黑龙江镜泊湖地区全新世玄武岩的地球化学特征及其深部过程探讨

镜泊湖地区全新世玄武岩分布在镜泊湖西北方向的“火山口森林”地区和蛤蟆塘地区。这两个地区相距只有１５ｋｍ,但其玄武质岩石在岩石学上具有明显的区别,前者为碱性橄榄玄武岩,后者为白榴石碱玄岩,并且具有钛角闪石、金云母和歪长石巨晶,而前者则没有这些巨晶。对它们的地球化学特征研究表明,两个地区的玄武夺石虽然均属于偏钠质的碱性玄武岩,但是白榴石碱玄岩相对于碱性橄榄玄武岩总体上具有高的Ａｌ２Ｏ３、Ｎａ２Ｏ、Ｋ２

Geochemistryof the Jingpohu Holocene basaltic rocks, Heilongjiang province, and discussion on theirdeep processes

Holocene basaltic rocks of the Jingpohu area are located in the "Crater Forest" and "Frog Pool" areas at the northwest Jingpohu Lake. Although there is only 15km between two areas, there is a difference in petrology between them: alkaline olivine basalt without any magacrsts in the "Crater Forest", and leucite tephrite with kaersutite, phlogopite and anorthoclasite megacrysts in the "Frog Pool". The studies on their geochemical characteristics show that leucite tephrite has higher contents of Al2O3, Na2O, K2O, more enrichment in LREE and LILE, and lower contents of MgO, CaO, lower Mg values and Na/K ratioes than alkaline olivine basalt, although both of them belong to sodic alkaline basalt. In contrast, their xenoliths have inverse geochemical characteristics. Disproof calculation shows that the great difference in petrology and geochemistry was not resulted from the various degrees of partial melting of the same source. Based on their Sr, Nd and Pb isotopic data, this paper proposes that the activity of the mantle plume during 68000 to 3490 years ago led to the different degrees of "metasomatism", which made the extreme mantle source heterogeneities beneath the Jingpohu area. Leucite tephrite was derived from the more enriched mantle source with lower degree of partial melting of mantle source than alkaline olivine basalt.