Graphite in metasedimentary rocks on mount greylock, western massachusetts

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ACCESS The Williams College Libraries are investigating the posting of theses online, as well as their retention in hardcopy. ./ Williams College is granted permission to maintain and provide access to my thesis in hardcopy and via the Web both on and off campus. ::-ic!ecttD;; this work. allows rese[...]... have medium graphite concentrations Additionally, rocks where graphite only appears as inclusions in plagioclase grains are almost always low in graphite concentration One thin section, however, has graphite inclusions that are so dominant that the slide is rated as medium in graphite concentration, even though graphite does not appear in the matrix Conversely, some samples have graphite disseminated evenly... Fifty-one slides contain graphite as inclusions within plagioclase grains, but not within the matrix Graphite inclusions may be thin black traces cutting across a plagioclase grain, or the graphite may be so concentrated within the grain that it looks as if a formerly white plagioclase grain has been painted black with a thick paintbrush Graphite inclusions exist in plagioclase grains ranging in size from... attributes table contains all data collected in the field and in petrographic analysis This information includes strike and dip of cleavage, bedding, and/or lineations where applicable; lithologic category assigned in the field; graphite concentration in thin section; graphite distribution in thin section; 28 deformation fabric; and nature of plagioclase inclusions I added a final category in the attributes... crossed polars If graphite inclusions exist, they extend to the edge of the crystal without interruption Zoned plagioclase grains have two or more rings or zones that are optically distinct Zoned plagioclase grains with graphite inclusions have some graphite- free zones and some graphite- rich zones, so graphite inclusions do not extend to the edges of the crystal boundary (Figure 2.14 C) These zones are sometimes... across Grains with inclusions may be undeformed or highly fractured In some cases, graphite inclusions within plagioclase preserve relict fabrics, such as foliations, that do not exist in the matrix (Figure 2.15) Not all plagioclase grains contain graphite inclusions Twenty-two slides have graphite concentrated along cleavage planes (Figure 2.12 C) These slides may also have plagioclase grains with graphite. .. graphite- rich zones localize faulting, and metamorphic fluids are channeled along faults, precipitating graphite, and therefore increasing the original graphite concentration (Selverstone, 2005) 6 Other studies have addressed spatial correlations between faulting, metamorphism, and graphite, although few studies have gone into detail about the relationship among these Scientists studying the KTB borehole in Germany... or medium concentration A comparable relationship exists between zonal crenulation cleavage and low graphite concentrations 51 out of 57 slides with zonal cleavage have little or no graphite Slides characterized as scaly also tend to have low graphite concentrations Out of 33 scaly slides, 17 slides are low graphite, and 10 have no graphite; only one slide is high in graphite concentration and four... graphite are dominated by a large quartz vein that takes up most of the field ofthe slide Graphite is never included in a quartz vein or crystal, even in graphitic samples Many low concentration slides only have graphite as inclusions in plagioclase grains This is an aspect of graphite distribution, which will be discussed in detail below The majority of slides with little or no graphite contain chlorite,... surrounding rock Graphite and Fault Zones The relationship between graphite and faulting is intriguing On the one hand, a stratigraphically distinct bed of black shale might preferentially promote faulting because its carbon content makes it weak compared to surrounding sedimentary or igneous rocks In this scenario, faults would be localized along the weaker, carbon-rich beds, which would be baked into graphite- rich... dominate the slide (Figure 2.11 C) High indicates that graphite is pervasive and dominant (Figure 2.11 D) (2) Graphite distribution refers to where graphite is found in the slide: no graphite (Figure 2.12 A), graphite existing only as inclusions in plagioclase grains (Figure 2.12 B), graphite concentrated along cleavage planes (Figure 2.12 C), and graphite disseminated throughout the slide (Figure 2.12 . plagioclase zoning and map unit 60 Graphs comparing silicon content with titanium and zirconium content. 61 Graph comparing silicon content with carbon content 62 Graphs comparing carbon content with. difficult to identify in the field, and in schist and marble thin sections it varies along a continuum rather than existing only within specific formations. The precipitation model for graphite formation better. baked into graphite- rich rocks during metamorphism and faulting. The weak bonds between carbon molecules in graphite make graphitic rocks more likely to localize strain during deformation than non-graphitic