T139 Zircon and Beyond: Quantitative Methods for Characterizing Provenance in Modern and Ancient Sediment Routing Systems

Monday, 23 September 2019
1:30 PM - 5:30 PM
Room 225AB, North Building

DETRITAL ZIRCON ANALYSIS OF LATE MISSISSIPPIAN-EARLY PENNSYLVANIAN SEDIMENTS AND IMPLICATIONS FOR THE RELIABILITY OF DOUBLE DATING IN PROVENANCE ANALYSIS IN THE CENTRAL US

Paper number: T139-12
Program: Technical Sessions
Time: 4:30 PM – 4:45 PM

Authors

Abstract

U-Pb and (U-Th)/He double dating of detrital zircons is a powerful tool for provenance analysis that provides both the crystallization age and cooling age of individual grains. Although such analyses may allow for identification of distinct U-Pb-He populations that can lead to refined provenance interpretations, the role of post-depositional hydrothermal events is seldom taken into consideration when interpreting results. This study focuses on double dating of five Upper Mississippian to Middle Pennsylvanian sandstones deposited within the Arkoma shelf and foreland basin, between the Ouachita orogenic front and world-class Mississippi Valley type (MVT) Pb-Zn districts in the Ozark region. (U-Th)/He analysis of 98 detrital zircon grains, with U-Pb ages corresponding to the Yavapai–Mazatzal (1800-1600 Ma), Midcontinent Granite–Rhyolite (1550-1300 Ma), Grenville (~1300–900 Ma) and Paleozoic (~500–350 Ma) age provinces, yields dates ranging from 202±16 Ma to 842±67 Ma, many of which (31-73%) are younger than the depositional ages of samples. Poor correlations between (U-Th)/He dates and effective U and measured grain widths suggest that neither radiation damage nor grain size are major factors controlling the anomalously young dates, and estimated maximum burial depths (< 3 km) of the sampled formations are too shallow to explain the He loss and reset ages. In contrast, homogenization temperatures, mineralization ages, and brine transport paths published for the MVT districts and adjacent carbonate and sandstone deposits fit well with the (U-Th)/He results. More than 90% of the (U-Th)/He dates fall into the late Paleozoic interval defined by MVT ore-formation ages, suggesting that the detrital zircon grains may have been partially to fully reset by these regional hydrothermal events after deposition. The results suggest the midcontinent could be a source of zircons with Devonian-Permian (U-Th)/He dates, but with variable U-Pb ages. The results have important implications for the application of double dating in orogenic systems and suggest that the potential effects of the regional hydrothermal systems, like those responsible for the formation of MVT Pb-Zn deposits, must be taken into consideration when interpreting datasets.

Geological Society of America Abstracts with Programs. Vol. 51, No. 5

doi: 10.1130/abs/2019AM-340383

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