The long-term burial and exhumation history of basement blocks in the footwall of the Wasatch fault, Utah

Abstract

Thermochronologic studies of the Santaquin and Farmington Canyon crystalline basement complexes, exposed in the footwall of the Wasatch fault in Utah, provide rare opportunities to investigate the long-term tectonic, burial, and exhumation history of this region. Both complexes underwent amphibolite-facies metamorphism at ~1700 Ma, followed by a complex pressure-temperature-time history. By 740-770 Ma, exhumation had brought both complexes to the surface from a depth of 9-10 km (3-3.5 kbar), followed by reburial by passive margin, Oquirrh Basin, and foreland basin sedimentation from Neoproterozoic through early Cretaceous time.The final structural pathway to present-day surface exposure of both complexes began in early Cretaceous time, with crustal contraction along the Sevier belt and resultant structural stacking. Structural breaching of the thrust culminations and final cooling of the crystalline complexes occurred as a result of Tertiary through Holocene extension and accompanying normal faulting.Inferred exhumation rates for the last 10-15 my are on the order of 0.3-0.6 mm/yr, although recent slip rates across the Wasatch fault appear to be several times higher. This suggests that: (1) periods of enhanced slip on the Wasatch fault from Miocene to present time may have been punctuated by periods of quiescence; and (2) the fault now may be experiencing an episode of rapid slip. Alternatively, strain may have been partitioned into multiple fault strands at a boundary between the Provo and Nephi segments.

Paleoproterozoic evolution of the Farmington zone: Implications for terrane accretion in southwestern Laurentia

“…There is no evidence in these data to suggest any signifi cant, high-T metamorphic event subsequent to ca. 1.67 Ga, in agreement with Nelson et al (2009).…”

“…1.7 Ga). Nelson et al (2009) summarized the thermal history of these rocks and concluded that peak metamorphic conditions were reached sometime before 1.7 Ga (e.g., Barnett et al, 1993). Samples reported here were collected from the quartzite-gneiss-schist and migmatite map-units of Bryant (1988 Table S1 (see footnote 1).…”

Monazite, zircon, and garnet growth in migmatitic pelites as a record of metamorphism and partial melting in the East Humboldt Range, Nevada

“…For comparison, the footwall of the Wasatch fault, a large-scale notably active normal fault in central Utah, gives an average exhumation rate of 0.3-0.6 km/m.y. since 10-15 Ma (Nelson et al 2009). It appears likely that the exhumation pulses recorded by the studied samples were not accommodated exclusively by normal sense shearing, and that focused erosion and/or ductile thinning played a significant role.…”

A reassessment of Mojavia and a new Cheyenne Belt alignment in the eastern Great Basin

“…A weakly to nonfoliated mafi c syenite (postdating peak metamorphism) yielded highly correlated, but strongly discordant zircons with an upper intercept of 1673 ± 23 (2σ) Ma. 40 Ar/ 39 Ar ages of hornblende from amphibolite range from 1623 to 1657 Ma (Nelson et al, 2002;Kurt Constenius, 2005, personal on June 3, 2011 geosphere.gsapubs.org Downloaded from these ages using a new decay constant (Min et al, 2000) and updated ages for the fl ux monitors (MMhb-1 = 523.1 Ma; Fish Canyon sanidine = 28.201 Ma) produces a range from 1645 to 1679 Ma (Nelson et al, 2009). The upper end of this range of ages is concordant with U/Pb results in syenite.…”