Neoarchean metagabbro and charnockite in the Yinshan block, western North China Craton: Petrogenesis and tectonic implications

Properly calibrating the magmatic record of mantle and crustal origin in Archean granite-greenstone terranes is crucial for understanding the petrogenetic and geodynamic processes that generated early continental landmasses. This geochronological and geochemical study documents a Neoarchean bimodal metaplutonic suite of metagabbro and charnockite from the Yinshan block, North China Craton. The meta-gabbroic rocks show an SiO2 range from 45.9 to 51.7% and high MgO content from 6.7 to 16.4%, with enrichment in Ba and light rare earth elements (La-N/Yb-N =3.11-5.99) and depletion in high field strength elements. Together with their enriched whole-rock Nd (epsilon(Nd)(t)= -0.23 to 1.49) and zircon Hf (epsilon(Hf)(t)= 0.1-6.9) isotopic signatures relative to the Archean depleted mantle in the craton, these rocks are supposed to originate from the second-stage high-temperature partial melting of refractory depleted mantle that experienced prior basaltic magma extraction and subsequent metasomatism by subduction-related fluids. The associated charnockites range in Si02 from 61.3 to 69.6% and exhibit a magnesian, calc-alkalic and metaluminous character, with variable Sr/Y and La-N/Yb-N ratios. These elemental features, plus their evolved isotopic compositions (epsilon(Nd)(t) = 0.93-1.85, zircon epsilon(Hf)(t) = -0.3 to 2.5), are consistent with partial melting of newly underplated mafic lower crustal protolith. In combination with widespread occurrence of metasomatized lithospheric mantle-derived magmas (e.g., high-Mg basalts, sanukitoid suites) and juvenile crust-extracted potassic granites in the NCC during Late Neoarchean time, such a mafic and felsic magma association not only attests to the establishment of a craton-scale subduction-related metasomatized sub-continental lithospheric mantle, but also encapsulates a scenario of coupled lithospheric mantle-crust formation at similar to 2.7 Ga and juvenile crustal reworking at similar to 2.5 Ga within a modern-style convergent continental margin possibly featuring episodic slab break-off events. (C) 2013 Elsevier B.V. All rights reserved.