【摘要】 根据化学热力学计算和现今地层水数据,探讨了川西凹陷须家河组二段碎屑岩钾长石钠长石化的热力学原理及其相应的成岩机制。研究表明:1)如果孔隙流体中的钾、钠离子质量浓度保持不变,随着埋深和温度的增加,钾长石钠长石化的趋势会得以加强,而如果温度一定,流体与钾长石、钠长石之间的平衡状态是控制钾长石能否发生钠长石化的另一因素;2)受上覆泥岩中酸性流体影响,同生—埋藏成岩作用初期以后,川西凹陷须二段偏基性的斜长石大量溶解,由此产生的Na+以扩散和对流方式迁出,不作为后期钾长石钠长石化过程中Na+的主要来源;3)随着埋藏的进一步加深(温度在120~140℃),系统接近封闭,上覆泥岩层中酸性流体很难影响到厚层砂岩内部,这使得体系中H+数量更加有限,钾长石溶解受阻,与此同时,蒙皂石的伊利石化消耗K+并向地层水提供额外的Na+,这时钾长石钠长石化便成了蒙皂石伊利石化的伴随反应,直到蒙皂石消耗殆尽,因而蒙皂石的伊利石化是川西凹陷须二段钾长石钠长石化过程中钾钠离子迁移的主要途径。更多还原

【Abstract】 Based on the calculation of chemical thermodynamics and the data of current formation water,the thermodynamic principle and diagenetic mechanism of albitization of detrital K-feldspar of T3x2 Member in western Sichuan Depression were discussed in this paper.The results show that if the content of K+ and Na+ keeps constant,there will be a growing tendency for albitization of K-feldspar with the increase of buried depth and temperature.The equilibrium state of fluid and K-feldspar and albite is another factor controlling whether albitization of K-feldspar can carry out if temperature is unchanging;influenced by acid fluids in overburden mudstone strata,the plagioclase of T3x2 Member in western Sichuan Depression is largely dissolved from syngenetic period to the early stage of diagenesis,but the Na+ generated by dissolution of plagioclase is not the main source of Na+ of albitization of K-feldspar in later period because it is removed in the way of spread and convection;with the further increase of buried depth(at 120-140 ℃),the system approaches to be closed and acid fluids in overburden mudstone strata can hardly affect the inside of thick-bedded sandstone,which hinders the dissolution of K-feldspar for the more limited of H+.Meanwhile,the illitization of smectite consumes K+ and provides extra Na+ to formation water,the albitization of K-feldspar turns to be a reaction closely associated with the illitization of smectite at this time,it does not stop until the smectite completely consums out.Thus,the illitization of smectite is the major route of migration of K+ and Na+ in the process of albitization of K-feldspar of T3x2 Member in western Sichuan Depression.更多还原