石家庄市西部古元古代火山岩地球化学特征

Geochemical Characteristics of Paleoproterozoic Volcanic Rocks in Western Shijiazhuang

石家庄西部古元古代火山活动形成一套火山—沉积岩系列,间歇明显,前期火山活动较弱,呈薄层状、透镜状产出,后期火山活动增强,火山岩呈厚层状产出。根据地质特征、岩石学特征研究,以及地球化学样品分析,石家庄西部古元古代火山岩大离子亲石元素(LILE)Rb、Ba明显富集,Sr表现出正异常,Nb和Ta相对亏损,指示其岩浆可能来源于地壳重熔,或在岩浆上升过程中受到了壳源物质的混染,所有样品中轻重稀土分异非常弱,没有明显的Nb、Ta、Zr、Hf负异常,与岛弧或者大陆边缘弧中的基性火山岩有明显的差异,类似于陆内玄武岩。通过研究系列的地球化学图解,古元古代甘陶河群碎屑岩夹基性火山岩沉积建造形成于板内拉张的构造环境。

Paleoproterozoic volcanic activity in Western Shijiazhuang formed a series of volcanic-sedimentary. The interval is obvious, the volcanic activity is weak in the early stage, and the volcanic activity is thin and lenticular. The volcanic activity is enhanced in the later stage, and the volcanic rocks are thick and layered. Based on the study of geological and petrological characteristics, geochemical samples were analyzed. The Paleoproterozoic volcanic rocks in Western Shijiazhuang are obviously enriched (LILE) Rb、Ba, Sr shows positive anomalies, Nb 、Ta are relatively deficient. It indicates that the magma may originate from crustal remelting or be contaminated by crustal materials during magma rising. The difference of light and heavy rare earth elements in all samples is very weak, and there are no obvious negative anomalies of Nb, Ta, Zr, Hf. The basic volcanic rocks in the island arc or continental margin arc are obviously different from those in the continental margin arc, similar to the intracontinental basalts. Based on a series of geochemical diagrams, the sedimentary formation of clastic rocks with basic volcanic rocks in the Paleoproterozoic Gantaohe Group was formed in a tectonic environment of intraplate tension.