Prograde evolution of Sulu UHP metamorphic rock in Yangzhuang, Junan region, deduced by combined Raman and petrological studies
Prograde evolution of Sulu UHP metamorphic rock in Yangzhuang, Junan region, deduced by combined Raman and petrological studies
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DOI：
10.1111/jmg.12203
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发表时间：
2016-09
影响因子：
3.4
通讯作者：
T. Taguchi;M. Enami;Y. Kouketsu
中科院分区：
文献类型：
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作者：
T. Taguchi;M. Enami;Y. Kouketsu
利用拉曼气压法对君安阳庄地区榴辉岩石榴石斑岩中SiO2相及其它矿物包裹体进行了分析，揭示了苏鲁超高压变质地体的进阶变质史。石榴石卟卟母细胞分为内、外两部分，其边界以粗晶含量的不连续变化为标志。内段SiO2相包裹体为α -石英，无致密体，无径向裂纹等残余特征。石英包裹体所保留的残余压力从晶体中心到内段边缘有系统地增加。根据残余压力计算和常规热力学计算估算，内段变质条件为500 ~ 630℃，1.3 ~ 2.3 GPa。榴辉石及其假晶状体以包裹体的形式出现在石榴石和基质榴辉石的外层。这一赋存状态与常规地温计估算的660 ~ 725℃、3.1 GPa的压力和温度条件一致。结果表明，在α -石英稳定条件下，内段的石英包裹体被石榴石捕获，并在变质峰阶段顺利过渡到钴矿。石榴石中的SiO2相和其他包裹体即使在发掘阶段也保留了前榴辉岩递进阶段的证据。本文使用的拉曼光谱和岩石学相结合的方法为获得涉及石榴石生长的更强大的约束条件提供了强有力的手段，其中不同的SiO2相作为包裹体存在。
The prograde metamorphic history of the Sulu ultrahigh‐pressure metamorphic terrane has been revealed using Raman‐based barometry of the SiO2 phases and other mineral inclusions in garnet porphyroblasts of a coesite eclogite from Yangzhuang, Junan region, eastern China. Garnet porphyroblasts have inner and outer segments with the boundary being marked by discontinuous changes in the grossular content. In the inner segment, the SiO2 phase inclusions are α‐quartz with no coesite or relict features such as radial cracks. The residual pressures retained by the quartz inclusions systematically increase from the crystal centre to the margin of the inner segment. The metamorphic conditions estimated by calculation from the residual pressure and conventional thermodynamic calculation range from 500 to 630 °C and 1.3 to 2.3 GPa for the stage of the inner segment. Coesite and its pseudomorph occur as inclusions in the outer segment of the garnet and matrix omphacite. This occurrence of coesite is consistent with the pressure and temperature conditions of 660–725 °C and 3.1 GPa estimated by conventional geothermobarometry. Our results suggest that the quartz inclusions in the inner segment were trapped by garnet under α‐quartz‐stable conditions and survived phase transition to coesite at the peak metamorphic stage. The SiO2 phases and other inclusions in the garnet have retained evidence of the pre‐eclogite prograde stage even during exhumation stage. The combined Raman spectroscopic and petrological approaches used here offers a powerful means for obtaining more robust constraints prograde stages involving garnet growth where different SiO2 phases are present as inclusions.