No abstract

ratio 1σ ratio 1σ ratio 1σ age 1σ age 1σ age 1σ LK41-

No abstract

No abstract

This study presents new geochronological and geochemical data for early Paleozoic igneous rocks of the Zhangguangcai Range, northeastern China, and uses these data to further define the early Paleozoic tectonic evolution of the Songnen-Zhangguangcai Range block (SZB) and the Jiamusi block, and provide insights into crustal growth and reworking processes in these blocks of the eastern Central Asian Orogenic Belt. New zircon U-Pb data indicate widespread early Paleozoic magmatism (ca. 516, and 426 Ma) in the southeastern SZB. The ca. 516 Ma magmatism formed Na-rich tonalites that contain low concentrations of rare earth elements, are enriched in Eu and Sr, have high CaO/Al 2 O 3 and Ba/La ratios, low Rb/Sr and Rb/Ba ratios, and negative Ce anomalies and zircon ε Hf (t) values. These features suggest an origin from magmas generated by partial melting of ancient accumulated gabbroic rocks with the addition of subducted-sediment-derived fluids. The ca. 496-482 Ma magmatism formed calc-alkaline I-type biotite granodiorites and monzogranites, whereas the ca. 475-461 Ma igneous rocks include biotite monzogranites with K-rich adakitic signatures and alkali-feldspar granites. These ca. 496-461 Ma granitoids have zircon ε Hf (t) values from -0.82 to +5.44 and two-stage depleted-mantle model (T DM2 ) ages of 1490-1103 Ma, suggesting they formed from magmas generated by partial melting of heterogeneous Mesoproterozoic lower crustal material. The ca. 426 Ma Na-rich tonalites are geochemically similar to the ca. 516 Ma tonalites and also originated by partial melting of ancient gabbroic or amphibolitic rocks with the involvement of subducted-sediment-derived fluids. The geochemistry of these early Paleozoic igneous rock assemblages is indicative of formation in an active continental margin setting associated with northwestward subduction beneath the southeastern SZB. The zircon Hf isotopic compositions of these early Paleozoic igneous rocks indicate that Paleoproterozoic-Mesoproterozoic crustal material was reworked during the early Paleozoic subduction-and collision-related tectonism.