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| Titel |
Elastic geobarometry and the role of brittle failure on pressure release |
| VerfasserIn |
Mattia Luca Mazzucchelli, Ross John Angel, Greta Rustioni, Sula Milani, Paolo Nimis, Maria Chiara Domeneghetti, Federica Marone, Jeff W. Harris, Fabrizio Nestola, Matteo Alvaro |
| Konferenz |
EGU General Assembly 2016
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| Medientyp |
Artikel
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| Sprache |
en
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 18 (2016) |
| Datensatznummer |
250133006
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| Publikation (Nr.) |
 EGU/EGU2016-13569.pdf |
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| Zusammenfassung |
| Mineral inclusions trapped in their hosts can provide fundamental information about
geological processes. Recent developments in elastic geobarometry, for example, allow the
retrieval of encapsulation pressures for host-inclusion pairs. In principle this method can be
applied to any mineral-mineral pair so long as both the residual pressure on an inclusion
(Pinc), and the equations of state for both host and inclusion are either known or
determined (Angel et al., 2015). However, Angel et al. (2014) outlined some boundary
conditions, one of which was that deformation in the host-inclusion pair has to be
purely elastic. Thus this caveat would exclude from analysis all the inclusions that
are surrounded by cracks, indicative of brittle deformation, which may result in
partial or complete release of the Pinc. If however the effects of cracks surrounding
trapped mineral inclusions could be quantitatively modelled, then the applicability of
“elastic” geobarometry might be extended to a much larger number of inclusion-host
pairs.
We report the results of a pilot experiment in which the stress states (i.e. the residual
pressure) have been determined for 10 olivine inclusions still entrapped in 5 diamonds.
Inclusion pressures were determined from the unit-cell volumes of the olivines measured
in-situ in the diamonds by X-ray diffraction. The olivine equations of state were determined
from the olivine compositions by in-situ X-ray structure refinement. Values of Pinc range
from 0.19 to 0.53 GPa. In order to quantify the degree of brittle failure surrounding the
inclusions, the same set of samples were also investigated by synchrotron X-ray
micro-tomography (SRXTM at TOMCAT, Swiss LightSource). Preliminary results showed
that at the spatial resolution of our experiments (pixel size of 0.34μm), 90% of the inclusions
trapped in our set of diamonds were surrounded by cracks. The volume of the cracks has
been determined from 3D reconstruction with an accuracy of about 4%. Our results
show that crack intensity increases with increase in inclusion size. In addition, the
residual pressure decreases with increasing inclusion volume (i.e. with increasing
brittle deformation). However, the actual release in pressure can only be estimated
knowing the composition and thus the exact equation of state of the infillings of the
cracks.
This work is supported by ERC starting grant 307322 to Fabrizio Nestola and by the
MIUR-SIR grant “MILE DEEp” (RBSI140351) to M. Alvaro.
References
Angel, R.J., Mazzucchelli, M.L., Alvaro, M., Nimis, P., and Nestola, F. (2014) Am
Mineral, 99, 2146-2149
Angel R.J., Nimis P., Mazzucchelli M. L., Alvaro M., Nestola F., (2015) J. Metamorph.
Geol. 33, 801–813. |
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