Petrogenetic Processes and Sources of Volcanic Rocks in the Central Andes: Constraints from Mafic Monogenetic Centers inBolivia (Collaborative Research)

对沿着安第斯山脉火山产物的研究表明， 化学沿着走向和沿走向随时间变化。 这些 变化可以通过两种对比模型来解释;（1） 化学变化仅仅反映了地幔的变化 来源（原始岩浆不会因与 （2）这些变化是由于 原始岩浆的修改，由于与 它们所经过的岩石圈。 在中安第斯山脉， 喷发的安山岩转变为典型的大陆地壳， 这反映了地幔到地壳的直接通量， 并支持了地壳增长通过岩浆添加的模型 安第斯山脉中部的地壳厚度 很难想象原始岩浆 不会在到达地面的途中被修改 替代 解释是安第斯山的安山岩在化学上类似于 因为它们被广泛污染 在地壳上 本项目将通过研究镁铁质岩石来解决这一关键问题。 玻利维亚的单基因中心。 现有数据表明， 这些是安第斯山脉中部最不分化的熔岩， 87 SR/86 SR与岛弧岩浆源区相似。 他们 因此代表了最接近原始岩浆的例子， 中部安第斯山脉，似乎是一个重要的窗口， 亚安第斯地幔的组成。

Studies of volcanic products along the Andes show a variation in chemistry along strike and across strike with time. These variations can be explained by two contrasting models; (1) that the chemical variations simply reflect variations in the mantle source (primary magmas are not modified by interaction with the lithosphere); or (2) that these variations are due to modification of primary magmas due to interaction with the lithosphere through which they pass. In the Central Andes, the similarity of the compositions of the erupted andesites to typical continental crust, has led to the suggestion that these reflect the direct mantle to curst flux, and support a model for crustal growth through magmatic addition at the subduction zone Crustal thicknesses in the Central Andes reach~70km, and it is difficult to envisage that primary magmas would not be modified en route to the surface. The alternative interpretation is that Andean andesites are chemically similar to continental crust because they have been extensively contaminated by the crust. This project will address this key issue by studying mafic monogenetic centres in Bolivia. Available data suggests that these are the least differentiated lavas in the Central Andes and have 87SR/86SR similar to the source of island arc magmas. They therefore represent the closest examples to primary magmas in the Central Andes, and appear to be a vital window into the composition of the sub-Andean mantle.