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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
1

Quantitative petrographic investigations of porphyritic rhyolitic laccoliths of the Halle Volcanic Complex, Germany

Mock, Alexander 13 July 2009 (has links) (PDF)
Felsic phenocrysts of the laccoliths have straight size distributions (characteristic lengths 3.4 to 36 mm) and R-values from 1.34 to 0.78 (randomly distributed, no touching frameworks). Laccoliths have crystallinities from 10 to 30%. Textural coarsening possibly played a role in crystallization history. Serial sectioning reveals true shapes, sizes and three dimensional size distributions, non-touching frameworks, aspect ratios from 1.7:1.5:1 to 8.7:1.9:1 and a minimum sampling size of ~200 crystals. Different textural varieties develop late in system evolution and differed in density (~1%), viscosity and, thus, level of emplacement. Phenocryst populations formed on a timescale between 10 days and 2000 years, growth during emplacement is negligible. Models for filling and cooling of laccoliths suggest timescales from few 100 to ~20000 years. Contacts of laccoliths appear brecciated and sometimes show intercalation of magma and host sediment under ductile deformation. Dimensions of laccoliths plot in the field for such intrusions on a logarithmic width vs. thickness plot. Laccoliths intruded as distinct magma batches. More laccoliths than recognised before can be distinguished. Comparing felsic laccolith complexes in Late Palaeozoic transtensional basins, gives rise to new types of laccolith complexes termed Donnersberg and Halle type.
2

Quantitative petrographic investigations of porphyritic rhyolitic laccoliths of the Halle Volcanic Complex, Germany

Mock, Alexander 02 July 2004 (has links)
Felsic phenocrysts of the laccoliths have straight size distributions (characteristic lengths 3.4 to 36 mm) and R-values from 1.34 to 0.78 (randomly distributed, no touching frameworks). Laccoliths have crystallinities from 10 to 30%. Textural coarsening possibly played a role in crystallization history. Serial sectioning reveals true shapes, sizes and three dimensional size distributions, non-touching frameworks, aspect ratios from 1.7:1.5:1 to 8.7:1.9:1 and a minimum sampling size of ~200 crystals. Different textural varieties develop late in system evolution and differed in density (~1%), viscosity and, thus, level of emplacement. Phenocryst populations formed on a timescale between 10 days and 2000 years, growth during emplacement is negligible. Models for filling and cooling of laccoliths suggest timescales from few 100 to ~20000 years. Contacts of laccoliths appear brecciated and sometimes show intercalation of magma and host sediment under ductile deformation. Dimensions of laccoliths plot in the field for such intrusions on a logarithmic width vs. thickness plot. Laccoliths intruded as distinct magma batches. More laccoliths than recognised before can be distinguished. Comparing felsic laccolith complexes in Late Palaeozoic transtensional basins, gives rise to new types of laccolith complexes termed Donnersberg and Halle type.

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