Oxygen and carbon isotopic systematics in the ultra-high temperature metamorphism

根据十年前在变质大理岩中发现的晶体内同位素分带(Wada，1988，自然)，我们预测这种分带将对地壳中变质流体运动的行为从微米级产生深远的影响，并最终形成一个*原始尺度的模型。通过使用二次离子质谱仪(SIMS)，这种同位素分带研究的方法更加精炼，结果加深了我们对同位素在晶体中扩散过程的认识(Graham等人，1998，Wada，合著者)。在这方面，在英国牛津举行的2000年Goldschmidt会议(Wada，2000)上，我们对大理岩上的流体流动进行了进一步的研究，重点是高温接触变质晕中的分带剖面。在这一年里，我们成功地将碳同位素地质测温应用于南印度麻粒岩地体的超高温变质大理岩中。如萨蒂什-库马尔、M Wada、H和ot…所示更多的是，她(2001)根据方解石和石墨中的微尺度同位素分带剖面，准确地确定了该地区的温度条件。这种下地壳麻粒岩的温度条件高达1000℃，与包括超高温指标矿物蓝宝石在内的岩石学矿物组合具有很好的匹配性。因此，碳同位素测温的应用为准确估计地壳深部的超高温变质条件提供了一种新的工具。这项资金支持的另一个项目是建立一个精确而详细的硅酸盐矿物相激光氧气提取系统。这利用了一种分解矿物中硅酸键的技术，在五氟化溴气氛中使用激光烧蚀来分离氧。系统的建设已经完成，真空条件的测试正在进行中。该系统的预测重现性将不如碳酸盐系统，后者现在得到的‰低于0.1CO2。造成这种低精度的重要障碍在于氧气制备系统和氧气到二氧化碳的转化系统。在模拟同位素扩散剖面和流体在这一过程中的作用时，需要这样准确的数据。为了达到与碳酸盐氧同位素相当的准确度，应在硅酸盐相分解后直接测量氧同位素。我们需要一种特殊的质谱计来直接从氧气中测量氧同位素。这也将有助于阐明天然样品中多种同位素(16O、17O和18O)的效应。

Based on the discovery of intracrystalline isotope zonations in metamorphosed marbles a decade ago (Wada, 1988, Nature), we have predicted that such zonation will have far reaching implications on the behavior of metamorphic fluid movement in the Earth's crust right from the micron scale and ending up in a *rustal scale model. This methodology of isotope zonation studies was more refined by using secondary ion mass spectrometer (SIMS) and the results advanced our knowledge on isotope diffusion process in crystals (Graham et al., 1998, Wada a co-author). In this respect, further studies on the fluid flow on marbles with a new emphasis on zonation profiles in high temperature contact metamorphic aureoles were presented at the Goldschmidt conference 2000 at Oxford, UK (Wada, 2000).During this year, we have succeeded in applying the carbon isotope geothermometry in ultrahigh temperature metamorphosed marbles from southern Indian granulite terrain. As shown in Satish-Kumar, M Wada, H and ot … More hers (2001), the temperature conditions were accurately determined for the region based on microscale isotope zonation profiles in calcite and graphite. The temperature conditions of such lower crustal granulites were as high as 1000℃, producing excellent matching with the petrologic mineral assemblages i ncluding the ultrahigh temperature index mineral of sapphirine. Thus the application of carbon isotope thermometry has provided a new tool in estimating accurately the ultrahigh-to high-temperature metamorphic conditions in the deep crust.Another project of this financial support involves the establishing of a precise and detail laser based oxygen extraction system for silicate mineral phases. This utilizes a technique of decomposition of silicate bonds in minerals to separate oxygen using laser ablation in a bromine penta-fluoride atmosphere. The *onstruction of the system is completed and testing the vacuum conditions is underway. The predicted reproducibility of this system will not be as good as for carbonates, where we are now getting a less than 0.1‰ The important hurdles for this low accuracy lies in the oxygen preparation system and in the oxygen to CO2 conversion system. There is necessity for such accurate data in modeling the isotope diffusion profiles and the effect of fluids in such process. In order to achieve accuracy comparable to those we have for carbonates oxygen isotopes should be measured directly, after decomposition from silicate phases. We need a special mass spectrometer designed to measure oxygen isotopes directly from oxygen gas. This will also benefit in elucidating the multiple isotope (16O, 17O ＆ 18O) effect in natural sample Less