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The Qinling orogenic belt in central China resulted fromthe final collision of theNorth China and South China blocks in the Triassic. Early Mesozoic granitoids are widespread in the Qinling orogen. Their genesis can provide key constraints on the tectonic evolution of this orogenic belt. The Late Triassic Baoji pluton, located in the North Qinling unit, consists of granodiorites, monzogranites, quartz monzodiorites, and K-feldspar granites. U-Pb zircon dating via the laser ablation ICP-MS technique yields ages of 217.4 ± 1.4, 212.3 ± 1.8, 212.6 ± 1.6, and 195.1 ± 2.0 Ma for granodiorites, monzogranites, quartz monzodiorites, and K-feldspar granites, respectively. The granitoids have high-K calc-alkaline, metaluminous to weakly peraluminous composition(s). Silica contents increase andMg, Fe, Ti, Ca, and P contents decrease from quartz monzodiorites through granodiorites to monzogranites and K-feldspar granites. Combining our findings with evidence from whole-rock Sr-Nd and zircon Hf isotopes, we suggest that the granodiorites formed by magma-mixing processes involving metasomatized lithospheric mantle and Mesoproterozoic crustal material. Themonzogranites record the contribution of an asthenospheric mantle source. The quartzmonzodiorites were derived fromametasomatized lithosphericmantle source. Partialmelting of crustal lithologies generated the K-feldspar granites. It is argued that the Baoji pluton formed in a late-collision setting. [ABSTRACT FROM AUTHOR]

Abstract: The North Qinling terrain reveals a different geological history from the North China block to the north and the South Qinling micro-continental block to the south. The timing of events and geochemical features of the North Qinling terrain are essential for understanding the evolution of the Qinling orogenic belt that joins the North and South China blocks. This study presents detrital zircon ages and Hf isotopic compositions from the Guandaokou Group, a cover sequence of the North China block, and from the Kuanping Group, an upper basement sequence of the North Qinling terrain. The youngest detrital zircon U–Pb ages constrain the initiation of sedimentation in the Guandaokou Group to 1.85Ga and the maximum depositional age of the Kuanping Group to ~640Ma. Zircon U–Pb ages and Hf data testify to a major phase of magmatism in the North Qinling terrain at ~1000–900Ma. The magmatic rocks were largely produced from reworking of early Paleoproterozoic (~2.5–2.0Ga) crust with minor contribution of late Paleoproterozoic (~1.7Ga) juvenile material. This age record differs in time from the two important thermal events of ~1.85Ga and ~2.5Ga, widely manifested in the North China block. The North Qinling terrain can thus be regarded as a separate micro-continent with a pre-Neoproterozoic evolution different from that of the North China block. The final assembly of the North Qinling terrain to the North China block took place after about 640Ma. [Copyright &y& Elsevier]

The Qinling orogen was ultimately formed by suturing of the South Qinling and Yangtze blocks, but the exact timing of the final amalgamation of the two blocks has not been well established so far. Partial melting of the Qinling orogenic continental crust resulted in the generation of migmatites, and such rocks may help to decipher the chronology of such event. In this paper, we report U–Pb ages, trace element, and Hf isotopic compositions of zircons from migmatites and diorite gneisses of the Foping dome, South Qinling. Zircons from migmatites form anhedral grains of variable sizes that are characterized by complex trace element compositions. Based on zircon U–Pb ages, the migmatites can be subdivided into two groups: Group 1 migmatites mainly retain Triassic zircons with U–Pb ages of 214–211 Ma and Hf model ages of ~ 1.46 Ga in core and rim domains; zircons from Group 2 migmatites record both Triassic (~ 210 Ma) and Neoproterozoic U–Pb ages, analogous to igneous rocks of the Wudang and Yaolinghe Groups exposed in South Qinling. Zircons from the diorite gneisses yield U–Pb ages of 216–210 Ma with Hf isotopic composition (T DM2 ages of ~ 1.46 Ga) similar to the migmatites. Evidence from whole-rock Nd isotopic analyses also points to a similar genesis between migmatites and diorite gneisses. It is proposed that Group 1 migmatites were derived by melting of Triassic diorites, while Group 2 migmatites were derived from Neoproterozoic igneous rocks, a major basement lithology of South Qinling. Partial melting of the orogenic crust took place at ~ 214–210 Ma, approximately consistent with the retrograde metamorphism of granulites exposed along the suture zone between the South Qinling and Yangtze blocks. We suggest that the collision of these two blocks occurred prior to ~ 215 Ma and that the Foping dome resulted from rapid collapse of an overthickened crust followed by partial melting enhanced by asthenospheric influx. [ABSTRACT FROM AUTHOR]