From Archean to Present: Field Trip to Montana/Wyoming, U.S.A

17th to 30th August

Dre Clementine Antoine, UNIGE Dre Renee Tamblyn, UNIBE Mme Lili Loth, UNIGE

Dre Clementine Antoine, UNIGE Pr Ilya Bideman, Professor, University of Oregon Geologist from the Stillwater Mine Mme Lili Loth, UNIGE Dre Renee Tamblyn, UNIBE

Studying Archean geology is a challenge in terms of sample availability as there are only few places where archean rocks remain and they underwent a lot of geological events. The Wyoming craton recorded almost 4 billion years of geological history. Some zircons found in quartzite are older than 3.6 billon years, making the Wyoming craton one of the oldest. Throughout the craton, we can retrace its history as well as the early Earth evolution. This region shows a complicated history of multiple deformation, contact, regional deformation, mafic to ultra-mafic archean complex, several episodes of igneous intrusion and modern volcanism. The purpose of this fieldtrip is to show the large diversity of Archean rocks hosted in the Wyoming craton and study metamorphism processes that occurred at this time and after. Two days in Ennis: Metamorphism on Madison River canyon. More than 1 kilometer long outcrop with bearing garnets paragneisses and migmatite. This canyon shows a diversity of metamorphism through the metasedimentary sequence. Metamorphism has been dated at 2.7 Ga, zircons of this sequence are soon-to-be dated. Two days in Nye: Stillwater Complex. Study of the famous mafic to ultra-mafic complex with a geologist from the Stillwater mine. Visit of the Stillwater mine to show how they extracted PGMs from this complex. 2 nights. One day in Alpine: Hiking near the Alpine lake to see different types of archean metamorphized rocks from the Wyoming craton: trondhjemite, granite, gneisses. 1 night. Four days in Red Lodge: • The Quad Creek outcrop presents an amazing diversity of archean rocks: trondhjemite, gneisses, quartzite, chromite, gabbros, peridotite. All these rockes are folded and really deformed. The point of working on this outcrop would be to study relationships between units and put it in perspective with the Wyoming craton, at a bigger scale. • Two days of hiking on the Hellroaring plateau to see the oldest gneisses of the Wyoming craton. 1 night camping up. • Driving on the scenic highway through the Beartooth Pass Vista kilometers scaled trondhjemite intrusion. Three days in Yellowstone: Study of Yellowstone and the 3 billion years that these place recorded from Archean rocks to Eocene magmatism related to subduction zone and finally to modern volcanism. Visit of a fossil site: Montana and Wyoming present large Cretaceous units with dinosaur fossils i

Montana (Beartooth mountain) and Wyoming (Yellowstone), USA

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