Silicic Volcanism and Crustal Evolution: Petrogenetic Studies in Central Chihuahua, Mexico, Uniquely Constrained by Mantle Isotopic Data

墨西哥西部的中新生代熔结凝灰岩构成了 世界上最大的流纹岩区， 关于它们的起源，必须记录在地壳深处， 上地幔的底部 在以往的岩石成因 对来自墨西哥和其他地方的大量熔结凝灰岩的研究， 无法定量评估相对 地壳和地幔成分对以下方面的贡献 原因：（1）地壳深部是不均匀的， 它的年龄和成分在火山区之下 只能推断。 (2)亚地壳同位素组成 大陆弧玄武岩岩浆的数量很少，因为任何 穿过大陆地壳的岩浆 地壳同位素特征 奇瓦瓦州的拉奥利瓦地区， 墨西哥提供了一个不寻常的机会来阐明起源 和演化的钙碱性岩石，包括大量的 熔结凝灰岩，利用地壳和地幔的数据 捕虏体 本研究的主要目的如下：（1）确定 地壳深部的岩浆和变质历史 奇瓦瓦州中部麻粒岩相锆石定年 捕虏体的SHRIMP离子探针和常规 技术. SHRIMP分析将由Roberta Rudnick进行 在澳大利亚国立大学。 (2)完全 深地壳捕虏体和火山岩的特征， 主要元素、同位素（Sr、Nd、Pb）、 地热-地压研究 (3)定量测试 将火山岩与特定深部联系起来的成岩模式 地壳岩性 这些模型受到以下因素的唯一约束： 来自地幔变辉石岩捕虏体的数据记录了 “未污染”大陆弧同位素组成 玄武岩浆 这项研究的最终结果应该是一个 关于大量生产的影响的特殊文件 地壳深部的岩浆活动

The mid-cenozoic ignimbrites of western Mexico constitute the largest rhyolite province in the world, and definitive evidence regarding their genesis must be recorded in the deep crust and upper mantle beneath the region. In previous petrogenetic studies of voluminous ignimbrites from Mexico and elsewhere, it has not been possible to quantitatively evaluate the relative contributions of crustal and mantle components for the following reasons: (1) The deep crust is heterogeneous, and almost invariable, its age and composition beneath the volcanic field can only be inferred. (2) The sub-crustal isotopic compositions of continental arc basaltic magma are rarely known because any magma that passed through the continental crust may acquire a crustal isotopic signature. The La Olivina area of chihuahua, Mexico provides an unusual opportunity to elucidate the origin and evolution of calc-alkalic rocks, including voluminous ignimbrites, by drawing on data from crustal and mantle xenoliths. The primary goals of this research are as follows: (1) Determine the igneous and metamorphic history of the deep crust beneath central chihuahua by dating zircons from granulite facies xenoliths using the SHRIMP ion microprobe and conventional techniques. The SHRIMP analyses will be made by Roberta Rudnick at the Australian National University. (2) Completely characterize the deep crustal xenoliths and volcanic rocks from the region by major element, isotopic (Sr, Nd, Pb), and geothermic-geobaric studies. (3) Quantitatively test petrogenetic models relating the volcanic rocks to specific deep crustal lithologies. These models are uniquely constrained by data from mantle metapyroxenite xenoliths that record the isotopic compositions of "uncontaminated" continental arc basaltic magmas. The final result of this research should be an exceptional documentation of the impact of voluminous silicic magmatism on the deep crust.