Petrographic, geochemical, zircon U-Pb geochronogical and Hf isotopic data are presented for the exposed metavolcanic rocks in Hengshan region to determine their eruption age, petrogenesis and geodynamic significance in the Trans-North China Orogen, North China Craton. Zircon U-Pb dating of the rocks yielded a weighted mean 207Pb/206Pb age of 2508 ± 20 Ma, indicating that their protoliths were erupted in the late Neoarchean. Geochemically, the Hengshan metavolcanic rocks are composed of basalt and basaltic andesite and marked by variable SiO₂ (45.51%–62.67%), FeOt (4.43%–15.72%) and MgO (3.75%–8.14%) contents, indicative of product of derivation from a mantle source with subsequent fractional crystallization of clinopyroxene, hornblende and magnetite. These metavolcanic rocks are characterized by enrichments in light rare earth elements (LREE) and large-ion lithophile elements (LILE), as well as depletions in heavy rare earth elements (HREE) and high-field-strength elements (HFSE), with relatively high Th content and Th/Yb values, similar to those of the typical calc-alkaline arc-like volcanic rocks. Such arc-like geochemical signatures, together with some incompatible elemental ratios (e.g., Nb/Yb, Zr/Yb and (Nb/La)N), reveal their origination from a sub-arc enriched mantle wedge variably metasomatized by the slab-derived dehydration fluids. Combined with the region geological background, these Hengshan metavolcanic rocks were developed on a continental arc setting in the late Neoarchean.

对恒山地区出露的变质火山岩开展岩相学、地球化学、锆石U-Pb年代学和Hf同位素研究, 旨在确定其形成时代, 探讨岩石成因及地球动力学意义。锆石U-Pb定年结果表明, 这些变质火山岩喷发于新太古代晚期(2508±20 Ma)。地球化学分析结果显示, 恒山变质火山岩由变质玄武岩和变质玄武安山岩组成, SiO₂(45.51%~62.67%)、FeOT (4.43%~15.72%)和MgO (3.75%~8.14%)含量变化幅度大, 是幔源岩浆经单斜辉石、角闪石和磁铁矿分离结晶的产物。这些变质火山岩富集轻稀土(LREE)和大离子亲石元素(LILE), 亏损重稀土(HREE)和高场强元素(HFSE), 具有相对高的Th含量和Th/Yb比值, 呈现钙碱性岛弧火山岩的特征。结合不相容元素比值 Nb/Yb, Zr/Yb和(Nb/La)N的特点, 推测其来源于俯冲带具流体交代特征的富集地幔源区。结合区域构造背景, 推断恒山变质火山岩形成于新太古晚期大陆弧环境。