Neoarchean crust-mantle interactions in the Yishui Terrane, south-eastern margin of the North China Craton: Constraints from geochemistry and zircon U-Pb-Hf isotopes of metavolcanic rocks and high-K granitoids

Abstract

The Neoarchean Yishui Terrane (YST) is situated in the east of Western Shandong Province (WSP), south-eastern margin of the North China Craton (NCC). The metavolcanic rocks of the YST are fine-grained hornblende plagioclase gneisses (Group #1) and fine-grained amphibolites (Group #2) in the Yangzhuangzhen area and fine- to medium-grained amphibolites (Group #3) in the Leigushan area. The high-K granitoids associated with Groups #1 and 2 are dominated by fine- to medium-grained monzogranitic gneisses. Zircon LA-ICP-MS U-Pb dating reveals that the magmatic precursors of Groups #1 and #2 were formed at 2641 Ma and the magmatic precursors of concomitant monzogranitic gneisses were emplaced from 2615 to 2575 Ma, whereas Group #3 represents a later 2500 Ma volcanic eruption, and all these metamorphic volcanic rocks and monzogranitic gneisses were subjected to subsequent 2470–2460 Ma metamorphism.The metamorphic volcanic rock samples in Group #1 exhibit the chemical compositions of calc-alkaline andesites, showing fractionated chondrite-normalized REE patterns ((La/Yb)N = 10.48–19.30) and negative Nb, Ta and Ti anomalies ((Nb/La)PM = 0.13–0.22), which are akin to those of typical high-Mg andesites (HMAs) in the subduction-related settings. The magmatic precursors of the Group #1 samples were derived from partial melting of a fluid- or melt-metasomatized depleted mantle wedge at deep levels in the upper mantle. Samples in Group #2 show calc-alkaline chemical compositions with less fractionated chondrite-normalized REE patterns ((La/Yb)N = 2.24–3.34) and negative Nb, Ta and Ti anomalies ((Nb/La)PM = 0.47–0.76), which are consistent with those of the volcanic rocks in the Aleutian island arc. The magmatic precursors of Group #2 were generated by partial melting of a fluid-metasomatized depleted mantle wedge at shallow levels in the upper mantle. The monzogranitic gneisses exhibit high SiO2 and K2O contents with high-K calc-alkaline affinities and peraluminous characteristics. Based on their distinct HREE contents and chondrite-normalized REE patterns, these granitoid samples are subdivided into low-Yb monzogranitic gneisses (LYMGs) and high-Yb monzogranitic gneisses (HYMGs). The LYMG magma was derived from partial melting of a mixed source of juvenile two-mica pelites and minor basic-intermediate igneous rocks at lower crustal levels with pyroxene + amphibole + garnet as the main residual phases, and the HYMG magma was derived from partial melting of multi-sourced juvenile two-mica pelites at middle to lower crustal levels with pyroxene + amphibole and subordinate plagioclase and garnet as the main residual phases. In addition, Group #3 resembles tholeiitic back-arc basalts in the Okinawa Trough and displays flat chondrite-normalized REE patterns ((La/Yb)N = 1.22–2.08) and slightly negative Nb and Ta anomalies ((Nb/La)PM = 0.35–0.59). This group was most likely derived from partial melting of a depleted mantle source that had been modified by the addition of subducted slab-derived fluids at shallow levels in the upper mantle. These metavolcanic rocks and concomitant high-K granitoids record important Neoarchean crust-mantle interactions involving the first modification and partial melting of the lithospheric mantle induced by oceanic crust subduction; then, upwelling and underplating of mantle-derived magmas triggered partial melting of the middle to lower crust and mixing between crust- and mantle-derived magmas. These processes imply that Neoarchean crust-mantle interaction played a crucial role in the evolution of the southeastern margin of the NCC.Available whole-rock Sm-Nd and zircon Lu-Hf isotopic data from metamorphic volcanic rocks and plutonic granitoids from this study and previous studies reveal that YST experienced three crucial juvenile crustal growth events from ~2.78–2.69 Ga, ~2.64–2.56 Ga and ~2.54–2.50 Ga.