塔里木盆地顺北地区中下奥陶统缝洞充填方解石地球化学特征及地质意义

利用微区阴极发光和原位元素测试技术，对塔里木盆地顺北地区中下奥陶统中的方解石样品进行了微量元素和稀土元素测试分析。该区稀土元素含量整体不高，为0.735~24.538 μg/g，平均为4.963 μg/g，表现出轻稀土元素明显富集、重稀土元素相对亏损，且两者分异明显、轻微正Ce异常和明显正Eu异常的特征；Sc、Th含量和Fe/Mn值均较低，U/Th和Sr/Ba值高，指示研究区方解石形成时期气候干旱且主要形成于相对还原的成岩环境中。对该区不同产状、不同期次方解石和附近围岩颗粒地球化学对比分析表明，储集体地质流体主要来源于海水性质地层水，局部存在大气水和富硅热液流体的混源叠加改造，证实了原始沉积围岩内稀土元素较为富集，方解石颗粒中稀土元素继承于附近围岩，但受流体改造强度的控制。

Geochemical characteristics and geological significance of calcite filled fractures and caves in Middle-Lower Ordovician,northern Shuntuoguole area,Tarim Basin

Micro-element cathodoluminescence and in situ elemental analysis were used to determine the trace and rare earth elements in calcite samples from the Middle and Lower Ordovician in the northern Shuntuoguole area of the Tarim Basin. The content of rare earth elements in calcite particles was not high, ranging from 0.735 to 24.538 μg/g, with an average of 4.963 μg/g. An obvious enrichment of light rare earth elements and a relative depletion of heavy rare earth elements was observed, with an obvious differentiation between them. There was a slight positive Ce anomaly and an obvious positive Eu anomaly. The Sc, Th contents and the Fe/Mn values were low, while the U/Th and Sr/Ba values were high, indicating that the calcites were deposited in a dry and reducing environment. The comparative geochemical analyses of different occurrences and different periods of calcites and surrounding rock particles were carried out. It is clear that the reservoir geological fluids in the study area mainly came from the formation water of seawater nature, and there were mixed sources of atmospheric water and silicon-rich hydrothermal fluids. It was confirmed that rare earth elements in the original sedimentary wall rocks were relatively rich, and the rare earth elements in calcite grains inherit from the surrounding rocks nearby, but were controlled by the strength of diagenetic fluid transformation.