Trace element and isotopic (Sr, Nd) geochemistry of volcanic rocks from the Lau Basin

Rock samples have been dredged clming S0-35 and SEAPSO JV cruises (1984 and 1985) from cliJTemnl spreading ridges in lhe Lau Basin, soulh-weslern Pacific. They were analyzed for major and lrace elemenls and isotopic ralios (Sr, Nd). Nmlhem Lau Basin samples show N-MORB type characlerislics, bolh in major andlrace elemenls, whereas soulhern Lau Basin ones are differenlialed and show significanl Ta-Nb negalive anomalies in lheir extended REE pallerns, which is characlerislic of subcluclion zones.lsolopic ralios (Sr, Nd) are quile helerogeneous and inlermediale bel ween MORB and island arc values. The norlhern Lau Basin Ridge has geochemical characlerislics suggeslive ofmedio-oceanic lype spreading, whemas lhe soulhem LauBasin Ridge (Valu Pa Ridge) wilh ils geochemical characleristics influenced by subcluclecl slab material, could eilher be a nascenl island arc or corresponcllo an inilial slage of back-arc opening. A comparison of lhe LauBasin resulls vvilh lhose from the North Fiji Basin andlhe Okinawa Trough shows geochemicallrencls thalmflecllhe evolution from a rifling slags (island arc charac:Lerislics) loa malum slage (MORB characteristics) of back-arc basins.