Effect Of Small-scale Heterogeneities On Interpretation Of Crustal Compositions Exemplified By A Layered Anorthosite

dc.creatorSemprich
dc.creatorJ.; Vrijmoed
dc.creatorJ. C.
dc.date2015-FEB
dc.date2016-06-07T13:37:00Z
dc.date2016-06-07T13:37:00Z
dc.date.accessioned2018-03-29T01:52:13Z
dc.date.available2018-03-29T01:52:13Z
dc.identifier
dc.identifierEffect Of Small-scale Heterogeneities On Interpretation Of Crustal Compositions Exemplified By A Layered Anorthosite. Elsevier Science Bv, v. 216, p. 298-314 FEB-2015.
dc.identifier0024-4937
dc.identifierWOS:000353851300021
dc.identifier10.1016/j.lithos.2014.12.019
dc.identifierhttp://www.sciencedirect.com/science/article/pii/S0024493715000043
dc.identifierhttp://repositorio.unicamp.br/jspui/handle/REPOSIP/244406
dc.identifier.urihttp://repositorioslatinoamericanos.uchile.cl/handle/2250/1308104
dc.descriptionFundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)
dc.descriptionThe composition of the lower crust has a significant effect on geodynamic processes because it influences physical rock properties such as densities and seismic velocities. Compositional differences in lower crustal rocks are potentially large and exist on the scales of centimeters up to kilometers resulting in non-unique seismic and gravity data. While larger heterogeneities can be detected as reflections on seismic profiles, irregular small-scale compositional variations are not likely to be discovered, but will influence the averaged seismic velocities and densities of an area. The extent and effects of such small-scale heterogeneities are explored on an exposed high-grade layered anorthositic body by providing a detailed field map, petrological descriptions, pycnometry measurements as well as whole rock and mineral analyses combined with thermodynamic phase equilibria calculations. To evaluate the results of our thermodynamic calculations, densities and mineral modes obtained from the modeled phase equilibria are compared to measured densities and estimated mineral modes from rock samples. The proportion of mafic to ultramafic (plagioclasepoor) rocks in the mapped field area amounts to 10-15% but higher proportions of these rock types in the lower crust are feasible. To further study the effects of compositional variations, we have generated mixtures of mafic to ultramafic and anorthositic/intermediate rocks until the average properties of these mixtures are comparable to those of mafic granulites (3000-3100 kg/m(3); 7.1-7.3 km/s). Mixtures of anorthosite with 40-45% and of tonalite with 50-60% high-grade mafic to ultramafic rocks yield average densities and seismic velocities similar to mafic granulites although they still contain 50-60 vol.% plagioclase. Hence small-scale mixing of certain rock types may result in the overestimation of the proportion of mafic (garnet) granulites in the lithologic interpretation of crustal compositions from seismic data. Since the transition to eclogite-facies in plagioclase-rich rocks is shifted to higher pressures and anorthositic/intermediate eclogites yield lower densities, a lower crust with higher modal amounts of plagioclase may not always provide the significant densification needed for certain geodynamic settings (e.g. delamination or subsidence). (C) 2015 Elsevier B.V. All rights reserved.
dc.description216
dc.description
dc.description
dc.description298
dc.description314
dc.descriptionNorwegian Research Council [175973]
dc.descriptionStatoil
dc.descriptionFundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)
dc.descriptionFundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)
dc.descriptionFAPESP [14/03334-0]
dc.description
dc.description
dc.description
dc.languageen
dc.publisherELSEVIER SCIENCE BV
dc.publisher
dc.publisherAMSTERDAM
dc.relationLITHOS
dc.rightsembargo
dc.sourceWOS
dc.subjectSedimentary Basin Underlain
dc.subjectSeismic Velocity Structure
dc.subjectWestern Gneiss Region
dc.subjectJotun-nappe-complex
dc.subjectContinental-crust
dc.subjectHigh-pressure
dc.subjectPhase-change
dc.subjectShear Zones
dc.subjectSw Norway
dc.subjectFennoscandian Shield
dc.titleEffect Of Small-scale Heterogeneities On Interpretation Of Crustal Compositions Exemplified By A Layered Anorthosite
dc.typeArtículos de revistas


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