Genesis and Characteristics of the Lamprophyre Dike from the Saima Alkaline Complex,Liaoning Province
The lamprophyre dikes are spatially associated with the Saima alkaline complex(nepheline syenite),whereas the genesis of lamprophyre and its relationship with the Saima alkaline complex are still unknown.Meth-ods of petrography,petrogeochemistry and geochronology were conducted to solve these issues.The Saima lampro-phyre belongs to perpotassic-potassic magnesium lamprophyre characterized by high content of Mg,K and low con-tent of Ti.High initial(87Sr/86Sr)i ratios and negative εNd(t)values with positive Pb anomalies in lamprophyre suggested that it originated from subduction-modified lithospheric mantle and probably experienced crustal assimi-lation during its magma evolution.The phenocryst of Saima lamprophyre is composed of fluorapatite and eastonite and its groundmass consists of subordinate minerals such as potassium feldspar and albite.Fluorapatite pheno-crysts are rich in S and Mn,indicating a relatively oxidized crystallization environment.The ratio of x(Fe2+)-x(Fe3+)-x(Mg2+)in compositionally zoned eastonite and the Titanium in biotite thermometer also demonstrate that it formed under relatively oxidized and higher temperature conditions than the Saima nepheline syenite.In ad-dition,the Rb-Sr age of biotite is(224.7±0.1)Ma,which is consistent with the age of the nepheline syenite(224～230 Ma)within the error ranges.Overall,similar formation age,geochemical characteristics and isotopic compositions between both the Saima lamprophyre dikes and nepheline syenite indicate that they were derived from the same enriched lithospheric mantle as products of different magmatism under the post-collision extensional tec-tonic environment.
万方数据
维普
