标题：Geochronology and geochemistry of Late Carboniferous dykes in the Aqishan–Yamansu belt, eastern Tianshan: Evidence for a post-collisional slab breakoff
摘要：AbstractWith aim of providing constraints on the Late Paleozoic tectonic evolution of the southern Central Asian Orogenic Belt (CAOB), an integrated study was conducted on the geochronological and geochemical data for dioritic, granitic and diabase dykes from the Aqishan–Yamansu belt in the eastern Tianshan, NW China. Zircon U-Pb dating indicates that the dioritic and granitic dykes were both emplaced in the Late Carboniferous (∼311 Ma and ∼315 Ma). The dioritic dykes show adakitic characteristics and have high Na2O and positiveεHf(t) values (+12 to +17), which suggest an origin from partial melts of a subducted oceanic slab. The granitic dykes have high SiO2and K2O contents and are characterized by enriched light rare earth elements (LREE) and slightly flat heavy rare earth elements (HREE), with negative Eu and Nb–Ta–Ti anomalies. These dykes are alkali-calcic and show geochemical features of highly fractionated I-type granites. Their positiveεHf(t) values (+16 to +17) suggest that they were derived from a juvenile accreted oceanic crustal source. The coeval diabase dykes have low SiO2and K2O contents but high TiO2, MgO and Mg# (54–59). They are enriched in LREE and show characteristics of enriched mid-ocean ridge basalts (E-MORB). The relatively high Ba/Th, slightly low Th/Ta ratios, and negative Nb-Ta anomalies imply a mantle source metasomatised by slab-derived fluids. Thus, these basic dykes were generated likely by partial melting of the upwelling asthenosphere mantle with a slight influence of slab-derived fluids. Therefore, we suggest that the formation of these Late Carboniferous dykes were triggered by a post-collisional slab breakoff and the Aqishan–Yamansu belt was a continental arc formed by south-dipping subduction of the Kangguer oceanic plate.Graphical abstractDisplay OmittedHighlights•Late Carboniferous dykes were identified in the Aqishan-Yamansu belt in Eastern Tianshan•The E-MORB-like diabase dykes originated from asthenosphere mantle with influence of slab-derived fluids•The adakitic dykes were formed by partial melting of subducted oceanic slab•The granitic dykes were derived from partial melts of juvenile crustal sources•Formation of these dykes were triggered by a Late Carboniferous post-collisional slab breakoff
关键词：KeywordsenCentral Asian orogenic beltEastern TianshanAdakiticHighly fractionated I-Type graniteSlab breakoff
