Magma Sources and Petrogenetic Processes in Continental Arcs: The Southern Volcanic Zone of the Andes

大陆弧岩浆作用反映了板块运动的一个主要过程 大陆板块和大洋板块的汇聚 大洋板块向大陆板块之下的俯冲 导致新大陆地壳的形成， 地壳物质进入对流地幔。 这些是 需要详细了解的重要过程， 来了解地球的演化。 安第斯火山 反映了海洋纳斯卡板块的俯冲活动 南美板块 南部火山带（SVZ） 安第斯山脉，从33 °-42 °，有主要的沿走向地质 变化;例如，从北到南， 俯冲地壳和大陆地壳厚度的关系。 与此同时，沿着和穿越主科迪勒拉山脉， 熔岩成分（主要和微量元素）系统地变化 丰度，放射性同位素比值）。 有几 这些地球化学趋势的替代解释。 私家侦探的 先前和拟议的研究的目的是了解 本区火山作用的起源与演化; 具体来说，就是定义组件的相对重要性 来自俯冲地壳、软流圈、岩石圈和 大陆地壳的弧岩浆，并确定 熔化程度变化的重要性，随后的熔化- 固体分凝、岩浆混合和地壳同化作用。 做 这种斑晶相组成加上全岩为主， 微量元素丰度和同位素比值（0，Sr，Nd，Pb）将 被利用 到目前为止，重点一直放在 SVZ的火山前沿 该项目将集中在最近的 玄武岩熔岩在火山前缘以东50至200公里处喷发。 因为这些弧后熔岩的演化程度低于 火山前锋熔岩，其地球化学特征更多 直接反映源成分（特别重要的是 确定地球化学特征的可能性 大陆地幔岩石圈）和地幔过程。 在 此外，沿着火山前缘， （比利亚里卡），熔岩之间的显著地球化学差异 从成层火山喷发出来， （卫星），小玄武岩锥已被发现。这些 差异可以解释为反映了更少的地壳 污染的卫星锥熔岩，或影响 在长寿命岩浆中平均化的源区不均匀性 成层火山下的洞穴 这些都很重要， 不同的解释。 检验…的普遍性 结果附近的比利亚里卡成层火山和区分 在这些解释之间， 与SVZ内其他成层火山的联系。***//

Continental arc magmatism reflects a major process in plate tectonics, the convergence of oceanic and continental plates. The subduction of an oceanic plate beneath a continental plate results in creation of new continental crust and incorporation of crustal material into the convecting mantle. These are important processes that need to be understood in detail in order to understand the evolution of the earth. Andean volcanoes reflect the active subduction of the oceanic Nazca plate beneath the South American plate. In the Southern Volcanic Zone (SVZ) of the Andes, from 33o-42oS, there are major along-strike geologic changes; e.g., from north to south there are decreases in the age of the subducted crust and continental crust thickness. Concurrently, along and across strike of the Main Cordillera the lavas vary systematically in composition (major and trace element abundance, radiogenic isotope ratios). There are several alternative explanations of these geochemical trends. The P.I.'s previous and proposed studies have the objective of understanding the origin and evolution of volcanism in this region; specifically, to define the relative importance of components from the subducted crust, asthenosphere, lithosphere and continental crust to the arc magmas, and to determine the importance of variations in degree of melting, subsequent melt- solid segregation, magma mixing and crustal assimilation. To do this phenocryst phase compositions plus whole-rock major and trace element abundances and isotopic ratios (0, Sr, Nd, Pb) will be used. To date emphasis has been on stratovolcanoes on or near the volcanic front of the SVZ. This project will focus on recent basaltic lavas erupted 50 to 200 km east of the volcanic front. Because these back (retro) arc lavas are less evolved than volcanic front lavas, their geochemical characteristics more directly reflect source compositions (especially, important is the possibility of determining geochemical characteristics of continental mantle lithosphere) and mantle processes. In addition, along the volcanic front near a single stratovolcano (Villarrica), significant geochemical differences between lavas erupted from the stratovolcano and several surrounding (satellite), small basaltic cones have been found. These differences can be interpreted as reflecting much less crustal contamination in the satellite cone lavas, or the influence of source heterogeneities which are averaged out in long-lived magma chambers beneath the stratovolcano. These are important and very different alternative interpretations. To test the generality of results near the Villarrica stratovolcano and to distinguish between these interpretations, satellite cone lavas associated with other stratovolcanoes in the SVZ will be studied. ***//