嫦娥五号月壤Rb-Sr同位素组成及其记录的复杂热改造过程

嫦娥五号月壤是迄今为止返回的最为年轻的月球样品,它为研究月球表面20亿年以来的改造历史提供了绝佳的机会.Rb-Sr同位素体系常被用作定年和示踪的工具,同时由于其放射性体系具有较低的封闭温度以及Rb具有较强的挥发性,该体系可以更好地记录月表的改造细节.本文报道了嫦娥五号返回月壤和玄武岩角砾的全岩Sr同位素以及凝结集块、岩屑和玄武质角砾的原位Sr同位素数据.斜长石具有较为均一的Sr同位素组成,代表了嫦娥五号玄武岩的初始Sr同位素在0.69971±0.0033(2SD,n=22).月壤、玄武岩岩屑和矿物晶屑的Rb-Sr同位素体系不同程度地偏离了20亿年等时线,作者认为这表明这些角砾记录了不同程度的热改造过程,可能与不同程度和不同阶段的Rb丢失有关.这些结果表明嫦娥五号月壤经历了复杂的元素挥发和热改造过程,月壤各组分具有不均一的Rb-Sr同位素组成,与嫦娥五号着陆区不同阶段的陨石撞击事件有关.

The distribution,characteristics and fluid sources of lode gold deposits:An overview

Lode gold deposits are among the most economically important types of gold deposits in the world.Globally,they formed mainly in three time intervals,2.8 to 2.5 Ga,2.1 to 1.8 Ga,and 700 Ma to the present.Sources of ore-forming fluids and other components are of critical importance in a better understanding of the genesis and the geodynamic controls of these deposits.Although ore-forming fluids were mostly derived from devolatization of sedimentary and/or volcanic sequences during greenschist to amphibolite facies metamorphism associated with orogenic deformation,magmatic hydrothermal fluids have been increasingly shown to be important in many gold deposits in various regions.In this review paper,we summarize the major features of lode gold deposits,possible sources of ore-forming fluids,and mechanisms of gold mineralization.While we acknowledge the critical role of metamorphically derived fluids in the genesis of such deposits worldwide,we emphasize that mantle-or basaltic magma-derived fluids may have been much more important than commonly thought.We use the Liaodong peninsula of the North China Craton as an example to demonstrate the significance of mantle-derived fluids.Integrating earlier studies and new data,we show that some of the late Mesozoic lode gold deposits in the North China Craton may have formed from magmatic hydrothermal fluids due to the extension and partial melting of the hydrated,metasomatized subcontinental lithosphere mantle,as best exemplified by the Wulong gold deposit.

Accurate Determination of Zr Isotopic Ratio in Zircons by Femtosecond Laser Ablation MC-ICP-MS with “Wet” Plasma Technique

This work evaluates the use of femtosecond laser ablation multiple collector inductively coupled plasma mass spectrometry(fs-LA-MC-ICP-MS) for Zr isotopic analysis in zircons. The mass fractionation caused by instrumental mass discrimination was corrected by a combination of internal correction using Sr as an internal standard(coming from a NIST SRM 987 standard solution) and external correction using a matrix-matched standard. Several important instrument parameters were investigated, such as the effect of the addition of N;and "wet" plasma condition, the mass fractionation behaviors between Zr isotopes and Sr isotopes, the position effect in laser ablation cell and the effect of laser ablation parameters(laser spot size and energy density). The Zr isotope compositions of seven zircons(GJ-1, 91500, Ple?ovice, Rak-17, Paki, Aus and Mala) were determined by the developed fs-LAMC-ICP-MS and thermal ionization mass spectrometry(TIMS). Our fs-LA-MC-ICP-MS results for Zr isotope compositions agreed with TIMS analyses within analytical uncertainties, indicating the presented method is a suitable tool to resolve isotopic zoning in natural zircons. The results also suggest that GJ-1, 91500, Ple?ovice, Paki, Aus and Mala had the homogenous Zr isotope composition and could be considered as the potential candidates for the Zr isotope analysis in zircons, except Rak-17 which presented the large Zr isotope variation.

Advances in Isotope Geochronology and Isotope Geochemistry:A Preface

Isotope geochronology and isotope geochemistry are important branches of geochemistry. They are based on variations in radiogenic or stable isotope ratios of elements and provide key chemical fingerprints to understand dynamic evolution of the Earth and other planetary bodies from the past to the present, and from their interior to exterior systems.

A novel method for simultaneous analysis of particle size and mineralogy for Chang’E-5 lunar soil with minimum sample consumption

The successful return of lunar soil samples from the northern Oceanus Procellarum by the Chang’E 5(CE-5) mission has provided unprecedented ground-truth information for the previously unexplored region of the Moon. In particular, the particle size and mineral constituents of the CE-5 soil samples are of critical importance to interpret remote sensing data. With a Raman-based particle analysis system, we show that the particle size properties and mineral constituents of the CE-5 soil can be simultaneously determined with a small sample size(ca. 30 μg). The CE-5 sample scooped from the lunar surface has an overall small size between 0.4 μm and 73.9 μm(mean=3.5 μm), and mainly consists of pyroxene(39.4%), plagioclase(37.5%), olivine(9.8%), Fe-Ti oxides(1.9%), glass(8.3%) and other minor or trace phases. The results are consistent with previous analyses with larger sample sizes. In addition to minimum sample consumption, this method requires very little sample preparation, and can rapidly build a large database with each particle precisely traceable. Therefore, this novel technique is particularly suitable for the analysis of future returned soil samples from extraterrestrial bodies.