Out‐of‐sequence thrusting in polycyclic thrust belts: An example from the Mesozoic Yanshan belt, North China Craton
Out‐of‐sequence thrusting in polycyclic thrust belts: An example from the Mesozoic Yanshan belt, North China Craton
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DOI：
10.1002/2016tc004187
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发表时间：
2016-09
期刊：
影响因子：
4.2
通讯作者：
Chengming Li;Changhou Zhang;T. Cope;Yi Lin
中科院分区：
文献类型：
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作者：
Chengming Li;Changhou Zhang;T. Cope;Yi Lin
燕山带是位于华北北方的一条板内褶皱冲断带，经历了多期时间间隔很大的变形，以不连续逆冲构造为特征。根据燕山带中部的详细测绘，可以识别出用于帮助确定逆冲断层是否具有非层序几何形状的五个几何和地层标准。它们是：（1）不整合关系;（2）断层面倾角;（3）视错距沿着走向的不规则变化;（4）相对于视错距的短断层长度;（5）层序几何形状。在这些准则的帮助下，在燕山带中部识别出晚于原始顺序逆冲的两代逆冲断层。在180 Ma之前形成的向南的褶皱冲断带被两个年轻一代的断层变形和切割，这些断层可能更根深蒂固，并被限制在172-165 Ma和152-135 Ma之间。在最后一个时期形成了一系列相反聚散的逆冲断层，导致了丰富的异常场关系，如年轻-老逆冲断层关系、褶皱截断和切割剖面。燕山带断裂的性质和产状表明，叠加变形是多旋回造山带的一个共同特征，是产生序外逆冲作用的机制。这增加了在文献中已经描述的机制，如保持恒定的临界锥度在造山规模，抑制变形前，和横向变化的性质的滑脱层。
The EW trending Yanshan belt, an intraplate fold‐thrust belt located in the northern North China Craton that has experienced several episodes of deformation widely separated in time, is characterized by out‐of‐sequence thrusts. According to detailed mapping in the central Yanshan belt, five geometric and stratigraphic criteria used to aid in determining whether a thrust has an out‐of‐sequence geometry or not can be recognized. They are (1) unconformable relationships, (2) inclination of fault surfaces, (3) irregular changes in apparent offset along strike, (4) short fault length relative to apparent offset, and (5) in‐sequence geometry. With the help of these criteria, two generations of out‐of‐sequence thrusts that postdate the original in‐sequence thrusting in the central Yanshan belt are recognized. The ancestral southward verging fold‐and‐thrust belt that formed prior to 180 Ma was deformed and cut by two younger generations of faults that are probably more deeply rooted and are constrained to between 172–165 Ma and 152–135 Ma. A series of thrusts with opposite vergence formed during the last period, resulting in abundant abnormal field relationships such as younger‐on‐older thrust relations, fold truncation, and cutting down‐section. The nature and occurrence of faults in the Yanshan belt implies that superimposed deformation, a common feature in polycyclic orogenic belts, is a mechanism for the generation of out‐of‐sequence thrusting. This adds to mechanisms already described in the literature, such as maintaining constant critical taper at an orogenic scale, inhibition of the deformation front, and lateral changes in the nature of the décollement horizons.