A 1.9‐Ga Mélange Along the Northern Margin of the North China Craton: Implications for the Assembly of Columbia Supercontinent

Abstract

AbstractThe involvement and location of the Neoarchean‐Paleoproterozoic North China craton in the supercontinent Columbia remains enigmatic, and the tectonic history along its margins impacts our understanding of connections between North China and other continents. Here we present structural observations from a Paleoproterozoic mélange that is located along its northern margin and that we refer to as the Bayan Obo mélange. It is composed of a structurally complex tectonic mixture of metapelites and metasedimentary rocks mixed with exotic blocks of ultramafic‐mafic rocks, metabasalts, metacarbonate and alkaline rocks, and tonalite‐trondhjemite gneisses. New zircon geochronology of the various constituent blocks suggest that it formed, and was subsequently deformed, at ca. 1.9 Ga. The oldest intramélange blocks are 2.45‐ to 2.54‐Ga tonalite‐trondhjemite‐granodiorite rocks and granitoids that signify the stabilization of the northern North China in the Neoarchean‐Paleoproterozoic. A ca. 2.45‐Ga plagiogranite block probably originated by partial melting of the older tonalite‐trondhjemite‐granodiorite rocks. We suggest that this mélange formed in a sedimentary setting near the subduction trench, on the basis of mixing of upper and lower plate volcanic rocks and textural relationships. The Bayan Obo mélange thus represents one of the oldest documented sedimentary mélanges on Earth, yet its fundamental characteristics strongly resemble Phanerozoic subduction complexes. Based on similar ages and styles of deformation, this zone may represent the ca. 1.9‐Ga collisional zone between North China and the southwestern margin of the Siberia craton. In this context, the North China craton became an integral component of the supercontinent Columbia starting at ca. 1.9 Ga.