Petrographic evidence for regional burial metamorphism of the sedimentary rocks in the Lower Benue rift

✍ Scribed by S.C Obiora; A.C Umeji

• Book ID: 104019801
• Publisher: Elsevier Science
• Year: 2004
• Tongue: English
• Weight: 426 KB
• Volume: 38
• Category: Article
• ISSN: 1464-343X
• DOI: 10.1016/j.jafrearsci.2004.01.001

✦ Synopsis

Results of thin section and X-ray powder diffraction (XRD) studies on the pre-Santonian sedimentary rocks outside the vicinity of exposed igneous rocks in the Lower Benue rift are presented. The thin section studies show that the rocks of the older sediments-the Asu River and the Eze-Aku Groups--are characterized by predominantly slaty fabrics whereas the psammitic rocks consist of poikilotopic texture in which the recrystallization of micrite cement has resulted in the expansion of the depositional fabrics and the isolation of the framework grains. The carbonate rocks consist of a hardened fabric in which sparry calcite has recrystallized in the matrix and in veinlets. These older sediments have attained the anchizonal grade or prehnite-pumpellyite facies of metamorphism. The diagnostic minerals of this facies as revealed by the XRD studies include pyrophyllite, paragonite and phlogopite. The following reactions:

Al 4 Si 4 O 10 ðOHÞ 8 Kaolinite