Temporal changes in arc magma geochemistry, northern Sulawesi, Indonesia.

Abstract

Late Miocene to recent subduction-related volcanics from the Sangihe Arc in northern Sulawesi show a pattern of geochemical change through time. The oldest of these suites have compositions that indicate that the mantle source underlying the arc has experienced a previous event of melt extraction, causing a relative depletion in incompatible elements. The geochemical signature of the subduction zone component in these volcanics implies early domination by a fluid, which was mainly derived from altered MORB. The geochemical and isotopic signature of the modern lavas, especially those from volcanic centres located furthest away from the trench, are different from those of the older lavas and indicate that the subduction zone component is now dominated by a melt of sedimentary origin. The change from a fluid-dominated to a melt-dominated subduction zone component may be related to the collision between the Halmahera and Sangihe arcs. These systematic changes appear to be superimposed upon quite variable parent magma compositions reflecting variation in mantle source composition.