Proterozoic accretionary tectonics at the southern margin of the Archean Wyoming craton

Duebendorfer, Ernest M.; Houston, Robert S.

doi:10.1130/0016-7606(1987)98<554:patats>2.0.co;2

Cited by 92 publications

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“…The boundary of the Archean Wyoming Province in the western United States is considered to be an accretionary [PT] I Now at the Alfred Wegener Institute for Polar and Marine Research, Postfach 120161, D-27515 Bremerhaven, Germany feature of a collision between a Proterozoic island arc and the Archean terrane in southeastern Wyoming [1][2][3][4][5][6]. Questions that remain open include the structure and composition of the midcrustal and lower crustal rocks and the character of the crust-mantle boundary of the deep crust of the Proterozoic belt south of the suture (Cheyenne Belt).…”

Section: Introductionmentioning

confidence: 99%

Seismic wide-angle study of accreted Proterozoic crust in southeastern Wyoming

Gohl

Smithson

1994

Earth and Planetary Science Letters

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A seismic wide-angle experiment was conducted in southeastern Wyoming, USA to investigate the seismic character of a postulated Proterozoic magmatic arc south of the suture (Cheyenne Belt) to the Archean Wyoming Province. Recordings from vibrator and dynamite sources with offsets between 34 and 126 km reveal no evidence for Moho reflections. The large-offset recordings contain multicyclic bands of reflective phases from the middle to lower crust. The data were transformed into the intercept time-ray parameter (~--p) domain to estimate local depth bounds. A subsequent 1D inversion using high-amplitude ~'-p arrivals shows that the reflective part of the crust ranges from the depths of 25 to 40 km. This part of the crust exhibits velocities increasing from about 6.5 to 7.5 km/s. Reflectivity modeling shows that the lower crust might consist of a zone of alternating low-and high-velocity layers with average velocity increasing. The average lower crustal velocity of about 6.9 km/s suggests a predominantly mafic composition with interlayered intermediate to felsic components generating impedance contrasts that cause observable amplitudes from reflections at large offsets but not at clearly pre-critical and near-vertical distances. Our model is consistent with observations of interlayered sequences of gabbroic to ultramafic rocks with more felsic anorthositic and charnockitic rocks in the exposed lower crust of magmatic arc complexes. The lack of wide-angle Moho reflections might be explained by a gradational compositional boundary, or a transitional phase change from granulite to eclogite facies.

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Section: Introductionmentioning

confidence: 99%

Seismic wide-angle study of accreted Proterozoic crust in southeastern Wyoming

Gohl

Smithson

1994

Earth and Planetary Science Letters

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“…the suture zone along which the Proterozoic Colorado province and Archean Wyoming province are juxtaposed (Duebendorfer & Houston 1987). Chamberlain et al (1993) originally coined the name 'Laramie Peak shear zone', although portions of the shear zone (system) had been recognized by previous workers (Condie 1969;Segerstrom et al 1977;Langstaff 1984;Snyder et al 1995).…”

Section: Geological Setting and Structural Subdivisionsmentioning

confidence: 99%

“…a major basement ramp) that rooted into a deep-crustal décollement zone that must have underlain the entire Palmer Canyon block during Palaeoproterozoic orogenesis. This décol-lement zone in turn would have rooted southward (in present geographic co-ordinates) into the evolving collisional zone that must have separated the Wyoming and Colorado provinces (now manifested by the Cheyenne belt, see Duebendorfer & Houston 1987). Internal deformation within the Palmer Canyon block would be manifested by heterogeneous general shear strain and folding.…”

Section: Evaluation Of Some Tectonic Modelsmentioning

confidence: 99%

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Laramie Peak shear system, central Laramie Mountains, Wyoming, USA: regeneration of the Archean Wyoming province during Palaeoproterozoic accretion

Resor

Snoke

2005

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The Laramie Peak shear system (LPSS) is a 10 km-thick zone of heterogeneous general shear (non-coaxial) that records significant tectonic regeneration of middle-lower crustal rocks of the Archean Wyoming province. The shear system is related to the 1.78–1.74 Ga Medicine Bow orogeny that involved the collision of an oceanic-arc terrane (Colorado province or Green Mountain block or arc) with the rifted, southern margin of the Wyoming province. The style and character of deformation associated with the LPSS is distinctive: a strong, penetrative (mylonitic) foliation commonly containing a moderately steep, SW-plunging elongation lineation. In mylonitic quartzo-feldspathic gneisses of the Fletcher Park shear zone, shear-sense indicators indicate southside-up, and this interpretation is supported by metamorphic and geochronological studies across the LPSS. We argue that distributed general shear (non-coaxial) involving high-strain zones and multiple folding events yielded a broad, en-masse uplift (Palmer Canyon block) during the late stages of the Medicine Bow orogeny. The LPSS is thus an excellent example of how crystal-plastic strain is distributed in sialic crust during an oceanic arc-continental margin collision. As magmatism (and attendant thermal softening) did not occur in the Wyoming province during its partial subduction beneath the oceanic-arc terranes of the Colorado province, the crystal-plastic strain manifested within the Wyoming province is mechanical in nature and was concurrent with crustal thickening. Strain is localized into discrete shear zones separated by weakly deformed rocks. These high-strain zones are commonly located along contacts between differing rock types and we propose that mechanical and chemical weakening processes may have contributed to strain localization.

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“…Prior to that time (circa 2.1-1.8 Ga), the southern margin of the Wyoming province was characterized by rifting and development of a passive margin [Karlstrom et al, 1983;Karlstrom and Houston, 1984;Chamberlain, 1998]. The Cheyenne Belt, a series of east to northeast trending, south dipping shear zones that are exposed in southern Wyoming, marks the current northern boundary of the Colorado province [Hills and Houston, 1979;Karlstrom and Houston, 1984;Duebendorfer and Houston, 1987;Houston et al, 1989;Chamberlain, 1998]. The southern boundary separating the Colorado/Yavapai province from the circa 1.65 Ga Mazatzal province [Karlstrom and Bowring, 1988] is a northeast trending diffuse zone that extends from southern Arizona to central Colorado [Bennett and DePaolo, 1987;Reed et al, 1987;Shaw and Karlstrom, 1999;Karlstrom et al, 2002].…”

Section: Overviewmentioning

confidence: 99%

Early Proterozoic oceanic crust in the northern Colorado Front Range: Implications for crustal growth and initiation of basement faults

Cavosie¹,

Selverstone

2003

Tectonics

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Early Proterozoic oceanic crust exposed in a shear zone in the northern Colorado Front Range provides insight into the tectonic evolution of the Colorado province. Tectonically intermingled mylonitic amphibolite (locally pillowed), metagabbro, clinopyroxenite, metachert, and mélange are preserved within the Buckhorn Creek shear zone west of Fort Collins. Whole rock geochemical data support formation of the igneous protoliths in an oceanic environment. Major and trace element data overlap samples from modern oceanic ridges, and are distinct from modern arc trends. Metagabbros and clinopyroxenites preserve a subhorizontal lineation defined by igneous pyroxenes; core and mantle microstructures indicate initial deformation at temperatures >900°C. Secondary amphiboles define both subhorizontal and subvertical lineations. Kinematic analysis indicates that the rocks experienced E‐W strike‐slip deformation prior to and during amphibolite‐facies metamorphism, followed by N‐S shortening. 40Ar/39Ar data from secondary hornblende yield age steps as old as 1.9 Ga. Based on the chemical data and kinematic evidence for strike‐slip deformation, we propose that the Buckhorn Creek rocks originated at an oceanic ridge‐transform intersection. The high‐T pyroxene fabrics formed during ocean floor deformation prior to 1.7 Ga regional deformation of the Colorado province. The Buckhorn Creek fragment likely represents original oceanic basement for 1.8–1.7 Ga arc magmatism and sedimentation that ultimately formed the Colorado province continental crust. Reactivation of original oceanic fracture zones may be responsible for the network of regularly spaced northeast trending shear zones in Colorado. Once formed, subvertical transform faults are likely to survive the transition from oceanic to continental crust and persist as long‐lived crustal discontinuities.

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Proterozoic accretionary tectonics at the southern margin of the Archean Wyoming craton

Cited by 92 publications

References 0 publications

Seismic wide-angle study of accreted Proterozoic crust in southeastern Wyoming

Seismic wide-angle study of accreted Proterozoic crust in southeastern Wyoming

Laramie Peak shear system, central Laramie Mountains, Wyoming, USA: regeneration of the Archean Wyoming province during Palaeoproterozoic accretion

Early Proterozoic oceanic crust in the northern Colorado Front Range: Implications for crustal growth and initiation of basement faults

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