Opening of an early Paleozoic limited oceanic basin in the northern Altyn area: Constraints from plagiogranites in the Hongliugou-Lapeiquan ophiolitic mélange

Abstract

This paper reports petrological and geochemical features and zircon U-Pb age of plagiogranite from the Hongliugou-Lapeiquan ophiolitic mélange belt in the northern Altyn Tagh. The zircon U-Pb dating results yield a mean 238 U/ 206 Pb age of 512.1  1.5 Ma, representing an emplacement time of the plagiogranites in the Middle Cambrian. The plagiogranites are interpreted to have derived from anatexis of hydrated amphibolites by ductile shearing during transports of the oceanic crust. Thus it is believed that the formation age of such type of plagiogranite was coeval to or slightly younger than the spreading of the Hongliugou-Lapeiquan limited oceanic basin. The new results from the plagiogranites suggest that an oceanic basin existed in the northern Altyn area during the Middle Cambrian. plagiogranite, limited oceanic basin, early Paleozoic, northern Altyn area Citation:Gao X F, Xiao P X, Guo L, et al. Opening of an early Paleozoic limited oceanic basin in the northern Altyn area: Constraints from plagiogranites in the Hongliugou-Lapeiquan ophiolitic mélange.

Early Paleozoic slab rollback in the North Altun, Northwest China: New evidence from mafic intrusions and high-Mg andesites

“…520 Ma. This is consistent with the presence of arc-related granitic rocks and the occurrence of early Paleozoic ophiolites in the belt (Gai et al, 2015;Gao et al, 2012;Yang et al, 2008). However, the tectonic evolution of this area was divided into different stages by previous scholars (e.g., Han et al, 2012;Liu et al, 2016;Meng et al, 2017).…”

“…Ophiolites are distributed sporadically between the areas of Hongliugou and Lapeiquan, and they consist primarily of serpentinized peridotite (harzburgite), cumulates (wehrlite, gabbro, anorthosite, plagiogranite), and basalts. Zircon U-Pb ages of the cumulates range from 520 to 480 Ma (Gai et al, 2015;Gao et al, 2012;Yang et al, 2008;Zhang et al, 2015), and the ophiolites have been interpreted to have formed in a suprasubduction-zone setting (Dong et al, 2013;Guo et al, 1998;Yang et al, 2008). Blueschists and eclogites occur as lenses surrounding the metapelites in the area of the Hongliugou ophiolites (Che et al, 1995).…”

“…In addition, their geochemical signatures are similar to those of the Hongliugou ophiolites (Figs. 10A and 10B;Gao et al, 2012;Yang et al, 2008). Therefore, we reason that the Dawan gabbros were derived from depleted asthenospheric mantle.…”

Cenozoic uplift of the Qimantage Mountains, northeastern Tibet: Contraints from provenance analysis of Cenozoic sediments in Qaidam Basin

“…Although the latter two orogenic products consist mainly of arc‐related rocks, oceanic crust, and so forth in early Paleozoic (e. g . , Che , Luo, & Liu, ; Gao et al, ; Ge, Liu, & Ren, ; Qi, Wu, & Li, ). In summary, the Altyn Orogen has experienced complex geological evolutions, and the rock records of Altyn Orogen are mainly in early Paleozoic and some older crustal materials in the Neoproterozoic, even the Archean (S. N. Lu, Li, Zhang, & Niu, ).…”

“…The Altyn Orogen has long been considered as an early Paleozoic orogen with Precambrian rocks (Figure ) and can be divided into four tectonic units: the A‐Bei block, Hongliugou‐Lapeiquan Ophiolitic Mélange, Milanhe‐Jinyanshan block, and Apa‐Mangya tectonic mélange (e.g., Xu et al, ; Xiao, ; J. X. Zhang, Zhang, & Xu, ). According to detailed petrology and geochemistry studies, there are mainly two pretectonic units, that is, the A‐Bei and Milanhe‐Jinyanshan blocks and the orogenic products, that is, Hongliugou‐ Lapeiquan and Apa‐Mangya Ophiolitic Mélange (Gao, Xiao, Guo, Dong, & Xi, ; Xu et al, ; J. X. Zhang et al, ). The former two pretectonic units have experienced the high pressure and ultrahigh‐pressure tectonic events in early Paleozoic from both the north and south sides.…”