

Abstract: The Yaken anticline is located on the southernmost side of Cenozioc Kuqa rejuvenated foreland basin in southern Tianshan. The anticline can be assigned to fault-bend-fold, which involved the Jurassic, Cretaceous, Tertiary and Quaternary strata. The length of the Yaken fold belt is about 80km in east-west direction, and the width in north-south direction is about 6～7km. The oldest deposits exposed in the anticline core is Pliocene in age, while the deposits exposed on both limbs and periclinal part are early Pleistocene Xiyu conglomerate, as well as late Pleistocene and Holocene alluvial-pluvial gravel beds. The anticline appears as a broad fold, both the southern and northern limbs of which are basically symmetric. Dip angles of the deposits on both limbs of the anticline are only 5°～17°. The reverse fault controlling the development of Yaken anticline is not exposed on the surface and occurs in the form of a blind reverse fault. Seismic reflection data indicate that the deposits above the Jurassic strata are folded, and that the reverse fault merges downward into the horizontal detanchment surface at about 7km depth. Three levels of terraces were developed in Yaken anticline zone. Among them, the third level terrace has the highest elevation, and was strongly dissected to form some gullies. The second level terrace consists of a large paleo alluvial pluvial fan, and connects with the modern desert plane on both sides of the Yaken anticline. The surface of the terrace is broad and smooth. The age of deposit collected at 0.3～0.5m depth below the surface is determined to be 39.5～43.6ka by thermoluminescent dating, while the time of the abandon of this terrace is about 4～1.2ka. The first level terrace exists only in large south-north-trending gully or on the plunging crown of the anticline. The amounts of uplift of the first, second, and third level terraces to the northwest of Yaha village are 6.5m, 40m and 50m, respectively. To the northwest of Shiyou-Wuqi farm, the amounts of uplift of the second and third level terraces are about 60m and 100m, respectively, while the amount of shortening of the second level terrace is about 47m. The rates of uplift and shortening for the second level terrace in the middle segment of the anticline in the vicinity of the Shiyou-Wuqi farm, are 1.5～5mm/a and 1.2～3.9mm/a, respectively. On the western plunging crown of the anticline, the time of the abandon of the first level terrace is less than 7.8ka. The amounts of uplift and shortening here are 20m and 17.9m, respectively, while the rates of uplift and shortening are 2.56mm/a and 2.29mm/a, respectively.

Key words: Yaken anticline, Active fold, Late Pleistocene, Tianshan