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 level and/or cooling history of the tektite-forming melts.Although magnetic properties of AASF tektites in different regions show large variations,individual specimens of AASF tektites from South China have relatively homogeneous magnetic properties,indicating that impact melt that formed each tektite specimen had similar compositions and experienced similar thermal history.This study demonstrates the feasibility of rock magnetic studies in untangling formation processes of AASF tektites,and it is an important reference to the search of the potential source crater.
NETL
NSTL
万方数据
