摘要
This Aliwula area in paper reports lithologic features, K-Ar age and geochemical data of riebeckite granophyres from the southern Da Hinggan Mts., aiming to reveal the petrogenesis of riebeckite granophyres. K- Ar age of riebeckite granophyres is 126± 2 Ma, implying that the riebeckite granophyres formed in the Early Cretaceous. The granophyres are rich in riebeckites and with a lot of melt-fluid inclusion in its quartz pheno- crysts. The granophyres are characterized by extensive enrichment in Si02, FeO, and （Na20 ＋ K20） and de- pletion in MgO and CaO, strong negative Eu anomalies and strong positive Ce anomalies. Additionally, the rie- beckite granophyres not only have high total REE contents and display enrichment of HFSEs （for example Zr, Hf, Nb, Ta）, but also are strong in depletion of LILEs （ e. g. Ba, Sr） as well as high Ga/A1 ratios. Primitive mantle-normalized REE pattern significantly displays REE M-W tetrad effect. REEs fractionate evidently and highly enrich in LREE, but are uneven distribution in the rocks. Taken together, we conclude that the riebeck- ite granophyres are similar to typical A-type granite, which could be derived from stretching environments in the Early Cretaceous. The granophyres originated from residual melt which underwent highly differentiation process, and were formed in magmatic-hydrothemal transition stage at last.
This paper reports lithologic features,K--Ar age and geochemical data of riebeckite granophyres from Aliwula area in the southern Da Hinggan Mts.,aiming to reveal the petrogenesis of riebeckite granophyres.K-Ar age of riebeckite granophyres is 126 ± 2 Ma,implying that the riebeckite granophyres formed in the Early Cretaceous.The granophyres are rich in riebeckites and with a lot of melt-fluid inclusion in its quartz phenocrysts.The granophyres are characterized by extensive enrichment in SiO2,FeO,and(Na2O+K2O) and depletion in MgO and CaO,strong negative Eu anomalies and strong positive Ce anomalies.Additionally,the riebeckite granophyres not only have high total REE contents and display enrichment of HFSEs(for example Zr,Hf,Nb,Ta),but also are strong in depletion of LILEs(e.g.Ba,Sr) as well as high Ga /Al ratios.Primitive mantle-normalized REE pattern significantly displays REE M--W tetrad effect.REEs fractionate evidently and highly enrich in LREE,but are uneven distribution in the rocks.Taken together,we conclude that the riebeckite granophyres are similar to typical A-type granite,which could be derived from stretching environments in the Early Cretaceous.The granophyres originated from residual melt which underwent highly differentiation process,and were formed in magmatic-hydrothemal transition stage at last.
