AUSTRALASIAN MICROTEKTITES IN A SUBSTRATE - A NEW CONSTRAINT ON FERROMANGANESE CRUST ACCUMULATION RATES

Microtektites belonging to the Australasian tektite strewn field are f ound in the substrate of a ferromanganese crust dredged from the Centr al Indian Basin. They are identified on their physical appearance, geo graphic occurrence and chemical composition, The ferromanganese crust has a thickness range of 6-17 mm, and its chemistry and mineralogy ind icate hydrogenic accretion. Because the Australasian strewn field has an age of approximately 0.77 Ma, this finding implies that the overlyi ng Fe-Mn crust has minimum accretion rates of 7.8-22.1 mm/Myr, which a re much higher than the average growth rates of hydrogenic crusts.