摘要
本次研究对分布于峨眉山大火成岩省(ELIP)中带,四川省沐川地区的玄武岩进行元素地球化学研究,初步探讨了其成因。研究表明,该玄武岩具有高钛(TiO2=3.81%~5.15%,Ti/Y=605.95~939.83)、高铁(TFe2O3变化于13.78%~17.61%)和相对低镁(MgO=3.50~5.16)的特点,属高钛碱性玄武岩系列。玄武岩Lu/Yb比值较低(0.11~0.15),在原始地幔标准化的微量元素蛛网图上,Ti显示正异常,Ta,Nb显示正常-弱负异常,指示母岩浆仅受到少量下地壳物质的混染。在Harker图解中,MgO与SiO2呈负相关,与Al2O3/CaO,TFe2O3,TiO2,P2O5,Cr呈正相关,暗示岩浆上升过程中很可能发生了橄榄石、单斜辉石、Ti-Fe氧化物(磁铁矿、钛铁矿)、磷灰石等矿物的分离结晶作用。玄武岩的元素地球化学组成显示岩浆源自OIB型地幔源区,进一步Sm/Yb,La/Yb比值分析显示,源区以石榴石二辉橄榄岩为主。由于峨眉山大火成岩省(ELIP)中、外带包括沐川、昭通、贵州和广西等地的高钛玄武岩具有相似的元素地球化学组成,且在Ti/Yb-Nb/Th图解上未显示大陆岩石圈地幔物质加入的趋势,推测这些玄武岩很可能是地幔柱头部物质在石榴石稳定区发生低程度部分熔融所形成。
The whole-rock elemental data of the Emeishan basalts in the Muchuan area are studied and their petrogenesis is discussed.It shows that the basalts are characterized by high titanium(TiO2=3.81%-5.15%,Ti/Y=605.95-939.83), high iron(TFe2O3=13.78%-17.61%) and relatively low magnesium(MgO=4.53-7.13),belong to high titanium alkaline basalt series.The Lu/Yb ratio of basalts is low(0.11-0.15),Ti shows enrichment and Ta,Nb show slight depletion in the primitive mantle-normalized spidergrams, indicating that the parental magma experienced minor crustal contamination.The negative correlation between MgO and SiO2, positive correlation among MgO and Al2O3/CaO,TFe2O3,TiO2,P2O5,Cr suggest that crystal fractionation of minerals,such as olivine,clinopyroxene,magnetite,ilmenite and apatite,may be a significant process in the genesis of the basalts.The geochemical compositions show that the basalts in the Muchuan area were derived from an OIB-type mantle source dominated with garnet and lherzolite,evidenced by the high Sm/Yb and La/Yb ratios.The high-Ti basalts in the Muchuan,Zhaotong,Guizhou and Guangxi areas in central and outer zones of ELIP have similar elemental compositions and they do not show the trend of the contamination of continental lithospheric mantle in Ti/Yb-Nb/Th diagrams. It is considered that the basalts are formed by low degree partial melting of mantle plume head material in garnet stable zone.
作者
程文斌
董树义
金灿海
赵兵
张玙
王畅
Cheng Wenbin;Dong Shuyi;Jin Canhai;Zhao BingZhang Yu;Wang Chang(College of Earth Science,Chengdu University of Technology,Chengdu,Sichuan 610059,China;Chengdu Center of China Geological Survey,Chengdu,Sichuan 610081,China)
出处
《矿物岩石》
CAS
CSCD
北大核心
2019年第4期49-60,共12页
Mineralogy and Petrology
基金
中国地质调查局地质调查项目(121201010000150002-11、DD20160019-06)
乌蒙山区地质矿产综合调查项目子课题(DD20160019-16)
关键词
峨眉山玄武岩
元素地球化学特征
岩石成因
沐川
Emeishan basalts
element geochemical characteristics
petrogenesis
Muchuan area
