Sudbury Area Field Trip

✦ Outcrop of Sudbury Breccia, Sudbury ON, Canada. This unique textured breccia, also known as 'pseudotachylite', was produced by the giant meteorite impact that produced the Subdbury Complex 1849 million years ago. The breccia was formed when the shock wave produced by the impact granulated, fluidized, and partially melted the country rock surrounded and carried larger fragments of Archean granite to granodiorite. See research on impacts here. Photo by Steve Shirey

✦ Disposition of Archean provinces and early to mid-Paleoproterozoic orogenic belts in the North American Craton. Traces of geophysically distinctive blocks beneath cover in the west are from Ross et al. (1991). RMTF, Rocky Mountain thrust front; IF, southern limit of Innuitian folding; ASF, Appalachian structural front; TTTZ, Thelon-Taltson tectonic zone; MCR, Midcontinent rift. (Caption and figure from Davidson, A. (2008). Late Paleoproterozoic to mid-Neoproterozoic history of northern Laurentia: An overview of central Rodinia. Precambrian Research, 160, 5–22.)

Sudbury area on the North American Craton

The Sudbury area is located at the southwestern side of the Canadian Shield astride the geological boundary between the middle- to late- Archean Superior Province and the Proterozoic Grenville Province and just east of the Midcontinent Rift. The area is known most notably for the world's second largest meteorite impact 1849 million years ago which created the Sudbury Intrusive Complex (SIC). The SIC is a crustal intrusion of bulk granodioritic composition. It has enormous reserves of the elements Ni, Cu, Co, Pt, Pd, Au, and Ag locked up in the sulfide minerals of its basal layers which host numerous underground mines. The Creighton Ni Mine also hosts an underground, ultra-clean physics laboratory known as the Sudbury Neutrino Observatory (SNO) where important physics experiments requiring cosmic ray shielding are conducted. It was for the physicists and geologists of SNO that this local field guide was created.

✦ Geological detail of the geo-neutrino circle. Red lines show the major boundaries between Superior and Grenville terranes, green lines is extent of Paleozoic sedimentary cover rocks, black dashed line outlines Mid-Con@nent RiR (MCR) basalts and sediments. Prominent structural boundaries: Great Lakes Tectonic Zone (GLTZ), Ottawa-Bonnechere Structure (OBS; Sims et al. 1980), Kapuskasing Structural Zone (KSZ) and Grenville Front (GF). Geophysical traverses shown in blue (from Snyder and Grutter, 2009). Basemap geology is taken from the Geologic Map of North America (Reed et al., 2005). Yavapai, Mazatzal, and Grenville boundaries under Paleozoic cover are taken from Holm et al. (2007) and Van Schmus et al. (2007).

Geological Terrane Map

Geological terranes of the Archean and Proterozoic age rocks of the mid-continent region are shown at left. North of the green boundary between Phanerozoic cover rocks and the exposed Precambrian, the lavas and sediments of the 1100 million year old Midcontinent Rift, the Proterozoic para- and ortho- gneisses of the Grenville Province, and the granite-greenstone terranes of the Superior Province are exposed.

A 500 km radius circle outlines the sphere of rocks that would produce geoneutrinos that could be detected at the second generation Sudbury Neutrino Observatory (known as "SNO+"). While all rocks in this region might produce detectable geoneutrinos, it is chiefly the very high U and Th content granitic rocks of the nearby Wawa-Abitibi Terrane and their Huronian sedimentary cover that would produce the largest geoneutrino signal.

Field Trip Stops

Three full days of field stops, each day highlighting a distinctive geological terrane in the Sudbury area are shown on this map. Day 1 (blue stops) is devoted to examination of typical rocks of the Abitibi granite greenstone terrane. Day 2 (pink stops) is devoted to looking at the ricks that characterize the Sudbury Instrusive Complex and the nearby high grade metamorphic rocks of the Grenville Province. Day 3 (green stops) is devoted to examination of early- to middle- Proterozoic Huronian sedimentary rocks which show interesting U mobility and progressive oxidation of the atmosphere.

The fish-shaped outcrop pattern of the Sudbury Intrusive Complex can be seen clearly near the center of the figure.

✦ Field trip stops on the geologic map of Canadian Shield around Sudbury. Stops are number by day first and stop number second. Digital geological map courtesy John Ayer.

Geologic Field Trip Guide of the Geoneutrino-Producing Rocks of the Greater Sudbury Area

by John Ayer and Steven Shirey

SNO+_SudburyFieldGuide_Ayers_Shirey copy 2.pdf