Abstract
Dissection of relicts of ocean plate stratigraphy (OPS) in orogens could provide important insights into oceanic evolution, orogenic formation and continental growth. Here we describe a study of petrology, geochronology, geochemistry and Sr–Nd isotopes for OPS in the South Qilian Accretionary Belt with the aim of providing new constraints on the evolution of the Proto-Tethys Ocean (PTO). Three types of OPS units were recognized by their differing petrological, geochemical and isotopic features. Type 1 OPS, representing relicts of ocean islands or seamounts, comprises ocean island basalt and gabbro ( t = 525 ± 4 Ma, ( 87 Sr/ 86 Sr) i = 0.7035–0.7039 and ε Nd ( t ) = +3.63 to +4.16) and (siliceous) carbonate rocks. Type 2 OPS, representing fragments of normal oceanic crust, consists of normal mid-ocean ridge basalt (N-MORB) and basaltic andesite (( 87 Sr/ 86 Sr) i = 0.7059–0.7063 and ε Nd ( t ) = +6.33 to +7.44), chert and siliceous mudstone. Type 3 OPS could be oceanic plateau-derived and comprises enriched (E)-MORB and dolerite (( 87 Sr/ 86 Sr) i = 0.7051–0.7064 and ε Nd ( t ) = +4.81 to +6.24), carbonate–siliceous mudstone and carbonate rock. These OPS units witnessed evolution of the PTO. Using available studies on regional arc-type magmatism and U–Pb geochronological data for detrital zircon in this study, a model of ‘trench jam accompanying subduction flip induced by accretion of the OPS’ is put forward. Supplementary material : Zircon U–Pb data, whole-rock major and trace element data and a supplementary figure are available at https://doi.org/10.6084/m9.figshare.c.6764637 Thematic collection: This article is part of the Ophiolites, melanges and blueschists collection available at: https://www.lyellcollection.org/topic/collections/ophiolites-melanges-and-blueschists
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