2014 GSA Annual Meeting in Vancouver, British Columbia (19–22 October 2014)

Paper No. 27-14
Presentation Time: 11:30 AM

THREE EPISODES OF VOLCANISM AND EROSION DURING NEOPROTEROZOIC EXTENSION IN EASTERN LAURENTIA REVEALED BY U-PB DATING OF ZIRCON FROM CLASTS OF RHYOLITE AND DETRITAL ZIRCON FROM SEDIMENTARY ROCKS OF THE MOUNT ROGERS FORMATION, SOUTHWEST VIRGINIA


HOLM-DENOMA, Christopher S., Central Mineral and Environmental Resources Science Center, United States Geological Survey, Box 25046, MS 973, Denver, CO 80225-0046, MCCLELLAN, Elizabeth, Department of Geology, Radford Univ, P.O. Box 6939, Radford, VA 24142 and SOUTHWORTH, Scott, U.S. Geological Survey, MS 926A National Center, Reston, VA 20192-0001

Laser ablation ICP-MS and ion-probe U-Pb geochronology of zircon from clasts of rhyolite and detrital zircon from sedimentary rocks of the Neoproterozoic Mount Rogers Formation (MRF) show evidence for three episodes of rift-related volcanism during early extension that led to the breakup of Rodinia.

Rocks of the area consist of Mesoproterozoic metagranitoid basement that are nonconformably overlain by Neoproterozoic metasedimentary and metavolcanic rocks (MRF), glaciogenic rocks of the Konnarock Formation (Zk), and locally, conglomerate of the Unicoi Formation. The lower MRF contains bimodal volcanic rocks interlayered with arkoses and polymict conglomerates containing pebble to boulder clasts of rhyolite, some granitoid, and minor quartz and sedimentary rocks. The upper MRF are rhyolite flows and pyro-volcaniclastic rocks.

Zircon U-Pb geochronology of ten clasts of rhyolite from the lower MRF yield ages (within error) of ~780-775 Ma (3 clasts), ~760 Ma (4 clasts), and ~753 Ma (3 clasts). Rhyolite flows of 760 and 753 Ma (U-Pb SHRIMP) comprise the upper MRF, however, the source of older rhyolite supports a more extensive volcanic field than is preserved.

Additionally, about 950 U-Pb detrital zircon analyses from ~20 samples of sedimentary rocks in the MRF and overlying glaciogenic rocks (Zk) have cumulative peak age populations at 1176, 1040, and 760 Ma, which were locally derived from Grenvillian basement and younger volcanic rocks.

About 190 detrital zircon analyses range from 800-700Ma with a primary peak age population of 760 Ma. Secondary peaks at ~780 and ~750 Ma correspond to the age of clasts of rhyolite.

The ages of rhyolite clasts and detrital zircons confirm that the rift-related volcanism of 755-750 Ma (existing U-Pb TIMS ages) was part of a system that began as early as ~780 and lasted ~30 my.

Session No. 27

T239. Precambrian Sedimentology: From the Field to the Laboratory I
Sunday, 19 October 2014: 8:00 AM-12:00 PM
204 (Vancouver Convention Centre-West)
Geological Society of America Abstracts with Programs. Vol. 46, No. 6, p.90
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