Abstract. The allochthonous complexes of Galicia – Trás-os-Montes Zone (NW Iberia) are part of the tectonic stack that unrooted the Variscan accretionary prism. They are formed by individual tectonic slices marked by specific tectono-metamorphic evolution, which was piled up in a piggy-back thrust complex onto its relative autochthon, the Central Iberian Zone (CIZ). Consequently, allochthony decreases towards lower, more external and younger thrust sheets. The lowermost unit of this pile of slivers is known as Schistose Domain or Parautochthon and bears low metamorphic grade, contrasting with the higher temperatures and pressures estimated for the upper allochthonous units, but sharing the stratigraphic sequence with the underlying autochthon. The Parautochthon is divided in two structural and stratigraphic sub-units: (i) the Lower (LPa) made of synorogenic flysch-type sediments with varied turbiditic units and olistostrome bodies, showing Upper Devonian-lower Carboniferous age on base of the youngest zircon populations and fossiliferous content; (ii) the Upper (UPa), composed of highly deformed pre-orogenic upper Cambrian-Silurian volcano-sedimentary sequence comparable with both the nearby autochthon and the HP-LT Lower Allochthon, laying structurally above. The UPa thrusted onto the LPa by the the Main-Trás-os-Montes Thrust; and the LPa detached from the CIZ relative autochthon by a regional structure (Basal Lower Parautochthon Detachment) which follows the favourable Silurian carbonaceous beds. A review on the detrital zircon studies of the synorogenic LPa complemented by 17 new samples geochronology is here presented. The results support the extension of the LPa underneath the NW Iberia allochthonous complexes, from Cabo Ortegal, to Bragança and Morais Massifs. Its current exposure follows the lowermost tectonic boundary between the Galicia – Trás-os-Montes (allochthon) and Central Iberian (autochthon) Zones. Youngest zircon age populations point to a maximum sedimentation age for the LPa formations ranging from Famennian to Serpukhovian and endorse the piggy-back evolution inside this unit, mimicking the general structure of the Galicia – Trás-os-Montes Zone. The zircon populations in the LPa allow constraining the sedimentary provenance areas, showing the intervention of nearby sources (mostly the UPa) and/or multiply recycled/long transport sediments with typically N-Central Gondwana age fingerprint, also found in the Lower Allochthon, UPa and Autochthon. Complementary geochronology of volcanic olistoliths trapped in the LPa sediments and of upper Cambrian to Upper Ordovician rhyolites from the UPa is also presented, showing a direct relation between the major block's source area (UPa) and the setting place (LPa). Old zircon age patterns show that the LPa sedimentary rocks were recycled from detrital rocks of the allochthon (advancing wedge) and the nearby autochthon (peripheral bulge).

中文翻译：

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伊比利亚西北部无根吸积棱镜底部的瓦里斯卡纳·弗里施（Variscan flysch）构造地毯：锆石的U-Pb年龄受沉积物和火山橄榄石的限制

摘要。加利西亚-特拉斯奥斯蒙特地区（NW Iberia）的异质复合体是构造叠层的一部分，该叠层没有扎根瓦里坎增生棱镜。它们由具有特定构造变质演化特征的单个构造切片形成，并以背thrust逆冲复合体的形式堆叠在其相对的自发体中部伊比利亚中部地区（CIZ）。因此，异位生菌朝着更小，更外部和更年轻的冲断层减少。这叠棉条的最低单位被称为Schistose Domain或Parautochthon，具有较低的变质等级，与较高的异源单位所估计的较高温度和较高压力形成对比，但与下伏的Autochthon共享地层层序。旁裂口分为结构和地层两个子单元：（i）下层（LPa）是由具有不同湍流单元和卵泡成虫体的协同成因的复理型沉积物制成的，根据最年轻的锆石种群和化石含量显示出上泥盆世-下石炭纪；（ii）上部（UPa），由高度变形的造山前寒武纪-西陆纪火山-沉积层序组成，其构造与附近的Autochthon和HP-LT Lower Allochthon相当。UPA由Main-Trás-os-Montes推力推入LPA；LPA沿着有利志留系碳质层床从区域构造（基底下Parautochthon分离）中脱离出来。本文介绍了对协同生成的LPa的碎屑锆石研究，并辅以17种新的样品年代学。研究结果支持了西北伊比利亚异质复合体下面的LPa的扩展，从卡波奥特加尔（Cabo Ortegal）到布拉干萨（Bragança）和莫赖斯地块（Morais Massifs）。它目前的活动遵循加利西亚–Trás-os-Montes（allochthon）和伊比利亚中部（autochthon）带之间的最低构造边界。最年轻的锆石年龄种群指向Lpa地层（从法门尼人到Serpukhovian）的最大沉积年龄，并支持该单元内部的背evolution式演化，模仿了加利西亚–Trás-os-Montes区的总体结构。LPa中的锆石种群可以限制沉积物来源地区，显示出对附近水源（主要是UPa）的干预和/或使回收的/长期运输的沉积物具有典型的N-Central Gondwana年龄指纹，也可以在UPa的下阿罗索顿发现和Autochthon。还介绍了在LPa沉积物中捕获的火山橄榄石和UPA的寒武纪上奥陶纪流纹岩到上奥陶纪流纹岩的互补地质年代学，显示了主要区块的源区（UPa）与凝结位点（LPa）之间的直接关系。古老的锆石年龄模式表明，LPa沉积岩是从异体碎屑（前进楔形）和附近的Autochthon（外围隆起）的碎屑岩中回收的。