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

在整个岛屿上发生的岩浆作用都反映在阿拉斯加阿留申弧区的岩石单元中。这些过程具有比当地更重要的意义，因为它们形成了很大比例的地体胶合体，也许还形成了整个大陆地壳。在阿留申弧区，大多数正在进行的岩浆研究都侧重于最近的火山岩。为了完成地壳横截面，该项目将侧重于以深成岩和捕虏体碎片为代表的更大的次火山级别。建议对阿留申中部神奈加岛第三纪火山岩和阿达克岛隐蔽海湾岩体中的深成包体进行具体研究。这些岩石单位指示了阿留申岩石圈中埋藏的大洋地壳成分，并记录了地壳中岩浆分离过程的细节。在阿图岛的阿留申西部和科曼多尔斯基群岛(苏联)，第三纪岩浆演化的显著模式反映了板块会聚的变化。在阿图，计划进行具体的研究，以研究这些变化的岩浆条件，如渐新世流纹岩、下中新世碱性岩、和上中新世钙碱性熔岩。地壳下岩浆源(含碱源)的演化与侵入钙碱性岩浆的地壳同化和分离结晶将对弧后地壳进行研究。分析研究包括主要和微量元素的矿物学分析以及同位素(氧、锶和钕)。它们将分别用作物理条件(P、T、挥发逸度)和同位素不同构造单元的示踪剂。

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.