Late Miocene volcanic rocks host the Sari Gunay epithermal gold deposit in NW Iran. These rocks are located within the Hamedan–Tabriz volcanic belt and occupy the northwestern part of the Sanandaj–Sirjan zone (SaSZ). The volcanic rocks span in composition from latite to dacite and rhyolite. Plagioclase, hornblende, biotite and quartz are the main phenocrysts in a fine-grained and glassy matrix. Laser ablation inductively coupled plasma mass spectrometry zircon U–Pb dating yielded crystallization ages of 10.10 ± 0.01 Ma and 11.18 ± 0.14 Ma for rhyolite and dacite, respectively. High ratios of Sr/Y (> 20) and La/Yb (> 20), high contents of Sr (≥ 400 ppm), low contents of MgO (≤ 6 wt%), Y ≤ 18 ppm (c. 16.5 ppm), Yb ≤ 1.9 ppm (c. 1.53 ppm) and weak negative Eu anomalies (Eu*/Eu c. 0.81) are compatible with a high-silica adakitic signature of the rocks. Regarding the location of the study area nearly 100 km from the Zagros suture zone, we argue that delamination of lithospheric mantle beneath the SaSZ has played a key role in the development of the adakitic rocks in a post-collision tectonic regime. The adakitic melts are suggested to have formed by partial melting of delaminated continental lithosphere and/or lower crustal amphibolite following the collision of the Arabian and Iranian plates.

As the remnant of the South Qilian Ocean, the South Qilian suture zone recorded abundant information on the Cambrian–Ordovician subduction history of the southern branch of the Proto-Tethyan Ocean. However, the closure timing of the South Qilian Ocean and subsequent collision are poorly constrained. In this study, we report early Silurian (433–435 Ma) U–Pb ages of felsic subvolcanic rocks from Lianhuashan, Ayishan and Shihuiyao of the Lajishan district within the South Qilian suture zone. They intruded the Late Ordovician – Silurian sedimentary or Late Ordovician volcanic rocks and have high SiO2 (61.43–73.06 wt%), Sr/Y ratios with significant different rare earth elements (REEs) and trace-element spider diagrams, and Sr–Nd isotopic compositions, probably implying that they were formed through distinctly different generation mechanisms. Geochemistry of the Lianhuashan dacites reveals compositions typical of adakitic rocks derived from partial melting of lower crust in a thickened setting. The Ayishan dacites were derived from partial melting of crustal materials with the involvement of minor peridotite mantle, and the Shihuiyao rhyolites were derived from partial melting of felsic crust. The similar geochemical characteristics of coeval post-collisional igneous rocks in the Central Qilian and South Qilian blocks indicates that the lower Silurian subvolcanic rocks were generated in a thickened crust of post-collisional setting. Considering their intrusive contacts with Late Ordovician – Silurian retro-foreland basin and Late Ordovician collisional volcanic rocks, we propose that the South Qilian suture zone was at a transitional stage from collisional to post-collisional during the early Silurian Period.

The Qinling–Dabie orogen in central China is one of the major orogenic belts in East Asia. In the eastern Dabie–Sulu region, mafic lamprophyres show the enriched signatures of old sub-continental lithospheric mantle. However, little is known about the mafic igneous rocks and their lithospheric mantle sources in the western Qinling Range. New 40Ar–39Ar age dating, major- and trace-element data, and isotopic analyses of Qinling lamprophyres reveal their differences from the Dabie Sulu lamprophyres. Biotite 40Ar–39Ar dating yielded a plateau age of 219±2 Ma, identical to the ages of rapakivi-textured granitoids in the area. The association of lamprophyre dykes and rapakivi-textured granitoids indicates that the Qinling region was a post-collisional setting at c. 220 Ma. The Qinling lamprophyres are calc-alkaline, and rich in large ion lithophile elements (e.g. Ba, K), but depleted in Nb, Ta and Ti. They show highly fractionated REE patterns with LaN>100 and HREE <10 times chondrite abundances. εNd (219 Ma) values range from −0.5 to −3.3 and initial Sr isotope values from 0.7036 to 0.7058. These features suggest generation of the lamprophyre by partial melting of a metasomatized, garnet peridotite mantle source. The Qinling lamprophyres are distinct from the Dabie–Sulu lamprophyres in emplacement age (c. 135 Ma for Dabie–Sulu) and isotopic composition, suggesting that the nature of the lithospheric mantle and geodynamic evolution of the Qinling region contrasts with that of the Dabie–Sulu region.