青藏高原北羌塘盆地杂多地区晚二叠世—早三叠世陆相火山岩的地球化学特征及其意义  

Geochemical characteristics of Late Permian-Early Triassic continental volcanic rocks in the Zadoi area,northern Qiangtang,Qinghai-Tibet Plateau

作　　者：李善平[1] 王毅智[1] 沈存祥[2] 许长青[1] 祁生胜[1] 曾小平[1] 

机构地区：[1]青海省地质调查院 [2]青海省乐都县国土资源厅,青海乐都810700

出　　处：《地质通报》2007年第6期675-681,共7页Geological Bulletin of China

基　　金：中国地质调查局<1:25万治多幅;杂多幅区域地质调查>项目(编号:146C003004;146C004004)资助

摘　　要：在北羌塘盆地东部杂多县特龙赛等地首次厘定出晚二叠世—早三叠世火山岩。该火山岩形成于陆相环境,由4个爆发一溢流相火山韵律组成一个完整的火山旋回。这些火山岩主要由强蚀变杏仁状橄榄玄武岩、岩屑晶屑凝灰岩、杏仁状安山岩等组成,TiO_2含量(1.33％～1.76％)与峨眉山低Ti玄武岩相当,MgO含量较低(2.23％～7.52％,平均为5.02％),富集轻稀土元素(LREE／HREE=4.16～13.44,平均为6.5),无明显的Eu异常(δEu=0.85～1.02,平均0.96),Nb、Ta轻度负异常,地球化学特征与大陆拉斑玄武岩相似。各种微量元素判别图解显示这些火山岩形成于大陆拉张带或陆内裂谷区。结合区域研究成果,晚古生代时整个羌塘地区很可能处于一种伸展背景。Late Permian-Early Triassic volcanic rocks were for the first time defined in the Telongsai area, Zadoi County, in the eastern part of the northern Qiangtang basin. The volcanic rocks formed in a continental environment and four explosive- effusive volcanic rhythms make up a complete volcanic cycle. These volcanic rocks consist predominandy of strongly altered amygdaloidal olivine basalt, lithic and crystal tuff and amygdaloidal andesite. They are characterized by low TiO2 contents （1.33-1.76%, equivalent to that of the low-Ti Emeishan basalt）, low MgO contents （2.23-7.52%, with a mean of 5.02%）, enrichment of LREE （4.16-13.44, with a mean of 6.5）, no pronounced Eu anomaly （SEu = 0.85-1.02, with a mean of 0.96） and weak negative Nb and Ta anomalies. These geochemical characteristics are similar to those of continental tholeiite. Discrimination diagrams of various trace elements indicate that these volcanic rocks formed in a continental extensional zone or intracontinental rift zone. The above-mentioned characteristics, combined with the regional research results, suggest that the whole Qiangtang area was very likely to lie in an extensional environment during the Late Paleozoic.

关 键 词：北羌塘盆地 晚二叠世-早三叠世 陆相火山岩 陆内裂谷环境 

分 类 号：P534.46[天文地球—古生物学与地层学] P588.14[天文地球—地质学]