Signs from the Precambrian: The geologic framework of Rocky Mountain region derived from aeromagnetic data

Finn, Carol A.; Sims, P.K.

doi:10.1029/154gm04

Cited by 14 publications

(15 citation statements)

References 66 publications

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“…Extrapolation of contacts and structural trends into areas covered by Phanerozoic sedimentary rocks (~90% of the continental U.S.) is aided by interpretation of aeromagnetic data (North American Magnetic Anomaly Group, 2002). Aeromagnetic maps have been used in the interpretation of basement lithotypes and structure, including the western United States (e.g., Lidiak, 1974;Ramberg and Smithson, 1975;Cordell and Grauch, 1985;Finn et al, 2001;Sims and Stein, 2003;Grauch et al, 2003;Finn and Sims, 2005), Canada (e.g., Pilkington et al, 2000;Ross et al, 1991), Australia (e.g., Gunn et al, 1997), and elsewhere (e.g., Henkel, 1991).…”

Section: Methodsmentioning

confidence: 99%

“…Magnetic intensities refl ect distribution of magnetite and other iron-bearing minerals in the crust. Sedimentary strata generally have little magnetic character and are transparent in regional aeromagnetic mapping (Finn and Sims, 2005). Large Cenozoic volcanic fi elds can obscure magnetic patterns in the basement, but for much of the western United States, Cenozoic volcanics tend to have short-wavelength anomalies related to known vent areas and fl ows such that the generally more persistent basement magnetic fabric is still decipherable.…”

Section: Methodsmentioning

confidence: 99%

“…Large Cenozoic volcanic fi elds can obscure magnetic patterns in the basement, but for much of the western United States, Cenozoic volcanics tend to have short-wavelength anomalies related to known vent areas and fl ows such that the generally more persistent basement magnetic fabric is still decipherable. In areas where there are outcrops (e.g., Rocky Mountains), granite and granodiorite plutons often are characterized by relatively high amplitude magnetic highs (20-200 nT), and this character has been used to extrapolate the contacts of plutons into covered areas Finn and Sims, 2005). In the southern Rocky Mountains, long-wavelength (>50 km), high-amplitude (>500 nT above base values) magnetic anomalies commonly correspond to 1.4 Ga plutons (Finn and Sims, 2005).…”

Section: Methodsmentioning

confidence: 99%

“…In areas where there are outcrops (e.g., Rocky Mountains), granite and granodiorite plutons often are characterized by relatively high amplitude magnetic highs (20-200 nT), and this character has been used to extrapolate the contacts of plutons into covered areas Finn and Sims, 2005). In the southern Rocky Mountains, long-wavelength (>50 km), high-amplitude (>500 nT above base values) magnetic anomalies commonly correspond to 1.4 Ga plutons (Finn and Sims, 2005). In this paper, this has been invoked for interpretations of the distribution and large areal extent of granitoid plutons in the mid-continent (Fig.…”

Section: Methodsmentioning

confidence: 99%

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2007

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This paper presents a plate-scale model for the Precambrian growth and evolution of the North American continent. The core of the North American continent (Canadian shield) came together in the Paleoproterozoic (2.0-1.8 Ga) by plate collisions of Archean continents (Slave with Rae-Hearne, then Rae-Hearne with Superior) as well as smaller Archean continental fragments (Wyoming, Medicine Hat, Sask, Marshfi eld, Nain cratons). The resulting Trans-Hudson orogen was a collisional belt similar in scale to the modern Himalayas. It contains mainly reworked Archean crust, but remnants of juvenile volcanic belts are preserved between Archean masses. The thick, buoyant, and compositionally depleted mantle lithosphere that now underlies North America, although dominantly of Archean age, took its present shape by processes of collisional orogenesis and likely has a scale of mantle heterogeneity similar to that exhibited in the overlying crust.In marked contrast, lithosphere of southern North America (much of the conti nental United States) was built by progressive addition of a series of dominantly juvenile vol canic arcs and oceanic terranes accreted along a long-lived southern (present coordinates) plate margin. Early juvenile additions ( Pembine-Wausau, Elves Chasm arcs) formed at the same time (1.84-1.82 Ga) the core was assembling. Following fi nal assembly of the Archean and Paleoproterozoic core of North America by 1.8 Ga, major accretionary provinces (defi ned mainly by isotopic model ages) were added by arc-continent accretion, analogous to present-day convergence between Australia and Indonesia. Also similar to Indonesia, some accreted terranes contain older continental crustal material [Archean(?) Mojavia], but the extent and geometry of older crust are not well known. Accretion-ary provinces are composed of numerous 10 to 100 km scale terranes or blocks, separated by shear zones, some of which had compound histories as terrane sutures and later crustalassembly structures. Major northeast-trending provinces are the Yavapai province (1.80-1.70 Ga), welded to North America during the 1.71-1.68 Ga Yavapai orogeny; the Mazatzal province (1.70-1.65 Ga), added during the 1.65-1.60 Ga Mazatzal orogeny; the Granite-Rhyolite province (1.50-1.30 Ga), added during the 1.45-1.30 Ga tectonic event associated with A-type intracratonic magmatism; and the Llano-Grenville province (1.30-1.00 Ga), added during the 1.30-0.95 Ga broader Grenville orogeny. During each episode of addition of juvenile lithosphere, the transformation of juvenile crust into stable continental lithosphere was facilitated by voluminous granitoid plutonism that stitched new and existing orogenic boundaries. Slab roll back created transient extensional basins (1.70 and 1.65 Ga) in which Paleoproterozoic quartziterhyolite successions were deposited, then thrust imbricated as basins were inverted.The lithospheric collage that formed from dominantly juvenile terrane accretion and stabilization (1.8-1.0 Ga) makes up about half of the present-day North American con...

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Section: Methodsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

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2007

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“…Aeromagnetic mapping of the Archean basement shows a contact between highly magnetic granitic rocks and weakly magnetic gneisses along the western margin of the uplift (Finn and Sims, 2005). However, gravity data for the Rock Springs uplift do not appear to support the concept of reactivation of an older basement structure (Mederos et al, 2005).…”

Section: Reactivation Of Precambrian Structuresmentioning

confidence: 94%

Concurrent growth of uplifts with dissimilar orientations in the southern Green River Basin, Wyoming: Implications for Paleocene-Eocene patterns of foreland shortening

Johnson

Andersen

2009

Rocky Mountain Geology

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The diverse orientations of Precambrian-involved and fault-bounded uplifts in the Rocky Mountain foreland region seem difficult to reconcile with the inferred Paleocene-Eocene shortening direction and plate convergence. Some have hypothesized that the shortening direction rotated as much as 90° over time, whereas others have hypothesized a relatively stable strain field involving concurrent oblique slip on faults with varied strikes.The stratigraphic thicknesses of the synorogenic Paleocene-Eocene Fort Union, Wasatch, and Green River Formations in the southern Green River Basin of Wyoming are used here to define the pattern of basin subsidence and to interpret the timing of movement on two contractional structures with contrasting orientations. Isopach maps and cross sections of three sequential time-stratigraphic intervals show thinning around the north-south-oriented Rock Springs uplift and regional southward thickening of these three stratigraphic intervals. The southward thickening evidently resulted from flexural subsidence in response to loading from the adjacent east-west-oriented Uinta uplift. Stratigraphic thinning in the vicinity of the Rock Springs uplift demonstrates that growth of the underlying blind thrust system produced an area of comparatively low accommodation space within the subsiding Green River Basin.The concurrent growth of the Rock Springs and Uinta uplifts does not support a rotation of shortening direction from east-west to north-south. The margin of a Neoproterozoic rift basin may have controlled the orientation of the thrust faults bounding the north flank of the Uinta uplift, and Late Cretaceous-throughEocene contraction caused oblique slip on these faults during structural inversion. A north-south-striking blind reverse fault underlies the west flank of the Rock Springs uplift, but Phanerozoic strata cover the Precambrian core of the uplift, so the structure within the Archean basement rocks is unknown. Despite contrasting strikes and different structural histories, the Uinta and Rock Springs uplifts responded concurrently to northeast-southwest-to east-northeast-west-southwest-directed shortening.

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Crustal velocity structure associated with the eastern Tennessee seismic zone: Vp and Vs images based upon local earthquake tomography

et al. 2014

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We present three-dimensional P and S wave velocity models for the active eastern Tennessee seismic zone (ETSZ) using arrival time data from more than 1000 local earthquakes. A nonlinear tomography method is used that involves sequential inversion for model and hypocenter parameters. We image several velocity anomalies that persist through most of the inversion volume. Some anomalies support the presence of known features such as an ancient rift zone in northern Tennessee. Other anomalies reveal the presence of basement features that can be correlated with regional gravity and magnetic anomalies. We image a narrow, NE-SW trending, steeply dipping zone of low velocities that extends to a depth of at least 24 km and is associated with the vertical projection of the prominent New York-Alabama magnetic lineament. The low-velocity zone may have an apparent dip to the SE at depths exceeding 15 km. The low-velocity zone is interpreted as a major basement fault juxtaposing Granite-Rhyolite basement to the NW from Grenville southern Appalachian basement to the SE. Relocated hypocenters align in near-vertical segments suggesting reactivation of a distributed zone of deformation associated with a major strike-slip fault. We suggest that the ETSZ represents reactivation of an ancient shear zone established during formation of the super continent Rodinia.

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Signs from the Precambrian: The geologic framework of Rocky Mountain region derived from aeromagnetic data

Cited by 14 publications

References 66 publications

Untitled

Untitled

Concurrent growth of uplifts with dissimilar orientations in the southern Green River Basin, Wyoming: Implications for Paleocene-Eocene patterns of foreland shortening

Crustal velocity structure associated with the eastern Tennessee seismic zone: Vp and Vs images based upon local earthquake tomography

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