The initiation of brittle faults in crystalline rock |
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Institution: | 1. Universidade de São Paulo, Instituto de Geociências, Departamento de Geologia Sedimentar e Ambiental, Rua do Lago, 562, São Paulo, SP 05508-080, Brazil;2. Comissão Nacional de Energia Nuclear, Centro de Desenvolvimento da Tecnologia Nuclear, Serviço de Tecnologia Mineral, Rua Mário Werneck s/n, Campus UFMG, Belo Horizonte, MG 31270-901, Brazil;3. Universidade Federal de Minas Gerais, Instituto de Ciências Exatas, Departamento de Física, Avenida Antônio Carlos 6627, Campus da Pampulha, Belo Horizonte, MG 31270-000, Brazil;1. Dipartimento di Scienze della Terra, Università di Napoli Federico II, Naples, Italy;2. Dipartimento di Scienze della Terra e dell''Ambiente, Università di Pavia, Via Ferrata, 1, Pavia, Italy;1. Department of Geological and Environmental Sciences, Stanford University, Stanford, CA, USA;2. US Geological Survey, Menlo Park, CA, USA;3. Petroleum Engineering Department, Colorado School of Mines, Golden, CO, USA;1. Department of Geology, Colby College, 5800 Mayflower Hill, Waterville, ME, 04901, USA;2. Department of Earth and Oceanographic Sciences, Bowdoin College, 6800 College Station, Brunswick, ME, 04011, USA |
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Abstract: | Faults in the upper crust initiate from pre-existing (inherited) or precursory (early-formed) structures and typically grow by the mechanical interaction and linkage of these structures. In crystalline rock, rock architecture, composition, cooling, and exhumation influence the initiation of faults, with contrasting styles observed in plutonic rocks, extrusive igneous rocks, and foliated metamorphic rocks. Brittle fault growth in granitic rock is commonly controlled by the architecture of inherited joints or preexisting dikes. In basalt, abundant joints control the surface expression of faulting, and enhanced compliance due to abundant joints leads to folding and deformation asymmetry in the fault zone. Highly reactive mafic minerals likely become rapidly evolving fault rocks. In foliated metamorphic rocks, fault initiation style is strongly influenced by strength anisotropy relative to the principal stress directions, with fracturing favored when the foliation is aligned with the directions of principal stress. The continuity of micas within the foliation also influences the micromechanics of fault initiation. Brittle kink bands are an example of a strain-hardening precursory structure unique to foliated rock. Each of these fault initiation processes produces different initial fault geometry and spatial heterogeneity that influence such properties as fault permeability and seismogenesis. |
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Keywords: | Joints Granite Basalt Foliation Damage zone Kink band |
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