High-temperature events in the protoplanetary disk: Formation conditions of chondrules and refractory inclusions

球粒陨石包含了太阳系形成的古老记录。球粒陨石的两个重要组分--球粒陨石和难熔包裹体在太阳系历史早期的原行星盘状环境中形成。球粒和一些难熔包裹体经历了短暂的高温加热阶段，导致熔融，然后快速冷却。热历史可以从对自然样品的化学和同位素研究以及对模拟成分的实验室研究中得到解释：典型的峰值温度约为1500摄氏度，典型的冷却速度在每小时数十至数百度的范围内。尽管很明显，这些高温事件影响了大量的磁盘材料，但关于加热机制仍有很大争议。存在几种不同的模型，包括来自原太阳的直接辐射加热，在盘内各种环境中产生的激波锋面的加热，以及行星之间的碰撞。为了改进和评估不同的模型，我们需要确定球粒和耐火包裹体本身对加热过程的强有力的限制。对太阳系外行星和原行星盘如HLTauri(见下文参考文献)的新天文观测使我们对行星系统的形成有了令人兴奋的新见解，而对球粒陨石的研究提供了这些环境的直接样本。这个博士项目将把对球粒陨石中的球粒和难熔包裹体的观察与旨在再现结构、矿物组合、矿物组成和同位素效应的实验研究结合起来。其目的是确定可用作球粒形成模型输入参数的球粒形成机制的约束条件。以前的实验已经对加热过程施加了广泛的限制，但仍然有许多问题没有得到回答。从亚毫米尺度的观测中，我们可以推断出在数千公里尺度上运行的过程(见图)。实验将在具有可编程温度控制的单气氛炉中进行。对天然样品和实验运行产品的研究将使用微束分析技术，包括扫描电子显微镜、电子探针分析、拉曼光谱和二次离子质谱仪。

Chondrite meteorites contain an ancient record of the formation of the solar system. Two importantcomponents of chondrites, chondrules and refractory inclusions, were formed in the protoplanetarydisk environment in the earliest stages of solar system history. Chondrules and some refractoryinclusions underwent brief high-temperature heating episodes that resulted in melting followed byrapid cooling. Thermal histories are interpreted from chemical and isotopic studies of naturalsamples, as well as laboratory studies of analog compositions: typical peak temperatures are around1500 C and typical cooling rates are in the range of tens to hundreds of degrees per hour. Eventhough it is clear that these high-temperature events affected large volumes of disk material, thereis much debate about the heating mechanism. Several different models exist, including heating bydirect radiation from the protosun, heating in shock fronts produced in a variety of settings withinthe disk, and impacts between planetesimals. In order to refine and assess the different models, weneed to determine robust constraints on the heating process from chondrules and refractoryinclusions themselves. New astronomical observations of extrasolar planets and protoplanetarydisks such as HLTauri (see reference below) are giving us exciting new insights into the formation ofplanetary systems, and studies of chondrites provide direct samples of these environments.This PhD project will combine observations of chondrules and refractory inclusions in chondriteswith experimental studies designed to reproduce textures, mineral assemblages, mineralcompositions and isotopic effects. The objective is to determine constraints on the chondruleformingmechanism that can be used as input parameters for chondrule formation models. Previousexperiments have placed broad constraints on the heating process, but there are still manyunanswered questions. From observations at the sub-millimetre scale, we can make inferencesabout processes that operated on a scale of thousands of kilometres (see figure). Experiments willbe carried out in a one-atmosphere furnace with programmable temperature control. Studies of natural samples and experimental run products will use microbeam analytical techniques includingscanning electron microscopy, electron microprobe analysis, Raman spectroscopy and secondary ionmass spectrometry.