The relationship between the rheology and phase equilibria of a picritic basalt from Kilauea Iki has been investigated at 1 atm along the QFM buffer. Between 1270 ø and 1180øC olivine and minor spinel are the only liquidus phases, and the melt volume decreases from 85 to 74 vol %. At the ol-sp-pc-cpx cotectic, melt is consumed more rapidly dropping to 47 vol % at 1139øC. The rheology of the magma is non-Newtonian, is characterized by time-dependent, pseudoplastic behavior, and is consistent with power law flow or Bingham pseudoplastic behavior. Non-Newtonian effects are most apparent when the crystal volume is greater than 25% and the shear rate is increasing. Once stirred, the magma approaches Newtonian rheology with decreasing shear rate. At 1170øC (approximately 25% suspended crystals) the apparent activation energy (calculated at unit shear rate) increases from 123 + 10 kcal mol-• to 452 + 21 kcal mol-X. When the change in liquid composition along the liquidus is included, the observed viscosities are in good agreement with those calculated from the Einstein-Roscoe equation for a serial size distribution of crystals. A quadratic fit to the shear stress-strain rate data yields a nonzero intercept indicative of a finite yield strength. The apparent yield strength increases with decreasing temperature reaching • 800 Pa at 1149øC. These extrapolated (and model dependent) values are in good agreement with those determined by other methods (Shaw et al., 1968' McBirney andMurase, 1984). The yield strengths can be fit by a power law expression, ao = 6500• b2'85, where ao is the yield strength and •b the crystal volume fraction. This expression recovers the yield strength estimates for other basalts, suggesting that it may be generally applicable to magmas in which the melt is of broadly basaltic composition. The magmas exhibit heating due to viscous dissipation during shearing. However, this effect is not large enough to produce the observed pseudoplasticity. We conclude that the non-Newtonian behavior in these magmas is due to reorientation of solids in the flow field and solid-solid interactions. We develop a model in which the time-dependent pseudoplasticity and yield strengths are produced by the relationship between solid phase contiguity (the fraction of solid internal surface area shared with other solids) and grain dispersive pressure due to shearing. Increased contiguity is related to increased apparent viscosities and yield strengths, while increased grain dispersive pressure due to shearing acts to diminish contiguity. Paper number 7B7035. 0148-0227/88/007B-7035505.00 cooled liquids (cf. Bockris and Lowe [1953, 1954], Bockris et al. [1955], Shaw [1963], Cukierrnan and Uhlmann [1973, 1974], Cranmer and Uhlmann [1981], and Urbain et al. [1982], among others). The variables investigated in these studies are temperature and bulk composition. Using these variables empirical models for the estimation of viscosity have been formulated [Shaw, 1972; Bottinga and Weill, 1972]. Other studies have concentrated upon th...

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The Nevada Nuclear Waste Storage Investigations Project has conducted experi ments to study the hydrothermal interaction of rock and water representative of a poten tial high-level waste repository at Yucca Mountain, Nevada. The results of these experi ments help define the near-field repository environment during and shortly after the thermal period that results from the emplacement of nuclear waste. When considered in conjunction with results contained in companion reports, these results cm be used to assess our ability to accelerate tests using the surface area/volume parameter and/or temperature. These rock-water interaction experiments were conducted with solid polished wa fers cut from both drillcore and outcrop samples of Topopah tuff, using both a natural ground water and distilled water as the reacting fluid. Pre-and post-test characterization of the reacting materials was extensive. Post-test identification and chemical analysis of secondary phases resulting from the hvdrothermal interactions were aided by using monoliths of tuff rather than crushed material. All experiments were run in Dicksontvpe, gold-bag rocking autoclaves that were periodically sampled at in situ conditions. A total of nine short-term (up to 66-day) experiments were run in this series; these experi ments covered the range from 90 to 250°C and from 50 to 100 bar. The results obtained from the experiments have been used to evaluate the modeled results produced by cal culations using the geochemieal reaction process code EQ3/6.

Mutual relationships of mobile lithospheric plates define two distinct tectonic environments each characterized by diagnostic magmatism. A compressional environment occurs at loci of plate convergence; quartz‐ and hypersthene‐normative intermediate, acid and basic members of the calc‐alkaline orogenic suite are emplaced above a dipping seismic zone. A tensional environment occurs mainly at loci of plate divergence, areas characterized by networks of deep fractures, offset by transform faults. Products of nonorogenic magmatism typically consist of abundant tholeiitic or alkali olivine basalt, possibly accompanied by rhyolite, trachyte, or phonolite (or plutonic equivalents); intermediate compositions are volumetrically insignificant. On a differentiation index versus frequency plot, orogenic suites define one maximum, nonorogenic suites two maximums. Orogenic rocks show no iron enrichment; nonorogenic suites do. Recognition of older igneous associations as orogenic or nonorogenic by employing chemical and mineralogical criteria can lead to inferences about tectonic environments during emplacement. Such criteria may provide a unique insight into regional tectonic evolution very difficult to deduce from structural investigations alone.