Post-kinematic lithospheric delamination of the Wuyi–Yunkai orogen in South China: Evidence from ca. 435 Ma high-Mg basalts
Yao, Weihua (Creator), Li, Zheng-Xiang (Creator), Li, W. (Creator), Wang, Xuan-Ce (Creator), Li, X. (Creator), Yang, J. (Creator)
Understanding the processes responsible for the intra-plate early Paleozoic Wuyi–Yunkai orogeny (> 460 Ma to 420–415 Ma) in the South China Block (SCB) is important for deducing the interactions of this block with other continents at that time, as well as the tectonic evolution of East Asia. One salient feature of the orogen is that despite the wide occurrence of syn- to late-orogenic (440 Ma to 420–415 Ma) granites in the orogen, neither syn- to late-orogenic volcanic rocks nor mafic rocks of any type have been reported. Such mafic rocks could shed clues about any mantle–crust interaction during such a major orogeny, thus help to understand the dynamics of the orogenic event. We present here, for the first time, geochronological, isotopic and geochemical data for a mafic-intermediate volcanic succession in northern Guangdong, near the edge of the metamorphic core of the orogen. The volcanic rocks unconformably overlie strongly deformed Cambro-Ordovician strata, but are in low-angle unconformable contact with overlying post-orogenic mid-Devonian strata. LA-ICP-MS and SHRIMP U–Pb dating of zircons from two andesitic and dacitic samples gives a consistent crystallization age of ca. 435 Ma, younger than the 460–445 Ma peak metamorphism of the orogeny but synchronous with the widespread late-orogenic (ca. 440–415 Ma) granitic intrusions. Nine least crustally-contaminated basaltic samples are characterized by high MgO (12.3–19.2 wt.%), Ni (214–715 ppm) and Cr (724–1107 ppm), but low TiO2 (0.6–0.8 wt.%), Al2O3 (10.2–12.8 wt.%) and Fe2O3T (total Fe as Fe2O3) (8.7–11.4 wt.%) contents. The basalts also exhibit low Nb/La ratios (0.4–0.8) and constant εNd(t) values (− 8.0 to − 8.4) with variable SiO2 (44.8–51.5 wt.%) contents, suggesting a likely sub-continental lithospheric mantle origin.These high-magnesian basalts have chemical compositions similar to their primary magma, which was estimated using geochemical modeling at SiO2 ≈ 50 wt.%, MgO ≈ 14 wt.% and FeOT ≈ 9 wt.%. The
Downloadable Archival Material, Undefined, 2012
Elsevier BV, 2012