From the Upper Ordovician unconformity to the core-mantle boundary: A review of the Ordovician events in the Canigó massif, Pyrenees

Variscan migmatites cropping out in the eastern Pyrenees were dated together with Late Variscan plutonic rocks. Upper Proterozoic–Lower Cambrian series were migmatized during a thermal episode that occurred in the interval 320–315 Ma coeval with the main Variscan deformation event (D 1 ). The calc-alkaline Sant Llorenç–La Jonquera pluton and the gabbro–diorite Ceret stock were emplaced during a later thermal episode synchronous with the D 2 deformation event. A tonalite located at the base of La Jonquera suite intruded into the upper crustal levels between 314 and 311 Ma. The gabbro–diorite stock was emplaced in the middle levels of the series in two magmatic pulses at 312 and 307 Ma. The thermal evolution recorded in the eastern Pyrenees can be correlated with that of neighbouring areas of NE Iberia (Pyrenees–Catalan Coastal Ranges) and SE France (Montagne Noire). The correlation suggests a NW–SE-trending zonation where the northeasternmost areas (Montagne Noire and eastern Pyrenees) would occupy relatively more internal zones of the orogen than the southwesternmost ones. Supplementary material: Methods and U–Th–Pb isotopic and REE geochemical data for zircon are available at www.geolsoc.org.uk/SUP18703 .

The Ordovician successions of France and neighbouring areas of Belgium and Germany are reviewed and correlated based on international chronostratigraphic and regional biostratigraphic charts. The same three megasequences related to the rift, drift and docking of Avalonia with Baltica can be tracked in Belgium and neighbouring areas (Brabant Massif and Ardenne inliers), western (Rhenish Massif) and northeastern Germany (Rügen). The remaining investigated areas were part of Gondwana in the Ordovician. The Armorican Massif shares with the Iberian Peninsula a Furongian–Early Ordovician gap (Toledanian or Norman gap), and a continuous Mid–Late Ordovician shelf sedimentation. The Occitan Domain (Montagne Noire and Mouthoumet massifs), eastern Pyrenees and northwestern Corsica share with southwestern Sardinia continuous shelf sedimentation in the Early Ordovician, and a Mid Ordovician ‘Sardic gap’. In the Ordovician, the Maures Massif probably belonged to the same Sardo-Occitan domain. The Vosges and Schwarzwald massifs display comparable, poorly preserved Ordovician successions, suggesting affinities with the Teplá-Barrandian and/or Moldanubian zones of Central Europe.

This contribution addresses the current state of knowledge of the mainly siliciclastic Ordovician rocks in Jordan, Syria and southern Turkey, including advances in palaeontology, stratigraphy, depositional facies analysis and supra-regional correlation. The extensive and excellent exposures of the sedimentary succession in southern Jordan represent the regional reference for the Ordovician System in the southern Levant. We discuss the sedimentological and faunal characteristics as well as the stratigraphy and correlation of the succession. For the northern Levant (especially southeastern Turkey) and the western and eastern Taurides, the Ordovician succession and an updated sedimentary architecture is explained, and a comprehensive correlation for the region is presented. Increased knowledge on the fossil content from these regions enables correlation across the southern parts of the Arabian Plate to southern Turkey, and with the greater Gondwanan regions, far field as southwestern Europe and northern Africa. The depositional environments in the southern and northern Levant and southern Turkey encompass non-marine to shallow-marine areas in the lower part of the Ordovician that are followed upsection by shelf deposits of variable proximity up to the glacial episode in the Late Ordovician that is traceable in each of the areas. Characteristic signals in the Ordovician succession are represented by the trans-regional early Darriwilian unconformity and by the base of the Hirnantian glacial-related deposits followed by lower Silurian strata, visible across the entire region. New data from zircon-based provenance analysis clearly implicate the Arabian Shield as the main source of a huge amount of the clastic detritus within the Ordovician succession. In the course of the entire Cambrian–Ordovician interval, progressive deeper erosion of the Arabian Shield occurred. Sediment sources from regions farther away indicate long time of exposure and resedimentation, and some long-distance transportation, but their sedimentary influence was only of minor extent. The excellent outcrops mainly in southern Jordan, in southeastern Turkey and in the Taurides represent potential regions for further research.

Detailed geological mapping of the La Cerdanya area (Canigó unit, Eastern Pyrenees) provides new data characterizing the different structural styles exhibited by Cambrian–Lower Ordovician (Jujols Group) and Upper Ordovician successions. Their unconformable contact, related to the Sardic Phase, ranges from 0° (paraconformity) to 90° (angular discordance). The Jujols Group rocks topped by the unconformity are affected by Sardic foliation-free open folds. The pre-Sardic succession, the Sardic Unconformity and the lower part of the post-Sardic succession (Rabassa Conglomerate and Cava formations) are cut and offset by several Late Ordovician NNE–SSW-trending synsedimentary extensional faults associated with hydrothermal activity, which dramatically affected the thickness of the lower part of the Upper Ordovician succession. We relate (1) the Mid-Ordovician Sardic uplift and erosion, and (2) a Mid- to Late-Ordovician upward propagating extensional fault system bounding the outline of half-grabens, subsequently infilled by alluvial deposits, to a thermal doming event (about 475–450 Ma) that led to the uplift and stretching of the Ordovician lithosphere. Thermal doming may be caused by mafic magma underplating and responsible for the coeval calc-alkaline magmatic activity broadly developed in the Eastern Pyrenees. We discuss the similarities between the Mid-Ordovician Sardic Unconformity and other Early Paleozoic unconformities described in neighbouring areas. Finally, we suggest a geodynamic scenario in which a regional-scale thermal event was related to the opening of the Rheic Ocean that led to the drift of Avalonia from the SW European margin of Gondwana.

The Ediacaran-Lower Ordovician successions exposed in the Eastern Pyrenees are updated and revised based on recent U-Pb zircon radiometric ages, intertonguing relationships of carbonate-dominated strata, and onlapping patterns marking the top of volcano-sedimentary complexes. A stratigraphic comparison with neighbouring pre-Variscan outcrops from the Montagne Noire (southern French Massif Central) and Sardinia is related to i) the absence of Cadomian deformation close to the Ediacaran-Cambrian boundary interval; ii) the presence of an episodic, Cadomian-related, acidic-dominant volcanism related to carbonate production punctuating the Ediacaran-Cambrian transition, similar to that recorded in the northern Montagne Noire; and iii) the lack of Guzhangian (Late Cambrian Epoch 3) regressive shoal complexes present in the Montagne Noire and probably in Sardinia.

Les Pyrénées centrales et orientales au début du Paléozoique (Cambrien s.l.): évolution paléogéographique et géodynamique

The lower Paleozoic succession of central Europe exposed in the Bohemian Massif is a classic area of geology with a long-standing tradition of research dating back to the eighteenth century. The Ordovician rocks form parts of sections in several units that sit on the Cadomian basement. These sedimentary and volcano-sedimentary fills of partial depressions in the basement are relics of the system of rift basins in the Gondwanan margin reflecting the rifting of the Rheic Ocean. The Ordovician sections are related to the subsidence period during the extensional regime accompanied by volcanism. They are underlain by Neoproterozoic or Cambrian rocks and continue up usually without breaks. After closure of the Rheic Ocean owing to the Gondwana–Laurussia collision, the Ordovician successions were incorporated into the Variscan Orogen belt and preserved in denudation relics such as the Bohemian Massif and its units. Ordovician strata with Gondwanan shelf affinities can be traced along the Variscans from Spain to central Europe, and are reflected in the regional stratigraphic scale based mainly on the succession in the Prague Basin. The Ordovician fill of this accumulation centre, together with relics of another preserved in the Schwarzburg Anticline, represents the main exposures in the Bohemian Massif. The individual features of the Ordovician successions, such as facies developments, fossil associations and volcanism, make them model areas both for understanding the palaeogeographic and geotectonic evolution of the peri-Gondwanan margin and a stratigraphic standard for a cool-water regime.

Aeromagnetic and field data suggest that meta‐igneous rocks exposed on the south coast of central Victoria at Waratah Bay, Phillip Island, Barrabool Hills and inland near Licola, are continuous—beneath Bass Strait—with Proterozoic/Cambrian igneous rocks in King Island and Tasmania. This correlation is supported by a pre‐Early Ordovician unconformity above gabbro protomylonite at Waratah Bay, age equivalent to the Tasmanian Tyennan unconformity. Cambrian volcanics at Licola and unusual features of the Melbourne Zone sequence indicate that Tyennan continental crust extends north as basement to the central Victorian portion of the Lachlan Fold Belt. In contrast, adjacent parts of the Lachlan Fold Belt in Victoria contain conformable sea‐floor sequences that span the Early Cambrian to Late Ordovician, with no evidence of either Cambrian deformation or underlying continental basement. The block of Tyennan continental crust beneath central Victoria—the Selwyn Block—is fundamentally different, and has influenced temporal and spatial patterns of sedimentation, deformation, metamorphism and plutonism. Palaeogeographical reconstructions suggest that the block was a submarine plateau that lay outboard of the Australian craton, upon which a condensed Ordovician sequence was deposited. The sequence above the Selwyn Block unconformity at Waratah Bay is similar to widespread post‐Tyennan sediments in western Tasmania. During Late Ordovician and Early Silurian deformation, the Selwyn Block protected much of the overlying sedimentary sequence. Instead, shortening was focused into the Stawell and Bendigo Zones to the west. These zones were sandwiched between the Selwyn Block and the Australian craton in a ‘vice’ scenario reminiscent of some Appalachian orogenic events. The region above the Selwyn Block was downwarped adjacent to the overthrust Bendigo Zone as a foreland deep, into which a conformable clastic wedge of sediment was deposited in Late Ordovician to Devonian time, prior to final Middle Devonian deformation. The Selwyn Block includes the Cambrian calc‐alkaline Licola and Jamieson Volcanics that are correlated with the Tasmanian Mt Read Volcanics. In Victoria, these form a basement high controlling the unusual down‐cutting thrusts in the overlying Melbourne Zone and explaining the major structural vergence reversal between the Melbourne and Tabberabbera Zones. The Selwyn Block has exerted some control on the timing, chemistry and distribution of post‐orogenic granites, and on central Victorian gold mineralisation. Reactivated faults in the block influenced deposition, and continue to control the deformation of the portions of the Otway and Gippsland Basins that lie above it.

The arrival of brachiopods of the Nicolella Community to the Mediterranean margin of Gondwana during the Late Ordovician: Palaeogeographical and palaeoecological implications

U–Pb zircon ages (SHRIMP) for Cadomian and Early Ordovician magmatism in the Eastern Pyrenees: New insights into the pre-Variscan evolution of the northern Gondwana margin

Pre-Variscan basement rocks from the Pyrenees provide evidence of several magmatic episodes with complex geodynamic histories from late Neoproterozoic to Palaeozoic times. One of the most significant episodes, consisting of several granitic and granodioritic bodies and volcanic rocks, mostly pyroclastic in nature, dates from the Late Ordovician period. In the Eastern Pyrenees, this magmatism is well represented in the Ribes de Freser and Núria areas; here, the Núria orthogneiss and the Ribes granophyre, both dated at c. 457–460 Ma, seem to form a calc-alkaline plutonic suite emplaced at different crustal levels. The presence of numerous pyroclastic deposits and lavas interbedded with Upper Ordovician (Sandbian–lower Katian, formerly Caradoc) sediments, intruded by the Ribes granophyre, suggests that this magmatic episode also generated significant volcanism. Moreover, the area hosts an important volume of rhyolitic ignimbrites and andesitic lavas affected by Alpine deformation. These volcanic rocks were previously attributed to late Variscan volcanism, extensively represented in other areas of the Pyrenees. Here we present the first five laser-ablation U–Pb zircon dates for this ignimbritic succession and two new ages for the Ribes granophyre. The ages of the ignimbrites, overlapping within error, are all 460 Ma, suggesting a genetic relationship between the plutonic and volcanic rocks and indicating that the Sandbian–Katian magmatism is much more voluminous than reported in previous studies, and possibly includes mega-eruptions linked to the formation of collapse calderas.

Late Ordovician magmatism is well-represented in all massifs of the Eastern Pyrenees and the Catalan Coastal Ranges but has not been reported in the central parts of the Pyrenean Axial Zone. This work shows the first geochronological evidence for Late Ordovician magmatism in the Pallaresa massif. This massif is a large E–W trending antiformal structure cored by Paleozoic rocks with a Variscan tectonothermal overprint. The lower Paleozoic sequence shows an Upper Ordovician succession lying unconformably on older Cambrian–Ordovician beds. Despite Variscan overprint, the Cambrian–Ordovician rocks record evidence of a pre-Variscan penetrative fabric which is not present in the rest of the overlying Paleozoic succession. In the eastern part of the Pallaresa massif, rhyodacitic to dacitic subvolcanic rock forming sills intercalated within the Cambrian–Ordovician succession close to the base of the Upper Ordovician rocks have been identified and sampled. These volcanic rocks have a Variscan penetrative foliation and lack the additional pre-Variscan deformation. U–Pb zircon dating of one these subvolcanic levels by U–Pb CA-ID-TIMS, has provided an age of 453.6 ± 1.5 Ma (Sandbian) and the zircon has given ɛHf450 values between − 2.4 and − 5.9, suggesting a mixed source. These new data strengthen the Paleozoic correlation of the Central and Eastern Pyrenees indicating that the Late Ordovician magmatism in the Pyrenees was associated with a pre-Variscan event responsible for the Upper Ordovician angular unconformity and the presence of a penetrative pre-Variscan deformation affecting the underlying Cambrian–Ordovician sequence. This new data, coupled with the occurrence of Zn–Pb SEDEX o Mississippi Valley type deposits associated with Upper Ordovician rocks, suggest the evidence of extensional tectonic activity during Late Ordovician times.

Cambrian–Ordovician depositional sequences in the Middle East: A perspective from Turkey

Magma emplacement during exhumation of the lower- to mid-crustal orogenic root: The Jihlava syenitoid pluton, Moldanubian Unit, Bohemian Massif

In this contribution, we investigate the spatial and temporal evolution of mid-crustal flow in the Agly Massif (North Pyrenean Zone) that represents the southern foreland of the Variscan orogenic plateau. In the Agly Massif, the middle crust is represented by an Ediacarian–Devonian series of metasedimentary rocks that recorded high-grade metamorphism synchronously with crustal thinning (D2) and dextral wrenching (D3) during Carboniferous. D2 crustal thinning formed a penetrative S2 flat-lying foliation and localized C2 extensional shear zones with a top-to-the-North kinematics. D2 planar fabrics are deformed by a D3 dextral transpression localized into a two-kilometer wide high-strain zone. We performed LA-ICPMS U–Th–Pb dating on zircon and monazite from small magmatic bodies and from metamorphic rocks showing strain features relative to D2 and/or D3. Our results, compiled with published data, argue that the middle crust of the Agly Massif reached high-temperature and suprasolidus conditions at ca. 325–320 Ma and was partially molten until ca. 300 Ma. They also indicate that the D2 thinning and top-to-the north shearing was active from ca. 325–290 Ma. D2 extension and D3 transpression were synchronous from ca. 308–290 Ma. Making a comparison with the Pyrenean Axial Zone, the Montagne Noire and the French Central Massif, we propose a two-step tectonic model for the mid-crustal flow with a horizontal flow towards South in both the orogenic plateau and the southern forelands between ca. 325 and 310 Ma and locally reoriented into an E–W longitudinal flow between 310 and 300 Ma in high-strain dextral strike-slip shearing domains.