北淮阳地区与斑岩型钼矿床相关岩浆岩的地质地球化学特征及成因

Geological and geochemical characteristics and genesis of magmatic rocks related to porphyry Mo deposits in the Beihuaiyang region

位于秦岭—大别造山带东段的北淮阳地区分布有众多的斑岩型钼矿床,其成矿与岩浆作用紧密相关。对该区与斑岩型钼矿床密切相关的岩浆岩进行了系统的岩石化学、微量元素和同位素地球化学研究,深入探讨了其成因。研究认为,成矿岩体规模较小,岩性为花岗(斑)岩类,受北东向与北西向区域性断裂的次级构造控制。岩石化学成分以高硅、高钾、富碱为特征,为高钾钙碱性-钾玄岩系列、准铝-过铝质岩石。岩石微量、稀土元素特征相似并显示壳源特征。岩石Sr-Nd-Pb-Hf同位素地球化学特征显示这些花岗质岩浆与整个大别地区白垩纪花岗岩的成岩物质来源一致,源于新元古界北大别片麻岩和扬子克拉通北缘TTG型岩浆,并混入一些古元古代扬子克拉通古老地壳物质(如崆岭杂岩)。在白垩纪发生的下地壳拆沉、软流圈上涌及大规模地壳伸展等机制下,扬子克拉通北缘的地壳熔融并提供了主要的成岩物质,幔源岩浆的上涌可能提供了热源,其物质的加入是次要的。该区与斑岩型钼矿床相关岩浆岩与东秦岭地区类似,属深源浅成型花岗岩类。

There are numerous porphyry molybdenum deposits located in the eastern Beihuaiyang area of Qinling-Dabie metallogenic belt,where the magmatism is closely related to mineralization.This study has investigated the intrusive rocks in the field which are closely related with porphyry molybdenum deposit,by using the method of whole-rock major elements,trace elements and isotope geochemistry research,and discussed its petrogenesis.This research shows that the scale of metallogenetic rock body is small,and the lithology is porphyry granite,which is controlled by the fault structure in northeast and northwest.The chemical composition of rocks is characterized by high silicon,and potassium alkali-rich,belonged to high-K calc-alkaine-shoshonitic series,metaluminous-peraluminous rocks.Trace and rare earth elements have similar characteristics and show features of crustal sources.Sr-Nd-Pb-Hf isotope geochemical characteristics show that those matallogenic granitic magma has the same sources with Dabie Cretaceous granites.They both originated from Dabie granitic gneiss and TTG-like magmatic rocks of the north Yangtze Block in the Neoproterozoic,and interfused some ancient crustal materials from palaeoproterozoic Yangtze craton（such as Kongling complex）.The lower crust delamination,asthenosphere upwelling and large-scale crustal extension happened in the Cretaceous,the northern margin of Yangtze craton crust melted and provided the mainly diagenetic materials.Upwelling of mantle derived magma probably provided heat source with little materials.The igneous rocks associated with Mo Deposits in this region are similar to Eastern Qinling metallogenic belt,which belongs to deep-hypabyssal granitoids.