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

Abstract

<p>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 <a href="https://www.sciencedirect.com/topics/earth-and-planetary-sciences/diorite" title="Learn more about diorites from ScienceDirect's AI-generated Topic Pages">diorites</a> 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 ⁸⁷Sr/⁸⁶Sr ratios (0.70592 to 0.70667), ε_Nd(t) values (−15.86 to −13.26), and low δ²⁶Mg (−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) <a href="https://www.sciencedirect.com/topics/earth-and-planetary-sciences/peridotite" title="Learn more about peridotite from ScienceDirect's AI-generated Topic Pages">peridotite</a>. 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 <a href="https://www.sciencedirect.com/topics/earth-and-planetary-sciences/craton" title="Learn more about Craton from ScienceDirect's AI-generated Topic Pages">Craton</a> and lithospheric extension via thermo-mechanical erosion at 145–110 Ma in the TNCO.</p>