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首页> 外文期刊>Journal of Metamorphic Geology >Metamorphic evolution of lawsonite eclogites from the southern Motagua fault zone, Guatemala: Insights from phase equilibria and Raman spectroscopy
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Metamorphic evolution of lawsonite eclogites from the southern Motagua fault zone, Guatemala: Insights from phase equilibria and Raman spectroscopy

机译：来自危地马拉南部Motagua断裂带的钠钙榴石榴辉岩的变质演化：相平衡和拉曼光谱的见解

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摘要

Lawsonite eclogite (metabasalt and metadolerite) and associated metasedimentary rocks in a serpentinite mélange from an area just south of the Motagua fault zone (SMFZ), Guatemala, represent excellent natural records of the forearc slab-mantle interface. Pseudosection modelling of pristine lawsonite eclogite reproduces the observed predominant mineral assemblages, and garnet compositional isopleths intersect within the phase fields, yielding a prograde P-T path that evolves from 20kbar, 470°C (M1) to 25kbar, 520°C (M2). The dominant penetrative foliation within the eclogite blocks is defined by minerals developed during the prograde evolution, and the associated deformation, therefore, took place during subduction. Thermometry using Raman spectra of carbonaceous material in metasedimentary rocks associated with the SMFZ eclogites gives estimates of peak-T of ~520°C. Barometry using Raman spectroscopy shows unfractured quartz inclusions in garnet rims retain overpressures of up to ~10kbar, implying these inclusions were trapped at conditions just below the quartz/coesite transition, in agreement with the results of phase equilibrium analysis. Additional growth of Ca-rich garnet indicates initial isothermal decompression to 20kbar (M3) followed by hydration and substantial cooling to the lawsonite-blueschist facies (M4). Further decompression of the hydrated eclogite blocks to the pumpellyite-actinolite facies (3-5kbar, 230-250°C) is associated with dehydration and veining (M5). The presence of eclogite as m- to 10m-sized blocks in a serpentinite matrix, lack of widespread deformation developed during exhumation and derived prograde P-T path associated with substantial dehydration of metabasites within the antigorite stability field suggest that the SMFZ eclogites represent the uppermost part of the forearc slab crust sampled by an ascending serpentinite diapir in an active, moderate-T subduction zone.
机译：危地马拉Motagua断层带（SMFZ）以南地区的蛇纹岩混杂岩中的Lawsonite榴辉岩（偏碱性和变质变石）及其相关的沉积沉积岩石代表了前陆板-幔界面的出色自然记录。原始钙钠榴石榴辉岩的伪剖面模型重现了观察到的主要矿物组合，并且石榴石的组成等值线在相场中相交，产生了从20kbar，470°C（M1）到25kbar，520°C（M2）的渐进P-T路径。榴辉岩块体中主要的渗透性叶面是由前生演化过程中发育的矿物定义的，因此相关的变形发生在俯冲过程中。使用与SMFZ榴辉岩相关的沉积沉积岩中含碳物质的拉曼光谱进行的测温得出的T峰估计约为520°C。使用拉曼光谱的气压计显示，石榴石边缘未破裂的石英夹杂物保留了高达〜10kbar的超压，这意味着这些夹杂物被捕集在恰好低于石英/柯氏体转变的条件下，与相平衡分析的结果一致。富含钙的石榴石的进一步生长表明初始等温减压至20kbar（M3），然后水合并充分冷却至钙钠石-蓝胶岩相（M4）。将水合榴辉岩块进一步减压至水手榴石-阳起石相（3-5kbar，230-250°C）与脱水和成脉作用有关（M5）。蛇纹岩基质中存在的榴辉岩为m到10m大小的块状，在掘尸过程中缺乏广泛的形变以及与抗蛇纹石稳定场中的变质岩大量脱水有关的衍生的PT PT路径表明，SMFZ榴辉岩代表了最上部。在活跃的中度T型俯冲带中，由上升的蛇纹岩斜生岩取样的前板地壳。

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