Abstract

Zircons from nine samples of the Sharon Conglomerate, a multi-cycle, quartzose sandstone and conglomerate, collected over a distance of 80 km in a NE-SW direction along the presumed direction of sediment transport, were studied to establish the nature and extent of variation in their physical properties. The ultimate aim was to quantify the characteristics of zircons in sedimentary rocks so as to provide a better base against which zircons in expected metasedimentary rocks might be compared. Mostly colorless, 20% of the zircons contain non-opaque inclusions, 18% exhibit extinction angles, and 7% are zoned. 89% of the zircons are rounded or subrounded; 9% are subhedral; and 2% are euhedral. Elongation histograms are right-skewed and typically bimodal. All mean elongations are less than 2.0. Volume histograms are right-skewed and polymodal. Correlation coefficients (for length and width) are extremely variable, most are low-positive, and several are negative. Reduced major axes vary considerably in slope, length, and Y-intercept. Multiple source areas and source rocks of the zircons are indicated by their variation in color, euhedrism, crystal habit, and reduced major axes and by their bimodal elongation histograms and polymodal volume histograms. Sedimentary (rather than igneous) parentage is indicated for a metamorphic rock if its zircons exhibit these variations and if they include some which possess extinction angles. The presence of negative correlation coefficients for zircon lengths and widths also suggests sedimentary parentage.

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