Chronostratigraphic framework and provenance of the Ossa-Morena Zone Carboniferous basins (SW Iberia)

Abstract

<jats:p>Abstract. Carboniferous siliciclastic and silicic magmatic rocks from the Santa Susana-São Cristovão region contain valuable information regarding the timing of synorogenic processes in SW Iberia. In this region of the Ossa-Morena Zone (OMZ), Late Carboniferous terrigenous strata (i.e. the Santa Susana Formation) unconformably overlie Early Carboniferous marine siliciclastic deposits alternating with volcanic rocks (i.e. the Toca da Moura volcano-sedimentary complex). Lying below this intra-Carboniferous unconformity, the Toca da Moura volcano-sedimentary complex is intruded and overlain by the Baleizão porphyry. Original SHRIMP and LA-ICP-MS U-Pb zircon are presented in this paper, providing chronostratigraphic and provenance constraints, since available geochronological information is scarce and only biostratigraphic ages are currently available for the Santa Susana-São Cristovão region. Our findings and the currently-available detrital zircon ages from Paleozoic terranes of SW Iberia (Pulo do Lobo Zone- PLZ, South-Portuguese Zone- SPZ, and OMZ), were jointly analyzed using the K-S test and MDS diagrams to investigate provenance. The marine deposition is constrained to the age interval of c. 335–331 Ma (Visean) by new U-Pb data for silicic tuffs from the Toca da Moura volcano-sedimentary complex. The Baleizão porphyry, intrusive in the Toca da Moura volcano-sedimentary complex, yielded a crystallization age of c. 317 Ma (Bashkirian), providing the minimum age for the overlying intra-Carboniferous unconformity. A comparison of detrital zircon populations from siliciclastic rocks of the Cabrela and Toca de Moura volcano-sedimentary complexes of the OMZ suggests that they derived from distinct sources more closely associated with the SPZ and PLZ than the OMZ. Above the intra-Carboniferous unconformity, the Santa Susana Formation is either the result of the recycling of distinct sources located in the Laurussian-side (SPZ and PLZ) and Gondwanan-side (OMZ) of the Rheic suture zone. The best estimate of the crystallization age of a granite cobble found in a conglomerate from the Santa Susana Formation yielded c. 303 Ma (Kasimovian-Gzhelian), representing the maximum depositional age for the terrestrial strata. The intra-Carboniferous unconformity seems to represent a stratigraphic gap of approximately 12–14 Ma, providing evidence of the rapid post-accretion/collision uplift of the Variscan orogenic belt in SW Iberia (i.e. the OMZ, PLZ and SPZ). </jats:p>

Syn-collisional detrital zircon source evolution in the northern Moroccan Variscides

“…Journal Pre-proof magmatic rocks are known in the Coastal Block (Pouclet et al, 2018), but they are restricted to volcanic focuses with limited spread. Therefore, we can infer that the Moroccan Variscides were only partially affected by the magmatism related to the Cambrian-Ordovician rifting, probably because of their more inland position in the Gondwana margin than other regions, such as the Ossa-Morena and Central Iberian Zones (Figure 1A), where this kind of magmatism was ubiquitous and Cambrian-Ordovician detrital zircon grains are usually present in syn-orogenic rocks (Martínez Catalán et al, 2008;Pastor-Galán et al, 2013b;Pereira et al, 2020b).…”

Reply to the interactive comment of referee#1

“…That is, until then, from Late Devonian to Early Carboniferous, they probably have had a different and independent geodynamic evolution. Using a different perspective than the one followed by the previous models, we consider that the geodynamic evolution in SW Iberia may have been related to the closure of two oceanic basins that will have coexisted in the Devonian as suggested by paleogeographic reconstructions (Cocks and Torsvik, 2006;Stampfli and Kozur, 2006;Stampfli et al, 2013); Our recently proposed geodynamic model (Pereira et al, in press) admits: i) the closure of the Rheic Ocean in the Late Devonian under Laurussia, with the development of a magmatic arc (well-documented in the Meguma terrane, Nova Scotia) and synorogenic basins; this active margin of Laurussian was progressively accreted to the Gondwana passive margin facing the Rheic Ocean; at the same time, the Gondwana C3 passive margin facing the Paleotethys Ocean was developing (i.e. OMZ), immediately after the two ocean basins have coexisted ; ii) the onset of the closure of the Paleotethys Ocean in the Early Carboniferous under Gondwana (i.e.…”