Zircon U-Pb ages of granites at Changba and Huangzhuguan in western Qinling and implications for source nature

Abstract

Mesozoic granitoids are widespread in the Qinling-Dabie-Sulu orogenic belt. Precise U-Pb dating on these granitoids can reveal the evolution of the continental collision orogen and thus provide information on the nature of magma sources. This study presents zircon LA-ICP-MS U-Pb dating and whole-rock geochemical analyses for two intrusions at Changba and Huangzhuguan in western Qinling. Zircon U-Pb ages for central and marginal phases of the Huangzhuguang intrusion are 214±1 Ma and 213±3 Ma, respectively. Zircons from the Changba intrusion yield a dominant cluster with an U-Pb age of 213±2 Ma. Collectively, these ages are younger than ages of 220 to 240 Ma for ultrahigh-pressure metamorphism due to the continental collision between the South China Block and the North China Block, corresponding to syn-exhumation magmatism. Some inherited zircons occur in the Changba intrusion, yielding a weighted mean of 206 Pb/ 238 U ages at 757±14 Ma. This indicates that the Changba intrusion has the crustal source of mid-Neoproterozoic ages and a tectonic affinity to the South China Block. Geochemically, the two intrusuons are both rich in LILE and LREE but depleted in HFSE and HREE, similar to arc-type igneous rocks. The Huangzhuguang intrusion exhibits linear correlations between SiO 2 and the other major oxides, implying chemical evolution from a cognate magma source. It contains mafic enclaves, suggesting possible mixing of felsic-mafic magmas. The Changba granite is rich in Si and K but poor in Fe and Mg as well as has a high value of Fe*, suggesting strong differentiation of granitic magma. Therefore, the two intrusions were derived from the Late Triassic anatexis of the continental crust of different compositions in the northern margin of South China Block. This process may be coupled with exhumation of the subducted continental crust in the stage of late collision.Qinling orogen, continental collision, granite, zircon U-Pb dating, whole-rock geochemistry, syn-exhumation magmatism Citation:Wang T G, Ni P, Sun W D, et al. Zircon U-Pb ages of granites at Changba and Huangzhuguan in western Qinling and implications for source nature.

A review of the Early Mesozoic granitoids in the Qinling Orogen: Implication for gold metallogeny

“…This suggests that these granitoids were derived from partial melting of old continental crust. However, available εHf(t) data obtained from zircon probably suggest the involvement of a juvenile component in their sources (Qin et al, ; Qin et al, ; Qin et al, ; Wang, Wang, Happala, & Lu, ; Wang et al, ; Zhang, Tang et al, ; Zhang, Wang, & Wang, ). Recently, zircon Hf analyses show a very clear decrease from SQB to NQB, with the mean values of εHf(t) changing from −1.1 to −15.1 (Li et al, ).…”

“…Regarding the location of the collisional suture, most authors believe that subduction and collision between the NCB and SCB mainly occurred along the Shangdan Suture with the Erlangping back‐arc basin (Figure ; Dong, Genser et al, ; Dong et al, ; Li, Sun, & Zhang, ; Xu et al, ; Zhang et al, ). However, some scholars proposed that the major suture is marked by the Erlangping ophiolitic mélange (Faure et al, ; Ratschbacher et al, ; Ratschbacher et al, ; Wang, Ni, Sun, Zhao, & Wang, ; Xue et al, ), which is located between the Kuanping Suture and the North Qinling Belt (Dong et al, ; Figure ). Moreover, the timing of the collision between NCB and SCB is also debated with ages varying from Early Paleozoic (Kröner et al, ; Mattauer et al, ), Devonian (Gao, Zhang, Gu, Xie, & Gao, ; Zhang, Gao, Zhang, Luo, & Lin, ), and Late Triassic (Enkin, Yang, Chen, & Courtillot, ; Hacker et al, ; Li, ; Okay & Sengör, ; Sengör, ; Zhao & Coe, ).…”

Geochemistry, geochronology, and petrogenesis of leucogranites in the Xiaogouli gold deposit in the West Qinling Orogen

“…The Indosinian granites are mainly distributed north of the Xiahe–Tanchang–Fengxian fault zone, largely parallel to the Gonghe–Guide–Linxia fault zone on the northern margin of the West Qinling Orogen. These granites are characterized by high‐K calc‐alkaline granite, and their formation ages are concentrated in two stages, that is, 248–234 and 225–210 Ma (Cao et al, ; Jin et al, ; Sun, Li, Chen, & Li, ; Wang, Ni, Sun, Zhao, & Wang, ; Wang, Zhang, Xu, & Cai, ; Zhu et al, ; Figure b).…”

Geochemical insights into the role of metasomatic hornblendite in generating alkali basalts

“…The oldest exposed crystalline basement in the West Qinling orogen is the Qinling Group, which predominantly consists of gneisses, amphibolites, and marbles, with Paleoproterozoic zircon U-Pb ages of 2.17-2.27 Ga [Meng and Zhang, 2000;Dong et al, 2011]. Voluminous granitoids rocks of Late Triassic were emplaced in West Qinling [Lu, 1999;Dong et al, 2011;Wang et al, 2011aWang et al, , 2013. There are also sporadic volcanic rocks, mainly composed of melilitite, alkali basalt, andesite, rhyolite, and carbonatite, erupted in West Qinling during the Late Triassic, Late Cretaceous, and Cenozoic periods [Li et al, 2013a[Li et al, , 2013bYu et al, 2011].…”

“…In particularly, there are sporadic occurrences of Early Cretaceous to Cenozoic alkali basalts in the West Qinling orogen [Qin et al, 2008[Qin et al, , 2009Li et al, 2013a;Yu et al, 2011], together with voluminous granitoids of Late Triassic [Dong et al, 2011;Wu and Zheng, 2013]. While numerous studies have been devoted to the Late Triassic granitoids [Qin et al, 2008[Qin et al, , 2009Wang et al, 2011aWang et al, , 2011b, less attention has been paid to the Early Cretaceous alkali basalts in the West Qinling orogen [Ding et al, 2013;Li et al, 2013a]. Based on relatively depleted radiogenic Sr-Nd isotope compositions, these alkali basalts were interpreted as derivation form the asthenospheric mantle [Fan et al, 2007a[Fan et al, , 2007bDing et al, 2013;Li et al, 2013a].…”