Geochronology and geochemistry of the Sikongshan intrusion in the Dabie Orogen, Central China: Implication for Mesozoic geodynamic background

Abstract

The Sikongshan (SKS) intrusion, the largest pluton situated in the Central Dabie unit of the Dabie Orogen (DBO), is composed of monzogranite and quartz diorite. A study combining whole‐rock major and trace element analysis, zircon U–Pb dating, as well as zircon in situ Lu–Hf isotopes was conducted for the SKS intrusion. Zircon dating yielded U–Pb ages of 136 ± 1.6 Ma and 134.6 ± 1.7 to 130.4 ± 1.7 Ma for quartz diorites and monzogranites, respectively, both types belonging to the early stage of the Mesozoic magmatism in the DBO. The quartz diorites exhibited high Na2O (Na2O/K2O = 1.60–1.86) and Sr (1,185–1,365 ppm) and low Y (11.6–14.2 ppm) contents, and therefore high Sr/Y (83.45–108.19) ratios. They also had high ratios of (Dy/Yb)N (48.42–54.91) and (Dy/Yb)N (1.47–1.53). The monzogranites were enriched in K2O (Na2O/K2O = 0.64–0.99) and were also characterized by low Y (5.6–14.7 ppm) contents and high Sr/Y ratios with a geochemical affinity similar to that of the adakites. However, the Sr (<358 ppm) and Al2O3 (3.31–14.92%) contents were much lower than those in typical adakites and quartz diorites. Both the quartz diorites and monzogranites had trace element signatures similar to that of continental crust with enriched levels of Rb, Ba, Th, U, and LREE and depleted levels of Nb, Ta, P, and Ti, indicating their crustal origin. Following an integrated review of these and other data from previous studies, it was concluded that the Sikongshan quartz diorite originated from the thickened lower crust of the DBO, with a composition similar to that of the Huangtuling granulite, which is the exposed lower crust of the DBO. The monzogranite was generated by plagioclase + amphibolite fractional crystallization of the adakitic Tiantangzhai melt. The adakitic rocks in the DBO originated in the western part during 143 to 134 Ma and then spread extensively throughout the whole orogen (134 to 130 Ma). The collapse of the thickened mountain root in the DBO at an extensional setting may be related to the roll‐back of the subducted Paleo‐Pacific slab.

Early cretaceous multi-stage extension in the North Dabie complex in the eastern central China: insights from structural and geochronological data

“…This extensional complex consists of the exhumed HP/UHP rock slices and juxtaposed supra-detachment basins as the rigid upper plate, while the viscously flowing mylonitic-gneissic-migmatitic-magmatic crust acts as the soft Radiometric ages related to the Early Cretaceous thermal events of the North Dabie complex and the bounding shear zones, compiled from previous studies (white boxes) and new data from this study (yellow boxes). Published data are from Chen et al (1995), Chen et al (2015), Deng et al (2014), Eide et al (1994), Hacker et al (1995), Hacker et al (1998), Ji et al (2017), Lin et al (2015), Liu and Yan (2020), , Ratschbacher et al (2000), Wang et al (2007), Wang et al (2018), , Wu et al (2007c), Xu et al (2002).…”

Zircon U-Pb Dating and Petrogenesis of Multiple Episodes of Anatexis in the North Dabie Complex Zone, Central China

“…In addition, both initial 87 Sr/ 86 Sr and 143 Nd/ 144 Nd ratios exhibit no distinct correlation with the whole-rock SiO 2 contents (Figure 11b,c). [72]). The Sr-Nd isotopic compositions of EMI and EMII are from [73].…”

“…Continental crustal rocks are generally devoid of free water, especially in the middle and lower structural levels, as a result of the high pressure and low porosity. In spite of the [72]). The Sr-Nd isotopic compositions of EMI and EMII are from [73].…”

“…Other symbols are the same as in Figure 5. [72]). The Sr-Nd isotopic compositions of EMI and EMII are from [73].…”

“…(a) 87 Sr/ 86 Sr i vs. ε Nd (130Ma) diagram; (b) SiO 2 (wt.%) vs. 87 Sr/ 86 Sr i diagram; (c) SiO 2 vs. 143 Nd/ 144 Nd i diagram. Representative data for the CDZ gneisses, NDZ gneisses and Dabie eclogites are from[72]). The Sr-Nd isotopic compositions of EMI and EMII are from[73].…”