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姚家庄超镁铁岩-正长岩杂岩体是华北克拉通北缘晚三叠世碱性岩带的代表性岩体之一.本文通过对该岩体细致的年代学、岩石学、矿物学和地球化学研究,对岩浆体系性质、岩石成因和地幔源区性质等进行了探讨,这对该碱性岩浆岩带的起源和构造背景提供了新的限制.岩体由堆晶超镁铁岩、辉石正长岩和伟晶正长岩三大类岩石组成.其中正长岩的锆石U-Pb年龄为209Ma.透辉石-普通辉石、黑云母和透长石-正长石是主要组成矿物,其次为磷灰石和磁铁矿.岩体富集LILE和LREE,亏损HFSE和HREE,初始87Sr/86Sr=0.7057～0.7061,εNd(t)=?9.4～?11.4.矿物学和地球化学数据表明姚家庄杂岩体的母岩浆为SiO2不饱和的过钾质碱性岩,富CaO,富P2O5,H2O和CO2等流体,高氧逸度,高温;源区为富含金云母-单斜辉石的富集岩石圈地幔,位于石榴石稳定区(>80km);此性质的地幔曾经历来自蚀变俯冲板片熔/流体的交代作用.岩浆在侵位过程中受到了少量古老TTG片麻岩的混染.姚家庄杂岩体的发育,指示晚三叠世时,华北克拉通北缘已进入了被破坏大陆边缘的强烈伸展演化阶段.
The Yaojiazhuang ultramafic-syenite complex is one of the representatives of Late Triassic alkaline rocks in the northern margin of North China Craton.Through the detailed geochronology, petrology, mineralogy And geochemical studies on the nature of the magma system, the genesis of the rock and the nature of the mantle source, etc., which provide a new limitation on the origin and tectonic setting of this alkaline magmatic belt.The pluton is composed of hematite , Pyroxene syenite and pegmatite, and the zircon U-Pb age of the syenite is 209 Ma. Diopside-pyroxene, biotite and peridotite-orthoclase Is mainly composed of minerals, followed by apatite and magnetite.The rock mass is enriched in LILE and LREE, the loss of HFSE and HREE, the initial 87Sr / 86Sr = 0.7057 ~ 0.7061, εNd (t) =? 9.4 ~? 11.4. And geochemical data show that the parent magma in the Yaojiazhuang complex is an SiO2 unsaturated overpotassium alkaline rock, rich in CaO, P2O5, H2O and CO2-rich fluids with high oxygen fugacity and high temperature. The source region is rich in phlogopite - Enriched lithospheric mantle of clinopyroxene, located in a stable zone of garnet (> 80 km); mantle of this nature has been experienced from alteration subduction slab melting / fluid During the emplacement, the magma was contaminated by a small amount of ancient TTG gneiss, and the development of the Yaojiazhuang complex indicates that during the Late Triassic, the northern margin of the North China Craton has entered a strong extension of the damaged continental margin Evolution stage.