五大连池等地钾质碱性玄武岩、幔源包体的微量元素特征及成因信息

黑龙江省五大连池、科洛、二克山火山岩的成因,是一个重要而又复杂的问题.作者根据岩相学、地球化学、模式计算等一系列工作,认为这组钾质玄武岩是含金云母的尖晶石二辉橄榄岩低度局部熔融的产物。岩浆在上升过程中,经历了结晶分异和同化混染,从而形成一套具成因联系的新生代大陆板内钾质碱性玄武岩。本文试从微量元素方面对此结论提供证据,并显示钾质熔岩及幔源包体的微量元素特征,由此说明地幔交代作用在钾质系列岩浆形成过程中的重要性。

Characteristics of the Trace Elements in Potassic Alkaline Basalts and mantle Source Inclusions and their Genesis informations from Wudalianchi and other Regions.

Wudalianchi, Kele and Erkeshan volcano clusters, Heilongjiang province, China, constitute a suite of consanguineous Cenozoic intra-continental potassic alkaline basalts. They are mainly characterized by such as K2O/Na2O>l, existence of leucite (0-20V%) and plagioclase-poor %), enrichment of REE and LIL. The lavas are divided into two types on basis of SiO2 content I Leu-cite picritic basalt (ultrabasic) and leucite basanite (basic). 2REE content of the lavas have 329-570ppm, and (La/Yb)CN = 54 - 64. The lavas enrich in all LIL elements in comparision with Jagoultz's mantle. The most plentiful LIL elements in lavas are K, Sr, Ba and almost 1-7 times more than the other basalts.The content of Cr, Ni decreased with the progress of ages. The similarities in the chondrite-normalized abundant patterns of incompati-ple elements, REE and Pearce's geochemical model between leucite picritic basalts and leucite basanites indicate that they are consanguineous, and assimilation and fractional crystallization had not significant effects on the abundance of LIL nad REE in the lavas. The interpretation of Pearce's geochemical model suggests that more than 90% of mobile elements such as K, Rb, Ba, Nb, Ce, P and more than 80% of Zr and Sm in the lavas were derived from the aqueous fluids for metasomatism. Being an evidence of trace elements this result shows that non-metasomatism enriched mantle is not capable for the fromation of potassic-rich magmas. The inclusions of phlogopite-bearing peridotites in the lavas support this argument