辽河盆地沙三期火山-侵入岩地球化学与岩石成因

辽河盆地沙三期火山-侵入岩为一套偏碱性的双峰式岩系，其基性端元为碱性玄武岩，中偏碱性端元为粗面质熔岩和侵入岩。碱性玄武岩富集高场强元素(如Nb、Th、Zr、Hf、V等)和轻稀土、Sr、Ba等大离子亲石元素，而亏损Rb和K，具有与板内碱性玄武岩和洋岛玄武岩类似的特征。粗面质岩石显示与基性端元相似的地球化学特征，其不相容元素含量总体上高于碱性玄武岩，但具强烈的Sr和Eu亏损。矿物学、岩石学及地球化学证据表明，玄武质岩石是软流圈地幔低程度部分熔融的产物，并经历了橄榄石和辉石的分离结晶作用，其源区可能有金云母和石榴石残留。玄武质岩浆上升到较浅部位后进一步发生橄榄石、辉石、斜长石和磁铁矿等的分离结晶作用而形成粗面质岩浆，地壳物质混染作用不显著。

Geochemistry and petrogenesis of Eocene volcanic-intrusive rocks in Liaohe basin, northeastern China

Liaohe basin lies in northeastern China. Volcanites of Eocene Shahejie Formation in this basin are bimodal in composition with mafic rocks being one end member and weakly alkaline intermediate rocks being the other. Alkaline basalts are enriched in high field strength elements (e. g. Nb, Th, Zr, Hf, etc.), light rare earth elements (LREE) and large ion lithophile elements (e. g. Ba, Sr) except Rb and K, indicating that these basalts were formed under an intraplate environment. Incompatible trace element patterns of the basalts are virtually comparable to those of typical ocean island basalts (OIB). Apart from strong Sr and Eu depletion due to feldspar fractionation, trachytic rocks have the same characteristics in trace element behaviours as alkaline basalts. Despite of a gap between alkaline basalts and trachytes, major and trace element distributions indicate both the basalts and trachiytes are produced by the same mantle-derived magma. Lines of evidence in mineralogy, petrology and geochemistry imply that basalts are produced by low- degree partial melting of an asthenospheric source with subsequent fractional crystallization of olivine and clinopyroxene, whereas trachytes were derived from the basaltic magma by fractionation of olivines, clinopyroxenes, plagioclases, magnetites at shallow crust, and crustal contamination is not significant in the evolution of the magmas.