Extremely fluid behavior of hydrous peralkaline rhyolites

被引:77
作者
Dingwell, DB [1 ]
Hess, KU [1 ]
Romano, C [1 ]
机构
[1] Bayer Geoinst, D-95440 Bayreuth, Germany
关键词
rhyolites; peralkalic composition; water; melts; viscosity; plastic flow; models;
D O I
10.1016/S0012-821X(98)00046-6
中图分类号
P3 [地球物理学]; P59 [地球化学];
学科分类号
0708 ; 070902 ;
摘要
The viscosities of a series of water-bearing peralkaline rhyolitic melts have been experimentally determined. The dry melt compositions are composed of a series of additions of Na2O to a metaluminous base composition. The melts, initially hydrated at high pressures and quenched isobarically, have been prepared by cutting and polishing, then reheating across the glass transition at 1 arm where they an annealed to a relaxed metastable state and then investigated dilatometrically using micropenetration methods. The measurements have been performed in the viscosity range of 10(8.5)-10(11.5) Pa s which corresponds to temperatures in the range of 675-220 degrees C for these compositions. Despite the relatively low viscosities of dry peralkaline melts in comparison with metaluminous melts of similar SiO2 content, the viscosities of peralkaline rhyolitic melts also decrease strongly and non-linearly with the addition of water. The resulting viscosity-temperature relationships for water-bearing peralkaline rhyolitic melts are shifted to much lower temperatures such that glass transition temperatures for moderate cooling rates correspond to extraordinarily low temperatures. A model is presented for the calculation of melt viscosities in the range of 10(8.5)-10(11.5) Pa s for peralkaline rhyolites with up to 7 wt% H2O. The very fluid nature of these peralkaline rhyolites over a wide range of water contents may facilitate a very efficient degassing history of glassy peralkaline rhyolites in nature. Efficient degassing might explain the apparent contradiction of the presence of common water-rich melt inclusions in phenocryst phases hosted in water-foe glassy rhyolites, versus the absence of vesicular layers or textural evidence for a vesicular past for the glassy rocks. (C) 1998 Elsevier Science B.V. All rights reserved.
引用
收藏
页码:31 / 38
页数:8
相关论文
共 17 条
  • [1] [Anonymous], 1986, NUMERICAL RECIPES C
  • [2] BEHRENS H, 1995, EUR J MINERAL, V7, P905
  • [3] CARMICHAEL ISE, 1980, EVOLUTION IGNEOUS RO, P233
  • [4] DINGWELL DB, 1990, EUR J MINERAL, V2, P427
  • [5] Dingwell DB, 1998, AM MINERAL, V83, P236
  • [6] The effect of water on the viscosity of a haplogranitic melt under P-T-X conditions relevant to silicic volcanism
    Dingwell, DB
    Romano, C
    Hess, KU
    [J]. CONTRIBUTIONS TO MINERALOGY AND PETROLOGY, 1996, 124 (01) : 19 - 28
  • [7] Dingwell DB, 1995, REV MINERAL, V32, P21
  • [8] Hess K. -U., 1996, THESIS U BAYREUTH
  • [9] HESS KU, 1995, AM MINERAL, V80, P297
  • [10] Hess KU, 1996, AM MINERAL, V81, P1297