90 Precambrian Geology (Posters)

Monday, 5 November 2012
9:00 AM - 6:00 PM
Hall B

DETRITAL ZIRCON AGES FROM PART OF THE CENTRAL APPALACHIAN PIEDMONT, PENNSYLVANIA

Paper number: 90-5
Program: Technical Sessions
Time: 9:00 AM – 6:00 PM

Authors

Abstract

This study reports the results of new LA-ICPMS U-Pb detrital zircon ages from the Octoraro and Peters Creek meta-sedimentary units of the Central Appalachian Piedmont (CAP). The CAP has a long and complex geologic history including multiple episodes of mountain building, metamorphism, and continental rifting from the Precambrian to Paleozoic. Significant, post-Paleozoic erosion has exposed a portion of the crystalline core of the CAP. In comparison with the northern and southern Appalachian metamorphic belts, the CAP has a paucity of detailed and systematic studies of major meta-sedimentary units synthesizing detailed geologic mapping and modern geochemical and geochronological methods. Detailed geologic mapping of the CAP conducted over the last several years has helped to broaden our understanding of the structural relationships between major meta-sedimentary units. However, the provenance, chemistry, and crustal affinity of many of these units have remained nebulous.

Both the Octoraro and Peters Creek Formations yield primarily Mesoproterozoic to earliest Neoproterozoic ages (1480 – 930 Ma). The Octoraro Formation samples contained four grains from 1880 to 1800 Ma, seven grains with a range of 2780 – 2580 Ma, and a single grain at 575 Ma. The Octoraro Formation also contained the oldest single grain age of 2926 Ma. The Peters Creek Formation samples showed a broadly similar distribution with ten Archean age grains (2746 – 2518 Ma) and three grains from the latest Neoproterozoic (600 – 552 Ma). The Peters Creek differed from the Octoraro having a significant number of grains (< 25) that yielded Paleoproterozoic ages (1921 – 1602 Ma) with the largest peaks around 1630 Ma – ages not found in the Octoraro.

The age of the youngest zircons constrain the maximum age of both units to the latest Neoproterozoic. The dominant Mesoproterozoic to Neoproterozic ages are consistent with Laurentian sources and most likely coincide with pre-Grenvillian magmatism, Grenville orogenic events, and Catoctin rift-related magmatism. The Archean ages are most likely derived from Superior province type sources. The Paleoproterozoic ages found in the Peters Creek Formation are more problematic. The ~1630 Ma peak may be related to Granite-Rhyolite province and earlier Laurentian juvenile arc sources.