NEW DATA ON METAMORPHIC CHLORITE AS A PETROGENETIC INDICATOR MINERAL, WITH SPECIAL REGARD TO GREENSCHIST-FACIES ROCKS
NEW DATA ON METAMORPHIC CHLORITE AS A PETROGENETIC INDICATOR MINERAL, WITH SPECIAL REGARD TO GREENSCHIST-FACIES ROCKS
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关于变质绿泥石作为成岩指示矿物的新数据，特别是绿片岩相岩石
作者：
A. Zane;R. Sassi;C. Guidotti
对于造岩矿物来说，只有在严格的岩石学框架的背景下考虑，固溶体的程度和行为才是可以理解的，正如《大都会》中反复表明的那样。形态学文献在此，我们提出了一个研究的组成三八面体的绿泥石，特别关注nen-limigillg minsl 4l 455 e6！低变质等级岩石中的碎屑。目标是辨别和理解由于T' P'和大块岩石组成的变化而引起的岩石组成的任何系统变化。研究中的变质辉石所显示的三个主要成分变化包括Fe/Mg比值、Tschermak置换程度和从三八面体向二八面体的偏离。我们的数据库包括2619个矿物成分，其中450个是从文献中选出的，涵盖了亚绿片岩-角闪岩相的温度范围，2169个是从绿片岩相岩石中新确定的成分。所有使用的样品根据变质等级、压力和brtk岩石成分进行分类，从而建立分析数据的组和亚组。这些数据被绘制在图表上，旨在使人们能够更具体地辨别块体岩石成分，温度和压力如何影响典型变质岩石的三个主要成分变化。每一个ttrese参数控制在一定程度上的岩石成分，但控制的整体岩石化学是明显占主导地位。它在很大程度上掩盖了温度和压力引起的系统成分变化。因此，尽管进行了多次尝试，但很明显，在绿片岩相的非限制性组合中，矿物成分本身对于地热测压目的是不可行的。尝试使用这种组合的矿物进行地质温压测量应仅限于涉及与某些共存相进行阳离子交换的方法。
For rock-forming minerals, the extent and the behavior of solid solution are understandable only if considered in ttre context of a rigorous petrological framework, as has been shown repeatedly in the met?morphic perology literature. Herein, we present a study of the composition of trioctahedral chlorites, with special focus on nen-limigillg minsl4l 455e6!lages in rocks of low metamorphic grade. The goal has been to discern and understand any systematic changes of chlorite composition due to changing T' P' and bulk-rock composition. The three main compositional variations shown by the metamorphic chlorite in this study include the ratio Fe/Mg, the extent ofTschermak substitution, and deviation from trioctahedral toward dioctahedral chlorite. Our database includes 2619 chlorite compositions, of which 450 are selected from literature covering the temperature range subgreenschist - amphibolite facies, and,2169 are newly determined compositions from greenschist-facies rocks. All samples used are classified according to metemorphic grade, pressure, and brtk-rock composition, thereby establishing groups and subgroups of analytical data. These data are plotted on diagrams aimed at enabling one to discern more specifically how bulk-rock composition, temperatue and pressure affect the three main compositional variations of chlorite from typical meramorphic rocks. Each of ttrese parameters controls chlorite composition to some extent, but the control by the bulk-rock chemistry is clearly dominant. Comm661y it largely obscures the systematic compositional changes caused by temperatue and pressure. Thus, despite numerous attempts, it is evident that chlorite composition by itself is non-viable for geothermobarometric purposes in the case of the non-lirniting assemblages tlpical of the greenschist facies. Attempts to use chlorite from such assemblages for geothermobarometry should be restricted solely to approaches involving cation exchange with some coexisting phase(s).