Tectonic constraints to Cretaceous magmatic arc deduced from detrital heavy minerals in northeastern Japan - evidence from detrital garnets, tourmalines and chromian spinels

Comparison of chemical composition of the chromian spinels between Lower and Upper Cretaceous deposits in northern Japan indicates that chromian spinels with very low TiO2 (<0.5 wt%) prevail in the Lower Cretaceous (Aptian-Albian). In contrast, chromian spinels showing moderately low TiO2 predominated in the Upper Cretaceous (Santonian-Campanian). This clear difference suggests the change of oceanic plate motion around Japan arc promoted the change of source rock assemblage and the arc volcanic activity in mid-Cretaceous time. Thus the characteristics of detrital heavy mineral composition of the Kuji Group give the key to clarify the interaction between the swaying of young and hot plate and development of the Cretaceous island arc in eastern Asian margin.