Abstract The 495 to 450 Ma Famatinian orogen, exposed throughout central and northwestern Argentina, formed from east-directed subduction under the Gondwanan margin. The Sierra de Narvaez and Sierra de Las Planchadas preserve a rare upper-crustal section of the Famatinian arc. New mapping, structural analysis, detrital U–Pb zircon geochronology, as well as major and trace element geochemistry in the Sierra de Narvaez – Las Planchadas are presented to give a comprehensive geodynamic portrait of the volcano-sedimentary, igneous, and deformational processes acting within the top of the Famatinian arc in the Ordovician. Field observations and bulk rock geochemistry agree with previous work indicating that the top of the Famatinian arc consisted of volcanic centers, mafic and felsic feeders, and plutons built into continental crust in a shallow marine arc setting, characterized by fossil-bearing, fine-grained marine sediments interbedded with coarse-grained volcanic-clastic material. Trace element chemistry is consistent with the Sierra de Narvaez – Las Planchadas region being a continuation along the main arc axis from the more southerly Sierra de Famatina, not a back arc setting as previously interpreted. Detrital zircon geochronology in Permian and Carboniferous sedimentary units unconformably overlying Ordovician units adds further constraints to the duration of Famatinian arc activity and the source of sedimentary material. Two peaks in detrital zircon ages within Carboniferous and Permian strata at 481 Ma and from 474 to 469 Ma, record periods of enhanced magma addition during Famatinian arc activity. Structural analysis establishes both Famatinian and post-Famatinian (largely Andean) deformation; contractional deformation in the Ordovician, although small relative to middle- to lower-crustal levels of the Famatinian orogen, caused crustal thickening and likely initiated surface uplift. Unlike the Famatinian middle to lower crust, however, where widespread ductile deformation is ubiquitous, shortening here is accommodated by open folding, pressure solution, and likely localized brittle faulting. We briefly speculate on the implications of variable shortening recorded at different crustal levels.

中文翻译：

---

阿根廷西北部纳瓦埃斯山脉和拉斯普兰查达山脉的上地壳结构和法马蒂尼亚弧活动记录

摘要 495~450 Ma Famatinian造山带出露于阿根廷中部和西北部，形成于冈瓦纳大陆边缘向东俯冲。Sierra de Narvaez 和 Sierra de Las Planchadas 保留了 Famatinian 弧的罕见上地壳部分。提供了新的绘图、结构分析、碎屑 U-Pb 锆石年代学，以及 Sierra de Narvaez – Las Planchadas 的主要和微量元素地球化学，以提供火山沉积、火成岩和变形过程的综合地球动力学画像。奥陶纪法马提阶弧顶。现场观测和大块岩石地球化学与先前的工作一致，表明法马蒂尼亚弧的顶部由火山中心、基性和长英质馈源组成，和在浅海弧环境中进入大陆地壳的岩体，其特征是含有化石的细粒海洋沉积物与粗粒火山碎屑物质互层。微量元素化学与 Sierra de Narvaez – Las Planchadas 地区是沿主弧轴从更偏南的 Sierra de Famatina 延续，而不是之前解释的后弧设置。二叠纪和石炭纪沉积单元中的碎屑锆石年代学与奥陶纪单元不整合地叠加，进一步限制了法马提阶弧活动的持续时间和沉积物质的来源。石炭纪和二叠纪碎屑锆石年龄在 481 Ma 和 474 至 469 Ma 的两个峰值，记录了法马提阶弧活动期间岩浆添加增强的时期。结构分析建立了法马提阶和后法马提阶（主要是安第斯）变形；奥陶纪的收缩变形，虽然相对于法马提阶造山带的中下地壳水平较小，但导致地壳增厚并可能引发地表隆升。然而，与 Famatinian 中下地壳不同，那里广泛的延性变形无处不在，这里的缩短是通过开放折叠、压力解决和可能的局部脆性断层来适应的。我们简要推测了在不同地壳水平记录的可变缩短的影响。导致地壳增厚并可能引发地表隆升。然而，与法马蒂阶中下地壳不同，那里广泛的延性变形无处不在，这里的缩短是通过开放折叠、压力解决和可能的局部脆性断层来适应的。我们简要推测了在不同地壳水平记录的可变缩短的影响。导致地壳增厚并可能引发地表隆升。然而，与 Famatinian 中下地壳不同，那里广泛的延性变形无处不在，这里的缩短是通过开放折叠、压力解决和可能的局部脆性断层来适应的。我们简要推测了在不同地壳水平记录的可变缩短的影响。