华北燕山带东部三叠纪和侏罗纪大地构造演化:来自备受争议的邓杖子组及相邻地层的线索(英文)

Triassic and Jurassic tectonics in the eastern Yanshan Belt,North China:Insights from the controversial Dengzhangzi Formation and its neighboring units

位于辽西凌源市南部的牛营子—邓杖子地区侏罗系地质问题多年来困扰着地质学家。争论最多的构造形迹是一套平面上呈狭长矩形,以断层为界的近直立中元古界常州沟组石英岩,及局部长城系顶部地层。这套地层绵延35km,呈北北东展布。其西界为近直立的大齐子断层(新命名断层)和大部分向东倒转的陡倾下侏罗统邓杖子组;东界为近直立的朱杖子断层(新命名断层)和西倾的中侏罗统郭家店组。前人的构造解释倾向于大齐子断层为邓杖子组一侧下降的陡倾正断层,朱杖子断层为郭家店组一侧下降的陡倾逆断层。文中不同意这样的解释,并发现有证据表明上述两个断层都形成于之前尚未识别出的侏罗纪构造事件时期。将大齐子断层解释为早侏罗世晚期—中侏罗世早期形成的一条向西逆冲的断层,沿着它使长城系推覆于邓杖子组之上,然后,该逆冲断层上、下盘地层共同卷入后期褶皱变形当中。朱杖子断层原本为正断层,形成于原来未识别出的中侏罗世伸展变形阶段,并构成了郭家店半地堑边界断层。朱杖子断层沿着向东倾斜的常州沟组石英岩与串岭沟组页岩的界面发育。随着断层的发育,位于常州沟组石英岩之上的串岭沟组及长城系上部地层发生拆离沉降并被埋藏在半地堑之下。随后,发生在中侏罗世晚期或晚侏罗世早期收缩构造变形,改造了邓杖子—常州沟—郭家店组构造组合的几何形态。本期改造导致以下结果:(1)朱杖子正断层发生反转成为逆断层;(2)蓟县系沿着杨杖子—瓦房店逆冲断层向东掩覆于断层围限的长城系地层及相邻侏罗系之上。同时,邓杖子组倾角加大并向东倒转。研究表明,辽西地区的侏罗纪构造演化过程远比原先所认为的要复杂。

The Jurassic geology of the Niuyingzi-Dengzhangzi area of western Liaoning province south of Lingyuan has challenged geologists for many years. Its most controversial structural element is a narrow （0. 1 -1.5 km）, subvertical, fault-bounded panel of Middle Proterozoic Changzhougou quartzite and, locally, higher Changcheng System units. The 35 km-long, NNE-striking panel is bordered on the west by the subvertical Daqizi fault （new name） and the steep, largely east-overturned Late Triassic-Early Jurassic Dengzhangzi Formation. It is bordered on the east by the subvertical Zhuzhangzi fault （new name） and west-dipping Middle Jurassic Guojiadian Formation strata. Previous structural interpretations have favored ideas that the Daqizi fault is a steep normal fault with Dengzhangzi side down, and that the Zhuzhangzi fault is a steep reverse fault with Guojiadian side down. We disagree with both interpretations and present evidence that both faults have formed during previously unrecognized Jurassic tectonic events. The Daqizi fault is interpreted as a late Early Jurassic to early Middle Jurassic west-directed thrust fault placing Changcheng strata across lower-plate Dengzhangzi strata. Both upper and lower plates were then folded. The Zhuzhangzi fault was originally a normal fault bounding a Guojiadian half-graben that formed during an episode of previously unrecognized Middle Jurassic extension. The fault was localized along the folded, east-dipping contact between Changzbougou quartzites and overlying shales of the Chuanlinggou Formation. As the fault developed, detached hanging wall Chuanlinggou and higher Changcheng strata above the Changzhougou quartzite were dropped down and buried beneath the halfgraben filk The geometry of the Dengzhangzi-Changzbougou-Guojiadian structural assemblage was subsequently modified by late Middle Jurassic or early Late Jurassic contraction. Among its effects were （1） reverse fault inversion of the Zhuzhangzi normal fault and （2） eastward Yangzhangzi-Wafangdian thrusting of Jixian strata across the Changcheng fault-bounded panel and its neighboring Jurassic units. Steepening and eastward overturning of Dengzhangzi strata occurred at this time. The results of our study indicate that the Jurassic tectonic history of the western Liaoning area was considerably more complicated than believed earlier.