An experimental study on semi-brittle and plastic rheology of Panzhihua gabbro |
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Authors: | Email author" target="_blank">Changrong?HeEmail author Yongsheng?Zhou Zunan?Sang |
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Institution: | 1. Institute of Geology and Laboratory of Tectonophysics, China Seismological Bureau, Beijing 100029, China 2. Institute of Geology and Laboratory of Tectonophysics, China Seismological Bureau, Beijing 100029, China; College of Management, China University of Geosciences, Wuhan 430074, China |
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Abstract: | We have carried out a systematic experimental study on semi-brittle and plastic deformation of fine-grained Panzhihua gabbro
under dry condition with temperature range of 700–1100 °C, confining pressure of 450–500 MPa, and strain rate of 1 × 10-4-3.1 × 10-6 s-1, using a triaxial testing system with a Griggs type solid medium pressure vessel. In terms of the parameters in the flow
law and microstructure after deformation, the rate-dependent deformation can be categorized into three modes: (i) In temperature
range of 700–800°C, the deformation is accommodated by semi-brittle flow, with activation energy Q = 612 ± 12 kJ/mol, and
stress exponent n = 14.6. The deformation in microscopic scale corresponds to the dislocation glide accompanied with microfracturing. (ii)
In temperature range of 90–950°C, the predominant deformation mechanisms in this phase are mechanical twinning and dislocation
glide, with activation energy Q =720 ± 61 kJ/mol, and stress exponent n = 6.4. (iii) In temperature range of 1000–1150°C, the major deformation mechanisms are dislocation glide and dislocation
climb with minor processes of partial melting, with activation energy Q = 699 ± 55 kJ/mol and stress exponent n = 4.1. The microstructure and deformation mechanism of our experiments are comparable to the results of clinopyroxene and
diabase as observed in previous studies. The flow stress of a mafic lower crust is calculated based on the rheological parameters
of dry fine-grained gabbro, which implies that a lower curst with mafic granulite may be brittle, and it is possible to fracture
and produce frictional slips. This may be an important implication for earthquake nucleation in the lower crust. |
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Keywords: | semi-brittle and plastic rheology reological parameters deformation mechanism gabbro |
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