Using Arrested Solid — Solid Multiphase Reactions in Geological Materials to Deduce the Rate of Crustal Uplift
The history geological terrains experience can be traced as a series of temperature and pressure changes. Each change drives the system toward a new state of thermodynamic equilibrium. The resultant overprinted rock fabrics, textures and chemical heterogeneities can be difficult to interpret. However, if carefully chosen, features from the scale of kilometers to nanometers can be used to reconstruct the history of mountain systems. Uplift of the Sri Lankan Central Highlands was rapid enough to preserve well-developed symplectite textures, some of which represent arrested solid-state diffusion-controlled reactions of garnet + O2 to form orthopyroxene + plagioclase + magnetite, as the rocks were exhumed from over 30 km in the earth’s crust. Our objective has been to determine the reaction mechanisms responsible for symplectite development, and to establish the time interval over which these reactions occurred, to constrain the rate of mountain uplift. Considering that the most rapid mechanism is solid st te grain-boundary diffusion of oxygen, the reaction time can be constrained by bounding the rate of oxygen supply to the reaction site. The solid state grain boundary diffusion rate of oxygen has been inferred to be ca. 10−14 m2-sec (Farver and Yund, 1991), but is sensitive to inferred grain boundary width. The range of rates thus determined allows the distinction between rapid uplift similar to that of the Himalayan Mountains, and the slow and progressive erosion of a less dramatic terrain. Further constraints on diffusion control and energetic relationships are determined from crystallographic relationships between the reactant and product phases, and submicron scale microstructures.
KeywordsBoundary Diffusion Oxygen Fugacity Geological Material Boundary Width Rapid Uplift
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- Ashworth, J.R., 1993, Fluid-absent diffusion kinetics of Al inferred from retrograde metamorphic coronas. Am. Min. 78:331.Google Scholar
- Kehelpannala, K.V.W., 1991, Structural evolution of high-grade terrains in Sri Lanka with special reference to the areas around Dodanaslanda and Kandy, in:The Crystalline Crust of Sri Lanka, Part I, A. Kroner, ed., Geological Survey Department, Prof. Paper No. 5, Republic of Sri Lanka, Colombo.Google Scholar
- Kriegsman, L., 1991, Structural geology of the Sri Lanka basement - A preliminary review, in.The Crystalline Crust of Sri Lanka, Part I, A. Kroner, ed., Geological Survey Department, Prof. Paper No.5, Republic of Sri Lanka, Colombo.Google Scholar
- Le Claire, A.D. 1963. The analysis of grain boundary diffusion measurements. Brit. J. Appl. Phys. 14:351.Google Scholar
- Schenk, V., Raase, P., and Schumacher, R., 1991, Metamorphic zonation and P-T history of the Highland Complex in Sri Lanka, in:The Crystalline Crust of Sri Lanka, Part I, A. Kroner, ed., Geological Survey Department, Prof. Paper No. 5, Republic of Sri Lanka, Colombo.Google Scholar