RETROGRADED ECLOGITES ON THE NORTHERN MARGIN OF NORTH CHINA CRATON, HEBEI PROVINCE, CHINA:MINERAL CHEMISTRY AND RETROGRESSIVE METAMORPHISM
RETROGRADED ECLOGITES ON THE NORTHERN MARGIN OF NORTH CHINA CRATON, HEBEI PROVINCE, CHINA:MINERAL CHEMISTRY AND RETROGRESSIVE METAMORPHISM
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发表时间：
2004
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通讯作者：
Ni Zhiyao;Wang Ren-min;Tong Ying
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作者：
Ni Zhiyao;Wang Ren-min;Tong Ying
华北陆缘北方退变质榴辉岩以构造透镜体形式产于古元古代红旗营子群中以角闪岩相共生为特征的黑云母-斜长片麻岩中。岩石学研究揭示了三个主要变质阶段：峰期榴辉岩相阶段、高压麻粒岩相阶段和减压期角闪岩相阶段。峰期榴辉岩相变质时，榴辉岩为富钙石榴石+绿辉石+金红石石英组合，其平衡温度为680-730 ℃，压力大于1.40-1.50 GPa。随后，在减压和继续变形的早期阶段，斜长石从绿辉石中出溶，生成麻粒岩相的钠质透辉石和斜长石的细粒蠕虫状合晶岩（An= 20.4 - 30.7）。石榴子石和钠质透辉石再结晶形成角闪岩相矿物组合（An=31.6-54.8），以石榴子石、粒状合晶岩和蠕虫状合晶岩为特征，其温度为530-610℃，压力为0.67- 0.81GPa。
The retrograded eclogites on the northern margin of the North China Craton occur as tectonic lenses within biotite-plagioclase gneisses in the Paleoproterozoic Hongqiyingzi Group characterized by amphibolite-facies parageneses. Petrographic studies revealed three main metamorphic stages: peak eclogite facies stage, high-pressure granulite facies stage and amphibolite facies stage during decompression. During the peak eclogite facies stage of metamorphism, the eclogites had Ca-rich garnet+omphacite +rutile quartz assemblages and must have equilibrated at 680-730 ℃ and more than (1.40-1.50) GPa. Subsequently, during the early stages of decompression and continuing deformation, plagioclase exsolved from the omphacite to give rise to granulite facies fine-grained vermicular symplectite of sodic diopside and plagioclase (An=(20.4)-30.7). And garnet and sodic diopside were variably recrystallised to give rise to the amphibilite facies mineral assemblages of pargasite,hornblende or tschermakite and plagioclase(An=31.6-54.8)that characterized by kelyphitic rim around garnet, granular symplectite and vermicular symplectite.The geothermometry of the amphibolite facies assemblages suggests the conditions of 530-610℃ and 0.67-0.81 GPa.