摘要
玄武岩中的斜长石矿物记录了岩浆过程的重要信息,可为揭示岩浆活动规律提供重要线索。马里亚纳海槽玄武岩中斜长石矿物具有两种产出类型:斑晶和微晶。岩相学特征指示,斜长石斑晶常具有聚片双晶结构、环带结构,偶见熔蚀结构和冷凝边;斜长石微晶呈半定向或杂乱分布在火山玻璃中,其中空骸晶结构表明斜长石微晶石在淬冷的条件下迅速形成。海槽18°N附近不同玄武岩样品中环带斜长石斑晶环带数与其寄主岩石Mg#值呈负相关,指示了在马里亚纳海槽扩张中心轴部地堑很小范围内获得的玄武岩样品经历的岩浆滞留时间以及岩浆混合作用周期存在一定程度的差异。海槽18°N,17°N和15°30′N附近3个位置的斜长石斑晶边部及斜长石微晶的An值接近,表明这3个位置的岩浆活动具有相似的岩浆上涌喷发通道结构及海底淬冷环境。与冲绳海槽相比,马里亚纳海槽玄武岩具有更深的产出水深;同时,研究区斜长石微晶An值总体上略高于前两者,这可能反映了水深对斜长石微晶An值的影响。研究区斜长石斑晶的形成温度范围比冲绳海槽更窄,暗示与冲绳海槽(陆缘弧后盆地)相比,马里亚纳海槽(洋内弧后盆地)岩浆过程所经历的物理化学环境可能相对更稳定。此外,微晶斜长石结晶温度略高于冲绳海槽,反映出两个弧后扩张区域岩浆喷出淬冷结晶时的水深的差异。
Plagioclase hosted by basalts records important information for magmatic processes,and can provide clues for indicating the characteristics of magmatic activities.Plagioclase phenocrysts and microlitesare studied in the basalts from the Mariana Trough.Petrographic characteristics show that plagioclasephenocrysts generally show polysynthetic twin or zoning textures and some have the melting corrosion structure and chilled margins.Plagioclase microlitesare randomly distributed in groundmass,and the hollow skeletal crystal texture for some microlites imply that they were formed under rapid crystallization and quenching conditions.The numbers of oscillatory zoning bands of plagioclase phenocrystsamong different basaltic rock samples （dredged from Axial Garben of Mariana Trough at 18°N） are negatively correlated with the Mg^# value of their host rocks,implying that magma form the Mariana Trough back-arc spreading center varies in periodicity of magma mingling and residence time in a small scale.For all samples from 18°N,17°N,15°30′N at Mariana Trough,the An values for rims of plagioclase phenocrysts are nearly equal to those for plagioclase microlites,indicating that there aresimilar magma upwelling channels and magma eruption environments in these three locations.The water depth of the Mariana Trough is deeper than that of Okinawa Trough,which is consistent with the higher An value of plagioclase microlites from basaltsin the Mariana Trough.The calculated crystallizing temperature range of plagioclase phenocrysts and microlites of Mariana Trough arenarrowerthan that of the Okinawa Trough,implying that magmas from the Mariana Trough （15°30′-18°00′N） may evolve under a relatively more stable physicaland chemical condition compared to those from Okinawa Trough （a nascentback-arc basin developed in the continental margin）.In addition,the crystallizing temperatures of plagioclase microlites in basaltic rocks from the Mariana trough is generally higher than that from Okinawa Trough,indicating that there are differences in magma eruption environments between these two troughs.
作者
张平阳
鄢全树
ZHANG Ping-yang YAN Quan-shu(The First Institute of Oceanography, SOA, Qingdao 266061, China Key Laboratory of Marine Sedimentology and Environmental Geology ,SOA ,Qingdao 266061 ,China Laboratory for Marine Geology ,Qingdao National Laboratory for Marine Science and Technology , Qingdao 266061, China)
出处
《海洋科学进展》
CAS
CSCD
北大核心
2017年第2期234-248,共15页
Advances in Marine Science
基金
国家自然科学基金项目--海底岩石学(41322036)
亚洲大陆边缘演化及环境效应(U1606401)
"全球变化与海气相互作用"专项--西太平洋俯冲带及弧后盆地体系(GASI-GEOGE-02)
青岛海洋科学与技术国家实验室"鳌山人才计划"项目(2015ASTP-ES16)
中央级公益性科研院所基本科研业务费专项资金资助项目--"束星北"青年学者项目(2016S01)
山东省泰山学者工程项目(2017-2021)
关键词
玄武质岩石
斜长石
矿物化学
结晶温度
马里亚纳海槽
Basaltic rocks
plagioclase
mineral chemistry
crystallizing temperature
Mariana Trough
