LATE-QUATERNARY FOLDING OF THE MINGYAOLE ANTICLINE SOUTHWESTERN TIP,PAMIR-TIANSHAN CONVERGENT ZONE

doi:10.3969/j.issn.0253-4967.2013.02.004

Abstract

Abstract:

Folding growth in three dimensions involves shortening in transversal direction,uplift in vertical direction and lateral propagation in longitudinal direction. The impact of these three components changes along the fold's strike: the middle part is dominated by shortening and uplift,and deformation neighboring the fold tip involves not only shortening and uplift,but also strong lateral propagation. Previous studies are focused on the middle part,and the fold tip,a relatively special part,however,is poorly investigated. Thereby,how does the fold tip grow,what is the deformation difference between fold tip and the middle part,and how do terraces deform in response to folding growth？Our study to the southwestern tip of the Mingyaole anticline,located at the Pamir-Tianshan convergent zone,indicates terrace surfaces are strongly back-tilted,and display increasing dips with age,implying a limb rotation mechanism. According to the OSL ages of the T_2b,T_3b and T_4a,as well as a magnetostratigraphy age of underlying bedrock,rotation angle increments of the dip domain 46° display a parabola tendency with the age of<～0.35Ma,(93.9±18.7)ka,(82.6±16.5)ka and(19.4±2.9)ka,and the average rotation rate is>(0.13±0.01)°/ka,(0.08±0.02)°/ka,(0.05±0.01)°/ka and(0.04±0.01)°/ka,which display an obviously decreasing tendency too. However,the shortening rate absorbed by this dip domain keeps constant.The fluvial terraces display not only tilted and uplifted in response to the shortening and uplift of the fold,but deformed in response to lateral propagation. Toward west,density,width and depth of gullies on the terraces decrease,and elevation to the riverbed of the terrace surface,height of the terrace riser as well as rotation angles of terrace surfaces display a decreasing tendency too,both of which are consistent with the fold's western-ward propagation. Based on the magnetostratigraphy age of～1.6Ma at the Kapake valley section,the average western-ward lengthening rate is about 16～16.8mm/a.

Key words: Tianshan Mountains, Pamir, Mingyaole anticline, late-Quaternary, fluvial terrace, limb rotation, fold tip

摘要：

褶皱在三维空间的生长包括横向缩短、垂向隆升和侧向扩展.沿褶皱走向不同位置这3个分量的比重是不同的: 在背斜中段以缩短和隆升为主; 靠近背斜端部,在缩短和隆升的同时也会发生强烈的侧向扩展.前人研究主要集中在褶皱中段,对端部这一相对独特的构造位置研究较少.那么褶皱端部是如何生长变形的,与褶皱中段有何不同,伴随褶皱生长同步变形的河流阶地具有怎样的发育特征？对帕米尔-天山对冲带明尧勒背斜西南倾伏端的研究表明,研究区内的4期河流阶地在垂直褶皱轴向上均发生了强烈反向掀斜,越老的阶地面掀斜角度越大,背斜在西南端的生长是以翼旋转机制进行的.据T_2b,T_3b,T_4a的细颗粒石英光释光年龄及下伏基岩的磁性地层年龄可得46°等斜岩区在距今约0.35Ma、(93.9±18.7)ka、(82.6±16.5)ka和(19.4±2.9)ka时期旋转角度大致呈抛物线曲线函数递减,平均旋转速率依次为>(0.13±0.01)°/ka、(0.08±0.02)°/ka、(0.05±0.01)°/ka和(0.04±0.01)°/ka, 呈明显减小趋势,但该等斜岩区吸收的缩短速率大致保持恒定.河流阶地在发生掀斜和抬升变形的同时,也发生了向西的侧向扩展变形: 由东向西,T_3a和T_4a阶地面上冲沟密度、宽度和下切深度明显减小,阶地拔河高度、陡坎高度和旋转角度也呈减小趋势,这些均反映了背斜向西的侧向扩展.据喀浪勾律克河谷和背斜西南剖面的磁性地层年代学结果,背斜向西侧向加长的速率恒定为16.0～16.8mm/a.

关键词: 天山, 帕米尔, 明尧勒背斜, 晚第四纪, 河流阶地, 翼旋转, 褶皱倾伏端

CLC Number:

P315.2

LI Tao, CHEN Jie, XIAO Wei-peng. LATE-QUATERNARY FOLDING OF THE MINGYAOLE ANTICLINE SOUTHWESTERN TIP,PAMIR-TIANSHAN CONVERGENT ZONE[J]. SEISMOLOGY AND GEOLOGY, 2013, 35(2): 234-246.

李涛, 陈杰, 肖伟鹏. 帕米尔-天山对冲带明尧勒背斜西南倾伏端晚第四纪褶皱变形[J]. 地震地质, 2013, 35(2): 234-246.

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