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Rcrust : a tool for calculating path-dependent open system processes and application to melt loss
ENGLISH ABSTRACT: Earth‘s continental crust is stabilised by crustal differentiation that is driven by partial melting and melt loss: Magmas segregate from their residuum and migrate into the upper crust, leaving the deep crust refractory. Thus, compositional change is an integral part of the met...
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| Format: | Thesis |
| Language: | en_ZA |
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Stellenbosch : Stellenbosch University
2016
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| Summary: | ENGLISH ABSTRACT: Earth‘s continental crust is stabilised by crustal differentiation that is driven by partial
melting and melt loss: Magmas segregate from their residuum and migrate into the upper
crust, leaving the deep crust refractory. Thus, compositional change is an integral part of the
metamorphic evolution of anatectic granulites. Current thermodynamic modelling
techniques have limited abilities to handle changing bulk composition. New software is
developed (Rcrust) that via a path-dependent iteration approach enables pressure,
temperature and bulk composition to act as simultaneous variables. Path-dependence allows
phase additions or extractions that will alter the effective bulk composition of the system.
This new methodology leads to a host of additional investigative tools. Singular paths within
Pressure-Temperature-Bulk composition (P-T-X) space give details of changing phase
proportions and compositions during the anatectic process, while compilations of paths
create path-dependent P-T mode diagrams. A case study is used to investigate the effects of
melt loss in an open system for a pelite starting bulk composition. The study is expanded
upon by considering multiple P-T paths and considering the effects of a lower melt
threshold. It is found that, for the pelite starting composition under investigation, open
systems produce less melt than closed systems and that melt loss prior to decompression
drastically reduces the ability of the system to from melt upon decompression. |
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