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Fold Kinematics and Fault Slip Rates From Progressively Deformed Terraces: Implications for Structural Evolution of Basins in the Kyrgyz Tien Shan
Tectonics ( IF 4.2 ) Pub Date : 2020-08-18 , DOI: 10.1029/2019tc005776
Jascha A. Coddington 1, 2 , Reed J. Burgette 1
Affiliation  

Active shortening across the Tien Shan is transforming dispersed basins and ranges into continuous high topography. The Jumgal Basin is an example of a basin in an intermediate phase of closure, with both a basin‐bounding reverse fault system and a >25 km long anticline growing in the basin interior. We used geologic mapping and surveying of progressively deformed fluvial terraces preserved across the anticline to measure deformation. A novel method of inverting deformed terrace data allows estimation of fault geometry at depth as well as incremental slip for terraces. The preserved northern portion of the Jumgal anticline is consistent with folding above a fault that ramps up from a low‐angle splay following bedding in synorogenic stratigraphy. The eastern part of the fold has grown by limb lengthening above an angular bend in the fault. Areas to the west record progressive rotation consistent with deformation above broadly curved portions of the fault. Slip rates determined with late Quaternary terrace ages from measured and correlated chronologies are consistent with slip rates that vary significantly from ~0.6 to 1.2 mm/year along the investigated portion of the anticline, with lower rates in the middle of the anticline. Rate variation may indicate along‐strike trade‐offs in slip between an emergent splay of the basin‐bounding fault and the intrabasin fold. Slip rates are rapid enough to build topography north of the basin since the Pliocene, and observations suggest the Jumgal Basin is progressively closing from west to east, influenced by earlier phases of basin partitioning.

中文翻译:

渐进变形阶地的褶皱运动学和断层滑移率:对吉尔吉斯天山盆地构造演化的启示

天山的主动缩短正在将分散的盆地和山脉转变为连续的高地势。Jumgal盆地是处于封闭中期的盆地的一个例子,盆地边界的逆断层系统和盆地内部生长的背斜线都长于25 km。我们使用地质图和对沿背斜保存的逐渐变形的河床阶地进行测量,以测量变形。反演变形的阶地数据的一种新颖方法可以估算深度断层的几何形状以及阶地的增量滑动。Jumgal背斜的保留的北部与断层之上的褶皱相一致,该断层在同成层地层中被层理后从低角度张开向上倾斜。褶皱的东部是通过断层上的角弯曲以上的肢体延长而生长的。向西的区域记录了渐进旋转,与断层宽弯曲部分上方的变形一致。根据实测和相关的年代学,以第四纪晚期阶地年龄确定的滑移率与沿背斜调查的部分在约0.6至1.2毫米/年之间的滑移率有显着变化,而在背斜中部则较低。速率变化可能表明盆地边界断层的新兴张开与盆地内褶皱之间的沿走滑权衡。自上新世以来,滑移速度足够快,可以在盆地北部建立地形,并且观测结果表明,受盆地划分早期阶段的影响,Jumgal盆地从西向东逐渐关闭。
更新日期:2020-08-18
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