This project will use field studies to determine the spatial and temporal distribution of Pliocene to Recent basic volcanic rocks in the east-central MVB. Selected samples will be analyzed for major elements, trace elements, Sr, Nd, Pb, and O isotopic ratios, in addition to electron microprobe analyses of minerals. Some of the older rocks will be dated K-Ar methods. This data will be combined with existing data on basic volcanic rocks in the MVB to develop and/or test models for the origin of basic magmas in the MVB by placing constraints on the composition of materials contributing to the source of these basic magmas. The project will determine any correlation that exist between the distribution of the various types of basic volcanic rocks with crustal structure, age of and depth to the subducted lithosphere, and age of the rocks. It will also document the occurrence of various types of basic volcanic rocks that have only recently been recognized to occur in subduction-related volcanic arcs, and will provide a basis upon which the more common, more fractionated, and/or more contaminated calc-alkaline rocks can be understood.
