冀北五凤楼煌斑岩年代学、地球化学特征及其成因

燕山地区中生代花岗岩类侵入体中发育煌斑岩，呈脉状产于冀北寿王坟—五凤楼一带，岩石类型主要为云煌岩。岩石化学属基性，富钠，富碱，高Mg#，高钛，属高钛、钠质钙碱性煌斑岩。岩石中富集LREE、Ba等大离子亲石元素和P，亏损HREE和Nb、Zr、Ta等高场强元素，基本无Eu异常。其LA ICP MS锆石U Pb年龄为(1352±13) Ma, 侵位于早白垩世，与寿王坟杂岩体是同一时期岩浆活动的产物。五凤楼煌斑岩锆石εHf(t)值为-193~-133，模式年龄远老于其成岩年龄，表明岩浆起源于富集地幔。较高的Ba/Th值(12309~43634)和Sr值(9154×10-6~1 257×10-6)，暗示源区在一定程度上受到了俯冲带流体的改造；较低的Rb/Sr值(002~011)及较高的Ba/Rb值(108~809)证明其源区含有角闪石。岩石地球化学特征显示，五凤楼煌斑岩由俯冲的古太平洋壳富钠流体交代形成的石榴石角闪二辉橄榄岩富集地幔的低程度(05％~15％)部分熔融上侵而成，起源深度为75~100 km。

Chronology,Geochemistry Characteristics and Petrogenesis of Wufenglou Lamprophyres in Northern Hebei,China

Mesozoic lamprophyres with lithological minette are developed as dykes near Shouwangfen Wufenglou in Yanshan region, North China Craton. Chemically, the lamprophyres are basic (SiO2 from 4825% to 5147%), have high values of sodium (Na2O/K2O values from 113 to 231), alkali (K2O+Na2O values from 661% to 740%), Mg# (6784 to 7134) and TiO2(131% to 165%), belonging to high Ti, Na rich calc alkaline lamprophyres. The rock is enriched in LREE, LILE and P, depleted in HREE and HFSE (Nb, Zr, Ta), and has no Eu anomalies. LA ICP MS zircon U Pb dating got an age of (1352±13)Ma, indicating that the lamprophyres were intruded at the same period of magmatic activity with the nearby granitic complex at Shouwangfen area in the Early Cretaceous. The εHf(t) values of lamprophyres are ranging from -193 to -133, the two stage Hf model ages are much older than the age of diagenesis, indicating an enriched mantle source. The high values of Ba/Th (12309 to 43634) and Sr (9154×10-6 to 1 257×10-6) imply the magma formation was effected by the subduction zone fluids. The low values of Rb/Sr(002 to 011) and the high values of Ba/Rb(108 to 809) showed that the source contained amphibole. It is concluded that the lamprophyres were derived from partial melting (05％ to 15％) of garnet amphibole lherzolite of enriched mantle that formed by the interaction between sodium rich subduction fluid and mantle wedge, and the origin depth is 75 km to 100 km.