Formation conditions of pyroxene-olivine and magnesian olivine chondrules
Formation conditions of pyroxene-olivine and magnesian olivine chondrules
复制标题
辉石橄榄石和镁橄榄石球粒的形成条件
DOI：
10.1016/0016-7037(90)90299-z
复制
发表时间：
1990
影响因子：
5
通讯作者：
R. Hewins
中科院分区：
文献类型：
--
作者：
P. M. Radomsky;R. Hewins
对第I类和第II/III类中间组分进行的动态结晶实验表明，球粒结构受非均质核的丰度控制。该系数由给定加热时间内相对于橄榄石消失温度的最高初始温度控制。玻璃状和放射状结构是由过热的熔体形成的，没有核心，条状结构形成的初始温度接近橄榄石消失温度。斑状和颗粒状结构形成，初始温度低于液相线，有丰富的核。对比实验橄榄石和天然斑状橄榄石球粒的分带特征，表明冷却速度为100~1000℃/h，而橄榄石形态表明条状橄榄石冷却速度为250~1000℃/h。结构/成分关系表明，球粒陨石经历了低于1750℃的初始温度。这些观察结果与球粒陨石是由太阳星云尘埃丰富区域(即中面)的瞬时加热形成的观点一致。
Dynamic crystallization experiments performed on a Type I and an intermediate Type II/III composition demonstrate chondrule texture is controlled by the abundance of heterogeneous nuclei. This factor is controlled by the maximum initial temperature relative to the olivine disappearance temperature for the given heating time. Glassy and excentroradial textures form from superheated melts with no nuclei, and barred textures form with initial temperatures near the olivine disappearance temperature. Porphyritic and granular textures form with initial temperatures below the liquidus with abundant nuclei. Comparison of zoning characteristics of experimental olivines with those in natural porphyritic olivine chondrules indicates cooling rates of 100 to 1000°C/h, whereas olivine morphology indicates barred olivines cooled at rates of 250 to 1000°C/h. Texture/composition relationships suggest chondrules experienced initial temperatures below 1750°C. These observations are consistent with the idea that chondrules formed by transient heating in dust-rich regions (i.e., in the midplane) of the solar nebula.