Abstract: Through the petrographic studies, it is found that the carbonate rocks in Northern Tarim Basin have developed a diagenetic paragenetic sequence of silicification → hydrothermal dolomitization → calcitization. Many lines of evidences, such as the quartz fluid inclusion with a high salinity and homogenization temperature, the positive Eu anomaly in REE pattern of the saddle dolomite, and the calculated δ¹⁸O_SMOW (+5.5‰ ? +12‰) of the fluid which precipitated the calcite crystals, all indicate that there exist magmatic hydrothermal fluids. It is also found that the hydrothermal diagenetic fluids have been mixed with organic carbon, meteoric water or the ⁸⁷Sr rich formation water in different degree. The carbonate rocks in the research area have a corresponding diagenetic response to the “magmatic hydrothermal fluids-formation water compound fluid system”. The magmatic hydrothermal fluids is an important source of Si and REE to the diagenetic fluid flow and is also a heat source that drives the magmatic hydrothermal fluids and formation water cycle underground. The acid dissolution mechanism indicates that the open fault area is a promising target for the petroleum reservoir exploration in the future.

Key words: magmatic hydrothermal fluids, diagenesis, saddle dolomite, silicolites, Tarim Basin

摘要： 通过对塔北地区多个碳酸盐岩露头的深入研究, 认为该区域碳酸盐岩依次经历了硅化→热液白云石化→方解石化3个主要的后期成岩作用改造。通过对包裹体、同位素及稀土元素地球化学的研究, 发现硅化流体具有高温度、高盐度特征; 热液白云石化流体具有相对基质白云石明显的Eu正异常以及更高的轻重REE的分异度, 而对方解石化流体的平衡水的计算可知, δ¹⁸O_SMOW主要分布在+5.5‰～+12‰区间内, 与岩浆热液流体的同位素值相一致。综合分析认为, 存在岩浆热液对塔北地区碳酸盐岩的后期成岩改造。此外, 通过对各露头碳、氧、锶同位素等的分析发现, 后期成岩流体具有复杂性和叠加性, 存在有机碳的影响以及大气淡水、壳源富⁸⁷Sr地层水的混溶。岩浆活动为热液循环提供了大量的热源, 异常的热事件驱动成岩流体进行广泛的循环流动, 对碳酸盐岩地层进行热液成岩改造, 同时岩浆热液也为成岩流体提供了诸如Si, REE等物质组分。晶洞内大量石英、硬石膏的发现说明研究区域的碳酸盐岩经历了广泛的酸性溶蚀作用, 具有岩浆活动背景的开启性断层发育带成为有利的勘探靶区。

关键词: 岩浆热液, 成岩作用, 鞍状白云石, 硅质岩, 塔里木盆地