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Fluid-enhanced low-temperature plasticity of calcite marble; microstructures and mechanisms

Liu Junlai, Jens M. Walter and Klaus Weber
Fluid-enhanced low-temperature plasticity of calcite marble; microstructures and mechanisms
Geology (Boulder) (September 2002) 30 (9): 787-790


Postmetamorphic carbonate fault rocks from the Damara orogen, Namibia, show the following features: (1) obvious contrasts between centimeter-scale grains in the clasts and nanometer- to micrometer-scale grains in the matrix, and between macroscopic cataclastic and microscopic mylonitic microstructures; (2) coexistence of tangled dislocations and organized dislocation walls; (3) occurrence of subgrains along margins of clasts and their transition into dynamically recrystallized grains in the matrix; and (4) new grains in grain sizes of a few nanometers to 3 mu m in diameter. The coexistence of brittle and ductile microstructures is attributed to comprehensive intragranular twinning, and kinking, fracturing, and subsequent dislocation remobilization or reorganization and recrystallization. Fracturing is triggered by dislocation pileups due to dynamic loading, twinning, and kinking. It also generates free dislocations and tangled dislocations. Fractures provide fluid paths, increase fluid-rock interfaces, and enhance the possibility of fluid-rock interaction. Fracturing is subsequently accommodated by low-temperature plasticity that is attributed to hydrolytic weakening, i.e., fluid-enhanced recovery and dynamic recrystallization due to the infiltration of fluids into the deforming grains. During hydrolytic weakening, remobilized free dislocations and tangled dislocations climb toward incoherent boundary-like fractures. The dislocations are reorganized into dislocation walls that commonly constitute parts of subgrains developing into new grains. We conclude that: (1) fluids may increase the rate of dislocation glide and dislocation climb and may also enhance the recovery of strain-hardened rocks to accommodate fracturing processes in calcite marbles at low temperatures; and (2) calcite marble may have low-temperature plasticity and may undergo crystal plastic deformation due to hydrolytic weakening at shallow crustal levels.

ISSN: 0091-7613
EISSN: 1943-2682
Serial Title: Geology (Boulder)
Serial Volume: 30
Serial Issue: 9
Title: Fluid-enhanced low-temperature plasticity of calcite marble; microstructures and mechanisms
Affiliation: Jilin University, Department of Geology, Changchun, China
Pages: 787-790
Published: 200209
Text Language: English
Publisher: Geological Society of America (GSA), Boulder, CO, United States
References: 38
Accession Number: 2002-067193
Categories: Structural geologyIgneous and metamorphic petrology
Document Type: Serial
Bibliographic Level: Analytic
Annotation: With GSA Data Repository Item 2002090
Illustration Description: illus.
S29°00'00" - S16°40'00", E11°30'00" - E25°15'00"
Secondary Affiliation: Georg-August-Universitaet Goettingen, Geowissenschaftliches Zentrum, DEU, Federal Republic of Germany
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2019, American Geosciences Institute. Reference includes data supplied by the Geological Society of America, Boulder, CO, United States
Update Code: 200221
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