Microlites and "nanolites" in rhyolitic glass: microstructural and chemical characterization |
| |
| Authors: | Thomas G Sharp Richard J Stevenson Donald B Dingwell |
| |
| Institution: | Bayerisches Geoinstitut, Universit?t Bayreuth, D-95440 Bayreuth, Germany, DE
|
| |
| Abstract: | We used transmission electron microscopy (TEM) and scanning electron microscopy (SEM) to study magmatic crystals in the Ben
Lomond rhyolite lava dome, Taupo Volcanic Center, New Zealand. Using TEM and SEM to investigate the size distributions of
these crystals, we identified three size populations: microphenocrysts (>1.2 μm wide), microlites (>0.6 μm wide), and smaller
crystals (<0.6 μm wide) which we term "nanolites". The predominant mineral phases of the microlites and nanolites are augites,
pigeonites, and hypersthenes. The compositions and microstructures within these pyroxenes indicate disequilibrium crystallization
at approximately 850–900 °C and undercoolings as high as 300 °C from equilibrium crystallization temperatures. Complex microstructures
resulting from subsolidus reactions in augite and pigeonite are consistent with moderate cooling rates within the upper obsidian
layer of the Ben Lomond rhyolite dome. This study demonstrates the existence of sub-micron magmatic crystals in a rhyolite
and illustrates the potential of TEM to provide unique information about the crystallization and cooling histories of glassy
volcanic rocks.
Received: May 8, 1995 / Accepted: November 27, 1995 |
| |
| Keywords: | Rhyolite Crystallization Size distribution Microphenocryst Microlite Nanolite Microstructures |
| 本文献已被 SpringerLink 等数据库收录！ |
|
