塔里木溢流玄武岩的喷发特征

The eruption characteristics of the Tarim flood basalt

通过对柯坪地区二叠系野外火山岩露头剖面和英买力、哈拉哈塘井区二叠系火山岩钻井剖面的对比,将塔里木早二叠世溢流玄武岩划分为三个旋回,从老到新依次是:库普库兹满溢流玄武岩旋回(KP),长英质火山碎屑岩旋回(FP)和开派兹雷克溢流玄武岩旋回(KZ)。KP旋回以巨厚溢流玄武岩夹凝灰岩为特征,在柯坪露头区和英买力井区均可划分出三层巨厚玄武质熔岩流,至哈拉哈塘井区减少为一层玄武岩流,但长英质火山碎屑岩和熔岩厚度增加。FP旋回在柯坪露头区自下而上包括空落相凝灰岩,熔结凝灰岩,再沉积火山碎屑岩和正常碎屑岩夹火山灰层,该层可与英买力及哈拉哈塘井区的凝灰岩层对比,表明在塔北存在一期面积广泛的长英质火山喷发。KZ旋回以溢流玄武岩为主,在开派兹雷克剖面识别出四期喷发共8层溢流玄武岩和一期安山质玄武岩,每期喷发之间夹少量碎屑岩,但未见长英质火山碎屑岩夹层,该特征与英买力和哈拉哈塘井区的火山层序组合不同,而与塔中溢流玄武岩类似。三个火山旋回的划分表明塔里木大火成岩省经历了"基性溢流玄武岩-酸性火山碎屑岩-基性溢流玄武岩"的演变过程,与Afro-Arabian溢流玄武岩省相似,可进行对比研究。

Integration of field investigation,regional stratigraphic comparison,remote sensing and image interpretation allow us to divide the Tarim Permian flood basalt province into three eruptive cycles listed by decreasing age：Kupukuziman flood basalt（KP）,Felsic pyroclastic rocks（FP）,Kaipaizileike flood basalt（KZ）,KP features flood basalt and tuff;in the outcrop in Keping and Yingmaili areas,it can be differentiated into two units containing three thick layers of basaltic lava flows,These three layers decrease to one layer of basaltic lava flow in the Halahatang area;however,felsic pyroclastic rocks and lava layer thicknesses increase in the Halahatang area,FP in the outcrop in Keping area consists of ash fall tuff,ignimbrite,resedimented pyroclastic rocks,and the tuff layer interbedded with the normal clastic rocks section from top to bottom,This section is comparable to the tuff layer in the Yingmaili and Halahatang area,thus reveals one layer of lava flow covering an extensive area due to a unit of the eruption of the FP,KZ mainly features flood basalt in its Kaipaizileike section,identifications of 4 eruptive units,8 layers of flood basalt,and 1 layer of andesitic basalt were made,Traces of clastic rocks were found between eruption units,but no FP interlayers were found,This characteristic is different from Yingmaili and Halahatang volcanic sequences,but similar to the flood basalt in Tazhong area,The differentiation between these three volcanic cycles reveals that Tarim flood basalt underwent a ＂flood basalt-felsic pyroclastic rocks-flood basalt＂ transformation,and is similar to Afro-Arabian large igneous province;thus,a comparative study between these two regions is merited.