Zircon U–Pb dating and geochemistry of intrusive rocks in the Shangdan suture zone of the Qinling Orogenic Belt: petrogenesis and tectonic implications

Abstract

A Paleozoic gabbro–diabase–granite association in the Shangdan suture zone (SDSZ) has been studied for zircon U–Pb ages, whole-rock geochemistry, and Sr-Nd isotopic compositions to constrain their petrogenesis and reveal tectonic implications. These rocks have distinctive crystallization ages: the Guchenggou gabbro yield zircon U–Pb ages of 423 to 424 Ma; the average age of Yueritan diabase is 411 Ma; and the Danfeng granites yield zircon U–Pb ages of 411 to 414 Ma. The Guchenggou gabbro was formed by partial melting of phlogopite-bearing garnet lherzolite modified by subduction fluid in a continental arc setting. The Yueritan diabase was generated by mixing phlogopite-bearing garnet lherzolite modified by subduction melt and continental crust in a post-collision setting. The Danfeng granites are weakly peraluminous I-type, formed by mixing juvenile crust and metagreywacks under high temperature and high pressure in a tectonic transition environment from compression to extension. We suggest that the subduction of the Shangdan Ocean induces the formation of gabbro. Meanwhile, the diabases and granites are related to the continental crustal relamination in response to the collision of North Qinling Belt (NQB) and South Qinling Belt (SQB), suggesting that the closure of the Shangdan Ocean may have occurred in ca. 410 Ma.

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

“…Previous studies have verified that the Shangdan Ocean subducted beneath the NQB in the Early Palaeozoic and produced voluminous subduction-related intrusive rocks and UHP/HP metamorphic rocks in the NQB (Dong et al, 2013;Jiang et al, 2022;Kang et al, 2022;Wang et al, 2013;Wang, Wang, & Zhang, 2015). In the Early Devonian, the Shangdan Ocean was closed based on source analysis of detrital zircon of the Liuling Group (Dong et al, 2013).…”

“…showing arc magma signatures (Jiang et al, 2022). Meanwhile, the Sr-Nd isotopic compositions show the characteristic of enrichment (initial 87 Sr/ 86 Sr ratios of 0.70399 and 0.70402; ε Nd (t) values of À2.1 and À2.8).…”

“…Besides, some subducted-related intrusive rocks yielded zircon U-Pb age at 534-420 Ma, which indicates subduction of the Shangdan Ocean during the Early Palaeozoic (Chang et al, 2021;Dong et al, 2013;Jiang et al, 2022;Wang, Wang, & Zhang, 2015).…”

“…The Qinling Orogenic Belt (QOB), extending east–west for about 1500 km, separates the North China Block (NCB) from the South China Block (SCB), which is recognized as a compound orogenic belt with a multi‐stage evolution history (Figure 1) (Dong & Santosh, 2016; Zhang et al, 2001). Earlier research has revealed that the formation of the QOB was associated with two‐stage convergent events along the Shangdan and Mianlue suture zones in both the Early Palaeozoic and Mesozoic (Dong & Santosh, 2016; Dong, Zhang, Hauzenberger, et al, 2011; Dong, Zhang, Neubauer, et al, 2011; Jiang et al, 2022; Wang et al, 2013; Zhang et al, 2001). The North Qinling Orogenic Belt (NQB), as a prominent tectonic unit of QOB, preserves abundant ocean–continent transition records in the Palaeozoic (Dong et al, 2003; Zhang, 1995; Zhang et al, 1994).…”

Geochronology, Petrogenesis and Tectonic Setting of the Late Jurassic I‐type Granites in the North Qinling Orogenic Belt, Central China

“…The Lantian and Muhuguan plutons underwent a complex process involving melting of ancient crust, wall-rock contamination, magma mixing and crystallization differentiation under an extensional setting (Liu et al, 2014). The Shenlin plutons in the East Qinling are the result of regional lithosphere delamination under the intraplate orogenic stage (Liang et al, 2021).…”