摘要
元素之间的相关特征一直是地球化学过程的重要判据。但通常只有少数几个元素的相关特征为人们所采用。本文通过对大庄科花岗杂岩系列研究表明,许多元素相互之间都存在着显著的线性相关特征,它们是协同共变的——协变特征;另一些元素包括成矿元素,挥发份等,不呈协变特征。前者可能反映岩浆的状态、结构等内部特征和岩浆过程;后者反映了岩浆的成矿专属性特征。
The Dazhuangke granitoid complex, 50km north from Beijing, is composed
of several intrusions with K-Ar age of 112-188Ma. and compositions ranging
from diorite-tonalite-monzonite-granodiorite-granite, accompanied by Mo-
mineralized breccia pipes. The rocks have characteristic mineral assemblages: ±
Py + Hb + Bi + P1 + Kf + Qz + Mt + Sp + Ap. Major element chemistry of the complex
shows a calcic-alkaline trend of granitoid series, with high Na/K ratio (0.83-
1.07) and low Al/(K + Na + 2Ca) ratio (0.83-1.03). It is suggested that the
Dazhuangke granitoid cogmplex, close to I-type granite, was formed in a tectonic
setting of intra-continental plate.
Abundances of REE are not high (REE, 75.81-211.12), with LREE enriched
and slight Eu negative anomalies shown in chrondrite-norinalized abundance
plots. The variation of major, trace elements and REE do not indicate that
fractionation has occurred. Elements quite different in chemistry, such as Sr,
Ba, LREE, Mg, Ca, Sc, Ti, Mn, P, Cl, Al, Ga, etc., show a strong matural
positive coherence. This suggests that other processes of magma chamber, e.g.
containation, liave appeared. The elements in the granitoid magma may behave
quite different from those in the basaltic magma.
Ore-forming elements (W, Mo, Cu, etc.) and F, Be, HREE change incohe-
rently. W, Mo, Cu, are enriched in the complex, which indicates a potential
of ore-forming process during magma evolution. Strong enrichment of W, Mo
in both rock and magnetite from an intrusion of the Dazhuangke granitoid
complex, which has higher contents of SiO2, K2O, Rb, F, Be and lower Co,
Ni, Ti, etc., suggests the W, Mo metallogenic specialization of the intrusion.
出处
《现代地质》
CAS
CSCD
1990年第1期78-89,共12页
Geoscience
