Petrogenesis of late Neoarchean high-K granitoids in the Western Shandong terrane, North China Craton, and their implications for crust-mantle interactions

Abstract

Late Neoarchean plutonic rocks in the eastern range of the Western Shandong (WSD) terrane, North China Craton, consist of fine-grained monzogranites (Group #1), fine-grained monzogranitic gneisses (Group #2), coarse-grained granodioritic gneisses (Group #3) and coarse-grained gabbro-diorites (Group #4). The first three groups of granitoids exhibit high SiO2 and K2O contents and plot in the quartz monzonite, granodiorite and granite fields in the TAS classification diagram and the high-K calc-alkaline series field in the SiO2 and K2O diagram. These granitoids show meta- to peraluminous characteristics in the A/NK versus A/CNK plot. In contrast, the gabbro and diorite samples display low SiO2 and K2O contents. LA-ICP-MS zircon U-Pb isotopic dating reveals that the high-K granitoids (Groups #1, 2 and 3) were emplaced at ∼2511–2497 Ma and that the gabbro-diorites were emplaced at ∼2511 Ma. All of these samples generally underwent regional metamorphism at ∼2475–2451 Ma. Detailed petrogenetic and geochemical studies suggest that the fine-grained monzogranites (Group #1) were derived from the hydrous partial melting of juvenile sediments at mid-crustal levels, while the fine-grained monzogranitic gneisses (Group #2) were most likely derived from the partial melting of metagreywackes at lower to mid-crustal levels. The gabbro-diorites (Group #4) were derived from the partial melting of a fluid-metasomatized mantle source at relatively deeper levels of the upper mantle. The granodioritic gneisses (Group #3) were generated from magma mixing between melts derived from the partial melting of metagreywackes (∼90%) and melts derived from a metasomatized depleted mantle source (∼10%) with minor ancient basement material additions.These findings, combined with previously obtained zircon U-Pb dating and Lu-Hf isotope data, suggest that crust-mantle interaction constituted the essential mechanism for the formation of high-K granitoids in the WSD terrane. The upwelling and underplating of mantle-derived magmas (Group #4) not only provided sufficient heat for melting crustal materials at various levels (Group #1 and #2) but also mixed mantle materials with crustal-derived melts, thereby generating the magmatic precursors of the granodioritic gneisses (Group #3).