淮北隐伏岩体的地球化学特征、岩石成因及构造意义

Geochemical characteristics,petrogenesis and tectonic significance of the hidden rock body in Huaibei area

通过对淮北隐伏岩体的岩相学、地球化学特征的研究,揭露了岩体的岩石成因、源区性质及构造环境。采集了6件化学分析样品用于主微量与稀土元素分析,6件岩矿鉴定标本用于镜下薄片分析。显微镜下特征显示,岩体岩性为石英二长闪长玢岩和石英角闪闪长玢岩。主量元素特征显示,岩体具富SiO_(2)(60.70%~68.28%)、富Na_(2)_(O)(3.81%~6.22%)、富Al_(2)O_(3)(14.07%~15.12%)的特征,且Mg^(#)值(43.75~61.25)较高,属准铝质高钾钙碱性岩石。稀土元素特征显示,岩体轻重稀土分馏明显,表现为轻稀土富集、重稀土亏损,无明显Eu异常(δEu平均值=0.95)和Ce异常(δCe平均值=0.92)。微量元素特征显示,岩体具高Sr(563~868 g/t)、低Y(3.79~11.4 g/t)、高Sr/Y比、低Yb(0.50~1.26 g/t)的特征,Rb/Sr比值较低(0.07~0.11)。综合研究表明,淮北隐伏岩体为具埃达克岩性质的岩石,形成于加厚下地壳发生拆沉的环境下,下地壳深部的石榴辉石岩相部分熔融产生岩浆,与地幔橄榄岩发生反应,在岩浆移出源区后,经历了不同程度的分离结晶,形成了石英二长闪长玢岩与石英角闪闪长玢岩。

By studying the petrographic and geochemical characteristics of the hidden rock body in Huaibei area,the petrogenesis,source characteristics and tectonic setting of the rock mass were revealed.In this work,a total of 6 chemical analysis samples were collected for the analysis of major,trace and rare earth elements,and a total of 6 rock and mineral identification samples were used for microscopic thin section analysis.Microscopic characteristics show that the rocks are composed of quartz monzodiorite porphyrite and quartz amphibolite diorite porphyrite.The major element characteristics show that the rock mass is rich in SiO_(2)(60.70%-68.28%),Na_(2)O(3.81%-6.22%),Al_(2)O_(3)(14.07%-15.12%),and the value of Mg^(#)(43.75-61.25)is high,which falls into quasi-aluminum high potassium calc-alkaline rocks.Rare earth elements(REE)characteristics show that the REE is enriched in LREE and depleted in HREE,and there is no significant Eu anomaly(δEu averaged 0.95)or Ce anomaly(δCe averaged 0.92).Trace element characteristics show that the rock mass is featured with high Sr(563-868 g/t),low Y(3.79-11.4 g/t),high Sr/Y ratio,low Yb(0.50-1.26 g/t),and low Rb/Sr(0.07-0.11).Comprehensive research shows that the hidden rock body in Huaibei area is a rock with the nature of adakite,formed in the environment where the thickened lower crust was delaminated,and the garnet pyrocene facies in the deep of the lower crust melted to produce magma,which reacted with the mantle peridotite.After the magma moved out of the source area,it experienced different degrees of fractional crystallization,thus forming the quartz monzodiorite porphyrite and quartz amphibolite diorite porphyrite.