Abstract U–Pb ages of detrital ( n = 2391) and magmatic ( n = 170) zircon grains from the Harz Mountains were obtained by LA-ICP-MS for provenance studies and absolute age dating. Results point to a complete closure of the Rheic Ocean at c. 419 Ma. A narrow Rhenish Seaway then re-opened in Emsian to mid-Devonian time ( c. 390–400 Ma). Devonian sedimentary rocks of the Harz Mountains were deposited on the northwestern (Rheno-Hercynian) and on the southeastern (Saxo-Thuringian) margins of the Rhenish Seaway. A new U–Pb zircon age from a plagiogranite (329 ± 2 Ma) within a harzburgite makes the existence of oceanic lithosphere in the Rhenish Seaway probable. The Rhenish Seaway was completely closed by Serpukhovian time ( c. 328 Ma). Existence of a terrane in the seaway is not supported by the new data. Provenance studies and spatial arrangement allow reconstruction of the thin- to thick-skinned obduction style of the Harz Mountains onto the southeastern margin of East Avalonia (Rheno-Hercynian Zone) during the Variscan orogeny. Detrital zircon populations define Rheno-Hercynian and Saxo-Thuringian nappes. Intrusion of the granitoid plutons of the Harz Mountains occurred in a time window of c. 300 to 295 Myr and constrained the termination of Variscan deformation.

Abstract The Taconian–Grampian tract was characterized by a diachronous collision of a north-facing oceanic arc–forearc terrane and associated backarc basins with an irregular Laurentian margin with hyperextended segments. Hyperextension produced outboard continental terranes, separated by exhumed subcontinental mantle from the inboard margin. The exhumed mantle facilitated continued subduction of the extended margin after it had entered the trench. Enhanced slab-rollback resulted in spreading in lenticular backarc basins, which gradually transitioned along-strike into extensional arcs where rollback was less. Obduction of the oceanic elements onto the irregular Laurentian margin was followed by diachronous slab breakoff and a subduction polarity reversal, such that south- and north-dipping subduction zones locally were coeval along-strike. The polarity flip changed the convergence obliquity from dextral to sinistral and was accompanied by shallowing of the subducting slab near the end of the Middle Ordovician. Strike-slip movements locally juxtaposed segments where tectonic events occurred at different times, producing conflicting relationships. Slab breakoff produced punctuated magmatism, largely driven by mantle-derived melts, and drove and/or enhanced metamorphism in the overlying and enveloping crustal rocks. Boninite was generated episodically over a time span of 32 myr; the oldest Cambrian phase in the Lushs Bight Oceanic Tract (LBOT) and correlatives was associated with subduction initiation.

ABSTRACT The Baie Verte Line in western Newfoundland marks a suture zone between (1) an upper plate represented by suprasubduction zone oceanic crust (Baie Verte oceanic tract) and the trailing continental Notre Dame arc, with related upper-plate rocks built upon the Dashwoods terrane; and (2) a lower plate of Laurentian margin metasedimentary rocks with an adjoining ocean-continent transition zone (Birchy Complex). The Baie Verte oceanic tract formed during closure of the Taconic seaway in a forearc position and started to be obducted onto the Laurentian margin between ca. 485 and 476 Ma (early Taconic event), whereas the Birchy Complex, at the leading edge of the Laurentian margin, was subducted to maximum depths as calculated by pseudosection techniques (6.7–11.2 kbar, 315–560 °C) by ca. 467–460 Ma, during the culmination of the Taconic collision between the trailing Notre Dame arc and Laurentia, and it cooled isobarically to 9.2–10.0 kbar and 360–450 °C by 454–449 Ma (M 1 ). This collisional wedge progressively incorporated upper-plate Baie Verte oceanic tract rocks, with remnants preserved in M 1 high-pressure, low-temperature greenschist-facies rocks (4.8–8.0 kbar, 270–340 °C) recording typical low metamorphic gradients (10–14 °C/km). Subsequently, the early Taconic collisional wedge was redeformed and metamorphosed during the final stages of the Taconic cycle. We relate existing and new 40 Ar/ 39 Ar ages between 454 and 439 Ma to a late Taconic reactivation of the structurally weak suture zone. The Taconic wedge on both sides of the Baie Verte suture zone was subsequently strongly shortened (D 2 ), metamorphosed (M 2 ), and intruded by a voluminous suite of plutons during the Salinic orogenic cycle. Calculated low- to medium-pressure, low-temperature M 2 conditions in the Baie Verte oceanic tract varied at 3.0–5.0 kbar and 275–340 °C, with increased metamorphic gradients of ~17–25 °C/km during activity of the Notre Dame arc, and correlate with M 2 assemblages in the Birchy Complex. These conditions are associated with existing Salinic S 2 white mica 40 Ar/ 39 Ar ages of ca. 432 Ma in a D 2 transpressional shear zone and synkinematic intrusions of comparable age. A third metamorphic event (M 3 ) was recorded during the Devonian with calculated low-pressure, low-temperature conditions of 3.2–3.8 kbar and 315–330 °C under the highest metamorphic gradients (23–30 °C/km) and associated with Devonian–early Carboniferous isotopic ages as young as 356 ± 5 Ma. The youngest ages are related to localized extension associated with a large-scale transtensional zone, which reused parts of the Baie Verte Line suture zone. Extension culminated in the formation of a Middle to Late Devonian Neoacadian metamorphic core complex in upper- and lower-plate rocks by reactivation of Baie Verte Line tectonites formed during the Taconic and Salinic cycles. The Baie Verte Line suture zone is a collisional complex subjected to repeated, episodic structural reactivation during the Late Ordovician Taconic 3, Silurian Salinic, and Early–Late Devonian Acadian/Neoacadian orogenic cycles. Deformation appears to have been progressively localized in major fault zones associated with earlier suturing. This emphasizes the importance of existing zones of structural weakness, where reactivation took place in the hinterland during successive collision events.

ABSTRACT The Porvenir serpentinites are an ~600-m-thick body of meta-peridotites exposed in SW Iberia (Variscan Orogen). The serpentinites occur as a horse within a Carboniferous, out-of-sequence thrust system (Espiel thrust). This thrust juxtaposes the serpentinites and peri-Gondwanan strata onto younger peri-Gondwanan strata, with the serpentinites occupying an intermediate position. Reconstruction of the pre-Espiel thrust structure results in a vertical juxtaposition of terranes: Cambrian strata below, Porvenir serpentinites in the middle, and the strata at the footwall to the Espiel thrust culminating the tectonic pile. The reconstructed tectonic pile accounts for yet another major thrusting event, since a section of upper mantle (Porvenir serpentinites) was sandwiched between two tectonic slices of continental crust (a suture zone sensu lato). The primary lower plate to the suture is now overlying the upper plate due to the Espiel thrust. Lochkovian strata in the upper plate and the Devonian, NE-verging folds in the lower plate suggest SW-directed accretion of the lower plate during the Devonian, i.e., Laurussia-directed underthrusting for the closure of a Devonian intra-Gondwana basin. Obduction of the Porvenir serpentinites was a two-step process: one connected to the development of a Devonian suture zone, and another related to out-of-sequence thrusting that cut the suture zone and brought upward a tectonic slice of upper mantle rocks hosted in that suture. The primary Laurussia-dipping geometry inferred for this partially obducted suture zone fits the geometry, kinematics, and timing of the Late Devonian suture zone exposed in NW Iberia and may represent the continuation of such suture into SW Iberia.

ABSTRACT This three-day field trip focuses on the stratigraphy and the structural characteristics of the late- and post-Taconian sedimentary basins of the southern Québec Appalachians, with a particular emphasis on N-to-S and W-to-E structural and lithological variations. In order to discuss various aspects of the regional structural evolution of these basins, we will visit a series of key outcrops following three sections, the Beauce/Thetford-Mines sections, the Sherbrooke section, and the Coaticook section. RÉSUMÉ Cette excursion de trois jours se concentre sur la stratigraphie et les caractéristiques structurales des bassins sédimentaires tardi- et post-Taconien des Appalaches du sud du Québec, en mettant l’accent sur les variations structurales et lithologiques du nord au sud et d’ouest en est. Afin de discuter des divers aspects de l’évolution structurale régionale de ces bassins sédimentaires, nous visiterons une série d’affleure ments clés en suivant trois sections, soient les sections de Beauce/Thetford-Mines, de Sherbrooke, et de Coaticook.

Abstract This chapter provides comprehensive descriptions of 52 numbered formations/rock units of the Southeastern Oman Mountains, based on available literature. The oldest eight siliciclastic and carbonate formations are positioned below the ‘Hercynian’ Unconformity. The overlying formation (9–16) mostly represent carbonates which accumulated in a passive margin platform setting during or after the opening of the Neo-Tethys Ocean. The passive margin slope and platform collapsed during the late Cretaceous because of the obduction of the Semail Ophiolite along with the deep marine Hawasina sedimentary rocks. The collapsing passive margin interval was recorded within the syn-obductional Aruma Group (17; Muti Formation). Above this formation are the allochthonous units (18–42) of the tectonically lower Hawasina deep-sea basin and the structurally overlying Semail Ophiolite. The former contains Permian to Upper Cretaceous formations, while the latter is Cenomanian in age. Above the allochthonous rocks, the Neo-autochthonous formations were deposited, starting with the post-obductional uppermost Cretaceous Aruma Group (43; Al-Khod Formation) until the Quaternary deposits (52). All these formations/rock units are depicted on an accompanying map and stratigraphic chart.

Abstract This chapter is concerned with the main faults and folds within the Southeastern Oman Mountains based on available literature. The main, best and most widely exposed thrusts are those related to the SW-directed late Cretaceous obduction of the allochthonous nappes onto the Arabian platform and margin. These thrusts are related to obduction of rocks, which had formed hundreds of kilometres offshore Oman. The thrusts were active from the Cenomanian to the Campanian. Obduction-related thrusts and folds are spectacularly exposed within the rocks of the Arabian platform in the eastern part of the Saih Hatat Dome, including large-scale recumbent cylindrical folds and sheath folds. At least six fold sets can be studied in the Southeastern Oman Mountains. At least two of them had formed prior to obduction and are exposed in the Pre-Permian formations of the Jabal Akhdar Dome. At least three fold sets formed in the course of obduction, while at least one fold set is postobductional in age. Besides the compressional structures, the Oman Mountains expose major post-obductional extensional faults, mostly at the margins of the Jabal Akhdar and Saih Hatat domes. The throw of these faults amounts to a few to several kilometres. Finally, this chapter provides an overview of the enigmatic Batinah Mélange which consists of slivers of Hawasina rocks, resting (unusually) structurally above the Semail Ophiolite.

Abstract The Southeastern Oman Mountains are dominated by two major culminations: the Jabal Akhdar and Saih Hatat domes, surrounded by allochthonous and/or neo-autochthonous rocks. In the cores of both domes, folded autochthonous and par-autochthonous pre-Permian metasedimentary rocks are exposed, subjacent to the ‘Hercynian’ Unconformity. Above the unconformity are Permo--Mesozoic shelfal sedimentary rocks, characterized by carbonates. These sedimentary rocks were openly folded. The open folds are large-scale elongate structures that define the shapes of both domes. The main elongation direction is NW--SE. Doming is syn- to post-obductional. Most margins of the domes are marked by major post-obductional, extensional faults. Reactivated basement faults along the eastern margin of the Jabal Akhdar Dome may be responsible for the straight NNE-striking eastern margin which is perpendicular to the main elongation direction of the domes. The deep structure of both domes is poorly known. However, the Moho depth below the centre of the Jabal Akhdar Dome is at 50 km. We present a geological map of both domes, depicting the main faults and folds, and schematic cross-sections, parallel and perpendicular to the Oman Mountains.