Geology, geochemistry, and geochronology of the paleoproterozoic Donggouzi mafic-ultramafic complex: Implications for the evolution of the North China craton

Abstract

The Paleoproterozoic tectonic setting and spatial-temporal evolution of the northern North China and Central Orogenic belt constrain the assembly of the North China craton. Here we describe a new Paleoproterozoic mafic-ultramafic unit and intermediate-mafic intrusions located between the Khondalite belt and Central Orogenic belt, which we refer to as Donggouzi mafic-ultramafic complex. This complex is structurally complicated, and comprises a mixture of peridotite, amphibole pyroxenite, and websterite blocks, with associated alkali granitoid and gabbroic dikes, which were intruded into Paleoproterozoic granulites. Zircon UPb geochronology of the granulite, intruding syenite and alkali granites together with the field observations constrain the formation of the Donggouzi mafic-ultramafic complex to between 1849 and 1845 Ma, i.e. 1.85 Ga. Geochemical and SrNd isotopic data indicate that the Paleoproterozoic mafic-ultramafic rocks were sourced from enriched metasomatized mantle by the fluid from a subduction slab. Emplacement of the complex occurred in a post-orogenic extensional setting, possibly associated with the collision along the northern margin of the North China craton at ca. 1.9–1.88 Ga. The ca. 1767 Ma gabbroic dike was emplaced in an intraplate extensional setting and experienced crustal contamination, which suggests that an upwelling mantle plume produced magmas that interacted with the lithosphere during the late Paleoproterozoic.