ASIAN CONTINENTAL NATURE OF SR-87/SR-86 RATIOS IN NORTH CENTRAL PACIFIC SEDIMENTS

Strontium isotopic compositions were determined for silicate detritus in 152 deep-sea and continental shelf surface sediment samples from the Pacific Ocean to trace their provenance. The major characteristics of the spatial variation of the Sr isotopes and the interpretation of this variation may be summarized as follows: (1) Sediments in the Pacific have a lower average Sr-87/(ST)-S-86 ratio (0.7112) with a narrower range (0.703-0.724) than in the Atlantic (0.7166; 0.704-0.743). Many western Pacific volcanoes together with young continental crust supply material with low Sr-87/Sr-86 ratios to the Pacific, in contrast to the large old cratonic crust that supplies material with high Sr ratio to the Atlantic. (2) The Sr-87/Sr-86 ratio is high in the north central Pacific (0.711-0.719). The Izu-Ogasawara and Mariana arcs supply low Sr-87/Sr-86 material to the western Pacific, but farther to east the abundant supply of loess carried by middle-latitude westerlies from the Asian continent (Sr-87/Sr-86 = ca. 0.720) dominates the north central Pacific.