Modeling compaction of olivine cumulates in the muskox intrusion

Abstract

We have developed numerical models for compaction of olivine cumulates by simultaneous grain boundary diffusion creep and power law creep. The simulation is a coupled model of compaction, porous medium flow, and heat transport that includes latent heat of fusion and advective heat transport by flow of interstitial liquid. It also includes precipitation from interstitial pore liquid and partial melting of cumulates caused by changes in temperature or passage of interstitial melt through regions of different temperature. Compositions and quantities of liquid and precipitated phases are determined from a fractional crystallization simulation using the computer program MELTS. We use these models to simulate the accumulation and crystallization of the Muskox intrusion. Simulations suggest that, regardless of their initial state, compaction will lithify cumulates into a cohesive mass within meters of the depositional interface. Upward velocity of interstitial liquid is also much too small to suspend or liquify the crystal column. The simulations produced rapidly cooled marginal zones at both top and bottom of the intrusion. High rates of compaction are found at the tops and bottoms of cyclic units as a result of both high temperature at the boundary and partial melting caused by upward flow of cooler interstitial liquid as it enters hotter, compositionally more primitive cumulates above the cyclic unit contact In contrast, upward movement of interstitial liquid into cooler cumulates contributes to precipitation both in the upper marginal zone and in the middle region of cyclic units. The degree of compaction of cumulates is strongly a function of temperature, but if temperature is sufficiently high, adcumulates can form in the interior of cumulate bodies by compaction alone.