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Complex storage of rhyolite in the central Snake River Plain

机译：蛇河平原中部流纹岩的复杂储藏

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摘要

Analysis of hundreds of co-existing individual clinopyroxene crystals and crystal aggregates from rhyolitic ig-nimbrites of the central Snake River Plain has revealed that magma storage prior to eruption was complex. Crystal aggregates are dominated by plagioclase, augite, pigeonite, ilmenite, magnetite and zircon, and commonly lack sanidine and quartz which may be present as single crystals. In the ignimbrites, multiple compositions of pigeonite and augite may occur as single crystals, yet within the crystal aggregates, only single compositions of augite and pigeonite are recorded. Multiple crystal aggregates may be present within a deposit containing the whole spectrum of clinopyroxene compositions within the unit, yet only one pair of clin-opyroxene compositions occur in a single aggregate. Evidence of compositional zonation is rare to absent both throughout the deposit as a whole and within individual pyroxene grains. The restricted compositions of the crystal aggregates are interpreted as reflecting a magmatic system in which the magma was physically segregated into a number of separate bodies evolving in parallel prior to eruption. One case was recorded whereby the composition of a crystal aggregate did not agree with the compositions of single crystals in that ignimbrite. This aggregate represents a silicic magma not currently recognised in surface outcrops and reflects entrainment of surrounding crystal mush. Although multiple compositions of pigeonite and augite appear to be present only in ignimbrites, no relationship exists between the volume of erupted material and the number of dinopyroxene compositions present within the deposit.
机译：分析数百条共存的单个单斜辉石晶体和中部蛇河平原流纹岩棉岩晶体聚集体，发现喷发前的岩浆储藏是复杂的。晶体聚集体主要是斜长石，钠长石，方铁矿，钛铁矿，磁铁矿和锆石，并且通常缺乏可能以单晶形式存在的Sanidine和石英。在火成岩中，可能会以单晶形式出现多种组成的皂石和褐铁矿，但在晶体聚集体中，仅记录了一种组成的褐铁矿和皂石。沉积物中可能存在多个晶体聚集体，该沉积物包含该单元内所有斜基吡啶组合物的整个光谱，但是在单个聚集体中仅存在一对斜对联吡啶组合物。无论是整个沉积层还是单个辉石颗粒，都几乎没有成分带状的证据。晶体聚集体的受限制成分被解释为反映了一种岩浆系统，其中岩浆在物理上被分离成许多独立的，在喷发前平行演化的物体。记录了一种情况，其中晶体聚集体的组成与该火成岩中的单晶组成不一致。该聚集体代表了目前尚未在表层露头中识别出的硅质岩浆，并反映了周围晶体糊状物的夹带。尽管似乎仅在火成岩中存在多种组成的皂石和a石，但喷出物的体积与沉积物中存在的二茂基ene组成的数量之间没有关系。

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  • 来源
    《Journal of Volcanology and Geothermal Research》 |2012年第15期|p.1-11|共11页
  • 作者

    Ben S. Ellis; John A. Wolff;

  • 作者单位

    School of Earth and Environmental Sciences, Washington State University, Pullman WA 99164, USA;

    School of Earth and Environmental Sciences, Washington State University, Pullman WA 99164, USA;

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