A microstructural and thermochronometric analysis of the Coyote Mountains detachment shear zone provides new insight into the collapse of the southern North American Cordillera. The Coyote Mountains is a metamorphic core complex that makes up the northern end of the Baboquivari Mountains in southern Arizona. The Baboquivari Mountains records several episodes of crustal shortening and thickening and regional metamorphism, including the Late Cretaceous‐early Paleogene Laramide orogeny which is locally expressed by the Baboquivari thrust fault. Thrusting and shortening were accompanied by magmatic activity recorded by intrusion of Paleocene muscovite‐biotite‐garnet peraluminous granites such as the ~58 Ma Pan Tak Granite, interpreted as anatectic melts representing the culmination of the Laramide orogeny. Following Laramide crustal shortening, the northern end of the Baboquivari Mountains was exhumed along a top‐to‐the‐north detachment shear zone, which resulted in the formation of the Coyote Mountains metamorphic core complex. Structural and microstructural analysis show that the detachment shear zone evolved under a strong component of noncoaxial (simple shear) deformation, at deformation conditions of ~450 ± 50°C, under a differential stress of ~60 MPa, and a strain rate of 1.5 × 10⁻¹¹ to 5.0 × 10⁻¹³ s⁻¹ at depth of ~11–14 km. Detailed ⁴⁰Ar/³⁹Ar geochronology of biotite and muscovite, in the context of the deformation conditions determined by quartz microstructures, suggests that the mylonitization associated with the formation of the Coyote Mountains metamorphic core complex started at ~29 Ma (early Oligocene). Apatite fission track ages indicate that the footwall of the Coyote Mountains metamorphic core complex experienced rapid exhumation to the upper crust by ~24 Ma. The fact that mylonitization and rapid extensional exhumation postdates Laramide thickening by ~30 Myr indicates that crustal thickness alone was insufficient to initiate extensional tectonic and required an additional driving force. The timing of mylonitization and rapid exhumation documented here and in other MCCs are consistent with the hypothesis that slab rollback and the effect of a slab window trailing the Mendocino Triple Junction have been critical in driving the development of the MCCs of the southwest.

中文翻译：

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郊狼山变质核心复合体（亚利桑那州）的挖掘：对北美南部山脉的造山塌陷的影响

土狼山脉脱离剪切带的微观结构和热年代计分析为南部北美山脉的塌陷提供了新的见识。土狼山是变质的核心复合体，它构成了亚利桑那州南部Baboquivari山脉的北端。巴博基瓦里山脉记录了数个地壳缩短和增厚以及区域变质的事件，包括由白博基瓦里逆冲断层局部表达的晚白垩世-早古生代拉拉酰胺造山运动。推力和缩短伴随着岩浆活动，古新世白云母-黑云母-石榴石高铝质花岗岩如〜58 Ma Pan Tak花岗石的侵入记录了岩浆活动。拉曼酰胺地壳缩短后，Baboquivari山脉的北端沿自上而下的脱离剪切带被掘出，这导致了Coyote山脉变质核心复合体的形成。结构和微观结构分析表明，在非同轴（简单剪切）变形的强分量下，在〜450±50°C的变形条件下，在〜60 MPa的压差下，应变速率为1.5× 10在〜11–14 km的深度处为⁻¹¹至5.0×10 ^-13  s ^-1。详细⁴⁰ Ar / ³⁹在由石英显微结构确定的变形条件的背景下，黑云母和白云母的Ar年代学表明，与土狼山变质岩心复合体形成有关的mylonitization开始于〜29 Ma（渐新世早期）。磷灰石裂变径迹年龄表明，土狼山变质岩心复合体的下盘壁在〜24 Ma时迅速发掘到上地壳。mylonitization和快速延伸性发掘出土的事实使Laramide增厚了约30 Myr，这表明仅地壳厚度不足以引发延伸性构造，并需要额外的驱动力。