The study of chromite from chromitite-bearing layered intrusions can provide significant insights into their petrogenetic origin and tectonic setting. The Fangmayu Alaskan-type ultramafic intrusion in the North China Craton contains layered and massive chromitite associated with a serpentinized ultramafic suite. This study presents zircon and apatite geochronology, chromite mineral chemistry, platinum-group element (PGE) and Re-Os isotopic data for the purpose of constraining the origin, evolution, and composition of the Fangmayu chromitite parental melts. Zircon U-Pb data from the chromitites define various age populations, with oldest age component (>2.49 Ga) interpreted to represent xenocrystic grains incorporated from crystalline basement. A dominant age component (~2.42 Ga) may represent the age of magma emplacement. Ages in the range of 2375–2068 Ma likely represent variable partial radiogenic Pb-loss during subsequent thermal events. Zircon ages in the range of 1.96–1.90 Ga record metamorphic events, potentially related to the collision between the Eastern Block and Western Block in the North China Craton. Ages of 1.85–1.81 Ga likely represent zircon growth during retrograde metamorphic process in a post-collisional setting; near contemporaneous apatite (~1.8 Ga) tracks cooling through ~500 °C. High Fo contents in olivine (Fo_90-92) and high Cr# in chromite (72–77) suggest a low Al₂O₃ ultramafic parental magma formed by a high degree of partial melting. However, total concentrations of PGEs are abnormally low, and the Re-Os system indicates multiple disturbances during later metamorphic events. Experimental data are used to recover the compositions of parental melts to the chromitite, the calculations yield parental melts with 10–11 wt% Al₂O₃ and 0.7–1.1 wt% TiO₂, which define the arc and IAB affinity. The high Cr#s, low Al₂O₃ (8–10 wt%), and high TiO₂ (0.58–0.96 wt%) contents of chromite, combined with calculated parental melt compositions, suggest that the parental magma of Fangmayu stratiform chromitites was a high-Ti island-arc basalt origin and formed within supra-subduction zone setting.

含铬铁矿层状侵入体中铬铁矿的研究可以提供有关其成岩成因和构造背景的重要见解。华北克拉通的Fangmayu Alaskan型超镁铁质侵入岩中含有层状且块状的铬铁矿，并伴有蛇形超镁铁质套装。本研究介绍了锆石和磷灰石的地质年代学，铬铁矿矿物化学，铂族元素（PGE）和Re-Os同位素数据，目的是限制方马屿铬铁矿母体熔体的起源，演化和组成。来自铬铁矿的锆石U-Pb数据定义了各种年龄种群，其中最老的年龄组分（> 2.49 Ga）被解释为代表从结晶基底中掺入的异晶晶粒。占优势的年龄成分（〜2.42 Ga）可能代表岩浆侵袭的年龄。2375-2068 Ma范围内的年龄可能代表随后的热事件中部分可变的放射性Pb损失。锆石年龄在1.96–1.90 Ga范围内记录了变质事件，可能与华北克拉通东部区块和西部区块之间的碰撞有关。1.85–1.81 Ga年龄可能表示在碰撞后环境中逆行变质过程中锆石的生长；同期磷灰石（〜1.8 Ga）附近的冷却温度约为500°C。橄榄石中的高Fo含量（Fo 81 Ga可能代表了在碰撞后环境中逆行变质过程中锆石的生长；同期磷灰石（〜1.8 Ga）附近的冷却温度约为500°C。橄榄石中的高Fo含量（Fo 81 Ga可能表示在碰撞后环境中逆行变质过程中锆石的生长；同期磷灰石（〜1.8 Ga）附近的冷却温度约为500°C。橄榄石中的高Fo含量（Fo_90-92）和亚铬酸盐中的Cr＃较高（72-77）表明低Al ₂ O ₃超镁铁矿母岩浆是由高度部分熔融形成的。但是，PGE的总浓度异常低，并且Re-Os系统表明在随后的变质事件中存在多种干扰。实验数据用于恢复铬铁矿母体熔体的成分，计算得出母体熔体含10-11 wt％的Al ₂ O ₃和0.7-1.1 wt％的TiO ₂，它们定义了电弧和IAB亲和力。高Cr＃s，低Al ₂ O ₃（8-10 wt％）和高TiO ₂ 铬铁矿含量为（0.58–0.96 wt％），再结合计算得出的母体熔体成分，表明芳马yu层状铬铁矿的母体岩浆是高钛岛弧形玄武岩成因，形成于超俯冲带环境中。