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The Tseel terrane in the Gobi Desert of SW Mongolia consists of a composite crustal segment of imbricated sheets of high- and low-grade metamorphic rocks of predominantly middle Palaeozoic age. New sensitive high-resolution ion microprobe (SHRIMP) zircon ages of 396 [+ or -] 3 Ma (20) and 397 [+ or -] 3 Ma (20) for two calc-alkaline metarhyolite samples indicate arc volcanism during the early Devonian. An undeformed feldspar porphyry cross-cutting the early Devonian low-grade sequence yielded an emplacement age of 279 [+ or -] 2 Ma (2[sigma]). Geochemical and Nd isotopic data for low-grade mafic metavolcanic rocks are consistent with melting of moderately depleted upper mantle sources in a transitional arc--back-arc setting. In addition, there are high- and low-grade felsic metaigneous rocks with subduction-related chemical signatures and heterogeneous Nd isotopic compositions indicating an origin from mixed sources, including juvenile and Precambrian crustal components. The field observations combined with the geochemical and isotopic data suggest that the Tseel terrane represents a segment of a mature Japan-type arc associated with a juvenile back-arc basin. Supplementary material: Latitudes and longitudes of sample localities, major- and trace-element abundances for rock samples, data for reference materials obtained by LA-ICP-MS and Sm--Nd isotopic data for rock samples are available at http://www.geolsoc.org.uk/SUP18338.

The Tanneron massif belongs to the southernmost segment of the Variscan belt in France and is composed of migmatitic orthogneisses and paragneisses cross-cut by a main tonalite-granite complex. Late Carboniferous detrital basins are bounded by north-south-trending ductile to brittle normal faults and delineate three distinct zones. Our new isotope dilution U-Pb monazite dating indicates a pre-Variscan history in the central part of the massif recorded by monazites from an orthogneiss yielding ages from 440 to 410 Ma, whereas monazites from a migmatitic paragneiss record a late Carboniferous high-Tevent at 317 [+ or -] 1 Ma. In the eastern part, a migmatization event is recorded by monazites from a synkinematic leucogranitic layer and a mylonitic orthogneiss yielding ages of 309 [+ or -] 5 and 310 [+ or -] 2 Ma, respectively. Later post-collisional magmatism related to lithospheric thinning is recorded by the intrusion of undeformed granitic bodies at 302 [+ or -] 4 and 297 k 5 Ma, and marks the final stage of the Variscan evolution. The data indicate the presence of two crustal blocks, displaying different levels of exposure of the Variscan crust. The overall tectonomagmatic evolution of this massif suggests a strong affinity with the internal part of the Variscan belt.