Geochemistry of the Martian Meteorite GRV 99027

GRV 90027 is a Martian lherzolitic shergottites （L-S） containing poikilitic, non-poikilitic, and melted pocket components. GRV 99027 is mainly composed of olive （55 vol% ） and pyroxene （37.5 vol% ）, with minor maskelynite （6 vol% ） and chromite （ 1.5 vol% ）, and trace whitelockite and troilite, ect. In this paper, the mineralogy and petrology of GRV 99027 are reported; in addition, the geochemical characteristics of the REEs and H isotopes in the GRV 99027 are also further investigated. The 2REE in GRV 99027 is relatively low; HREEs are enriched in olivine and pyroxene grains; LREEs are enriched in plagioclase with a high positive Eu anomaly. High EREE value is found in rare mineral whitlockite （less than 0. 2 vol% ）, LREE ≈ HREE, and whitlockite has a negative Eu anomaly. The REE distribution patterns of the whole -rock of GRV 99027 is similar to but different from that of other L-S Martian meteorites, indicating that they came from different location of Mars. GRV 99027 has a high 8D value. Different water-bearing minerals give different contribution for 8D value. The 8D of phosphates generally does not correlate with water content, and 8D has a weak negative correlation with water content. GRV 99027 can be classified as an L-S Martian meteorite based on mineralogical assemblage patterns, REE distribution patterns, and hydrogen isotope. The isotope data of Sr, Nd, Pb, Os and REE from other L-S Martian meteorites were collected to discuss the formation history of the GRV 99027. Similar to other L-S Martian meteorites, GRV 99027 originated from part of Mar＇s mantle; during one strong impact event about 4M years ago, the meteorites were ejected from deep mantle into space, and traveled for a different duration in space （indicated by different cosmic exposure time）, and captured by the Earth later in different time, ultimately falling on the Antarctica as L-S Martian meteorites.

Shock metamorphism in meteorites

Shock metamorphism resulting from hyperveloeity collisions between planetary bodies, is a fundamental processes in the solar system. The term ＂shock metamorphism＂ is used to describe all changes in rocks and minerals resulting from the passage of shock waves. Most meteorites have experienced coUisions and have a record of shock metamorphism, which includes brecciation, deformation, phase transformation, local melting and crystallization. The key to reading this record is to use the shock features to estimate the pressure and duration of shock event. In this paper, the history of the study of shock metamorphism is reviewed; basic knowledge of shock physics is discussed; recent 10 years＇ studies of shock-induced melt veins are summarized; and finally a short note to the shock metamorphism in general is given.

A comparative study of natural and experimental nano-sized grinding grain textures in rocks

In three shallow-level fault systems in eastern China, nano-sized (30―100 nm) grinding grain textures are found in the thin-shelled rheological layer representing frictional-viscous high strain field. The surface layer near slipping plane is composed of stacks of grinding grains with high sphericity and uniform nano-sized diameter, while the underlying layer appears as a mixture of irregular ones with diverse diameters. Rock deformation experiments indicate that the grinding grain texture is a common phenomenon in shearing fractures, suggesting a potential transition from sliding friction to rolling one during the rock deformation process. This transition is crucial for many tribological processes in geo- logical fields.

Nano-texture of penetrative foliation in metamorphic rocks

By observing four samples obtained from Jiangxi Province, China, under the scanning electron mi-croscope (SEM), we discovered that nano-particle layers were commonly formed on sliding planes of the penetrative foliation in metamorphic rocks. We also successfully reproduced this phenomenon with a tri-axial pressure experiment. Having gone through the granulitization-alienation-partition in the shear sliding process, the nano-particles (40-95 nm in diameter) display different individual shapes and dis-tinct layered textures. This nano-confinement layer is essentially a frictional-viscous stripe with vis-cous-elastic deformation. In the micro-domain stripe, activities in structural stress field-rheological physical field-geochemical field are very dynamic, corresponding to the three stages (i.e., shear sliding strengthening-weakening-exfoliating) of the foliation development in metamorphism rocks. As such, the viscous-elastic deformation behavior helps shed light on the understanding of the micro-dynamic mechanism of the structural shearing.

Ore-forming fluid constraints on illite crystallinity(IC)at Dexing porphyry copper deposit,Jiangxi Province

Illite, a distinctive kind of clay minerals of potassiumalteration within the hydrothermal alteration zone, frequently occurs at the Tongchang porphyry copper deposit ore field. The illite crystallinity (IC) value and expandability are mainly affected by water/rock ratio or fluid flux. It was formed by illitization of plagioclase and micas during hydrothermal fluid-rock interaction within the porphyry body and near the contact zone with wall rocks. Moreover, the negative correlation between illite index (IC) and copper grade indicates that within the alteration zone, the smaller the illite crystallinity value, the higher the alteration degree, and the higher the copper grade due to higher water/rock ratio. At lower levels of the porphyry body, however, the illite crystallinity (IC) values are mainly controlled by temperature and time duration.

Experimental study on crystallization kinetics of alkali feldspar under high T-P conditions

In the granite-NaF-H2O system, there exists a nucleation lag in the course of alkali feldspar crystallization indicated by experiments on crystallization kinetics. The nucleation lag time is about 18 h at 700℃ and about 6 h at 650℃.nucleation rate and crystal-growth rate of alkali feldspar are not constant during the crystallization process, but vary with crystallization time. Here we suggest that the lag time should be taken into account in the calculation formula of nucleation rate and crystal-growth rate to obtain more reliable parameters.

Early Paleozoic whole-rock Ce anomalies and secular eustatic changes in the Upper Yangtze region

The 65 whole-rock REE samples studied come from the classic sections of Early Cambrian to Early Silurian in the Yichang area, Hubei Province. REE concentrations tested on ICP-AES are normalized to the North American Shale Composite (NASC), and Ce anomaly values are calculated based on log[3Cen(2Lan+Ndn)]. With the whole-rock Ce anomaly used as a quantitative index of sea-level changes, 5 prominent eustatic circles are recognized, and a good corresponding relationship is observed between the black shale episodes and the transgressive events. On account of the global distributions of coeval black shales and the specified paleogeographic background of South China, a genetic hypothesis based on the model of O2-minimum zone expansion is suggested for the Early Paleozoic multi-episode black shales in South China.