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Structurally Concordant Relationship Between Lower Keweenawan
Precambrian Geology of the Lake Superior District
11 other sections not shown
age dates Aldrich amygdules appears Archean rocks base Bessemer Formation Bessemer Quartzite biotite calcite chemical analyses chert chlorite clinopyroxene commonly contact metamorphic contact metamorphic zone Copper Harbor Conglomerate cross-bedding deposition diabase dikes Duluth Gabbro epidote exposed exposure feet thick feldspar Felmlee Figure fine-grained flows of Unit Freda Sandstone gabbro body geologic Gogebic Range granite gray graywacke graywacke beds Hise and Leith hornfels inches indicate interbedded intrusion Ironwood Formation Keweenaw fault Keweenawan rocks Keweenawan volcanic rocks Lake Superior Lake Superior area Lake Superior district lava flows locally Lower Keweenawan sedimentary mafic magnetite Mellen Gabbro Complex Michigan Middle Keweenawan volcanic minerals Montreal River muscovite Nonesuch Shale northwest Oronto Group Outcrop overlying pebbles Penokean Orogeny phenocrysts plagioclase plagioclase feldspar plot Precambrian primary structures quartz quartzite radiogenic rock types sedimentary rocks sediments Sibley Series siltstone structurally concordant subalkaline texture thin sections Tyler Formation unconformably Upper Keweenawan volcanic flows Wisconsin