Granitoid Petrogenesis and Tectonic Implications of the Late Triassic Baoji Pluton, North Qinling Orogen, China: Zircon U-Pb Ages and Geochemical and Sr-Nd-Pb-Hf Isotopic Compositions

Abstract

A B S T R A C TThe Qinling orogenic belt in central China resulted from the final collision of the North 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 5 1.4, 212.3 5 1.8, 212.6 5 1.6, and 195.1 5 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 and Mg, 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. The monzogranites record the contribution of an asthenospheric mantle source. The quartz monzodiorites were derived from a metasomatized lithospheric mantle source. Partial melting of crustal lithologies generated the K-feldspar granites. It is argued that the Baoji pluton formed in a late-collision setting.

Late Palaeozoic tectonic transformation of the North Qinling Orogenic Belt: Insight from the geochronology, geochemistry and Sr‐Nd‐Hf isotopes of Carboniferous magmatic rocks

“…Data for the Early Devonian shoshonitic diabase, and the Cambrian shoshonitic monzodiorite were from Jiang et al, 2022; Zheng et al, 2020). Other data were from Xue et al, 2018, and references therein. (b) ε Hf ( t )‐ t diagrams of the granite after Wang, Wang, et al, 2009.…”

Compositional Diversity of Early Mesozoic Granites in South Qinling: Derivation from Heterogenous Basement Rocks in the Orogenic Belt

“…They are exposed as large plutons usually in the terrain, constituting intermediate to felsic rocks in composition, and are often emplaced in different time or magmatic stages, ranging from ~250 Ma to ~180 Ma [20][21][22][23][24]. Representatives of these are the Miba, Guangtoushan, Wulong, and Dongjiangkou plutons in the east of the Hui-Cheng basin [6,25,26] and the Baoji and Mishuling plutons in the north of the basin [5,27]. Several plutons contain numerous mafic microgranular enclaves, such as the Miba, Dongjiangkou, and Mishuling plutons [5,6], and have geochemical characteristics of I-type granite, while some large plutons, e.g., the Guangtoushan and Baijiazhuang plutons, have an S-type affinity in geochemical composition and mineral assemblage [4,26].…”

Single-Grain Detrital Apatite Sr Isotopic Composition as an Indicator to Trace Sedimentary Sources: A Case Study of Sedimentary Rocks in the Hui-Cheng Basin, South Qinling, China

“…All zircon grains from the Jurassic conglomerate (samples YX07 and YX08) are measured as having 206 Pb/ 238 U isotopic ages between 268 Ma and 198 Ma, clustering around ~220 Ma (Figure 4). Most of them are idiomorphic, less round in morphology, and have internal zoning structures in CL images with high Th/U values (>0.30), suggesting that they were originally magmatic zircon and were likely derived from early Mesozoic granitoid rocks exposed in South Qinling, such as the Baoji and Mishuling granitoid plutons adjacent to the basin [45,47]. The distribution patterns of detrital zircon ages imply that the early Mesozoic granitoid rocks had been uplifted to the surface during at least the deposition of the Jurassic conglomerates and provided major sedimentary materials.…”

“…Similar to the distribution patterns of detrital zircon U-Pb isotopic ages, detrital apatite grains from the Jurassic and Neogene clastic rocks have distinguishable features in Sr isotopic composition, providing further evidence for the characteristics of source materials or rocks. Thirty detrital apatite grains separated from the Jurassic conglomerate samples display a narrow range of 87 Sr/ 86 Sr values clustering from 0.7076 to 0.7100 (Figure 5), making them comparable to whole-rock Sr isotopic compositions of the early Mesozoic and Neoproterozoic period igneous rocks exposed in South Qinling [45,47,55]. Thirtythree grains of the Neogene conglomerate yield a wide range of 87 Sr/ 86 Sr values from of 0.7055 to 0.7534 (Figure 5), implying complex source materials for the Neogene clastic rocks.…”

“…Figure 4. Age histogram of detrital zircon grains from Neogene and Jurassic conglomerate samples.Data sources: igneous rocks in the Qinling orogenic belt[23,33,36,[40][41][42][43][44][45][46][47][48].…”