岩庄陨石中快速固化金属一陨硫铁颗粒的金属相微形态特征及冷却速率研究

A STUDY ON COOLING RATE AND MICRO-SHAPE CHARACTERISTIC OF THE METAL PHASE IN RAPIDLY SOLIDIFIED METAL-TROILITE GRAINS IN YANZHUANG CHONDRITE

通过对岩庄陨石中快速固化的金属一陨硫铁颗粒进行研究，并根据金属相的微形态特征，把这些颗粒分别划分为具金属枝晶、金属胞晶的球状颗粒和不规则状金属胞晶的金属一陨硫铁颗粒三种类型．它们呈金届一陨硫铁共结交生集合体状产出。金属一陨硫铁颗粒中枝晶或胞晶结构发育，枝晶臂间距或胞晶于宽度约为6～100μm。在研究金属一限硫铁颗粒形态特征的基础上，估算出岩庄陨石中冲击成因的金属熔融体在950～1400℃高温范围内的固化速率为0．8～2935℃／s，冲击作用形成的熔融体的表现直径为1～35mm．表明岩庄陨石经历了极为强烈的冲击作用和原地熔融过程，并详细地探讨了冲击熔融体的冷凝条件和固化历史。

Rapidly solidified metal-troilite grains in the Yanzhuang chondrite have been studied.These grains are classified as three kinds, including metal-troilite grains with dendritic texture,metal-troilite grains with cellular texture and lrregular cellular metal-troilite grains. They are alleutectic intergrowths of Fe-Ni metal and troilite minerals. Based on the shape characteristics ofmetal phases in the metal-troilite grains, cooling rates in the interval 1 400-950 ℃ were calculatedfrom the spacing of secondary dendrite arms or cell widths which are 100-6 μm, and the publishedexperimental data range from 0. 8 to 2 935 ℃/s; the apparent size of shock-melt body is 35-1 mm.It is indicated that the Yanzhuang chondrite parent body underwent a violent sh0ck event and wasshock-melted in-situ on the surface. The cooling history and solidified condition of the shock-induced melts are also discussed in detail. respectively.