UVM Theses and Dissertations
Format:
Print
Author:
Dyess, Patrick Gregory
Dept./Program:
Geology
Year:
2013
Degree:
MS
Abstract:
This thesis demonstrates that through the integration of petrology, microstructural analysis, cathodoluminescence imaging, Titanium in Quartz ("TitaniQ") thermobarometry and stability modeling one can identify and interpret trace element zoning within quartz to help quantify P-T-D histories of rocks in poly-deformed terranes. In addition, this multilateral approach shows the importance that foliation development plays in the geochemical recycling of quartz in metapelites.
This study uses the Rowe-Hawley Belts in central Vermont as a case study. Sampling was conducted along a structural transect from Rochester to Bethel, Vermont; incorporating a sequence of interbedded phyllites, quartzites, and calcic schists that have been exposed to both Taconic and Acadian deformation and metamorphism. Cathodoluminescence (CL) imaging on quartz was conducted to qualitatively assess [Ti] zoning wjthin grains to provide intracrystalline context to quantitative analysis. Microprobe spot analyses and X-ray mapping of garnet porphyroblasts was performed to estimate peak P-T conditions using P-T-X plots as well as gamet-biotite thermometry. Secondary ion mass spectrometry (SIMS) analyses were conducted to determine [Ti] for TitaniQ calculations due to low [Ti]-in-quartz (<10 ppm).
Results from this investigation indicate that quartz grains in different microstructural domains record five distinct portions of the P-T-D history. These major quartz equilibration stages are: 1) preservation of inherited detrital grains from high grade sources; 2) burial and pre-Taconic solution transfer and vein emplacement related to lithostatic loading and burial metamorphism; 3) quartz precipitation in S₂ microlithons as a result of solution transfer related to the development of Taconic S₂ schistosity and compositional banding; 4) further precipitation during continued fabric development during isobaric heating following Taconic crustal thickening; and 5) further solution transfer during the development of Acadian S₃ crenulation cleavage development prior to Acadian peak metamorphism.
This study uses the Rowe-Hawley Belts in central Vermont as a case study. Sampling was conducted along a structural transect from Rochester to Bethel, Vermont; incorporating a sequence of interbedded phyllites, quartzites, and calcic schists that have been exposed to both Taconic and Acadian deformation and metamorphism. Cathodoluminescence (CL) imaging on quartz was conducted to qualitatively assess [Ti] zoning wjthin grains to provide intracrystalline context to quantitative analysis. Microprobe spot analyses and X-ray mapping of garnet porphyroblasts was performed to estimate peak P-T conditions using P-T-X plots as well as gamet-biotite thermometry. Secondary ion mass spectrometry (SIMS) analyses were conducted to determine [Ti] for TitaniQ calculations due to low [Ti]-in-quartz (<10 ppm).
Results from this investigation indicate that quartz grains in different microstructural domains record five distinct portions of the P-T-D history. These major quartz equilibration stages are: 1) preservation of inherited detrital grains from high grade sources; 2) burial and pre-Taconic solution transfer and vein emplacement related to lithostatic loading and burial metamorphism; 3) quartz precipitation in S₂ microlithons as a result of solution transfer related to the development of Taconic S₂ schistosity and compositional banding; 4) further precipitation during continued fabric development during isobaric heating following Taconic crustal thickening; and 5) further solution transfer during the development of Acadian S₃ crenulation cleavage development prior to Acadian peak metamorphism.