Tectonothermal effects of mid- and upper-crustal magmatism

dc.contributor.advisorCloos, Mark
dc.creatorBeam, Eric Christopher, 1966-
dc.date.accessioned2019-03-11T15:57:59Z
dc.date.available2019-03-11T15:57:59Z
dc.date.issued1996
dc.description.abstractThis study considers the effects of the addition of heat and fluids to the earth's middle and upper crust by magmatism, as well as methods by which these effects may be distinguished in rock fabrics. A series of axisymmetric finite element transient heat conduction models were constructed to estimate crystallization rates, a proxy for fluid production. Crystallization rate varies from a high of ~80 km³/ky to a low of ~10 km³/ky. The shape of the crystallization rate histories is also highly variable, with thinner batholiths having high, sharp, early peaks. High fluid production rates will favor pooling of magmatic fluids in cupolas at the tops of stocks. In some cases this may trigger explosive eruptions, but in others could lead to economic mineralization. A computer program was written to simulate the formation of inclusion trails in porphyroblasts growing in deforming rocks. This program models synkinematic porphyroblast growth as a series of steps of growth and rotation. Resultant inclusion trails are complex. This complexity is a result of the variable relative rates of rotation of the inclusion and the cleavage. In some cases foliations are generated which could easily be interpreted as an included crenulation cleavage, other cases give an apparent sense of rotation opposite to the actual rotation. Theory describing the rotation of rigid inclusions is applied to biotite, garnet, and amphibole porphyroblasts in order to evaluate the sense of shear, magnitude of strain, and strain path (pure vs. simple shear) in deformed metamorphosed rocks adjacent to a tonalite sill in the Maclaren Glacier Metamorphic Belt (MGMB), south-central Alaska. Mean shear strains determined from biotite populations in thin sections range from γ = 2.4 to 3.3. Coupled temperature-displacement finite element models were constructed to simulate a cooling pluton in a zone of simple shear, using a realistic power law rheology. From these models it is clear that the thermal anomaly associated with a cooling pluton can concentrate deformation not just in the pluton, but into a laterally extensive zone running through the pluton. This may explain the deformation observed in the MGMB.en_US
dc.description.departmentEarth and Planetary Sciencesen_US
dc.format.mediumelectronicen_US
dc.identifier.urihttps://hdl.handle.net/2152/73578
dc.identifier.urihttp://dx.doi.org/10.26153/tsw/720
dc.language.isoengen_US
dc.relation.ispartofUT Electronic Theses and Dissertationsen_US
dc.rightsCopyright © is held by the author. Presentation of this material on the Libraries' web site by University Libraries, The University of Texas at Austin was made possible under a limited license grant from the author who has retained all copyrights in the works.en_US
dc.rights.restrictionOpenen_US
dc.subject.lcshMagmatism
dc.subject.lcshEarth (Planet)--Crust
dc.titleTectonothermal effects of mid- and upper-crustal magmatismen_US
dc.typeThesisen_US
dc.type.genreThesisen_US
thesis.degree.departmentGeological Sciencesen_US
thesis.degree.disciplineGeological Sciencesen_US
thesis.degree.grantorUniversity of Texas at Austinen_US
thesis.degree.levelDoctoralen_US
thesis.degree.nameDoctor of Philosophyen_US

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