| 胶东海阳所堆积辉长岩的变质反应结构、石榴石形成及P—T演化 |
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| 引用本文： | 袁建平,倪志耀,王仁民.胶东海阳所堆积辉长岩的变质反应结构、石榴石形成及P—T演化[J].高校地质学报,2001,7(3):316-328. |
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| 作者姓名： | 袁建平 倪志耀 王仁民 |
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| 作者单位： | 1. 中国科学院地质与地球物理研究所，北京 100029; 2. 北京大学地质学系，北京 100871 |
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| 基金项目： | 国家自然科学基金项目 (4 9872 0 6 5 )，高等学校博士学科点专项科研基金项目 (96 0 0 0 12 1)，北京大学分析测试基
金项目资助 |
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| 摘 要： | 海阳所堆积辉长岩由橄长岩、橄榄辉长岩和辉长岩组成。在橄长岩和橄榄辉长岩中发育有典型的变质反应结构：主要为橄榄石与斜长石之间形成由斜方辉石、尖晶石、角闪石和石榴石等矿物组成的多期次次变边，并有三个不同世代变质矿物，早期Cpx＋Opx＋Spl，中期Amp，晚期Grt；期次是钛铁矿与斜长石之间形成石榴石次变边，相对比较简单，只有一个世代变质矿物，为Grt＋Amp＋Rut或Grt＋Rut岩中石榴石是通过斜长石与角闪石或斜长石与钛铁矿之间的变质反应形成的，虽为峰值变质作用的产物，但变质反应的期次及类型不同导致了所形成石榴石的温度和压力有所不同。堆积辉长岩形成演化的温压计算表明，堆积辉长岩在经过近等压降温的岩浆作用之后的变质作用早期，仍为近等压降温，而晚期则表现为近等温升压。这一特殊的P－T演化可能反映了堆积辉长冷侵位与深俯冲特征。
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| 关 键 词： | 堆积辉长岩 变质反应结构 石榴石 P－T演化 矿物组合 橄长岩 辉长岩 |
| 文章编号： | 1006-7493(2001)03-316-13 |
| 收稿时间： | 2001-09-20 |
| 修稿时间： | 2000年12月4日 |
Corona Texture, Garnet Formation and P-T Evolution of Gabbroic Cumulate from Haiyangsuo Area Eastern Shandong Province, China |
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| NI Zhi yao ,WANG Ren min ,YUAN Jian ping.Corona Texture, Garnet Formation and P-T Evolution of Gabbroic Cumulate from Haiyangsuo Area Eastern Shandong Province, China[J].Geological Journal of China Universities,2001,7(3):316-328. |
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| Authors: | NI Zhi yao WANG Ren min YUAN Jian ping |
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| Institution: | 1.Institute of Geology and Geophysics，Chinese Academy of Sciences，Beijing 100029; 2. Department of Geology, Peking University，Beijing 100871 |
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| Abstract: | The granite gneiss of the Late Proterozoic Jinning stage is the main exposed rock in Haiyangsuo area，eastern Shandong Province，China. These are some lenses and structural blocks of ultramafic rocks(serpentinite)，metamorphic gabbro，plagioclase amphibolite and metamorphic silicalite with varying dimensions and proportions in the granite gneiss. The strong deformation and metamorphism took place in these structural blocks，but the Yaodao accumulative gabbros，that formed through the mineral accumulation under the low pressure and isobaric cooling condition，have the distinct gabbro texture and rhythmic structure，and consist of troctolite，olivine gabbro and amphibole gabbro. Multistage metamorphic reaction textures were preserved in the troctolite and olivine gabbro.
There are two different mineral assemblages for the corona texture in the accumulative gabbros. The one is between plagioclase and olivine. It contains the mineral assemblage of orthopyroxene, spinel，amphibole and garnet; The another is between plagioclase and ilmenite. It is only in the olivine gabbro. The mineral assemblage is more simple and contains garnet，amphibole and rutile or garnet and rutile. The former may be divided into three generations on the basis of petrographic evidence. The early mineral assemblage is characterized by orthopyroxene，dinopyroxene and spinel that formed through a reaction between olivine and plagioclase at temperature of about 760℃—876℃ and pressure of 0.44—0.60GPa; the intermediate mineral assemblage is marked by appearance of tschermakite and disappearance of clinopyroxene via the reaction between plagioclase and clinopyroxene subsequently at temperature of about 660℃— 700℃ and pressure of O.40—0.5O GPa: the late mineral assemblage is characterized by formation of garnet and pargasite or pargsitic hornblende resulted from the reaction between tschermakite and plagioclase at temperature of 650℃—660℃ and pressure of 0.83—0.92 GPa The latter is only one generation and marked by the formation of garnet by the reaction between ilmenite and plagioclase at temperature of about 620℃—630℃ and pressure of 0.71—0.86GPa.
The temperature and pressure of metamorphism process indicate that the early metamorphism is isobaric cooling and the late metamorphism is isothermal boosting for gabbroic cumulates after magmatism of isobaric cooling This special P-T evolution may reflect the characteristics of
cool emplacement and deep subduction of accumulative gabbros. |
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| Keywords: | gabbroic cumulate cornoric texture garnet formation P T evolution Haiyangsuo area eastern Shandong Province |
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