Crystal fractionation in the friction melts of seismic faults (Alpine Fault, New Zealand) |
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| Authors: | Laurence N Warr Ben A van der Pluijm |
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| Institution: | aCentre de Géochimie de la Surface (CNRS-ULP), 1 rue Blessig, 67084-Strasbourg, France;bDepartment of Geological Sciences, The University of Michigan, Ann Arbor, MI 48109, USA |
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| Abstract: | Compositional variations are documented in friction melts along the Hari Hari section of the Alpine Fault, New Zealand, with multiple stages of melt injection into quartzo-feldspathic schists. Intermediate to felsic melts were heterogeneous in composition, but all fractions show a common trend, with a tendency for the younger melt layers and glasses to be more alkali − (Na + K) and Si-enriched, while being depleted in mafic (Fe + Mg + Mn) components. These changes are attributed primarily to crystal fractionation of the melt during transport. Farther traveled molten layers were on the whole less viscous, mostly due to a higher melt-to-clast ratio; however, compositional change, together with a decrease in volatile content, produced a progressively more viscous liquid melt with time. The glass phase is interpreted as a remnant of this high viscosity felsic residual melt that was preserved during final quenching. Following initial failure, the formation of largely phyllosilicate-derived, volatile-rich, lower viscosity melt corresponds with a phase of fault weakening. Subsequent rapid crystal fractionation during melt transport, the loss of volatiles and freezing of residual melt contributed to the strengthening of the fault during seismic slip. |
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| Keywords: | Pseudotachylyte Friction melting Crystal fractionation Glass Alpine Fault Lubrication |
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