William Peck: Geology Research in the Adirondack Highlands

William Peck

Associate Professor of Geology; Chair of the Geology Department
Geology, 422 Ho Science Center
p 315-228-6798
Temperatures determined in this study, and regional isotherms from previous work.
Cathodoluminescence images of representative core/rim relations of detrital zircons and their metamorphic rims from the Irving Pond quartzite.

William Peck's Research: Thermometry and Metamorphic Mineral Growth in the Southern Adirondack Highlands

Quartzite outcrops on the shore of Irving Pond, southern Adirondacks
Supported in part by grant EAR-0106890 from the National Science Foundation

The Adirondack Highlands are an exposed section of the mid-crust that dates from 1.0-1.3 Billion years ago. This research focuses on constraining the metamorphic conditions that these rocks experienced by using the a variety of geochemical and petrologic tools.

The results of oxygen isotope thermometry in Adirondack quartzites yields metamorphic temperatures 700-800°C, consistent with granulite-facies mineral assemblages. Samples from the Irving Pond quartzite record D(Qtz-Grt)=2.58±0.58‰, corresponding to peak metamorphic conditions of 733±37°C. This agrees well with some new estimates from garnet-biotite exchange thermometry, and similar quartz-garnet temperatures are obtained from three other localities on the periphery of the Adirondack Highlands. All of these temperatures are higher than previous regional temperature estimates. Peak metamorphic temperatures are preserved in rocks with varying quartz:feldspar ratios and garnet sizes. Similar fractionations from all of these slowly-cooled rocks suggest slow rates of oxygen diffusion in quartz, feldspar, and garnet, consistent with the results of anhydrous diffusion experiments and low water fugacities in Adirondack quartzites. These results suggest low water activity in most (if not all) samples of this suite during cooling after metamorphism.

These quartzites contain detrital zircon with ubiquitous metamorphic overgrowths. Zircon cores are resorbed, preserve a variety of internal zoning styles and inclusions, and have ages of 1.3 to 2.7 Ga. Metamorphic overgrowths formed in the quartzites during the Shawinigan orogeny (1.20-1.14 Ga). The average volume of overgrowths has a positive correlation between zircon growth and melt productivity during metamorphism. Crystal-size distributions suggest zircon coarsening by the dissolution of small crystals and Zr transfer via a partial melt, and thus zircon overgrowths date anatexis. These results have implications for provenance studies, as dissolution of small zircons could bias age spectra of metasedimentary rocks.

Related References

(*indicates student author)

Peck, WH, McLelland, JM, Bickford, ME, *Nagle, AN, *Swarr, GJ, 2010, Mechanism of zircon overgrowth formation of a granulite-facies quartzite, Adirondack Highlands, Grenville Province, New York: American Mineralogist, v. 95, p. 1796-1806.

Peck, WH, and Valley, JW, 2004, Garnet-quartz oxygen isotope thermometry in the southern Adirondack Highlands (Grenville Province, New York): Journal of Metamorphic Geology, v. 22, p. 763-773

Peck, WH, and Valley, JW, 2003 Oxygen isotope thermometry of quartzites, southern Adirondack Highlands, Geological Society of America Abstracts with Programs, v.35, n. 7., p. 592.

Peck, WH, Valley, JW, and Graham, CM, 2003, Slow oxygen diffusion rates in igneous zircons from metamorphic rocks: American Mineralogist, v. 88, p. 1003-1014.