Late Jurassic magmatism in the interior South China Block and its implication

The NE-SW-trending Qin-Hang Belt and east-west-trending Nanling Range are two critical magmatic and mineralization zones in the southeastern South China Block (SCB). However, the formation timing and petrogenesis of the magmatism in these zones, along with the relationship with the Pacific subduction, remain hotly debated. Herein, this study presents a set of zircon U-Pb geochronological, Lu-Hf isotopic and whole-rock geochemical data for the Late Jurassic Mashan and Nandu shoshonitic intrusions in the Qin-Hang Belt. All the samples are enriched in large ion lithophile elements and light rare earth elements. They have high epsilon Nd-(t) (from -1.4 to + 4.4) and zircon epsilon Hf-(t) values (from -1.0 to + 3.4) and low initial Sr-87/Sr-86 (0.70426-0.70696), distinct from those of the Triassic shoshonitic rocks but comparable with those of the Jurassic shoshonitic rocks in the region. Such signatures suggest that the Mashan and Nandu igneous rocks mainly derived from a Jurassic metasomatized lithospheric mantle in response to asthenospheric upwelling, without significant contribution from subducted slab-derived components. Our new data, together with other geological observations, reveal a spatial change of magmatic activities, structural patterns, sedimentary basins and palaeocurrent directions during the Middle-Late Jurassic, probably associated with the far-field effects of the Pacific subduction in the interior SCB.