不纯碳酸盐岩中的变质矿物

METAMORPHIC MINERALS IN IMPURE CARBONATE ROCKS

不纯大理岩中变质矿物的稳定程度既与温度有关,也与压力有关。在低压时(压力小于150MPa)金云母与方解石、石英反应产生钾长石和透闪石。大干上述压力,金云母与方解石、石英反应产生钾长石和透辉石。透闪石和透辉石的产生温度与二氧化碳分压有关。二氧化碳分压高时,透闪石出现的温度较高,两者呈正比关系。橄榄石的产生温度与总压和二氧化碳分压均呈正比关系。帘石在大理岩中仅出现在二氧化碳分压低的区域。

The stability of metamorphic minerals in impure carbonate rocks depends not only on temperature, but also on pressure. Reaction of phlogopite with calcite and quartz to form K-feldspar and tremolite at 100 MPa is noted in impure dolomitic limestone in the Marysville aureole, Montana. At 150 MPa phlogopite coexists with calcite, quartz, tremolite and diopside without K-feldspar in impure carbonate rocks in the northeast of Beijing. At 200-300 MPa the association of Phlogopite, calcite and quartz without K-feldspar at temperatures between 500℃ and 570℃ is stable in Klamath, California, USA. It indicates that the reaction of phlogopite with calcite and quartz to form K-feldspar and tremolite does not occur at a pressure higher than 150 MPa. At higher pressures and higher temperatures the reaction of phlogopite with calcite and quartz produces K-feldspar and diopside.The formation temperature of tremolite and diopside is related to the partialpressure of CO_2. The higher the partial pressure of CO_2 is, the higher the formation temperature of tremolite will be—both are positively correlated. In the Haizhou Group in northern Jiangsu, at the kyanite-zone metamorphic conditions tremolite does not appear in rocks with a high CO_2 partial pressure, whereas it is present in rocks with a low CO_2 partial pressure. As for diopside, in the low CO_2 partial pressure region, the formation temperature positively correlates with the partial pressure of CO_2, whereas in the high CO_2 partial pressure region, negatively. In the Ji'an Group of southern Jilin, tremolite-diopsidite is flanked by tremolite marble and tremolite bearing quartzite, i. e. the rocks on both sides contain only tremolite but no diopside, while the rocks in the middle contain both tremolite and diopside. The cause is due to higher CO_2 partial pressures during metamorphism of the rocks in the middle, the formation temperature of olivine is positively correlated with both the total pressure and the partial pressure of CO_2. Epidote in impure carbonate rocks only forms at a low partial pressure of CO_2.