THE NORTH FIJI BASIN BASALTS AND THEIR MAGMA SOURCES .2. SR-ND ISOTOPIC AND TRACE-ELEMENT CONSTRAINTS

Sr-Nd isotope and trace element data are reported for basalts from the North Fiji Basin (NFB). NFB basalts are characterized by extreme variations in isotopic ratios and trace element abundances which are related to mantle heterogeneities. Values of Sr-87/Sr-86 for basalts from the northern segments. N160-degrees and triple junction range from 0.7029 to 0.7041, whereas Nd-143/Nd-144 values vary from 0.51281 to 0.51313. Most of the basalts from these segments are characterized by strong relative enrichments in Rb, Ba, Sr, K, Nb, Ta La, Ce and Ti that are comparable to OIB components. The central segments, N15-degrees and N-S have Nd-143/Nd-144 ratios between 0.51298 and 0.51363 and Sr-87/Sr-86 ratios between 0.7029 and 0.7033, and are depleted in large ion lithophile, light rare-earth and high field strength elements similar to N-MORB. Covariation between trace element and isotopic ratios among NFB basalts supports a model in which melts from the NFB rift system are derived by mixing of OIB-type and depleted N-MORB mantle components. The Sr-Nd isotopic and trace element variability indicates that the NFB basalt source is heterogeneous on the scale of individual melt batches.