Stratal Extension in Thrust Footwalls, Makran Accretionary Prism: Implications for Thrust Tectonics
Stratal Extension in Thrust Footwalls, Makran Accretionary Prism: Implications for Thrust Tectonics
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逆冲下盘的地层伸展、莫克兰增生棱柱：对逆冲构造的影响
DOI：
10.1306/9488565b-1704-11d7-8645000102c1865d
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发表时间：
1986
期刊：
影响因子：
--
通讯作者：
J. Leggett
中科院分区：
文献类型：
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作者：
J. Platt;J. Leggett
巴基斯坦西南部Makran增积棱柱中的小范围地层伸展通常与逆冲断层有关。低角度正断层相对于逆冲断层沿输送方向倾斜，在断层带和复式构造中很常见，也可能切割下盘和上盘，在那里它们造成地层伸展。这些断层很可能是Riedel剪刀。我们研究了在一个顺层-平行逆冲作用下更复杂的伸展变形的宽广区域。该带破坏了早期的挤压构造，并影响了相当大的下盘体积。正常断层以向后的顺序启动，从逆冲层分叉出来，向下切割到下盘，在较低的地层水平合并。因此，推覆位移的一部分被传递到该水平，下盘的碎片被分离并在上盘下方向南转移。后者保持不变形，住宿结构仅限于下墙。这些影响可能是由沿断层滑动阻力的变化引起的。如果逆冲推力以这种方式将其部分或全部位移沿正常断层向下传递，然后最终向上切割到地表，它将从穿过该地平线的初始坡道前方的位置分离出一块无根的底盘岩石。这一过程可以被称为“脚下拔毛”。例如，它可以解释沿冲断带的无根基底岩片，并对剖面恢复技术和冲断带的解释具有重要意义。
Small-scale stratal extension is commonly associated with thrust faults in the Makran accretionary prism of southwest Pakistan. Low-angle normal faults, dipping in the direction of transport relative to the thrust, are common in gouge zones and duplexes, and may also cut the footwall and hanging wall, where they cause stratal extension. These faults are probably Riedel shears. We have studied a broad zone of more complex extensional deformation beneath one bedding-parallel thrust. The zone disrupts earlier compressional structures and affects a significant volume of the footwall. Normal faults, initiating in a rearward sequence, branch off the thrust and cut down into the footwall, merging at a lower stratigraphic level. Part of the thrust displacement was thereby transfe red to that level, and fragments of the footwall were detached and transferred southward beneath the hanging wall. The latter remained undeformed, and accommodation structures are confined to the footwall. These effects may have been caused by variations in sliding resistance along the fault. If a thrust transfers part or all of its displacement down section along normal faults in this way, before eventually cutting back up toward the surface, it will detach a rootless fragment of footwall rocks from a position forward of the initial ramp through that horizon. This process can be referred to as "footwall plucking." It can explain rootless basement slices along thrusts, for example, and it has important implications for section restoration techniques and the interpretation of thrust belts.