| Impact events are common in the solar system,especially in the early stages of planetary formation.Impact events are a very important process in meteorite formation and their evolution history.Meteorite impact is an extreme geological condition.The high temperature and high pressure conditions at the instant of impact will cause a series of petrological and mineralogical changes and various of shock characteristics of the target rock.The iron meteorite of"Tears of Allah"in Aletai,Xinjiang is a large iron meteorite discovered in the Clan Grand Canyon of Aletai in 2011..The impact melting breccia from the Aletai iron meteorite in Xinjiang is a monomineral breccia that it formed by iron meteorite that impacted the target rock,which resulted in the partial melting of the target rock and the rapid cooling.High pressure phase minerals are not found in the sample.Some zircon decomposition occasionally,developed of the graphic structure on the margin.It shows that the sample is partially melted during the impact process.The molten glass is formed by rapid cooling of mineral melting.There are two main types of the impact melt glass:Gray yellow glass and White glass.The composition of gray yellow glass include SiO2（56.33 wt.%）,Al2O3（18.93 wt.%）,FeO（6.04 wt.%）,MgO（3.47 wt.%）,CaO（6.77wt.%）,Na2O（3.24 wt.%）,K2O（3.22 wt.%）。And the composition of white glass include SiO2（63.4wt.%）,Al2O3（21.64 wt.%）,FeO（1.13 wt.%）,CaO（3.01 wt.%）,Na2O（4.76 wt.%）,K2O（5.92wt.%）。The content of main elements in glass is highly similar to that of glass composition known as impact crater.The study of impact melt breccia plays an important role in finding craters.Based on the study of rock structure,mineral chemistry and impact metamorphism characteristics of the impact melt breccia,we get the following understandings.（1）The sample is impact melt breccia with a vitroporphyritic texture and block structure.The breccia is quartz and zircon.The matrix is impact melt glass,and a large number of bubbles are contained in the matrix.（2）Quartz formed mosaic structure by strong deformation.Quartz has partial melting and obvious wavy extinction under high temperature and high pressure.The flow of molten glass affects the flow structure,and the volatile matter from the mineral formed bubbles.（3）The pressure of the impact melt breccia is about 50–60 GPa.（4）The gas contained in bubbles may be H2O,O2 and H2.,but raman spectra did not show the characteristic peaks of common gases.It may be due to the low gas content inside the bubble,which is lower than the detection limit of Raman spectrometer.（5）The composition of the glass in this sample is similar to that from known impact pits,such as molten glass,tektites and microtektites.But there are slight differences.The differences depends on the composition and nature of the meteorite and the target rock.（6）The composition of glass in this sample is normalized by CIPW standard mineral,and the results shows that the original rock of these glass is granite–monzonitic granite.It is accord with the geology feature of the surrounding rock,where the Aletai iron meteorite was found. |
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