摘要
Preliminary investigation has been conducted on the thermal history of the Jilin meteorite with special reference to the criteria of thermal and impact metamorphisms.The characteristics of thermal metamorphism are discussed in more detail for Meteorite No. I, which weighs about 1,770 kilograms and measures approximately 100×80×50 cm^3. Systimatic sampling were carried out with respect to depth (i.e., 5, 20, 35 and 50 cm) from this meteorite. Microscopy, together with statistics of chondrule content and of the proportions between the various kinds of chondrules, shows that: (1)Chondrule content or the number of chondrule per unit area (cm^2) increases gradually with the distance from the core of the meteorite mass outwards. (2) The content of devitrified and fan cbondrules tends to increase from the core to the rim in spite of the fact that no obvious variation has been noticed in the proportion between various kinds of chondrules. (3) The outline of chondrules becomes increasingly clear in going from the core to the outer parts, which is probably accounted for by a higher degree of thermal metamorphism and recrystallization, and therefore a higher metamorphic temperature, in the inner portion than that in the outer parts. This temperature gradient is presumably a function of the buried depth (20km), the large difference in cooling rate or the uneven temperature distribution due to heterogeneous arrangement of radioactive elements within the meteorite parent body.
Preliminary investigation has been conducted on the thermal history of the Jilinmeteorite with special reference to the criteria of thermal and impact metamorphisms.The characteristics of thermal metamorphism are discussed in more detail for MeteoriteNo. Ⅰ, which weighs about 1,770 kilograms and measures approximately 100×80×50cm^3. Systimatic sampling were carried out with respect to depth (i.e., 5, 20, 35and 50 cm) from this meteorite. Microscopy, together with statistics of chondrule con-tent and of the proportions between the various kinds of chondrules, shows that: (1)Chondrule content or the number of chondrule per unit area (cm^2) increases graduallywith the distance from the core of the meteorite mass outwards. (2) The content ofdevitrified and fan chondrules tends to increase from the core to the rim in spite ofthe fact that no obvious variation has been noticed in the proportion between variouskinds of chondrules. (3) The ortline of chondrules becomes increasingly clear ingoing from the core to the outer parts, which is probably accounted for by a higherdegree of thermal metamorphism and recrystallization, and therefore a higher meta-morphic temperature, in the inner portion than that in the outer parts. This tem-perature gradient is presumably a function of the buried depth (20 km), the large dif-ference in cooling rate or the uneven temperature distribution due to heterogeneousarrangement of radioactive elements within the meteorite parent body.
出处
《地球化学》
CAS
1978年第1期13-18,79-80,共8页
Geochimica
