粤北佛冈岩体中粒斑状花岗岩地球化学、年代学及地质意义

佛冈岩体是南岭地区最大的复式岩基,主体岩性为中粒斑状黑云母二长花岗岩,近期在佛冈岩体北缘新发现了大型离子吸附型稀土矿床。对佛冈花岗岩岩石样品进行了LA-ICP-MS锆石U-Pb定年,得出结晶年龄分别为160.5±2.9Ma、161.9±2.6Ma和164.5±2.4Ma,表明岩体形成于中晚侏罗世。岩体具有高硅、富碱富铝的特征(K2O/Na2O=1.48~2.17,A/CNK=1.05~1.27),属钙碱性过铝质钾玄质花岗岩;富集Rb、Th、U、K、Pb、Nd、Zr和Hf等元素,亏损Ba、Nb、Ta、La、Ce、Sr、P和Ti等元素,具明显的负Eu异常(δEu=0.17~0.41)。初步研究结果表明,佛冈岩体主体由上地壳砂-泥质岩在高温条件下部分熔融而成,是陆壳改造型(即S型)花岗岩,形成于古太平洋板块向欧亚板块俯冲的构造背景。

Geochemistry,Chronology and Geological Significance of Medium Grain Porphyritic Granite in the Fogang Intrusion,Northern Guangdong

Fogang intrusion is the largest composite batholith in Nanling Range. Its main lithology is medium-grained porphyry biotite monzonitic granite. Recently, a large ionic absorption type rare earth deposit has been discovered in the northern margin of Fogang intrusion. The LA-ICP-MS zircon U-Pb dating of Fogang granite shows that the crystallization ages are 160.5±2.9 Ma, 161.9±2.6 Ma and 164.5±2.4 Ma, respectively, indicating that the batholith was formed in the Middle and Late Jurassic. The Fogang granite is characterized by high silicon and alkali-rich and aluminium-rich (K2O/Na2O=1.48-2.17, A/CNK=1.05-1.27) and belongs to calc-alkaline peraluminous potassium basaltic granite. It is rich in Rb, Th, U, K, Pb, Nd, Zr and Hf, and depleted in Ba, Nb, Ta, La, Ce, Sr, P and Ti, with obvious negative Eu anomalies (δEu=0.17-0.41). The preliminary results show that the main body of Fogang granite is formed by partial melting of upper crustal sand-mudstone at high temperature. It is a continental crust reformed granite (S-type), formed in the environment of the subduction of the Paleo-Pacific plate to the Eurasian plate.