Range front structural style: An example from Surghar Range, North Pakistan
Range front structural style: An example from Surghar Range, North Pakistan
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发表时间：
2014
期刊：
影响因子：
3.5
通讯作者：
Fayaz Ali;Muhammad Irfan Khan;Sajjad Ahmad;Gohar Rehman;Ishrat Rehman;T. H. Ali
中科院分区：
文献类型：
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作者：
Fayaz Ali;Muhammad Irfan Khan;Sajjad Ahmad;Gohar Rehman;Ishrat Rehman;T. H. Ali
苏尔加尔山脉是巴基斯坦北部印度河盐山脉的最东端延伸，看起来像一个弧形的山脉。该山脉在毗邻科哈特高原南部时总体上呈东西向构造趋势，并沿班努盆地东侧沿着转为南北向趋势。作为一个活动的山脉前缘，它在出露和非出露岩石中保存了多种构造样式。该山脉的东西走向部分的演化归功于古生代-中生代岩石中基底滑脱冲断作用的前缘斜坡，并以低角度前缘冲断的形式出现，称为苏尔加尔冲断。苏格哈尔冲断带的上盘是中等至紧密褶皱的，苏格哈尔背斜是最突出的断层弯曲褶皱构造。前冲断层沿着的构造几何学特征表明，它在西部是弱出露的，向东逐渐转变为强出露至尖状逆冲断层前缘。山脉的这一部分主要揭示了一个南缘构造系统，与南部的旁遮普前陆相碰撞。相反，苏尔加尔山脉的南北走向部分已经演变为一个向东逐渐变细的构造楔，由古生代-古新世岩石插入始新世-上新世岩石之下。构造楔包括南北走向的马卡尔瓦尔背斜，该背斜在古生代-中生代岩石中的基底滑脱的斜坡之上发展，并形成楔的基底。马卡尔瓦尔背斜下的斜坡，而不是出现在侵蚀表面，在大约800米的深度变平，形成一个浅的水平单位。Makarwal背斜的东侧沿山脉前缘沿着向东倾斜，并被一个向西的活动逆冲断层（即Makarwal活动逆冲断层）推覆，该逆冲断层形成了构造楔的上部。Makarwal活动逆冲断层在位于基底断层尖部线的侏罗系岩石上盘切离处与地下的东向基底断层相连。Makarwal主动逆冲断层沿着与另一个东倾主动逆冲断层从Makarwal背斜下方的埋藏背斜的前缘向外伸展，形成第二个构造楔的顶部。活动逆冲断层一词适用于西缘断层，因为它们的上盘和下盘地层在楔体插入的作用下发生了积极的变形。
The Surghar Range is the easternmost extension of the Trans-Indus Salt ranges of North Pakistan that appears as an arcuate mountain belt. The range follows in general an east-west structural trend while bordering the southern Kohat Plateau and switches to north-south trend along the eastern flank of the Bannu Basin. Being an active range front it preserves variety of structural styles in the outcropping and non-outcropping rocks. The east-west trending segment of the range owes its evolution to frontal ramping from basal decollement thrusting within the Paleozoic-Mesozoic rocks and emerges as a low angle frontal thrust named as the Surghar Thrust. The hanging wall of Surghar Thrust is moderately to tightly folded with Surghar Anticline being the most prominent fault bend fold structure. The structural geometries along the frontal thrust fault suggest that it is weakly emergent in the west and changes its character to strongly emergent to tip-stick thrust front progressively towards east. This part of the range dominantly reveals a south verging structural system impinging upon the Punjab Foreland in the south. In contrast the north-south trending segment of the Surghar Range has evolved as an easterly tapering tectonic wedge of Paleozoic-Paleocene rocks inserted underneath the Eocene-Pliocene rocks. The tectonic wedge comprises north-south trending Makarwal Anticline that has developed above a ramp from basal decollement within Paleozoic-Mesozoic rocks and forms the base of the wedge. The ramp beneath the Makarwal Anticline instead of emerging out at erosional surface gets flattened at an approximate depth of 800 meters to form a shallow level flat. The eastern flank of the Makarwal Anticline is steeply east dipping along the range front and is thrust over by a west verging active back thrust namely the Makarwal Active Back Thrust that forms the upper part of the tectonic wedge. The Makarwal Active Back Thrust is linked with the east verging basal fault in the subsurface at the hanging wall cut off of the Jurassic rocks located at the tip line of the basal fault. The Makarwal Active Back Thrust along with another east vergent active back thrust splays from the forelimb of a buried anticline underneath the Makarwal Anticline forming the top of a second tectonic wedge. The term active back thrust is applied to the west verging faults because their hanging and foot wall strata is actively deforming in response to wedge insertion.