IGGOS as a potential partner in IGOS

This short note reviews our thinking on how IGGOS can best achieve a high status within the set of global monitoring programmes. If such a high status can be obtained, then the importance of geodetic networks and services will be recognized more widely, and their activities will consequently be better resourced in the long term. One particular aspect concerns how IGGOS can complement the roles of the various IGOS partners within global monitoring. The different ways in which IGGOS can contribute to IGOS are outlined.     

P-T evolution and fluid inclusion characteristics of retrograded eclogites,Münchberg Gneiss Complex,Germany

Kyanite eclogites occur as part of the Münchberger nappe pile in NE-Bavaria, West Germany. Eclogites are overprinted by subsequent amphibolite facies metamorphism. The preservation of primary eclogitic textures as well as symplectitic textures are indicative of rapid decompression. Eclogite formation is estimated to have occurred under conditions of high H₂O-activities at pressures between 20 and 26 kbar and temperatures ranging between 590 and 660° C, as is shown by the coexistence of omphacite (Jd 50), kyanite, zoisite and quartz. Minimum pressure estimates, independent of the water activity, range between 9 and 16 kbar at the relevant temperatures. Detailed studies of fluid inclusion reveal two predominant groups of aqueous-brine inclusions: high salinity (14–17 wt% NaCl equiv.) and low salinity (0–8 wt% NaCl equiv.) inclusions. Fluid compositions of both groups of inclusions yield isochores passing close to the estimated amphibolite facies PT-field. The compositions of these fluids are in good agreement with fluid compositions considered from mineral equilibria. None of the fluid inclusions has densities appropriate for eclogite facies metamorphism, but probably reflect later amphibolite facies metamorphism.     

The rare alkalies in hydrothermal alteration at Wairakei and Broadlands,geothermal fields,N.Z.

Drillcores and waters from Wairakei and Broadlands geothermal areas New Zealand have been analyzed for Li, Rb, Cs, Na, K, Mg, Ca, Al, Ti, Mn, and Be. The drillcores were altered to various degrees at temperatures below 300°C in slightly alkaline chloride water, probably derived from rock-water interaction in untapped horizons at higher temperature. It changes its composition as it leaches Ca and Na from the rock and adds K, Rb, Cs and Li. Evaluation of these changes in relation to the dimensions of the altered zone under observation suggests that a high mass ratio of water to rock (e.g., 100) and a period of up to 1 million years are responsible for the present stage of alteration.Increase of K and Rb in the altered rocks is a result of the formation of abundant adularia in addition to illite. The $\text{K}\text{Rb}$ ratio of the rock decreases during alteration but remains higher than that of the fluid. Only clay materials and zeolites that preferentially absorb Rb give slightly lower $\text{K}\text{Rb}$ ratios than the fluid.The mineral phases responsible for the uptake of lithium during alteration are chlorite (300 ppm Li) and quartz (up to 430 ppm Li). Li uptake in quartz is considered to be the mechanism by which Al-rich quartz crystallises from alumino-silicates. $\text{Li}\text{Al}$ atomic ratios of 0.3–0.57 and Al concentrations up to 3000 ppm have been observed.Relatively small concentrations of Cs are found in potassic minerals (e.g. 10 ppm Cs in adularia, 44 ppm Cs in illite). However, 240 ppm Cs are found in wairakite from Wairakei equilibrated at 235°C. Lower equilibration temperatures may lead to higher cesium concentrations. This effect, in conjunction with a more concentrated hydrothermal fluid, could explain a content of 4500 ppm Cs in wairakite extracted from a drillcore taken in the El-Tatio geothermal field in Chile.     

西天山榴辉岩石榴石中的水及其分布特征

运用电子探针和显微Fourier变换红外光谱技术，对新疆西天山3个榴辉岩样品中的石榴石进行了详细的主量元素和结构水分析。结果显示，石榴石发育以核部富锰铝榴石组分、边部富镁铝榴石组分进变质作用的成分环带。石榴石中OH^-1分布也具有规律：核部→边缘。其结构水OH^-1逐步增加，即从核部的89-239ppm增加到边部的367-658ppm；与石榴石边部相比，石榴石的核部含有较低的OH^-1，却含有较高的H2O和Mn含量。这表明，在蓝片岩向榴辉岩进变质作用过程中，含水矿物脱水反应而释放出大量的分子水，这部分水促进了高压变质反应，形成榴辉岩相矿物，石榴石核部的结晶就是在富水和Mn的条件下进行的。随着高压变质作用的继续，石榴石核部的分子水逐步失水而进入石榴石晶格，形成结构水。因此，在高压变质作用过程中，OH^-1演化实际上是一个由内部不平衡逐步向平衡转变过程。P588．348