【摘要】 镁铁质-长英质杂岩体的成因研究对探讨秦岭造山带在三叠纪时期的地球动力学背景具有重要的意义。对位于秦岭造山带西段的安王山透辉石岩-二长岩杂岩体进行了系统的锆石U-Pb定年和原位Hf同位素分析、全岩主元素和微量元素分析及全岩Sr-Nd同位素分析。透辉石岩-二长岩杂岩体主要由透辉石岩、辉长岩和二长岩组成。锆石U-Pb定年显示二长岩形成于（233±1） Ma。该杂岩体具有非常高的Ba （1395～5500μg/g）和Sr （652～2560μg/g）含量、平行且分馏的稀土元素分布模式、弱的Eu异常及相似且富集的Sr ((⁸⁷Sr/⁸⁶Sr)_i=0.70587)和Nd(ε_Nd（t）=-1.85～-3.89)同位素组成。来自杂岩体的二长岩具有中度解耦的Hf-Nd同位素系统和负的Δε_Hf（t）（-2.41～-4.90）值,这说明透辉石岩-二长岩杂岩体起源于被大陆碎屑沉积物熔体交代的富集地幔,并且在上升、侵位至地壳过程中经历了分离结晶作用。透辉石岩-二长岩杂岩体的成因研究表明,剪刀式大陆碰撞过程中出现的南东向板片撕裂导致了秦岭造山带内三叠纪镁铁质-长英质岩浆作用的形成。更多还原

【Abstract】 A petrogenetic study of the mafic-felsic complex in the Qinling orogenic belt is crucial to determine the Triassic geodynamic processes, which have been poorly documented until now. In this contribution, we report new zircon U-Pb ages and in-situ Hf isotope, whole-rock major and trace element, and Sr-Nd isotope compositions of the Anwangshan diopsidite-monzonite complex in the western part of the Qinling orogenic belt. This complex is mainly composed of diopsidite, gabbro, and monzonite. Zircon U-Pb dating shows that the monzonite was emplaced at（233±1） Ma. The complex is characterized by extremely high Ba and Sr contents（1395–5500 μg/g and 652–2560 μg/g, respectively）, parallel and fractionated REE patterns, insignificant Eu anomalies, and similar and enriched Sr and Nd isotopic compositions((⁸⁷Sr/⁸⁶Sr)_i of 0.70587 and ε_Nd（t） from-1.85 to-3.89). The monzonites from the complex exhibit mild Nd-Hf isotopic decoupling and negative Δε_Hf（t） values（-2.41 to-4.90）, which indicate that the diopsidite-monzonite complex was formed by partial melting of the enriched mantle which was hybridized by terrigenous-sediment-derived melts and experienced fractional crystallization during its ascent and emplacement into the crust. This petrogenetic study of the diopsidite-monzonite complex illustrates that slab tearing occurred as a result of the northwestward propagating, scissor-like continental collision, which triggered the onset of Triassic mafic-felsic magmatism in the Qinling orogenic belt.更多还原