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

在阿拉斯加阿留申弧发现的岩石单元反映了发生在整个岛屿上的岩浆作用。这些过程具有比局部更重要的意义，因为它们形成了很大比例的陆地拼贴岩，也许总的来说是大陆地壳。在阿留申弧，大多数正在进行的岩浆研究都强调最近的火山岩。为了完成地壳剖面，本项目将重点研究以岩体和xenolithic碎片为代表的体积更大的次火山层。对阿留申群岛中部的Kanaga岛第三系火山岩和Adak岛隐湾火山岩的深成捕虏体进行了具体研究。这些岩石单元表明阿留申岩石圈中存在埋藏的海洋地壳成分，并记录了地壳岩浆分离过程的细节。在阿留申群岛西部的阿图岛和苏联的科曼多尔斯基群岛，第三纪岩浆演化模式反映了板块收敛的变化。在阿图，拟对渐新世流纹岩、下中新世碱性岩、上中新世钙碱性熔岩等反映的岩浆条件变化进行具体研究。研究了地壳下岩浆源（包括碱性岩浆源）的演化以及侵入弧后地壳的钙碱性岩浆的地壳同化和分晶作用。分析研究包括主要元素和微量元素以及同位素（O， Sr和Nd）的矿物学分析。它们将分别用作物理条件（P、T、挥发性易失性）和同位素上不同的构造单元的示踪剂。

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.