乍得Bongor盆地基底岩性特征及形成时代

Basement Lithology Characteristics and Forming Age of Bongor Basin Chad

摘要: 乍得Bongor盆地基底为早寒武世之前形成的一套结晶基岩，该套岩石富含油气，因此，对盆地基底岩石类型及形成时代的研究越显重要。本文主要以岩心观察、描述为基础，采用岩石薄片鉴定、单颗粒锆石U-Pb同位素测定等方法，对乍得Bongor盆地基底岩性进行鉴定和划分，并对其形成和演化时代进行分析。结果认为：岩性为由变质岩和岩浆岩组成的杂岩体，岩性包括2大类14个亚类；单锆石测年年龄集中在550~600 Ma，变质岩原岩年龄主要集中在616 ± 6~526.5 ± 2.7 Ma，最老的原岩年龄1006 ± 12~946 ± 5 Ma，变质年龄在553 ± 19~464 ± 5 Ma，岩浆岩的年龄主要集中在621 ± 16~525.3 ± 2.5 Ma。由于岩石类型、性质及形成时代的差异，造成后期地质作用改造和储层的发育程度不同。

Abstract: The basement of the Bongor basin Chad is formed by a set of crystalline basement rocks before the Early Cambrian, which is rich in oil and gas. Therefore, it is more important to study the type of basement rocks and the formation age of the basin. This paper is mainly based on the core observation and description, by identification of rock slice, single grain zircon U-Pb isotope determination, Chad Bongor basin’s basement lithology of identification and delineation, and the formation and evolution of era were analyzed. The results show that the lithology is composed of metamorphic rocks and magmatic rocks, which are composed of 14 kinds of 2 sub categories; Single Zircon dating was concentrated in the age of 550 - 600 Ma, the age of metamorphic rocks was mainly con- centrated in 616 ± 6 - 526.5 ± 2.7 Ma, the oldest old rock age was 1006 ± 12 - 946 ± 5 Ma, metamorphic age was 553 ± 19 - 464 ± 5 Ma, the age of magmatic rock was mainly concentrated in 621 ± 16 - 525.3 ± 2.5 Ma. Because of the difference of the rock type, nature and the age of formation, the transformation of the geological function and the development of the reservoir are different in the later stage.