【摘要】：川中地區(qū)茅口組白云巖主要位于茅口組二段中、上部和茅口組三段下部,根據(jù)巖石學特征可分為含灰質(zhì)細—中晶白云巖、細—中晶白云巖、角礫白云巖,且以后兩者為主。對比泥晶灰?guī)r與不同類型白云巖樣品地球化學特征后發(fā)現(xiàn),白云巖相對于同層灰?guī)r具有較低的Fe含量、較高的Mn含量和較低的Sr含量;泥晶灰?guī)r與不同類型白云巖具有相似的稀土配分特征,均表現(xiàn)為LREE虧損、輕微正La異常和負Ce異常,且白云巖樣品具有微弱的Eu正異常;細—中晶白云巖與角礫白云巖δ~(18)O值均明顯低于原始灰?guī)r,而~(87)Sr/~(86)Sr比值則明顯高于原始泥晶灰?guī)r。不同類型白云巖與灰?guī)r相似的稀土配分特征表明茅口組白云巖形成過程中保留了原始灰?guī)r的部分地球化學特征,而白云巖微弱Eu正異常及其與灰?guī)r同位素差異性可能是由于白云巖化過程中高溫地質(zhì)熱流體的參與而引發(fā)的。茅口組白云巖化作用受多種因素控制:地層殘余海水和巖漿活動伴生的熱液流體為白云巖化作用中Mg的主要來源;峨眉山大火成巖省熱效應為白云巖化提供異常高的古地溫背景;斷裂系統(tǒng)為異常地溫對流和白云巖化流體提供了快速運移通道;顆粒灘相灰?guī)r較好的孔、滲性使之比泥晶灰?guī)r更易發(fā)生白云巖化。峨眉山大火成巖省伴生的異常地溫和充足Mg供給是茅口組發(fā)生白云巖化的關鍵,不同類型白云巖形成于白云巖化過程的不同階段。
[Abstract]:The dolomite of Maokou formation in central Sichuan is mainly located in the middle of the second member of Maokou formation, the upper part and the lower part of the third member of Maokou formation. According to the petrological characteristics, it can be divided into fine gray-mesocrystalline dolomite, breccia dolomite and the latter two. Comparing the geochemical characteristics of mudstone and different types of dolomite, it is found that dolomite has lower Fe content, higher Mn content and lower Sr content compared with the same layer limestone. The mudstone and dolomite have similar REE distribution characteristics, all of them show LREE deficiency, slight positive La anomaly and negative Ce anomaly, and the dolomite samples have weak Eu positive anomaly. The 未 ~ (18) O value of fine-mesocrystalline dolomite and breccia dolomite is obviously lower than that of the original limestone, while the ratio of ~ (87) Sr/~ _ (86) Sr is obviously higher than that of the primitive marl limestone. The REE partitioning characteristics of different types of dolomite and limestone indicate that some geochemical characteristics of the original limestone were preserved during the formation of the Maokou formation dolomite. The weak Eu positive anomaly of dolomite and its isotopic difference with limestone may be caused by the participation of high temperature geological thermal fluid in dolomitization. The dolomitization of Maokou formation is controlled by many factors: the hydrothermal fluid associated with residual sea water and magmatic activity is the main source of Mg in dolomitization; The thermal effect of Emeishan igneous rocks provides a high paleogeothermal background for dolomitization, and the fault system provides a rapid migration channel for anomalous geothermal convection and dolomized fluids. The porosities of granular beach limestone are more likely to occur dolomitization than that of mudstone. The abnormally moderate and sufficient Mg supply associated with the great igneous rocks in Emeishan province is the key to the dolomitization of the Maokou formation. Different types of dolomite are formed in different stages of dolomitization.
【作者單位】： 北京大學地球與空間科學學院;北京大學石油與天然氣研究中心;
【基金】：國家自然科學基金項目(No.41672123,No.41272137)資助
【分類號】：P618.13

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