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Carboniferous magmatism in southwestern Iberia was continuously active for more than 60 m.y. during the development of the Appalachian-Variscan belt of North America, North Africa and Western-Central Europe. This collisional orogen that records the closure of the Rheic Ocean is essential to understanding the late Paleozoic amalgamation of the Pangea supercontinent. However, the oblique convergence between Laurussia and Gondwana that lasted from the Devonian to the Carboniferous was likely more complex. Recently, a new tectonic model has regarded the Iberia Variscan belt as the site of coeval collisional and accretionary orogenic processes. Early Carboniferous plutonic rocks of southwest Iberia indicate arc magmatism in Gondwana. The Ossa-Morena Zone (OMZ) acted as the upper plate in relation to the geometry of the Paleotethys subduction. This active accretionary-extensional margin was progressively involved in a collisional phase during the Late Carboniferous. Together, the Évora Massif and the Beja Igneous Complex include three successive stages of bimodal magmatism, with a chemical composition indicative of a long-lived subduction process lasting from the Tournaisian to the Moscovian in the OMZ. The earliest stage of arc magmatism includes the Tournaisian Beja and Torrão gabbro-dioritic rocks of the Layered Gabbroic Sequence. We present new geochemical and Nd isotopic and U-Pb geochronological data for magmatic rocks from the Main (Visean-Serpukhovian) and Latest (Bashkirian-Moscovian) stages of arc magmatism. Visean Toca da Moura trachyandesite and rhyolites and Bashkirian Baleizão porphyries and Alcáçovas quartz diorite share enriched, continental-crust like characteristics, as indicated by major and trace elements, mainly suggesting the addition of calc-alkaline magma extracted from various mantle sources in a subduction-related setting (i.e., Paleotethys subduction). New U-Pb zircon geochronology data have allowed us to establish a crystallization age of 317 ± 3 Ma (Bashkirian) for Alcáçovas quartz diorite that confirms a temporal link with Baleizão porphyry. Positive εNd(t) values for the Carboniferous igneous rocks of the Beja Igneous Complex and the Évora gneiss dome indicate production of new juvenile crust, whereas negative εNd(t) values also suggest different grades of magma evolution involving crustal contamination. The production and evolution of Carboniferous continental crust in the OMZ was most likely associated with the development of an active continental margin during the convergence of the Paleotethys Ocean with Gondwana, involving juvenile materials and different grades of crustal contamination. Full article

The Yamansu deposit, which is hosted in the volcanic-sedimentary sequence of the Carboniferous Yamansu Formation in Eastern Tianshan, NW China, contains many skarns, and the orebodies occur in the ore district in stratoidal, banded or lenticular forms. Four alteration stages, namely, albite–tourmaline–apatite–Grt1 (Stage I), K-feldspar–Grt2 (Stage II), magnetite–chlorite–epidote (Stage III), and quartz–calcite–axinite–Grt3 (Stage IV), are distinguished in the Yamansu deposit. The mineral geochemistry associated with each different stage is presented to provide a better understanding of the corresponding metallogenic processes. The ore-forming fluid in Stage I was derived from a magmatic–hydrothermal source and formed at high temperatures with many volatiles. This ore-forming fluid, which contained considerable metallogenic materials during the early stage, likely experienced diffusive metasomatism in a closed system with low water/rock (W/R) ratios. Mineral geochemical analyses show that the Fe content gradually increases from Stage I to Stage II, indicating that accumulated ore-forming materials were available during changes in the physicochemical conditions from a reducing environment with neutral pH to oxidizing conditions with mildly acidic pH. During the main metallogenic stage (Stage III), mineral assemblages reflect moderate- to high-temperature conditions, and the ore-forming fluid was created and destroyed periodically; the magnetite ores were deposited in a fluctuating fluid system. The multilayered orebodies, multigenerational garnets, and minerals with oscillatory zoning indicate that the ore-forming fluid may have developed periodic fluctuations, and this special multistage fluctuation of the hydrothermal fluid in the Yamansu deposit was the key factor controlling the multiple extraction, enrichment and precipitation of metallogenic materials. Full article