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巴西东南海域被动陆缘盆地岩浆活动特征及期次——以桑托斯盆地B区块火成岩为例
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Abstract:
巴西东南海域被动陆缘盆地内部岩浆活动频繁，导致火成岩分布广泛。本文以桑托斯盆地B区块火成岩为研究对象，通过对其岩石学、矿物学、年代学和岩石地球化学等研究，明确了区内火成岩岩石类型及分布，重点分析了岩浆活动特征及期次，尝试总结不同期次火成岩的油气地质意义。B区块至少经历了阿普特期(113.3 ± 1.2 Ma~122.5 ± 0.6 Ma)和圣通–坎潘期(77.4 ± 0.4 Ma~86.5 ± 5.9 Ma)两期岩浆活动。其中，Aptian期岩浆属钙–碱性，以喷发岩为主，集中分布在Itapema组及以下，属盆地裂陷初期的岩浆活动，经历了多次喷发过程，通过改变湖盆底部地形地貌，影响并控制同时期Itapema组介壳灰岩沉积；圣通–坎潘期岩浆以碱性辉绿岩为主，属于侵入岩，不仅在盐下分布，也可以穿透盐层进入盐上或滞留盐内，并对围岩进行烘烤，产生接触热变质，降低储层孔渗性，增加储层复杂程度。
Multiple magma events induced widespread distribution of igneous rocks in the passive conti-nental margin basins in the South-East offshore of Brazil. This paper takes igneous rock associa-tions in Block B in Santos Basin as a study case. Through the study of petrology, mineralogy, chronology and petrochemistry, the types and distribution of igneous rocks are clarified firstly, then the characteristics and stages are analyzed, and finally their petroleum significance is attempted to be summarized respectively. In Block B, at least two stages of magma events were developed, the Aptian period (113.3 ± 1.2 Ma~122.5 ± 0.6Ma) and Santonian-Campanian period (77.4 ± 0.4 Ma~86.5 ± 5.9 Ma) respectively. The Aptian magma is calcium-alkaline and occurs in the facies of eruption. They are mainly distributed in Itapema Formation and its lower sections. It belongs to the earlier magma in the rift stage of the basin and has experienced multiple eruptions, which influenced and controlled the deposition of the Itapema Formation by changing the topography and geomorphology of the lake bottom. The Santonian-Campanian magma is mainly alkaline diabase, which belongs to intrusive rock, not only distributed within the pre-salt, but also penetrated the salt layer and post-salt layers, baking surrounding rock, producing contact thermal metamorphism, reducing reservoir permeability and increasing reservoir complexity.
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