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  

Geochemistry of the Jingpohu Holocene basaltic rocks, Heilongjiang province, and discussion on their deep processes.

作　　者：张招崇[1] 李兆鼐[1] 李树才[2] 辛影 李兆木 王先政 

机构地区：[1]中国地质科学院地质研究所,北京100037 [2]黑龙江省地质矿产局地质科学研究所,哈尔滨150036

出　　处：《岩石学报》2000年第3期327-336,共10页Acta Petrologica Sinica

基　　金：国土资源部专项项目 (编号 :地科专 96-17)

摘　　要：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15 km ,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 ,两个地区的玄武质岩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 Al2 O3、Na2 O、K2 O含量、强烈富集轻稀土和大离子亲石元素和低的 Mg O、Ca O、Mg#值和 Na/ K比值为特征 ,而它们所含的二辉橄榄岩包体的地球化学特征则刚好与其寄主岩石相反。反演计算表明 ,玄武质岩石的岩石学和地球化学特征的巨大差异不是由同一源区的地幔部分熔融程度造成的。结合 Sr、Nd、Pb同位素数据 ,证明由于在 6 80 0 0～ 34 90年时 ,地幔柱的作用使该区地幔发生不同程度的交代富集作用 ,由此导致了该区地幔的强烈不均一性。相对于碱性橄榄玄武岩 ,白榴石碱玄岩来自于更加富集的地幔源区 。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.

关 键 词：幔源 碱性玄武质岩石 地球化学 全新世 

分 类 号：P588.145[天文地球—岩石学] P534.632[天文地球—地质学]