New radiometric data from the South Maradi Pan-African formations, southern Niger

Abstract

AbstractThe Pan-African Province (PAP) of South Maradi (Niger) corresponds to the northeastern part of the Benin–Nigerian Shield. In this framework, schist belts outcrop in NE–SW bands of mylonitic gneiss, associated with granitoid intrusions. This study focuses on geochronological dating of the South Maradi PAP formations. Four samples were dated by K–Ar on a MI-1201 IG mass spectrometer and two of them were re-dated by U–Pb on a inductively coupled plasma mass spectrometer. The Dan Issa porphyritic gneiss indicated two weighted average U–Pb zircon ages: 638.3 ± 3.0 Ma (MSWD = 5.4) and 589.6 ± 1.9 Ma (MSWD = 0.39). Dating of the Maraka schist using the U–Pb on zircon method gave a weighted average age of 617.9 ± 2.8 Ma (MSWD = 2.3), while the same sample recorded a K–Ar age (whole rock) of 505 ± 15 Ma. The Rourouka porphyroid granite gave a K–Ar (whole-rock) age of 508 ± 10 Ma. The Fiawa-Garin Wali mylonitic gneiss indicated ages of 491 ± 10 Ma (K–Ar on feldspar) and 475 ± 10 Ma (K–Ar on whole rock). These preliminary radiometric data reveal the polycyclic character of the Pan-African remobilization which ranges from the Neoproterozoic to the early Paleozoic.