The Great Falls Tectonic Zone is a major intracontinental shear zone between the Hearne craton and Wyoming craton basement rock of the Archean Eon which form part of the North American continent. [1] [2] [3] [4] [5] The zone is an area about 100 miles (150 km) wide extending from the southwestern Idaho- Montana border across Montana to the northwestern Montana- Saskatchewan- North Dakota border. [4] [6] It is named for the Great Falls of the Missouri River, a major geologic feature of the area. The central and western portions of the zone are believed to be about 1.1 to 3.3 billion years old. [7] The central part of the zone lacks Archean rock, however, leading at least one group of scientists to speculate that it was formed very late in the Paleoproterozoic Era. [7]
The Great Falls tectonic zone has been periodically active since the Proterozoic, and possibly as late as the Holocene. [6] Little of the zone is visible due to Phanerozoic cover, the exception being the Little Belt Mountains. [2] However, it is believed that the tectonic zone controlled the geologic development of nearby basins and subbasins. [8]
The Great Falls tectonic zone was first identified in 1985. [4] Geologists originally believed the zone was part of the Wyoming craton, but now conclude that it is distinct from it. [2] There is continuing controversy over whether the region is a shear zone or suture, [1] [9] and the role the zone played in the formation of the North American continent. [2] At one time, both the Great Falls Tectonic Zone and the Vulcan structure were both considered sutures, but debate remains open on the point. [2] At least one group of geologists has concluded the zone represents the closure of an ocean basin. [2] The zone lacks gravity anomalies or electromagnetic signatures which would allow scientists to conclude that it was generated by subduction. [4] There is significant evidence that the zone has been periodically remineralized since Precambrian times. [10] Square Butte, Shaw Butte, Crown Butte and the other structures of the Adel Mountains Volcanic Field lie astride the tectonic zone near the city of Great Falls. [11]
The Great Falls Tectonic Zone is a major intracontinental shear zone between the Hearne craton and Wyoming craton basement rock of the Archean Eon which form part of the North American continent. [1] [2] [3] [4] [5] The zone is an area about 100 miles (150 km) wide extending from the southwestern Idaho- Montana border across Montana to the northwestern Montana- Saskatchewan- North Dakota border. [4] [6] It is named for the Great Falls of the Missouri River, a major geologic feature of the area. The central and western portions of the zone are believed to be about 1.1 to 3.3 billion years old. [7] The central part of the zone lacks Archean rock, however, leading at least one group of scientists to speculate that it was formed very late in the Paleoproterozoic Era. [7]
The Great Falls tectonic zone has been periodically active since the Proterozoic, and possibly as late as the Holocene. [6] Little of the zone is visible due to Phanerozoic cover, the exception being the Little Belt Mountains. [2] However, it is believed that the tectonic zone controlled the geologic development of nearby basins and subbasins. [8]
The Great Falls tectonic zone was first identified in 1985. [4] Geologists originally believed the zone was part of the Wyoming craton, but now conclude that it is distinct from it. [2] There is continuing controversy over whether the region is a shear zone or suture, [1] [9] and the role the zone played in the formation of the North American continent. [2] At one time, both the Great Falls Tectonic Zone and the Vulcan structure were both considered sutures, but debate remains open on the point. [2] At least one group of geologists has concluded the zone represents the closure of an ocean basin. [2] The zone lacks gravity anomalies or electromagnetic signatures which would allow scientists to conclude that it was generated by subduction. [4] There is significant evidence that the zone has been periodically remineralized since Precambrian times. [10] Square Butte, Shaw Butte, Crown Butte and the other structures of the Adel Mountains Volcanic Field lie astride the tectonic zone near the city of Great Falls. [11]