Precambrian petrochemistry of the northern Park Range, Colorado, and its implications for studies of crustal derivation

Snyder, George L.; Brandt, E.L.; Smith, Vicki

doi:10.3133/pp1343

Cited by 9 publications

(8 citation statements)

References 21 publications

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“…The Green Mountain Formation is intruded by two coeval plutonic units: Encampment River Granodiorite and the mafi c-ultramafi c rocks of Elkhorn Mountain (i.e., the "gabbro of Elkhorn Mountain"; Snyder, 1980;Snyder et al, 1988). The Encampment River Granodiorite is dominantly a biotite-hornblende granodiorite that intrudes the Green Mountain Formation and is deformed with it (Lackey, 1965;Divis, 1976;Schmidt, 1983).…”

Section: Green Mountain Formation and Coeval Plutonic Rocksmentioning

confidence: 99%

“…The Encampment Granodiorite has been dated at 1779 ± 5 Ma (Premo and Van Schmus, 1989), coeval with the Green Mountain Formation. The gabbro of Elkhorn Mountain is a mafi c plutonic body, ranging in composition from minor peridotite to abundant gabbro to subordinate diorite (Snyder et al, 1988). It has been interpreted as derived from arc-related magmas Houston, 1993;Premo and Loucks, 2000).…”

Section: Green Mountain Formation and Coeval Plutonic Rocksmentioning

confidence: 99%

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New models for Paleoproterozoic orogenesis in the Cheyenne belt region: Evidence from the geology and U-Pb geochronology of the Big Creek Gneiss, southeastern Wyoming

Jones

Snoke

Premo

et al. 2010

Geological Society of America Bulletin

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The disputed age of the deep crust of the Colorado Province is central to hypotheses for Paleoproterozoic crustal growth in the region. We studied the high-grade Big Creek Gneiss, southeastern Wyoming, as a potential exposure of pre-1780 Ma basement rocks. New geologic mapping and U-Pb geochronological data indicate that the Big Creek Gneiss exposes a deeper, but coeval, level of the Green Mountain arc relative to the predominantly supracrustal section to the west. The Big Creek Gneiss is composed of: supracrustal rocks; a ca. 1780 Ma Green Mountain arc-correlative, bimodal intrusive suite; a ca. 1763 Ma extensional(?) bimodal intrusive suite; and widespread ca. 1630 Ma pegmatitic leucogranite. The mafi c member of the younger bimodal suite is documented here for the fi rst time. U-Pb zircon ages from migmatite leucosomes indicate penetrative deformation of the Big Creek Gneiss at ca. 1750 Ma.We fi nd that the postarc intrusive suite is mantle-involved, implying a second period of crustal growth. Shortening postdates arc magmatism by ~20 m.y., implying that termination of arc magmatism and accretion were separate events. Finally, criteria previously used to constrain the polarity of subduction for the Green Mountain arc are not reliable. We propose two competing models: (1) southward-dipping Green Mountain arc subduction (present coordinates), with slab breakoff-related magmatism following arc accretion; or (2) northward-dipping subduction, with extensional postarc magmatism. In both models, high-temperature deformation coincides with accretion along the Cheyenne belt, and extensional magmatism is an impor-tant component of crustal growth. We prefer the northward-dipping subduction model because it can be better integrated with regional tectonic events and published isotopic compositions of the igneous rocks.

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Section: Green Mountain Formation and Coeval Plutonic Rocksmentioning

confidence: 99%

Section: Green Mountain Formation and Coeval Plutonic Rocksmentioning

confidence: 99%

New models for Paleoproterozoic orogenesis in the Cheyenne belt region: Evidence from the geology and U-Pb geochronology of the Big Creek Gneiss, southeastern Wyoming

Jones

Snoke

Premo

et al. 2010

Geological Society of America Bulletin

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“…The area is characterized by a high-T/medium-P, upper-amphibolite facies metamorphism. Sillimanite is the predominant index mineral in metapelites distributed throughout the range, although andalusite and scarce kyanite are also present (Snyder et al, 1988). The supracrustal sequence is intruded by felsic and mafic plutons (Snyder, 1978), including two that are present in the study area: the N 1.75-Ga Buffalo Pass pluton (Premo and Van Schmus, 1989) and N 1.4-Ga Mount Ethel pluton (Snyder, 1978(Snyder, , 1980a.…”

Section: Regional Settingmentioning

confidence: 96%

“…Major-element analyses in this study were found to be similar to published data on the nearby N 1.4-Ga Sherman Granite (Snyder, 1978;Edwards, 1993 as reported in Frost and Frost, 1997), indicating that the Mount Ethel pluton and Sherman Granite may have been produced by similar processes. Snyder et al (1988) suggested that renewed melting of the lower continental crust after subduction led to emplacement of the Mount Ethel pluton. However, association of a small volume diorite/gabbro suite with the Mount Ethel pluton, as well as with the Sherman Granite (Frost and Frost, 1997), may indicate both mantle and crustal sources for various components of the N 1.4-Ga magmatic suite.…”

Section: Mount Ethel Pluton Areamentioning

confidence: 98%

“…The Precambrian supracrustal rocks of the northern Park Range, Colorado, consist mainly of highly deformed metavolcanic and metasedimentary units that are similar to rocks located throughout Colorado and southern Wyoming (Snyder et al, 1988;Houston et al, 1989). The area is characterized by a high-T/medium-P, upper-amphibolite facies metamorphism.…”

Section: Regional Settingmentioning

confidence: 99%

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Metamorphism and deformation near the 1.4-Ga Mount Ethel pluton, Park Range, Colorado

Barinek

Foster

Chaplinsky

1999

Rocky Mountain Geology

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The ~1.4-Ga Mount Ethel pluton is a northeast-trending elliptical body of granodiorite to quartz monzonite surrounded by Lower Proterozoic (1.8-1.7 Ga) rocks in the Park Range, northeast of Steamboat Springs, Colorado. The contact along the northern and southern margins of the pluton is concordant with the northeast-striking regional foliation, whereas the western margin is discordant to the regional foliation. The southern margin of the pluton is adjacent to the subvertical, northeast-striking, northwest-dipping Soda Creek-Fish Creek shear zone, which is located entirely within metasedimentary and metavolcanic country rocks. Kinematic indicators within the shear zone yield a north-side-down sense of shear with a left-lateral component. In contrast to several other well-studied ~1.4-Ga plutons associated with shear zones in the western U.S., penetrative strain related to the shear zone does not appear to extend into the pluton. Late dikes, which appear to be genetically related to the Mount Ethel pluton, cut the main penetrative fabric of the shear zone but are also offset by narrow, discontinuous mylonites of the shear zone. Scarce discontinuous mylonites are also present along the southern margin of the pluton. The pluton contains magmatic fabrics that parallel the strike of the shear zone along the north and south margins of the pluton, but are at a high angle to it along the western margin. These data suggest that early deformation associated with the Soda Creek-Fish Creek shear zone occurred prior to pluton emplacement, that the Mount Ethel pluton was emplaced along a northeast-striking zone of anisotropy, and that some shearing also took place after crystallization and cooling of the pluton.Country rocks in the vicinity of the Mount Ethel pluton with garnet-biotite-plagioclasemuscovite f sillimanite have two generations of garnet: one that is syntectonic and another that is post-tectonic relative to the northeast-striking foliation. Core compositions of pre/ syntectonic garnet paired with matrix biotite compositions yield temperatures of > 600' C at 4 kbar that are associated with early (pre-Mount Ethel) deformation within the Soda CreekFish Creek shear zone. Core compositions of post-tectonic garnet paired with matrix biotite compositions reveal a temperature gradient on the south side of the pluton that increases from ~5 4 0 ' C 5 km away to > ~6 3 0 ' C within 1 km of the Mount Ethel pluton. This may represent the thermal aureole around the intrusion, or it may represent a gradient that pre-dated the pluton. Garnet-rim compositions from both syntectonic and post-tectonic garnet, paired with compositions of biotite near garnet, yield consistent temperatures of 4 5 0 f 5 0 ' C that are spatially unrelated to the Mount Ethel pluton. These rim temperatures may be related to a third thermal event; or alternatively, they may represent partial re-equilibration of garnet rims with nearby biotite during cooling following the last metamorphism.

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Nodular sillimanite rocks as field indicators to metamorphosed massive sulfide deposits

Spry

McFadden

Teale³

et al. 2022

Ore Geology Reviews

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Precambrian petrochemistry of the northern Park Range, Colorado, and its implications for studies of crustal derivation

Abstract: PLATE 1. Generalized geologic map and distributions of selected metamorphic minerals. 2. Tracings of thin sections showing significant minerals and textural relations in metamorphic rocks.

Cited by 9 publications

References 21 publications

New models for Paleoproterozoic orogenesis in the Cheyenne belt region: Evidence from the geology and U-Pb geochronology of the Big Creek Gneiss, southeastern Wyoming

New models for Paleoproterozoic orogenesis in the Cheyenne belt region: Evidence from the geology and U-Pb geochronology of the Big Creek Gneiss, southeastern Wyoming

Metamorphism and deformation near the 1.4-Ga Mount Ethel pluton, Park Range, Colorado

Nodular sillimanite rocks as field indicators to metamorphosed massive sulfide deposits

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