P–T-deformation-Fe3+/Fe2+ mapping at the thin section scale and comparison with XANES mapping: application to a garnet-bearing metapelite from the Sambagawa metamorphic belt (Japan)

Quantitative X‐ray maps of composition from a chlorite, K‐white mica, albite, quartz and garnet bearing thin section from a Sambagawa blueschist facies metapelite were combined with a multi‐equilibrium calculation method to calculate a P–T‐Fe³⁺/Fe²⁺‐deformation map at the millimetre scale. The studied sample was chosen because elongated chlorite crystallization tails (pressure shadows) rimmed by phengite are present, which is an appropriate assemblage for the quantification of the P–T evolution. Chlorite temperature and Fe³⁺ content maps were calculated by successive iterations for each pixel analysis of Fe³⁺ until convergence of the four chlorite‐quartz‐H₂O equilibria that can be written using the Fe‐ and Mg‐amesite, clinchlore, daphnite and sudoite chlorite end‐members. The calculated map of Fe²⁺/Fe³⁺ in chlorite is in good qualitative agreement with the in situ mapping of this ratio using XANES (X‐ray absorption near edge structure) techniques. The temperature map indicates that high temperature chlorite zones with low Fe³⁺ contents alternate with lower temperature zones and higher Fe³⁺ contents in the crystallization tail. Late fractures perpendicular to the elongation axis of the tail are filled by very low temperature chlorite (<250 °C) showing Fe³⁺/Fe_total up to 0.4. Groups of chlorite and mica pixels were then identified based on compositional and structural criteria, and a P–T‐deformation map was calculated using representative analyses of these groups. The calculated P–T‐deformation map suggests that in contrast to chlorite, the composition of most mica did not change significantly during exhumation. Mica reequilibrated in late EW shear bands only. EW shearing was already active at 0.1 GPa, 500 °C, which corresponds to the peak temperature (and probably pressure) conditions, at reduced redox conditions. The intensity of deformation probably decreased with decrease in temperature to ～350–400 °C. At this temperature, a second main deformation event corresponding to a further EW stretching occurred and was still active below 250 °C and more oxidizing conditions. These results indicate that the scale at which P–T data can be obtained is now close to the scale of observation of structural geologists. A close link between deformation and mineral reaction is therefore possible at the microscopic scale, which provides information about the relationship between deformation and mineral reactivity, the modalities of deformation with time and the P–T conditions at which it occurred.     

The Abbey Evaluation of Reference Sample IF-G. The Significance of Abbey's Method For Laboratory Quality

Abbey's select laboratories method has been applied to the reported data for major and minor elements in the proposed GIT-IWG reference sample IF-G. The final values obtained by this method have been compared with the recommended values published by Govindaraju in 1984. Slightly different percentages are suggested for MgO, K₂O and Fe₂O₃T. The importance of applying the Abbey method by participants in co-operative studies is emphasized. Such an application gives a better understanding of data treatment and of the degree of reliability of published final values; furthermore the objective score obtained for laboratory quality will stimulate participating laboratories to improve their analytical methods and procedures. As an illustration some improvements in the laboratory of the authors are mentioned.     

Ag, Te and Pd in 17 Geochemical Reference Materials by Mass Spectrometric Isotope Dilution Analysis

Seventeen geochemical reference samples have been analysed for Ag, Te, Pd using mass spectrometric isotope dilution analysis. For most samples, analytical data on these elements were lacking. The concentration range encountered was generally in the nanogram levels.     

青海省东北部地区春季空中水资源潜力分析

采用动力气象学原理计算了青海高原东北部春季水汽输送、辐合辐散情况 ,利用微波辐射计观测总水汽含量 (V)、液态水 (L)的情况。经计算 ,青海高原东北部大气水汽状况为输入大于输出 ,且有近 83%的水汽影响该地区后移出青海 ,有较大的潜在水资源 ;从液态水含量情况来看 ,尽管水汽含量比平原地区少 ,但液态水含量却比平原地区偏高。另外还计算了 1997年 3月下旬至 5月上旬的云总凝结水和降水效率 ,大气总凝结水量为 2 84× 10 8t,但实际降水量为 34× 10 \+8t,平均降水效率为 0 .12。如果能提高 1%的降水效率 ,则可增加约 2 .5× 10 8t降水 ,且具有较好的人工增雨潜力。     

高原东部春季降水云层的微物理特征分析

利用人工增雨飞机和机载PMS粒子探测系统，对高原东部地区春季人工增雨主要降水云层的微物理结构进行大量探测研究。根据1995年和1997年共15架次的飞行探测资料，分析研究了高原东部低层大气气溶胶微粒的分布特征及其与大气层结的关系，着重分析了高原东部春季降水云层的云粒子、降水粒子以及冰晶、过冷水的一些初步分布特征。     

A new petrogenetic grid for low-grade metabasites

Abstract We have used internally-consistent thermodynamic data to present calculated phase equilibria for the system Na₂O-CaO-MgO-Al₂O₃-SiO₂-H₂O (NCMASH), in the range 0–500° C and 0.1–10 kbar, involving the phases anorthite, glaucophane, grossular, heulandite, jadeite, laumontite, lawsonite, paragonite, prehnite, pumpellyite, stilbite, tremolite, wairakite, zoisite with excess albite, clinochlore, quartz and pure water. Average activity terms derived from published mineral chemical data were included for clinochlore, glaucophane, prehnite, pumpellyite, tremolite, and zoisite. The new petrogenetic grid delineates stability fields and parageneses of common index minerals in zeolite, prehniteactinolite, prehnite-pumpellyite, pumpellyite-actinolite, blueschist and greenschist facies metabasites. The stability fields of mineral assemblages containing prehnite, pumpellyite, epidote, actinolite (+ albite + chlorite + quartz) were analysed in some detail, using activity data calculated from five specific samples. For example, the prehnite-actinolite facies covers a P-T field ranging from about 220 to 320° C at pressures below 4.5 kbar. The transition from the prehnite-actinolite and pumpellyite-actinolite to greenschist facies occurs at about 250–300° C at 1–3 kbar and at about 250–350° C at 3–8 kbar. P-T fields of individual facies overlap considerably due to variations in chemical composition.