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| Titel |
The brittle-ductile transition in crystal- and bubble-bearing felsic magmas |
| VerfasserIn |
Mattia Pistone, Luca Caricchi, Peter Ulmer, Luigi Burlini |
| Konferenz |
EGU General Assembly 2010
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 12 (2010) |
| Datensatznummer |
250036820
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| Zusammenfassung |
| Torsion experiments at high temperatures (673-1023 K) and high pressure (200 MPa) were conducted using a HT-HP internally-heated Paterson-type rock deformation apparatus (Paterson and Olgaard, 2000) in order to investigate the brittle-ductile transition and, thus, the viscoelastic response of crystal- and bubble-bearing silicic melts while subjected to progressive deformation. The strain response of magma is critically dependent upon its viscosity and the magnitude and time-scale of the application or release of the stress (Dingwell, 1997); therefore, the response of magma may either be ductile or brittle.
The experimental results reveal a clear strain rate and temperature dependence of brittle-ductile behavior of deformed magmas. The failure onset divides the two different regimes (brittle and ductile) and corresponds to the failure of a hydrous crystal- and bubble-free haplogranitic melt at the glass transition temperature (673 K), considered as reference material. The samples deformed and fractured during the experiments are characterized by variable degrees of crystallinity (24-65 vol.%), but identical bubble contents (9-12 vol.%). Samples deformed at strain rates exceeding 5•10-4 s-1 are liable to fracture, with an apparent viscosity (ratio between the viscosity of the mixture and the viscosity of the pure melt phase) ranging between 10^9 and 10^12 Pa•s. Fractures are distributed according to an antithetic trend with respect to shear strain markers, they crashed quartz crystals and many of them even passed through gas-pressurized bubbles, where CO2-rich gas evidently prevented melt from closing the fractures under high confining pressure.
BIBLIOGRAPHY
Dingwell D.B. (1997). The brittle-ductile transition in high-level granitic magmas: material constraints. Journal of Petrology, 38 (12), 1635-1644.
Paterson M.S., Olgaard D.L. (2000). Rock deformation tests to large shear strains in torsion. Journal of Structural Geology 22, 1341-1358. |
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