摘要
燕山造山带中段(冀北下板城)中晚侏罗世髫髻山组火山岩主要由粗安岩和粗面岩组成.火山岩具有高的SiO2(＞55%)、Al2O3(15.70%～17.55%)、Na2O(3.79%～5.42%)、Na2O+K2O(5.99%～9.38%)、CaO(2.31%～6.48%)和低的MgO(≤4.01%,Mg#≤0.50),高Sr(428～816μg/g)及Na2O/K2O比值(一般1.11～1.88),轻稀土元素富集,Sr/Y和Rb/Sr比值低.其中,粗安岩相对亏损重稀土元素(YbN＜8.5,Y＜19μg/g),Y/Yb(12.62～15.06)和(Ho/Yb)N(1.23～1.50)比值较高,Eu负异常不明显(Eu/Eu*=0.90～0.95),具有埃达克岩地球化学特征.我们认为髫髻山组粗安岩起源于大陆下地壳玄武质岩石的部分熔融,粗面岩为粗安岩浆结晶分异的产物.
The volcanic lavas of the middle-late Jurassic of Tiaojianshan formation in the middle section of Yanshan Orogen (from Xiabancheng county in North Hebei province) are composed of trachyandesite and trachyte. These rocks have high SiO2 (> 55%), Al2O3 (15.70 similar to 17.55%), Na2O (3.79 similar to 5.42%), Na2O + K2O (5.99 similar to 9.38%) and CaO (2.31 similar to 6.48%) contents and low MgO (less than or equal to4.01%, less than or equal to0.50 in Mg-#) contents, and high Sr (428 similar to 816ppm) contents and Na2O/K2O(1.11 similar to 1.88) ratios, as well as low Sr/Y, Rb/Sr ratios, and are characterized by strongly fractionated LREE and positive Sr anomalies. Compared with trachyte, trachyandesite is HREE depleted with low Yb-N(<8.5), Y(<19ppm) content, negligible negative Eu anomalies(Eu/Eu-* = 0.90 similar to 0.95), high Y/Yb(12.62 similar to 15.06) and (Ho/Yb)(N) (1.23 similar to 1.50) ratios, and has geochemical features of adakite. We think that trachyandesites are products of magmas derived from partial melting of lower continental calc-alkaline basaltic crust, and trachytes are products of crystallization differentiation of trachyandesite magma.
出处
《岩石学报》
SCIE
EI
CAS
CSCD
北大核心
2004年第3期501-510,共10页
Acta Petrologica Sinica
基金
中国科学院知识创新工程项目(批号KZCX2-102)资助
关键词
埃达克岩
粗安岩-粗面岩
下地壳
髫髻山组
冀北
燕山造山带
adakite
trachyandesite-trachyte
lower crust
Tiaojishan formation
North Hebei Province
Yanshan Orogen
