HR: 1340h
AN: T33C-1495    [Abstracts]
TI: Magnitude of contractional strain accommodated across stylolites in micritic limestone
AU: * Benedicto, A
EM: antonio.benedicto-esteban@u-psud.fr
AF: Antonio BENEDICTO, Universite Paris Sud XI, UMR Tectonique, Bat. 504, Orsay, 91405, France
AU: Schultz, R A
EM: schultz@mines.unr.edu
AF: Ricahrd SCHULTZ, University of Reno, Department of Geological Sciences and Engineering, Reno, 89557, United States
AB: In fault zones, stylolites result from water-assisted pressure solution and participate in mass-transfer and volume loss in the rock as an important deformation mechanism in faults involving carbonate rocks. Although it is well known that the orientations of stylolite surfaces and the associated teeth track the direction of the local stress state, making them reliable paleostress indicators, the amount of contractional strain accommodated by a stylolite remains difficult to assess given its dependence on the properties and chemical heterogeneity of the rock and the paucity of appropriately constrained field examples. We analyse a population of fault-related stylolites by comparing the amplitudes of stylolitic teeth and spikes to independent measures of thinning in the rock, and investigate the scaling relations between along strike trace length (L) and the maximum (Dmax) and average (Davg) amplitudes of teeth. The studied stylolites occur in a 212-mm-thick limestone layer dragged into the damage zone of the Gubbio normal fault zone in Central Italy. Layer thinning was assessed independently from the layer geometry, with a maximum value of ~23% nearest the fault. 28 mm of thinning is related to 24 stylolites whose lengths range from 6.4 to 146 mm and average amplitudes from 0.1 to 1.3 mm. The average and maximum amplitudes of teeth generally increase with stylolite length, with Davg = 0.0011L0.17, r2 = 0.57, consistent with stylolites being analogous mechanically to anticracks and compaction bands that propagate to greater lengths as contractional strains increase along them. The stylolites increase in number and amplitude into the most thinned area, correlating with increasing contractional strain accommodated by the layer. Although the maximum amplitude scales with stylolite length, its location along the stylolite appears random, consistent with recent work that associates maxima with processes at the grain scale, such as the positions and surface energies of less soluble grains. In contrast, the average amplitude appears related to continuum-scale factors such as rock stiffness. By summing lengths and average amplitudes, the contractional strain accommodated by the stylolites increases from zero far from the fault to ~5% in the area of greatest layer thinning. The average amplitude of stylolites visible in outcrop provides a measure of the minimum magnitude of contractional strain in the rock, although other mechanisms such as grain-scale dissolution appear necessary to account for the remaining layer thinning.
DE: 5104 Fracture and flow
DE: 8010 Fractures and faults
DE: 8020 Mechanics, theory, and modeling
DE: 8030 Microstructures
DE: 8099 General or miscellaneous
SC: Tectonophysics [T]
MN: 2007 Fall Meeting