Low temperature grain-scale retrograde alteration of detrital minerals in Ajali formation from Benin Flank Of Anambra Basin, Nigeria

Petrographical study of detrital and authigenic minerals from the Ajali Formation in Benin flank Anambra Basin was carried out with aim interpreting textural characteristics alteration patterns. Samples were collected Ayowgiri sand quarry site along Fugar-Agenebode road where good exposures Sandstone occurred. Heavy concentrated using bromoform according to standard procedures. The heavy mineral concentrates mounted on glass slides araldite glue. In addition, thin sections sandstone prepared. samples studied aid polarizing microscopes. features relationships among used interpretations. results indicate that (Fe-Ti oxides garnet) have undergone a very low-temperatureretrograde changes rather than ordinary in-situ dissolution by weathering burial diagenesis. Fe-Ti resulted into formation leucoxene chlorite while garnet only chlorite. Detrital magnetite partially dissolved skeletal remains grains showed well preserved structures. re-equilibration these partial probably due rise temperature change chemistry water. Reducing acidic conditions at elevated favoured Fe-oxides hematite aided oxidizing condition. Temperature increase induced either underneath lithospheric plate or igneous activities center basin. conversion replacement structures represent typical case retrograde reaction which could be described as evidence low-temperature anchi-metamorphism grain level.
 Key words: Authigenic, chlorite, Fe-oxides, garnet, retrograde, anchi-metamorphism.