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An open‐system, two‐layer crustal stretching model for the Eastern Great Basin
Author(s) -
Gans Phillip B.
Publication year - 1987
Publication title -
tectonics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.465
H-Index - 134
eISSN - 1944-9194
pISSN - 0278-7407
DOI - 10.1029/tc006i001p00001
Subject(s) - geology , crust , basin and range topography , magmatism , basin and range province , extensional definition , volcanism , structural basin , cenozoic , seismology , plateau (mathematics) , petrology , tectonics , paleontology , mathematical analysis , mathematics
New geological and geophysical information from the eastern Great Basin sheds light on how Cenozoic extensional strain is partitioned throughout the crustal column and provides broad constraints on how much new material was added to the crust as a consequence of synextensional magmatism. The total amount of extension across the eastern half of the northern Basin and Range province is estimated to be 141 km or 77%, but varies dramatically on more local scales. Individual domains, several tens of kilometers across, have experienced supracrustal extensional strains that vary from 15% to 300%. Volcanism in this region initiated in the early Oligocene and has continued sporadically to the present. The major eruptions appear to be both temporally and spatially associated with large‐magnitude extension. A COCORP deep seismic reflection profile across the eastern Great Basin indicates a uniform present crustal thickness of 30 to 35 km. The preextensional crustal thickness is inferred to have tapered westward from the 40‐ to 45‐km thickness of the Colorado Plateau to a maximum of 50 km in the thickened root zone of the Sevier fold and thrust belt. Simple mass‐balance calculations employing the present and inferred preextensional crustal thicknesses together with the amount of extension suggest that approximately 5 km of the present crustal thickness was added to the crust during Cenozoic extension and magmatism. The lack of relief on the reflection Moho suggests that the crust as a whole may have stretched quite uniformly. A model for crustal stretching that incorporates a heterogeneously deforming (brittle) upper crust decoupled from a more uniformly deforming (ductile) middle and lower crust, together with a significant flux of mantle‐derived magmas into the crust, best explains the geological and geophysical observations from the eastern Great Basin. This open‐system, two layer stretching model has important thermal and mechanical implications and helps account for many of the enigmatic aspects of Cenozoic extension and magmatism in the western United States.