南天山柯坪塔格推覆体前缘断裂活动性质及速率

ACTIVITIES AND SLIP RATE OF THE FRONTAL FAULTS OF THE KALPINTAG NAPPE,TIANSHAN MOUNTAINS,CHINA

柯坪塔格推覆体位于天山西南麓,由多排NEE—EW向的褶皱-逆断裂带组成。文中介绍了皮羌—巴楚磷矿以西3排褶皱-逆断裂带前缘断裂的活动性质及速率。新获资料表明,各排褶皱-逆断裂带前缘皆由多条断裂构成,都具典型的逆断层性质。其中最新活动断裂位于褶皱-逆断裂带的最前缘,活动时代为晚更新世—全新世。它们切割冲沟T0、T1、T2、T3阶地堆积,形成不同高度的断层陡坎。根据陡坎剖面测量和年龄样品测试,求得T0面形成以来断裂的垂直位移量、位移速率、地壳缩短量和缩短速率分别是0.9～1.1m、0.53～0.65mm/a、1.93～2.56m和1.14～1.52mm/a;T1面形成以来分别是1.4～1.8m、0.36～0.46mm/a、3.00～3.86m和0.77～0.99mm/a;T2面形成以来分别是2.1～3m、0.31～0.45mm/a、4.50～6.98m和0.67～1.04mm/a;T3面形成以来分别是3.4～4.2m、0.28～0.35mm/a、7.29～9.22m和0.61～0.77mm/a。根据T0面形成以来的缩短量和缩短速率,计算柯坪塔格推覆体约1.7ka以来总的地壳缩短量是9.65～12.80m,缩短速率5.68～7.53mm/a。

The Kalpintag nappe is located at the southwestern foot of the Tianshan Mountains, consisting of several rows of NE- to EW-trending fold-reverse fault zones. This paper demonstrates the activities and slip rate of the frontal faults of the first to third row fold-reverse fault zones located to the west of the Piqiang-Bachu phosphorite mine. The newly-found evidence shows that the front of each fold-reverse fault zone is composed of several faults of typical reverse fault type. The faults with newest activity are located at the forefront of the fold-reverse fault zones, and the active period of the faults is late Pleistocene-Holocene. They dissect the To , T1, T2and T3 terraces, resulting in fault scarps of different heights. According to the in-situ measurement of the fault scarps and the dating data of the relevant samples, it is estimated that the amount and rate of vertical displacement along the faults since the formation of the To terrace are 0.9 - 1. 1 m and 0.53 -0.65mm/a, respectively, while the amount and rate of the corresponding crustal shortening are 1.93 -2.56m and 1.14 - 1.52mm/a, respectively. Similarly, it is estimated that the amount and rate of vertical displacement since the formation of the T1 terrace are 1.4 - 1.8m, and 0.36 -0.46mm/a, with the corresponding crustal shortening of 3.00 - 3.86m, and shortening rate of 0.77 - 0.99mm/a. The vertical displacement amount and rate since the formation of the T2 terrace are about 2.1 -3.0m and 0.31 -0.45mm/a, respectively, and the amount and rate of the corresponding crustal shortening are 4.50 - 6.98m and 0.67 - 1.04mm/a. The amount and rate of vertical displacement since the formation of the T3 terrace are 3.4 - 4.2m and 0. 28 -0.35mm/a, and the amount and rate of the corresponding crustal shortening are 7.29 -9.22m and 0. 61 -0.77mm/a, respectively. Based on the obtained amount and rate of crustal shortening since the formation of To terrace, the total amount and rate of crustal shortening of the Kalpintag nappe since 1.7ka can be estimated to be 9.65 - 12.80m and 5.68 -7.53mm, respectively.