SHRIMP zircon U-Pb age and significance of Early Paleozoic volcanic rocks in East Kunlun orogenic belt, Qinghai Province, China

Abstract

Early Paleozoic volcanic rocks in Nuomuhong area occurred as basalt slice and meta-volcanic slice. SHRIMP zircon U-Pb dating of the basalt slice and the meta-volcanic slice show that the age of the basalt slice is 419±5 Ma, and that of the meta-volcanic slice is 401± 6 Ma. These ages directly testify that there existed Early Paleozoic ocean-continent transform in East Kunlun, the basalt slice was formed in an extensional mid-ocean ridge setting and the meta-volcanic rock slice was formed in an extrusion subduction and collision setting. The inherited zircon age of 1734 Ma in volcanic rocks reflects that the base of East Kunlun may be Middle Proterozoic.A great deal of practical data in recent years have proved that the East Kunlun orogenic belt and even the China central orogenic belt are complex orogenic belts that underwent polycycle orogenic evolvement [1][2][3][4][5][6][7] . Each orogenic cycle has left a compositional print, the multi-period ophiolites [4][5][6] and various types of tectono-magmatic production in the same orogenic belt. There is a suite of shallow metamorphic volcanic rocks in the Nuomuhong area in the east part of the East Kunlun orogenic belt. There exists disputation for its forming time all along. Previous study reveals that the volcanic rocks were composed of two different slices, namely basalt slice and meta-volcanic rock slice. Volcanic rocks of these two slices are obviously different in composition and tight intergrowth with meta-peridotite, pyroxenite and siliceous rock, and composed of typical ophiolite. So the determination of these volcanic rocks is very important in investigating early ocean-crust transform processes and tectonic evolution history of the East Kunlun orogenic belt. This paper reports the zircon SHRIMP dating of these two slices and discusses their geological significance.

Petrogenesis and tectonic significance of the Late Permian–Middle Triassic calc-alkaline granites in the Balong region, eastern Kunlun Orogen, China

“…1). It underwent Early Palaeozoic and Early Mesozoic subduction and collision processes, during which time the Nuomuhong-Qingshuiquan and the Anyemaqen-Buqingshan suture zones were formed successively (Yang et al 1996;Bian et al 2004;Zhu et al 2006). The eastern Kunlun Orogen consists traditionally of three tectonic units, the Northern, Middle and Southern Zones, separated by the North and Central Kunlun faults, respectively (Jiang et al 1992).…”

“…It constitutes an important component of the Early Palaeozoic Nuomuhong suture zone (Wang, Jia & Zhu, 2003, pp. 1-98;Zhu et al 2006). The Devonian sedimentary rocks are typical molasse deposits and include conglomerates, sandstones, mudstones and rarely volcanic rocks.…”

The Early Silurian Gabbro in the Eastern Kunlun Orogenic Belt, Northeast Tibet: Constraints on the Proto-Tethyan Ocean Closure

“…Especially, it is debated when the postcollisional extension regime was initiated. For example, Zhu and Lin [7] suggested that subduction of the oceanic crust lasted until the Early Devonian, while Dong and He [8] argued that the Proto-Tethys Ocean in the EKOB had closed and that the postcollisional extension setting occurred since the Early Devonian. Zhou and Dong [9] suggested that the postcollisional extension regime was initiated during the Late Ordovician.…”

The Early Silurian Gabbro in the Eastern Kunlun Orogenic Belt, Northeast Tibet: Constraints on the Proto-Tethyan Ocean Closure

“…Especially, it is still debated when the post-collision extension regime was initiated. For example, Zhu, Lin [7] suggested that subduction of the oceanic crust still existed during the Early Devonian, while Dong, He [8] argued that the Proto-Tethys Ocean in the EKOB had been closed and that the post-collision extension setting occurred since the Early Devonian. Zhou, Dong [9] considered that the post-collision extension regime was initiated during the Late Ordovician.…”