自然体系中元素的分布

Further readings



W.M. White, Geochemistry. A on-line text book. S.R. Taylor and S.M., 1995. The Continental Crust: Its Composition and Evolution. Blackwell, Oxford. W.F. McDonough and S.Sun, The Composition of the Earth, Chemical Geology, 120: 223-253. Geochemical Earth Reference Model (GERM)
Goldschmidt‟s classification of elemenil] n. 亲石元素
lithophile ['liθəufail] n. 亲石元素 siderophile n. 亲铁元素 chalcophile ['kæ lkə,fail] adj. 亲铜的， 亲硫的
Firn 粒雪 Katabatic 下降的 ablation
Classification of meteorites according to texture and chemical composition (White, 2001)
Achondrite 不含球粒陨石 aubrite： 顽火无球粒陨石
Ivuna meteorite
A 0.7-kilogram carbonaceous chondrite (type CI1, see below) which landed near Ivuna, Tanzania, on December 16, 1938. It was subsequently split into a number of samples. Ivuna was one of four meteorites, including the Orgueil meteorite, in which Bartholomew Nagy and George Claus1 claimed to have found evidence of primitive extraterrestrial fossils. Subsequent analysis led to this claim being discredited. However, in 2001, investigation by a team from the Scripps Institution of Oceanography, the Leiden Observatory in the Netherlands, and the NASA Ames Research Center,2 showed the presence in Ivuna of two simple amino acids, glycine and beta-alanine, and linked Ivuna with a likely origin in the nucleus of a comet. For more on this discovery and its implications, see the entry for the Orgueil meteorite.
Various meteorit sizes
Iron meteorite
Stony meteorite
南极洲
Ivuna meteorite fragment
Meteorite


Esquel Pallasite（石铁陨石） Found in Esquel, Argentina
Where is the best place to find meteorites on Earth?
atmophile： 亲气元素
Classification of elements
(McDonough and Sun, 1995)
Classification of elements according to volatility
Ca-Al inclusion
There is much interest in high T component, i.e., the so-called Refractory Inclusions (RI) or Ca-Al inclusions (CAI), because their composition represents that of the first condensates from a high T gas.
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Life on Mars!
Relative abundance of major types of meteorite falls
Characteristics of chondrite groups
Carbonaceous chondrites are the most volatile-rich and the most primitive.
CI1 chondrite

Ivuna – up to 20 wt.% water
Condensation（冷凝） sequence of a gas with a solar composition
Condesation sequence of minerals
perovskite [pə'rɔvzkait] n. 钙钛矿 corundum [kə'rʌndəm] n. 金刚砂，刚玉 troilite ['trəuilait, 'trɔil-] n. 陨硫铁

Chondrites – Heated but have not melted
– Tend to contain chondrules – Aggregates of high- and low-temperature components

Achondrites – Heating to the point of melting
– Tend to differentiate
Where material segregates due to densit achondrite [ei'kɔndrait] n. 不含球粒陨石
Carton illustrating the process involved in formation of chondrites and their components

Chondritic body

Differentiated body
Types of Stony Meteorites
Why do we study element abundances?

Fundamental for any geochemical studies
Confusing terms


Abundance: for a large system, e.g., Cosmos, Sun, Moon, Earth, crust, regional crust Content/concentration: for a smaller system, e.g., rocks, minerals, natural water.
1 The Chemical Composition of the Solar System and the Earth
Two suggestions


Expertise comes from making all possible mistakes (Niels Bohr) Nothing can be obtained in geochemistry without careful analytical work (C.J. Allegre)
Aside: Meteorite Classification
Carbonaceous Chondrites (Primit ve, organic rich, cont ain CAI s) Ordinary Chondrites (Aggregates of chondrules, CAI s, metal, matrix) Irons Stony-irons (cores of dif f erentiat ed planet esimals) (mechanical mixes of Fe and rock) Basaltic Achondrites (Crusts and mant les of dif f erent iated planetesimals)
Part 1 The Solar/Cosmic system
Sources for studies



Meteorite Sun‟s Photosphere Cosmic rays Earth and moon
Ahnighito meteorite
QuickTime?and a TIFF (Uncompressed) decompressor are needed to see this picture.
What does the classification CI1 mean?
Ivuna is one of only nine known meteorites that are classified as type CI1 carbonaceous chondrites. These meteorites contain “heavy elements” (i.e., elements other than hydrogen and helium) in nearly the same abundances as in the Sun, which means that they are essentially unaltered since they were formed at about the same time as the solar system itself, some 4.6 billion years ago. The designation CI1 indicates that Ivuna underwent a high degree of aqueous alteration (or chemical change due to the presence of water). This alteration took place in the parent body of the meteorite at low temperatures, probably in the range of 20–50°C, and in a water-rich environment. By contrast, ordinary chondrites have experienced thermal metamorphism under dry conditions in a temperature range of 600–900°C. CI1 type meteorites are very dark, because of their high carbon content, contain a high proportion of of iron-rich clays or phyllosilicates(层状硅酸盐), and have very fine grain size. In Ivuna, there is also a complete absence of chondrules, owing to the fact that they have all been altered to clays and iron oxides.