| 内蒙古温都尔庙群高压变质带中几个标型矿物特征 |
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| THE NATURES OF SEVERAL TYPOMORPHIC MINERALS FROM HIGH PRESSURE METAMORPHIC ZONE OF ONDOR SUM GROUP, NEI MONGOL |
| The Ondor Sum Group includes two metamorphic facies, greenschist and glaucophane facies. The former is characterized by common presence of cham. Icodite and extreme lack of biotite, indicating a high-pressure subfacies syste-The latter belongs to typic high-pressure facies system as the occurrence of glaucophane, lawsonite, aragonite and phengite. Thus undoubtedly, there exist lawsonites in the Ondor Sum Group to constitute lawsonite + aragonite + calcite + albite + chlorite + quartz and lawsonite + epidote + chlorite + spinelline assemblages.Phengite occurs in glaucophane-quartz-schist aad is associated with glau cophane, anorthose, chalcodite and quartz. Texture of 2M, type and some 3T type were determined with X-ray diffraction method; phengite was determined by infrared spectrum;and an endothermic effect before 1100℃ was displayed by the method of differential thermal analysis.Aragonite occurs in aragonite-lawsonite-chlorite schist and is associated with lawsonite, calcite, chlorite, anorthose and quartz.Galucophane occurs in phengite-anorthose-glaucophane-quartz-schist and hematitized glaucophane-quartzite and is associated with phengite, chalcodite, anorthose, deerite and minnesotaite, including glaucophane, crossite, Toren -drikite and riebeckite (only crossite and rare riebeckite recognized previous-ly).The presence of various types of glaucophane in the glaucophane schists of the Ondor Sum Group indicates the uneven pressure and temperature in the subduction zone.Garnet occurs in the eclogite by two stages.The mineral assemblage in the metamorphic zone of the Ondor Sum Group may be useful to researching the nature of plate movement as mineral evidence.The ions of A1V1 in all the metamorphic minerals, such as glaucophane, lawsonite and garnet, indicate their formation under a condition of high-pressure and low-temperature in one aspect.The number of Si ion in the phengite is 3.52 and 3.42, and 3.46 in a-verage, indicating the T-P gradient of 40℃/Kb and geothermal gradient of 12℃/Km, which is the geothermal gradient of subduction zone. In the diagram of P-T steady curves of phengite, it is roughly estimated that the pressure is 6-7Kb and the temperature between 380℃ and 425℃ while Si= 3.46.The facies diagram of calcite and aragonite shows 220℃ at 6 Kb and 300℃ at 7Kb.Based on the above analyses, the writers estimate the temperature of 250-400℃ at pressure of 6-7 Kb in the metamorphic zone of the Ondor Sum Group.The mineral assemblage of glaucophane facies, especially lawsonite, occurring in the Ondor Sum Group provides a new support for the inference of presence of the plate movement in the Early Paleozoic, even as early as in the Late Precambrian time. |
| YAN Zhu-jun,TANG Ke-dong.1984.THE NATURES OF SEVERAL TYPOMORPHIC MINERALS FROM HIGH PRESSURE METAMORPHIC ZONE OF ONDOR SUM GROUP, NEI MONGOL[J].Acta Geoscientica Sinica,6(3):179-194. |
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