Petrology-mineralogy And Classification Of 10 Meteorites From Hami In Xinjiang And The Discussion On Enrichment Mechanism

Meteorites are from interplanetary space through the atmosphere of earth after ablation to meteoroid surface residue,representative the evolution of the solar system in different time and space. China has the earlist recognized and the most reliable records of meteorites of the world. But there are few meteorites preserved and the types are uncomplete in the history. In addition to a large number of meteorite samples obtained from the Antarctic, we find fewer meteorite samples. In addition to the Antarctic, desert is the main source of meteorites. China has a vast territory especially the desert regions, providing favorable geographical conditions for the preservation of meteorites. Therefore, searching and collecting the desert meteorites will play a great role to promote the research in this area. In addition, the types of meteorites are determined based on the petrography, mineralogy and chemical composition characteristics of meteorites. The classification of meteorite is the basis for further research of meteorites.This dissertation explores the enrichment mechanism of meteorites in the first professional meteorite study area of Hami in China based on the analysis of geography, climate and accumulation instance of meteorites. In addition, this thesis attempts to establish the enrichment model of meteorites in this region and provide a reference for subsequent searching of the desert meteorites in China. Hami desert and nearby Gobi areas provided favorable climatic conditions to preserve Hami meteorites for a long time as these areas are drought with little or sparse vegetation. The collection area of meteorites is located along both sides of the Kumtag ridge. Also it may result in the formation of sand ridge terrain as the wind toward the opposite direction converges at the ridge. Therefore, scattered meteorites with other sands are migrated toward sand ridge with the push of wind. In addition, meteorites accumulated in the area where they are obstructed at raised terrain on migration direction. This collection area is located at four defined regions both sides of sand ridge（I, II, III and IV）. In addition to scattered monadnocks through weathering present in the areas II and III, the land is largely flat. Area I is located at 20 miles west side of Kumtag ridge, near the south-central Alatage mountains. Area II is located at 50 miles east side of Kumtag ridge, near the south Yamansu town. Area III is located at 5 miles east side of Kumtag ridge, the searching area closest to sand ridge. Area IV is located at 20 miles east side of Kumtag ridge, close to Nanhu town and the northernmost searching area. Meteorites were collected from area I. The mass ofmeteorite decreased toward the direction of sand ridge. The mass of the meteorites collected in the area of the II, III and IV are all greater than 100 g, the heaviest about 700 g. Meteorites were found near the bottom of residual sand dune. It is most likely that the meteorites landed on the mountain slopes and then under the aid of gravity, rolled down to the foot of the slope. Therefore, the enrichment mechanism of Hami desert meteorites are as follows: 1) accumulated at the front of barrier area along the windward side; 2) in the broad flat area near the sand ridge;3) the foot of the steeper slope.This article is also studing the characteristics of the petrology, mineralogy and chemical composition of the representative 10 meteorite samples from 46 meteorites collecting in xinjiang Hami.Determining their chemical groups, petrographic types, shock stages and weathering scale.Grinding to the polished section and slice under the anhydrous conditions. Observing characteristics of the petrography and mineral of polished section and thin section by optical microscope,such as the structural characteristics of chondrules and matrix, the kind of opaque minerals, content and distribution, the degree of shock metamorphism and weathering characteristics. 10 meteorites are have typical chondrule structure, belonging to ordinary chondrites. Kumtag014 has the clear spherulitic textures in the chondrules, various types of chondrules, matrix without recrystallization,determing the petrographic type as type 3. The other nine meteorites experienced obvious thermal metamorphism, matrix of secondary recrystallization, the vague contours of chondrules, but can still be resolved,determing their petrographic types as type 5.The limonite of Hami003, Hami004 and Kumtag014 only around the edge of metal, weathering degree is W1. The iron- nickel metal and troilite of AM007, AM008, AM011, AM015, AM020, Hami005 are part oxidized into limonite, weathering degree for W2.The iron-nickel metal and troilite of AM027 are strong oxidation into limonite, weathering degree for W3. Kumtag014 have intact olivine grains without cracks, no metal molten droplet, shock metamorphic stages for S1. The olivine gramins of AM015, AM020, AM027 and Hami004 have cracks, no metal molten droplet, shock metamorphic stages for S2. The metal molten droplets of AM007, AM008, AM011, Hami003 and Hami005 are widely distributed, shock metamorphic stages for S3.The chemical composition of silicate and opaque mineral were measured by electron microprobe. The experimental conditions of quantitative analysis of electron microprobe are accelerating voltage 15 k V, beam 20 n A, silicate minerals with natural standards, the use of metal or metaloxide standards. Analyze datas were corrected by the method of ZAF（atomic number, absorption effect and fluorescence effect）. Kumtag014（Fa₉.1-48.3, PMD=51.0; Fs₂.8-30.3, PMD=54.2） belong to L group,changes in chemical composition of mineral composition. On the basis of the percent mean deviation of the olivine Fa（PMD=51.0） further determine its petrographic type as 3.4 subtype, belonging to the rather primitive chondrite sample. AM007、AM008、AM011、AM015、AM020、AM027 �'� Hami004（Fa₂2.6- 25.9, Fs17.6 21.4）,belong to L groups. Hami003 and Hami005（Fa18.2²0.8,Fs₁6.0¹7.8） belong to H groups.