海底熔岩风化作用及其地质意义  

Weathering of Seafloor Lavas and Its Geological Significance

作　　者：鄢全树[1,2,3] 张平阳 石学法 张海桃[1,2] 

机构地区：[1]国家海洋局第一海洋研究所,山东青岛266061 [2]海洋沉积与环境地质国家海洋局重点实验室,山东青岛266061 [3]青岛海洋科学与技术国家实验室海洋地质过程与环境功能实验室,山东青岛266061

出　　处：《海洋科学进展》2017年第3期369-381,共13页Advances in Marine Science

基　　金：国家自然科学基金项目--海底岩石学(41322036)和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(2015ASTPES16);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

摘　　要：海底熔岩风化作用过程的研究对于澄清元素地球化学迁移具有重要的意义。首先简要介绍了海底熔岩风化作用及鉴定标志。在细致的岩相学工作前提下,利用指示风化程度的特征风化矿物如橙玄玻璃、黏土矿物(蒙脱石和蒙皂石)、沸石(钙十字沸石)以及铁的氧化物和氢氧化物,结合烧失量(L.O.I),K_2O/(K_2O+Na_2O)比值和Fe_2O_3/(FeO+Fe_2O_3)比值等识别风化岩石的化学鉴别指标,辨识了马里亚纳海槽熔岩(弧后盆地玄武岩,BABB)和火山玻璃、西太平洋海山省(白垩纪碱性洋岛玄武岩,OIB)及中生代洋壳(洋脊玄武岩,MORB)的风化程度,探讨了风化作用的原因及其对岩石地球化学数据的影响。结果表明,与超过5 Ma的海山和洋壳玄武岩相比,马里亚纳海槽玄武质熔岩风化程度很低,仅基质中的隐晶质和玻璃质及玄武岩的玻璃质边缘略微橙玄玻璃化,其余基本保持新鲜岩石结构。马里亚纳海槽熔岩和火山玻璃的很低的风化程度是因其在海底经历的风化作用时间很短。最后,我们指出,马里亚纳海槽处海底熔岩风化作用没有造成显著的元素迁移,对精确获得其全岩的元素和同位素地球化学数据不产生明显影响,而对超过5 Ma的海底熔岩的地球化学数据解释时要谨慎。The investigation on the weathering of seafloor lavas plays a significant role on understanding element mobility.First,this paper briefly introduces the ocean floor weathering processes and the characteristics of weathered rocks.Then,we determined the degree of weathering of seafloor lavas（back arc basin basalt,BABB）dredged from Mariana Trough,west Pacific seamount province（Cretaceous oceanic island basalt,OIB）and Mesozoic oceanic crust（mid-oceanic ridge basalt）through detailed petrographic observation（the appearance of palagonite,clay minerals,etc.）,and the geochemical indices（the loss on ignition（L.O.I）,K_2O/（K_2O＋Na_2O）and Fe_2O_3/（FeO＋Fe_2O_3）values）.Finally,we discussed the cause of weathering and its influence on the geochemical data of Mariana Trough basalts.Our results indicate that,compared to submarine lavas older than 5Ma,Mariana Trough basalts suffered very low degree of rock weathering.Only the cryptocrystalline and glassy matrix,and glassy margin of basaltic flow could be altered into palagonite.The low degree of weathering mainly results from the relatively short duration since eruption.We suggest that these on-axis or near-axis submarine lavas from the Mariana Trough did not undergo severe weathering,so the whole rock major-and trace element and radiogenic isotopic compositions of lavas remained almost unchanged.However,the effect of weathering should be removed when the whole chemical compositions of lavas older than 5 Ma are used to interpret the petrogenesis.

关 键 词：海底风化作用 玄武岩 马里亚纳海槽 烧失量 元素迁移 

分 类 号：P736[天文地球—海洋地质]