Th, Pb, Nd and Sr Isotope Variations in Volcanic Rocks from the Lesser Antilles

Abstract

Th, Pb, Nd and Sr isotope data on Recent volcanic rocks from the Lesser Antilles arc provide constraints on melting processes and the relative contributions of various source components. Although many of the samples are close to U-Th equilibrium, the total range in (23~ is from 0.72 to 1.76 and (23Su/232Th) from 0.66 to 1.59 thus the data extend to both sides of the Th-U equiline (z3~ = 0.75-2.07), though Th excess predominates. There is no apparent correlation between the degree of disequilibrium, or U versus Th excess, and position from North (low-K tholeiitic) to South (calc-alkaline to s h o s h o n i t i c ) a l o n g the are. H o w e v e r , (23~ shows a broad negative correlation with S7Sr/S6Sr, 2~176 2~176 2~176 and is positively correlated with t43Nd/144Nd. The (23~ 87Sr/S6Sr and