Structural Architecture and Attenuation of the Ductile Lower Plate of the Ruby Mountain‐East Humboldt Range Metamorphic Core Complex, Northeast Nevada
Structural Architecture and Attenuation of the Ductile Lower Plate of the Ruby Mountain‐East Humboldt Range Metamorphic Core Complex, Northeast Nevada
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DOI：
10.1029/2021tc007162
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发表时间：
2022-08
期刊：
影响因子：
4.2
通讯作者：
A. Zuza;D. Levy;Seth M. Dee;J. DesOrmeau;F. Cheng;Xiangzhong Li
中科院分区：
文献类型：
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作者：
A. Zuza;D. Levy;Seth M. Dee;J. DesOrmeau;F. Cheng;Xiangzhong Li
北美科迪勒拉变质核杂岩（MCC）中出露的强烈变形的下盘岩石是通过韧性减薄、糜棱岩剪切和拆离断层作用而被剥露出来的。这些构造是通过低角度正断层作用适应了底辟上涌还是区域伸展，这一点存在争议。内华达州东北部的鲁比山 - 东洪堡岭变质核杂岩记录了变形的元古宙 - 古生代地层和更古老基底向西上的正断层剥露。我们对东洪堡岭西南部进行了1:24000比例尺的测绘，并结合结构、地球化学和地质年代学分析来描述糜棱岩化下盘伸展和剥露的几何形态与运动学特征。基岩地层普遍被白垩纪、始新世和渐新世的侵入体侵入，但对一个连续地层剖面的观察表明，新元古代到奥陶纪的岩石垂直减薄超过80%。这些岩石具有向西上的运动学特征，被普遍剪切。因此，剪切带经历了纯剪切和简单剪切（即一般剪切）的组合应变。我们认为，该剪切带相对于渐新世的深成作用是同运动期/后运动期的，因为：（a）糜棱岩剪切在空间上与之前的渐新世侵入体相对应；（b）热年代学显示，剪切带在渐新世深成作用之后经历了显著的冷却和剥露；（c）糜棱岩被未确定年代但可能是渐新世晚期的淡色花岗岩横切。我们提出，始新世地幔源岩浆作用和热孕育导致了中地壳在渐新世的底辟上涌，韧性拉伸集中在这个上拱的侧翼。区域的盆岭伸展在中新世中期稍后开始。因此，东洪堡岭剪切带的发育不是由区域伸展和耦合的拆离断层作用驱动的。
Strongly deformed footwall rocks exposed in metamorphic core complexes (MCC) of the North American Cordillera were exhumed via ductile attenuation, mylonitic shearing, and detachment faulting. Whether these structures accommodated diapiric upwelling or regional extension via low‐angle normal faulting is debated. The Ruby Mountains‐East Humboldt Range MCC, northeast Nevada, records top‐west normal‐sense exhumation of deformed Proterozoic‐Paleozoic stratigraphy and older basement. We conducted 1:24,000‐scale mapping of the southwestern East Humboldt Range, with integrated structural, geochemical, and geochronological analyses to characterize the geometry and kinematics of extension and exhumation of the mylonitized footwall. Bedrock stratigraphy is pervasively intruded by Cretaceous, Eocene, and Oligocene intrusions, but observations of a coherent stratigraphic section show >80% vertical attenuation of Neoproterozoic to Ordovician rocks. These rocks are penetratively sheared with top‐west kinematics. The shear zone thus experienced combined pure‐ and simple‐shear (i.e., general shear) strain. We argue that this shear zone was syn‐/post‐kinematic with respect to Oligocene plutonism because: (a) mylonitic shearing spatially corresponds with preceding Oligocene intrusions; (b) thermochronology reveals that the shear zone experienced substantial cooling and exhumation after Oligocene plutonism; and (c) the mylonites are crosscut by undated, but likely late Oligocene, leucogranite. We propose that Eocene mantle‐derived magmatism and thermal incubation led to Oligocene diapiric upwelling of the middle crust, with ductile stretching focused on the flanks of this upwarp. Regional Basin and Range extension initiated later in the middle Miocene. Therefore, the development of the East Humboldt Range shear zone was not driven by regional extension and coupled detachment faulting.