The supercontinent of Pangaea formed through the diachronic collision of Laurussia and Gondwana during the Late Paleozoic. Whilst magmatism associated with its formation is well documented in the Variscan orogeny of Europe and Alleghanian orogeny of the USA, little is known about the Sonora orogeny of Northern Mexico. This paper reports geochronology (U-Pb zircon), whole rock geochemistry and Lu-Hf zircon isotope data on basement cores from the Western Gulf of Mexico, that are used to develop a tectonomagmatic model for pre-to post-Pangaea amalgamation. Our results suggest the existence of three distinct phases of magmatism, produced during different stages of continental assembly and disassembly. The first phase consists of Early Permian (294-274 Ma; n= 3) granitoids with geochemical signatures indicative of a continental arc tectonic setting. This phase formed on the margins of Gondwana during the closure of the Rheic Ocean, prior to the final amalgamation of Pangaea. It likely represents a lateral analogue of Late Carboniferous-Early Permian granitoids that intrude the Acatlán and Oaxacan Complexes. The second phase of magmatism includes Late Permian-Early Triassic (263-243 Ma; n= 13) granitoids with suprasubduction geochemical affinities. However, Lu-Hf isotope data indicate that these granitoids formed from crustal anatexis, with ɛHf values and two-step TDM(Hf) model ages comparable to the Oaxaquia continental crust that they intrude. This phase of magmatism is likely to be related to coeval granitoids in the Oaxaca area and Chiapas Massif. We interpret it to reflect late-to post-collisional magmatism along the margin of Gondwana following the assembly of Pangaea. Finally, the third phase of magmatism includes Early-Middle Jurassic (189-164 Ma; n= 2) mafic porphyries that could be related to the synchronous supra-subduction magmatism associated with the Nazas arc. Overall, our results are consistent with Pangaea assembly through diachronous collision of Laurussia and Gondwana during subduction of the Rheic Ocean. They suggest that post-orogenic magmatism in the western termination of the Rheic suture occurred under the influence of a Panthalassan subduction zone, before opening of the Gulf of Mexico.
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.
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