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首页> 外文学位 >Field, geochemical, and isotopic constraints on the genesis of rhyolite ash-flow tuffs and related rocks of the Tomochic volcanic center, Sierra Madre Occidental, Mexico.
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Field, geochemical, and isotopic constraints on the genesis of rhyolite ash-flow tuffs and related rocks of the Tomochic volcanic center, Sierra Madre Occidental, Mexico.

机译：墨西哥Sierra Madre Occidental流线型火山灰凝灰岩及相关岩石成因的田间，地球化学和同位素约束。

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摘要

Field, chronologic, geochemical, and isotopic data constrain the genesis of rhyolite ash flows and related magmas at a volcanic center that was active during the final ;Geochemical and isotopic data are consistent with rhyolite genesis by fractional crystallization of two-pyroxene andesite. The least-evolved vista sample represents no more than 40% the original mass of andesite; an additional ;The evolution of volcanism at the Tomochic volcanic center, from andesitic to rhyolite-dominated with late extrusion of basaltic andesite, occurred elsewhere in the volcanic field as well, and roughly coincided with a sharp decrease in the rate of Farallon plate subduction. It is proposed that this decrease contributed to (a) the onset of brittle crustal extension and shorter residence times for mafic melts formerly ponded in the deep crust, and (b) a decreased flux of mafic melts into the crust from below, leading to (i) the stalled ascent and subsequent differentiation of earlier-formed andesitic magmas, (ii) eruption of derivative rhyolite ash flows, and (iii) the termination of calcalkalic volcanism throughout the Sierra Madre Occidental.
机译：野外，年代，地球化学和同位素数据限制了流纹岩灰分流和火山岩的成因，该火山岩和相关岩浆在最终活动期间处于活跃状态;地球化学和同位素数据与通过2 rox石安山岩的分步结晶而形成的流纹岩成因相一致。演化最少的远景样品代表不超过安山岩原始质量的40％；附加的；在Tomochic火山中心，从安山岩到流纹岩为主的火山岩演化，以及玄武岩安山岩的后期挤压，也发生在火山场的其他地方，大致与Farallon板块俯冲速率急剧下降相吻合。有人认为这种减少有助于（a）以前积聚在深地壳中的镁铁质熔体开始脆性地壳伸展和缩短停留时间，（b）镁铁质熔体从下方进入地壳的通量减少，导致（ i）较早形成的安山岩浆的停滞上升和随后的分化，（ii）流纹岩灰烬流的喷发，以及（iii）整个西马德雷山脉的钙碱性火山作用的终止。

著录项

  • 作者

    Wark, David Austin.;

  • 作者单位

    The University of Texas at Austin.;

  • 授予单位 The University of Texas at Austin.;
  • 学科 Geology.;Geochemistry.
  • 学位 Ph.D.
  • 年度 1989
  • 页码 242 p.
  • 总页数 242
  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类
  • 关键词

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