Permian doleritic dikes in the Beishan Orogenic Belt, NW China: Asthenosphere–lithosphere interaction in response to slab break-off

摘要: Abstract Extensive Permian mafic–ultramafic intrusions crop out within the Central Asian Orogenic Belt (CAOB). Because magmatic activity is spatially and temporally associated with Tarim Large Igneous Province (LIP), a mantle plume has been invoked to explain petrogenesis of these rocks. In order test this hypothesis, we present new geochronological geochemical data for doleritic dike swarms in Beishan area, southern CAOB. Zircon U–Pb dating Yinaoxia Gubaoquan dikes indicates that they were emplaced during Early (ca. 282 Ma). The have higher Mg# (52–74) eNd(t) values (9.0–9.1) than (Mg# = 35–56; eNd(t) = 5.8–7.4), indicating former are more primitive latter. characterized by Ba/Nb (15–276), Ba/La (6–103), Th/Yb (0.12–0.24) Th/Nb (0.20–0.36) ratios, suggesting their parental magmas contained subduction-related material. Calculated compositions equilibrium Cr-rich clinopyroxenes LREE-depleted flat REE patterns ((La/Yb)N = 0.57–1.28) negative slightly positive Nb anomalies ((Nb/La)PM = 0.33–0.91). These suggest may generated interaction between depleted asthenospheric metasomatized lithospheric mantle. Using clinopyroxene–liquid thermobarometers, estimate temperature range 1142 °C–1276 °C, indicative an upper source. Although coeval LIP, petrological do not abnormally high temperatures or OIB-like signatures characterize source LIP magmas. This means cannot account formation does extend area. Instead, probably derived from partial melting upwelling was subsequently contaminated various degrees slab break-off scenario.