Microscopic deformation of the Neoarchean oceanic lithospheric mantle: evidence from the Zunhua Neoarchean ophiolitic mélange, North China Craton *

Abstract

Abstract The microstructures of the mantle tectonites in the Zunhua Neoarchean ophiolitic melange are mainly coarse-mosaic structures with locally interstitial impregnated melts. Olivine and orthopyroxene occur as residual porphyroclastic blasts, dynamic recrystallization neoblasts or elongated to be tabular. The podiform chromitites are mostly strongly deformed with the development of pull-apart structure. These microstructures are typical high-temperature plastic deformation in oceanic upper mantle resulting from ocean-floor spreading. Besides the high-temperature plastic deformation, undeformed magmatic intrusions such as undeformed podiform chromitite. dunite and pyroxenite intrusions are also preserved in the mantle tectonite. Structures of high-temperature plastic deformation and intensive magmatic activity prove that the Zunhua ophiolite was formed under fast spreading oceanic ridge, similar to the Oman ophiolite. And the microstructures of country rocks, such as quartz ribbon, core and mantle stru...