北淮阳东段河棚岩体地球化学特征、LA-ICP-MS锆石U-Pb年龄及地质意义

Geochemical characteristics and LA-ICP-MS zircon U-Pb geochronology of the Hepeng intrusion in the eastern section of North Huaiyang and their geological significance

河棚岩体位于北淮阳东段河棚地区,为似斑状细粒黑云钾长花岗岩,具较高的SiO_2和碱质含量,属于偏铝质碱性系列岩石。稀土元素含量中等,LaN/YbN与LREE/HREE值均较大,HREE相对于LREE明显亏损,Eu弱负异常,具较弱的Ce负异常,轻稀土分馏较明显,重稀土较平坦,属轻稀土富集型。岩石富集大离子亲石元素Rb、Ba、K和高场强元素Th、U、Ce、Zr、Hf,亏损Nb、Ta、Sr、Ti、P。通过LA-ICP-MS锆石U-Pb定年,获得河棚岩体206Pb/238 U年龄为128.6±2.1 Ma,表明该岩体形成于燕山晚期,是早白垩世早期岩浆活动的产物,代表河棚岩体的成岩年龄。主、微量元素地球化学特征表明河棚岩体属于非造山A型花岗岩,形成于燕山晚期伸展构造环境。

The Hepeng intrusion, located in the Hepeng area in the eastern section of North Huaiyang, consists mainly of porphyritic fine-grained biotite-feldspar granite. It has high SiO2 and alkali contents, belonging to the metaluminous alkaline rock series. The Hepeng intrusion is characterized by medium REE content, high LaN/YbN and LREE/HREE ratios, distinct HREE depletion relative to LREE, weak nega- tive Eu anomalies and weaker negative Ce anomalies, and distinct fractionation of LREE relative to that of HREE, indicating it belongs to a LREE-enriched terrane. Large-ion lithophile elements （LILE）, such as Rb, Ba and K, and high field strength element （HFSE）, such as Th, U, Ce, Zr and Hf, are significantly enriched, while Nb, Ta, Sr, Ti and P are depleted. LA-ICP-MS zircon U-Pb dating yields a z06 pb/2asU age （128. 6＋2.1 Ma） for the Hepeng intrusion, indicating the diagenetic age of the Hepeng intrusion is in late Yanshanian and the Hepeng intrusion was the product of the Early Cretaceous magmatic activity. Geochemical characteristics of major and trace elements show that the Hepeng intrusion belongs to the anorogenie A-type granites and formed in extensional tectonic environment at late Yanshanian period.