摘要
熔积岩是岩浆物质(岩浆侵入体、熔岩流、热火山碎屑流)与未固结的湿冷沉积物发生同生混合的产物,以浆源(岩浆凝固裂解的浆源碎屑)-沉积物源(宿主沉积物)的二元组分为典型特征。熔积岩独特的熔积结构与其成因机制密切相关,也是鉴定熔积岩的主要依据。根据浆源碎屑的形态,熔积岩主要分为块状(多数浆屑呈多边形状)和流态(多数浆屑具曲面外形)两种类型,并分别对应着不同的熔积作用机制。块状熔积岩主要产生于淬冷、自碎裂、水汽岩浆爆发、岩浆内溢气爆发等机制,而流态熔积岩的形成则得益于岩浆表面稳定蒸汽膜的维持使岩浆碎屑缓慢凝固、免于骤冷。沉积物的流体化是熔积作用得以发生的必要条件,流体化的沉积物为岩浆的驱入腾挪空间并形成对流,因此,固结成岩的沉积岩无法与岩浆物质相互熔积。熔积岩具有重要的地质意义:精确限定岩浆活动与沉积作用的同生等时性,以及利用宿主沉积物的沉积环境精确限定火山活动时的地质背景。近年来我们在国内多处发现典型的熔积岩,并应用于中国关键大地构造问题的研究中。在中亚造山带西准噶尔晚古生代火山-沉积地层中发现熔积岩,据此限定了达拉布特—白碱滩蛇绿岩带两侧上古生界的连续性,推断达拉布特—白碱滩蛇绿岩带不是典型的板块俯冲边界的缝合带,西准噶尔晚古生代是渐浅充填的残余洋盆系统。我们还首次在大火成岩省中识别出熔积岩,如在峨眉山大火成岩省中央带下部火山碎屑层序中发现以灰岩和以橙玄玻璃角砾凝灰岩为宿主沉积的熔积岩,表明中央带早期处于海相环境,从而判定火山喷发之前不具有因地幔柱上涌而诱发的大规模地表抬升效应。在塔里木大火成岩省印干剖面中发现的熔积岩以灰质宿主,证明喷发早期并非完全为陆上环境,塔里木大火成岩省喷发期间(二
Peperites are mingling products of hot magma materials （magma shallow intrusions, lava flow, and pyroclastic flow） and unconsolidated sediments; therefore, they are characterized hy the two lithologieal components： juvenile clast （cooled and fragmented magma） and host sediment. Peperites have unique peperitic textures, the forms of which are related to different forming mechanisms of peperites. Peperites can be subdivided into two classification end-numbers： blocky peperites in which juvenile clasts have polyhedron shapes and fluidal peperites in which juvenile clasts have curved and irregular shapes. Blocky peperites are generated by quenching, autobrecciation, hydromagmatic explosion and magmatic explosivity, whereas fluidal peperites are generated within a vapor film covering the surface of magma that insulated magma from cold water hence avoiding quenching. Sediment fluidization is necessary for the mingling process because it provides room for magma bulldozing; magma can＇t mingle with consolidated sediment rock. Peperites have great geological significances.- （1） they can be indicator of contemporaneity between volcanism and sedimentation, and （2） host sediments in peperites can be used to constrain sedimentary environment during volcanism. We found several classic observations of peperite in China and used them into researches of key tectonic events of China. We found peperites in the west Junggar, the geological settings of which belong to Central Asian Orogenic Belt. These peperites act as a ＂marker bed＂ for constraining continuity of the upper Paleozoic in both sides of the Darbut-Baijiantan ophiolite belt; therefore, we suggest that the Darbut-Baijiantan ophiolite belt is not as former regarded as a suture zone but generated in a shoaling marine basin system. We also found peperites in the only two Large Igneous Provinces （LIPs） in China. In central zone of Emeishan LIP, we identified two kinds of peperites which were hosted by limestone and palagonitized lapilli tuff in th
出处
《地学前缘》
EI
CAS
CSCD
北大核心
2015年第2期174-186,共13页
Earth Science Frontiers
基金
国家自然科学基金项目(41272239)
关键词
熔积岩
火山作用
中亚造山带
峨眉山大火成岩省
塔里木大火成岩省
peperite
volcanism
Central Asian Orogenic Belt
Emeishan Large Igneous Province
Tarim Large Igneous Province
