ILSG - Iron Mountain, 2018

We are planning a whole bunch of great trips for the 2018 meeting. Although nothing is guaranteed yet, here is a list of what we have so far to whet your apetite

Pre-Meeting trips

1. Archean and Paleoproterozoic geology of the Felch District, Central Dickinson County, Michigan

Tuesday May 15th, 2018
Leaders: William F. Cannon, Klaus J. Schulz, Robert A. Ayuso, and Tom Mroz

This trip examines the stratigraphy, structure, and economic geology of Precambrian rocks near the town of Felch in central Dickinson County of northern Michigan. Precambrian rocks range in age from Archean to Paleoproterozoic, and outliers of Cambrian sandstones are also widespread. Relationships along the basal Cambrian unconformity are included in the trip. Much of the interest in the area, both geologically and economically, has been focused on the Felch trough where Paleoproterozoic rocks of the Chocolay and Menominee groups form a complex syncline that is infolded and infaulted with Archean gneisses. Minor amounts of iron ore were produced in the early history of the area and a major concentrating-grade mine, the Groveland, was active in the 1960’s and 1970’s.

2. Hemlock Formation

Tuesday May 15th, 2018
Leaders: Tom Waggoner

This trip will examine the major rock types that make up the 1,874 Ma Paleoproterozoic Hemlock Formation. The ~10,000-meter thickness of the primarily tholeiitic basalt of the Hemlock is particularly rich in iron oxides and could easily have provided both the iron and silica incorporated in major portions of the Lake Superior Iron District. The first stop will examine the Lake Ellen Kimberlite, which intrudes the upper Hemlock and is the only easily accessible kimberlite in the Upper Peninsula Kimberlite District. The trip will also examine the differentiated West Kiernan Sill, which has a base-metal-rich differentiate near the lower section of the metagabbro sill and an upper transition zone where plagioclase approaches 80%, accompanied by significant titaniferous magnetite and apatite. Other stops will highlight volcanoclastic, amygdaloidal and pillowed basalts of the Hemlock, and examine the Mansfield iron-bearing slate member, one of the formation’s several areal restricted iron formations.

Post-meeting trips

3. Menominee Iron Range

Friday May 18th, 2018
Leaders: Tom Mroz and William F. Cannon

The field trip will look at the stratigraphy and structure of the Vulcan Iron-Formation and other rocks exposed in the southern part of Dickinson County, Michigan. Attendees will have the opportunity to observe metamorphic and deformational features in the Archean Carney Lake Gneiss, a large exposure of the basal Fern Creek conglomerate at Sturgeon Falls, and take a trip underground at the Iron Mountain Iron Mine to see the internal structure of the Traders iron-bearing, Brier slate, and Curry iron-bearing members of the Vulcan. The trip will also visit an example of the angular unconformity between Cambrian sandstone and the iron formation. Outcrop stops of the Hanbury and Brier slates, Sturgeon quartzite, and Randville dolomite expose many of the highly-folded structures and faulting related to the Penokean deformation of this sequence of sediments. New Archean age dates and access to recently exposed outcrops present an opportunity to see more detailed stratigraphy and structure than previously available, and show the complexity of deformation as the suture zone is approached to the south along the Niagara fault.

4. Granitoid rocks of the Pembine-Wausau Terrane in Northeastern Wisconsin

Friday May 18th, 2018
Leader: Klaus J. Schulz

In 1984 Paul Sims, Zell Peterman and Klaus Schulz led a ILSG field trip to the Dunbar gneiss-granitoid dome and adjacent areas in northeastern Wisconsin. The Dunbar dome is one of several domes in northern Wisconsin that have cores of gneiss, migmatite, and granitiod rocks and are mantled by metavolcanic and metasedimentary rocks. This trip will re-examine some of the stops from the 1984 trip but will also visit new stops. Outcrops will include the syn- to post-tectonic intrusions that comprise the Dunbar dome as well as older, arc-related intrusions, such as the Twelve Foot Falls quartz diorite, and younger intrusions, such as the Athelstane quartz monzonite and Yavapai-age Amberg granite. On the trip, we will discuss what the granitoid rocks tell us about the evolution of the Penokean orogen and what has been learned since 1984.

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