Petrogenesis and tectonic affinity of Early Cretaceous potassic diorites in the northern Taihang Mountain, Trans-North China Orogen

Abstract

• Early Cretaceous potassic diorites are identified within the central Trans-North China Orogen. • Lithospheric delamination and thermo-mechanical erosion explain lithospheric structures during the Early Cretaceous in the North China Craton. • Early Cretaceous magmatism in the study area was linked to slab sinking and rollback. • The subducted Izanagi plate may be a candidate for carbonated peridotite at ∼140 Ma. Mesozoic mantle-derived potassic magmatic rocks in the Trans-North China Orogen (TNCO) are important for constraining tectonic evolution. However, potassic intermediate plutons in this orogen are rarely reported in literature, despite the significance of such a potassic magmatic event being well understood. Here, we describe the petrography of the Longmen potassic diorites and present zircon U–Pb ages and elemental and Sr–Nd–Mg isotopic compositions for this pluton. The Longmen potassic diorites were emplaced during the Early Cretaceous (ca. 140 Ma), showing shoshonite features with marked depletion of high-field strength elements relative to large ion lithophile elements with a slightly negative Eu anomaly. It possesses restricted ranges of initial 87 Sr/ 86 Sr ratios (0.70592 to 0.70667), ε Nd (t) values (−15.86 to −13.26), and low δ 26 Mg (−0.37 to −0.26‰). Low-degree partial melting of the ancient and enriched mantle, characterised by amphibole-bearing lherzolite in the spinel–garnet transition zone, was the likely mantle source of the evaluated Longmen potassic diorites, resulting from fluid-related metasomatism and upwelling mantle (carbonated) peridotite. Minor crustal materials were present in the lithospheric mantle because of Eastern Block and Western Block subduction/collision during the Paleoproterozoic. Based on our data and previous studies, slab sinking and rollback of the Izanagi plate (Paleo-Pacific plate) may have created an ancient, enriched mantle beneath the East Asian continent, inducing lithospheric thinning and heterogeneity of the lithospheric mantle in the North China Craton and lithospheric extension via thermo-mechanical erosion at 145–110 Ma in the TNCO.