Left-lateral intraplate deformation along the ancestral rocky mountains: Implications for late paleozoic plate motions
Abstract
North America underwent synchronous orogenic events during the late Paleozoic along its eastern margin (Alleghanian orogeny), southern margin (Ouachita orogeny), and within the southwestern part of the continent (Ancestral Rocky Mountain orogeny). All three orogenies were initiated in the late Mississippian to early Pennsylvanian, reached the greatest intensity in the middle Pennsylvanian, and ended in the early Permian. The Alleghanian and Ouachita orogenies have been related to the closing of the proto-Atlantic and the collision between North America and South America-Africa: it is here proposed that the Ancestral Rocky Mountains were produced by a collision between eastern North America and Africa. The Ancestral Rockies were formed as the result of reactivation of the Wichita megashear, a preexisting zone of weakness that extends from southern Oklahoma to eastern Utah. Previous plate tectonic models have implied that the megashear was a zone of right-lateral strike-slip faulting and north-northwest-directed compression. However, structural and stratigraphic data from Oklahoma and Texas suggest that the Wichita megashear was a major left-lateral fault zone formed under east-northeast-oriented compression. Palinspastic reconstruction of pre-mid-Devonian strata across the megashear in Texas indicates that 120 to 150 km of left slip occurred during the Desmoinesian (middle Pennsylvanian). The proposed plate tectonic model for the Ancestral Rocky Mountain orogeny includes: (1) movement of the North American plate eastward from a spreading center in the proto-Pacific;
(2) closing of the proto-Atlantic Ocean; (3) collision of North America-Europe (Laurussia) and South America-Africa (Gondwana) resulting in the Hercynian, Alleghanian, and Ouachita orogenies; (4) differential movement across the Wichita megashear and formation of a left-lateral strike-slip fault zone (Ancestral Rocky Mountain orogeny) as the result of east-west compression within the North American plate: (5) relative northward movement of Gondwana against Laurussia producing the Marathon and Arbuckle orogenies; and (6) development of a subduction zone to the west of the North American continent.- Publication:
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Tectonophysics
- Pub Date:
- December 1986
- DOI:
- 10.1016/0040-1951(86)90032-6
- Bibcode:
- 1986Tectp.132..195B