ALEUTIAN ARC MAGMATISM IN SPACE AND TIME: A GEOCHEMICAL AND PETROLOGIC STUDY

点击翻译按钮获取中文摘要

Magmatic processes occurring over an entire island are crustal section are reflected in rock units found in the Aleutian arc, Alaska. These processes assume more than local importance in that they have shaped a large proportion of terrane collagesw, and perhaps the continental crust in general. In the Aleutian arc, most on-going magmatic studies emphasize recent volcanic rocks. To complete the crustal cross-section, this project will focus on the more voluminous subvolcanic levels as represented by plutons and xenolithic fragments. Specific studies are proposed for plutonic xenoliths from Tertiary volcanic rocks on Kanaga Island and the Hidden Bay pluton on Adak Island in the central Aleutians. These rock units indicate a buried oceanic crustal component in the Aleutian lithosphere and record details of the processes of magmatic segregation in the crust. In the western Aleutians on Attu Island and in the Komandorski Islands (USSR), a striking pattern of Tertiary magmatic evolution reflects changes in plate convergence. On Attu, specific studies are planned to study these changing magmatic conditions as reflected by Oligocene rhyolites, lower-Miocene alkaline rocks, and upper- Miocene calc-alkaline lavas. The evolution of subcrustal magma sources (including alkaline sources) and the crustal assimilation and fractional crystallization of calc-alkaline magmas intruding back-arc crust will be studied. Analytical studies include mineralogical analyses of major and trace elements as well as isotopes (O, Sr, and Nd). These are to be used uespectively as tracers of physical conditions (P, T, volatile fugacities) and isotopically distinct tectonic units.