Recognizing different types of Ocean Plate Stratigraphy at the southeastern South Qilian Accretionary Belt, northeastern Tibet Plateau

Abstract

Dissection of relicts of Ocean Plate Stratigraphy (OPS) at orogens could provide important insights into oceanic evolution, orogenic formation, and continental growth. Here we put forward a study of petrology, geochronology, geochemistry, and Sr–Nd isotopes for OPS at the South Qilian Accretionary Belt (SQAB) with aim to provide new constraints on evolution of the Proto-Tethys Ocean (PTO). Three types of OPS units were recognized by their discrepant petrological, geochemical, and isotopic features. Type 1 OPS as relicts of ocean islands/seamounts comprises OIB-type 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 crusts, consists of N-MORB-like basalt 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 E-MORB-like basalt 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 witnessed evolution of the PTO. By available studies on regional arc-type magmatism and U-Pb geochronological data of detrital zircon in this study, a model of “trench jam accompanying with subduction flip induced by accretion of the OPS” is put forward. 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 Supplementary material: https://doi.org/10.6084/m9.figshare.c.6764637