华南地区澳大利亚-亚洲远撞击溅射玻璃的磁学性质研究  

Magnetic Property Study of Australasian Tektites from South China

作　　者：潘卿 肖智勇 Pan Qing;Xiao Zhiyong(Planetary Environmental and Astrobiological Research Laboratory,School of Atmospheric Sciences,Sun Yat-sen University,Zhuhai,Guangdong Province 519000,China)

机构地区：[1]中山大学大气科学学院行星环境与宜居性研究实验室,广东珠海519000

出　　处：《地球科学》2024年第8期2766-2788,共23页Earth Science

基　　金：国家自然科学基金(No.42241108);中国科学院战略性先导科技专项B类(No.XDB 41000000)。

摘　　要：地外天体物质的高速撞击深刻地影响着地球系统各个圈层的协同演化.撞击过程产生了广泛分布的气化、熔融和冲击变质物质,其中,一部分飞行距离超过母坑半径五倍的气化和熔融物快速冷却形成远撞击溅射玻璃(tektites).远撞击溅射玻璃是极端高温高压环境的忠实记录者,其蕴含的磁性信号是研究撞击过程、撞击体和靶体物质的关键信息.澳大利亚—亚洲散布区(Australasian strewn field;AASF)是目前已知面积最大(~1×10~8 km2)、时代最新(78.8万年前)的远撞击溅射玻璃散布区.该散布区是一颗小行星或彗星自北向南倾斜撞击地表的产物,形成的tektites和microtektites主要分布在下靶区方向(中南半岛—澳大利亚—南极洲及其毗邻地区).但是,形成澳亚散布区的母坑至今仍未被发现,探索该母坑及其地质响应是地球和行星科学领域的重要科学问题.华南属于澳亚散布区的上靶区,区内存在丰富的tektites,它们是解译本次大型撞击过程、追溯母坑位置的重要载体,但其研究程度相对较低.我们近年来对采自广东省、广西壮族自治区和海南省的tektites进行了系统的岩石磁学研究.结果表明:华南tektites具有显著的顺磁性信号和微弱的铁磁性信号;在整个澳亚散布区内,华南芒农型tektites的磁化率最低,飞溅型tektites的天然剩磁强度和饱和等温剩磁强度最低;矿物包裹体的晶体学研究发现,华南芒农型tektites中存在纳米级磁铁矿颗粒,与检测到的单畴或假单畴磁铁矿信号吻合.本研究提出撞击熔体受到的冲击程度和经历的冷却历史影响着磁性颗粒的含量和粒径变化,进而控制了不同地区和不同类型AASF tektites磁性信号的差异表达.相同形态类型的AASF tektites的磁性信号变化范围较大,而单块样品内部的磁性信号较均一,表明厘米级熔体具有相同的原岩组分并经历了相似的热历史.本研究证明磁学性�Hypervelocity impact of extra-terrestrial materials is one of the key controlling factors in the evolution of the Earth system.Impact cratering produces wide spread vaporized,molten and shock metamorphic materials.Tektites,part of distal impact ejecta that are located at more than five radii of the source crater,are quenched from vaporized and molten materials during flight.Tektites are faithful recorders of extreme high-temperature and high-pressure environments,and their magnetic signatures are key information for decoding impact cratering process.The Australasian strewn field(AASF)is the largest(~1×108 km2)and youngest(788,000 years ago)Cenozoic strewn field of tektites and microtektites on Earth,but its source crater is undiscovered yet.AASF tektites formed in an oblique impact from north to south,and the majority of AASF tektites are distributed in the downrange area,i.e.,the Indochina Peninsula⁃Australia⁃Antarctica and their adjacent areas.South China is part of the uprange area of this strewn field and tektites from this area are insufficiently studied compared to those from the rest of the strewn field.Here,we present rock magnetism study of AASF tektites from Guangdong,Guangxi,and Hainan Provinces.The results show that AASF tektites from South China are dominated by significant paramagnetic signals,and weak ferromagnetic signals are detected.In the entire strewn field,splash-form tektites from South China exhibit the lowest natural remanent magnetization,and saturation isothermal remanent magnetization,and Muong Nong-type tektites from South China exhibit the lowest magnetic susceptibility.Crystallographic investigation of mineral inclusions reveals the presence of nanoscale magnetite particles in Muong Nong-type AASF tektites from South China,consistent with the detected signals of pseudo-single domain magnetite.This study suggests that observed heterogeneous magnetic properties are mainly caused by the different contents and sizes of magnetic particles,which can be explained by the different shock

关 键 词：远撞击溅射玻璃 岩石磁学 澳亚散布区 撞击过程 华南 行星地质 

分 类 号：P691[天文地球—地质学]