The geochemistry and petrogenesis of the Paleoproterozoic Green 1 Mountain arc: a composite(?), bimodal, oceanic, fringing arc 2 Daniel S. Jones 1 , Calvin G. Barnes 2 , Wayne R. Premo 3 , Arthur W. Snoke 1 3 1 Department of Geology and Geophysics, University of Wyoming, Laramie, WY 82071, USA 4 2 Department of Geosciences, Texas Tech University, Lubbock TX, 79409, U.S.A. 5 3 U.S. Geological Survey, MS 963, Box 25046, Denver Federal Center, Denver, CO 80225, U.S.A. 6 7 Outline 8 Abstract ................................................................................................................................... 2 9 Introduction ............................................................................................................................ 3 10 Geological Setting.................................................................................................................... 4 11 Rock units ................................................................................................................................ 6 12 Green Mountain Formation ............................................................................................................. 8 13 Gabbro of Elkhorn Mountain ........................................................................................................... 9 14 Gabbro of Blackhall Mountain ......................................................................................................... 9 15 Blackhall Mountain area ..................................................................................................... 9 16 East Ridge ......................................................................................................................... 11 17 Big Creek Gneiss amphibolite............................................................................................ 11 18 Granodiorite of Coon Creek ........................................................................................................... 12 19 Analytical Procedures ............................................................................................................ 13 20 Results................................................................................................................................... 14 21 Big Creek Gneiss amphibolite ........................................................................................................ 14 22 Blackhall Mountain gabbro ............................................................................................................ 14 23 Equigranular and metaporphyritic samples ..................................................................... 14 24 Comparison with the Green Mountain Formation basalt ............................................................. 21 25 Coon Creek granodiorite ................................................................................................................ 22 26 Comparison with Green Mountain Formation felsic rocks ............................................................ 26 27 Discontinuity between the mafic and felsic rocks ......................................................................... 27 28 Nd isotope ratios............................................................................................................................ 27 29 U‐Pb Geochronology ...................................................................................................................... 29 30 Discussion ............................................................................................................................. 30 31 Origin of the mafic suite ................................................................................................................ 31 32 Crystallization conditions .................................................................................................. 31 33 Evidence for arc affinity .................................................................................................... 32 34 Could the subduction signature be inherited? .................................................................. 33 35 Origin of the coeval felsic rocks ..................................................................................................... 35 36 Relation to mafic rocks ..................................................................................................... 35 37 Crustal melting origin of the Coon Creek granodiorite ..................................................... 36 38 Origin of the Green Mountain Formation felsic magmas ................................................. 38 39