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Production of andesite in the western Mexican arc: Constraints from argon chronology, volume analysis, and geochemistry.

机译：墨西哥西部弧形安山岩的生产：氩气年代学，体积分析和地球化学的限制。

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摘要

40Ar/39Ar geochronology is coupled with quantitative volume determinations (utilizing field mapping, digital elevation models, ortho-airphotos and Geographic Information System software) to constrain magma eruption rates at the Ceboruco-San Pedro and the Volcan Tepetiltic volcanic fields in the western Trans-Mexican arc. Each volcanic field is dominated by an intermediate composition stratovolcano (∼51 and ∼42 km 3, respectively) that was built in tens of kyrs. The smaller volume peripheral lavas (1 km3) are more geochemically diverse than the large volume flows associated with the main edifices. The peripheral flows tend to be crystal-poor (5% phenocrysts) and show little evidence for magma mingling or disequilibria. Based on silica content, there is no systematic progression to the composition of magma type (basalt, andesite, dacite, rhyolite) erupted with time, at either the individual stratocones or across the entire volcanic field. On the basis of eruptive sequence, proportions of lava types, phenocryst assemblages, and geochemistry, the lavas in the Ceboruco-San Pedro volcanic field and the lavas at Volcan Tepetiltic do not each reflect the differentiation of a single parental liquid in a long-lived magma chamber. The distinct geochemical signatures were present prior to magma emplacement in the upper crust, whereupon subsequent degassing and crystallization led to variable phenocryst abundances and assemblages.; The crystal-poor lavas peripheral to the central stratocones provide insight into the generation of magmas at volcanic arcs. The composition of plagioclase is strongly dependent on the water concentration of the melt from which it crystallized. This relationship is used to develop a new plagioclase hygrometer to estimate water content in the melt. The plagioclase in the crystal-poor lavas span a broad range in composition and reflect crystallization from magmas with different amounts of dissolved water. Textures in the plagioclase (abundant melt inclusions) reflect rapid crystallization. These two separate lines of evidence suggest that crystallization is degassing induced.; The broader tectonic evolution of western Mexico is explored with a detailed geochronology study of the silicic volcanism over the last ∼80 Myr. A previously unrecognized volcanic flare-up in the Pliocene suggests that western Mexico may have been part of an aborted rifting event.
机译：40Ar / 39Ar地质年代学与定量确定体积（利用野外测绘，数字高程模型，正航照相和地理信息系统软件）相结合，以限制跨西太平洋地区Ceboruco-San Pedro和Volcan Tepetiltic火山场的岩浆喷发速率。墨西哥弧。每个火山场都以中间构造的平流火山为主（分别为〜51 km和〜42 km 3），其构造为几十个基尔。与主要建筑物相关的大流量相比，较小体积的外围熔岩（<1 km3）在地球化学上更具多样性。外围流动趋向于晶体贫乏（<5％隐晶），几乎没有证据表明岩浆混合或失衡。基于二氧化硅的含量，在单个平流锥或整个火山场中，随时间喷发的岩浆类型（玄武岩，安山岩，榴辉岩，流纹岩）的组成没有系统的进展。根据火山喷发的顺序，熔岩类型的比例，隐晶相组合和地球化学，Ceboruco-San Pedro火山场中的熔岩和Volcan Tepetiltic的熔岩均不能反映出长寿的单一母体液的差异。岩浆房。在岩浆进入上地壳之前就存在明显的地球化学特征，随后进行的脱气和结晶作用导致了变晶体的丰度和组合。中央平流层外围的晶体贫瘠的熔岩提供了对火山弧岩浆形成的见解。斜长石的组成在很大程度上取决于其结晶的熔体的水浓度。这种关系用于开发新的斜长线湿度计，以估算熔体中的水分含量。晶体贫乏的熔岩中斜长石的成分范围很广，并反映出岩浆结晶的溶解水量不同。斜长石中的纹理（大量熔体包裹体）反映出快速结晶。这两个单独的证据表明，结晶是由脱气引起的。通过对最后80迈尔的硅质火山作用进行详细的年代学研究，探索了墨西哥西部的广泛构造演化。在上新世以前未被识别的火山爆发表明，墨西哥西部可能是裂谷事件的一部分。

著录项

  • 作者

    Frey, Holli M.;

  • 作者单位

    University of Michigan.;

  • 授予单位 University of Michigan.;
  • 学科 Geology.
  • 学位 Ph.D.
  • 年度 2005
  • 页码 305 p.
  • 总页数 305
  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类 地质学;
  • 关键词

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