ABSTRACT: Detailed Pt Profiles and Their Stratigraphic Interpretation in Ferromanganese Crusts
Denys L. Vonderhaar, Doris Puteanus, Gary M. McMurtry
Although there is a general paucity of Pt data for ferromanganese crusts, the data that do exist show that Pt is found at anomalously high levels in the ferromanganese crust when compared to earth crustal values. Detailed Pt profiles were obtained for three ferromanganese crusts, ranging in thickness from ^sim55-95 mm, recovered in the same dredge on Schumann Seamount in the Hawaiian EEZ. These analyses were performed on a VG Elemental laser probe in conjunction with an inductively coupled plasma-mass spectrometer and show considerable variation in the Pt values with depth into the crust.
Platinum values range from ^sim500 to 4000 ppb in sample 1-b and from ^sim0 to 700 ppb in samples 2 and 5. Samples 1-b and 2 have similarly shaped Pt profiles with two distinct peaks. The upper peak is broader in both samples than the lower peak, which exhibits higher Pt values. The third sample, 5, has a broad Pt peak at the same depth into the crust as sample 2. There is a smaller Pt peak lower in this crust that appears to be part of the upper peak when compared with the major and minor element data.
An average accumulation rate of 1.14 mm/m.y. is obtained for sample 1-b, using the 40Ar/39Ar age of the seamount of 82 m.y. Applying this accumulation rate to the sample, the basal intervals of the two Pt peaks in this crust correspond to 36 and 65 m.y., the age of the Eocene-Oligocene and Cretaceous-Tertiary boundaries. Both these events are recognized in sample 2, at ^sim30 mm and 75 mm into the crust. Sample 5 appears to contain the Eocene-Oligocene event only.
AAPG Search and Discovery Article #90097©1990 Fifth Circum-Pacific Energy and Mineral Resources Conference, Honolulu, Hawaii, July 29-August 3, 1990