The Grouse Creek block is a Precambrian basement province of 2.45 to 2.70 billion year old orthogneisses. The Grouse Creek block is one of several Proterozoic and

Archean The Archean Eon ( , also spelled Archaean or Archæan) is the second of four geologic eons of Earth's history, representing the time from . The Archean was preceded by the Hadean Eon and followed by the Proterozoic. The Earth during the Arc ...

accreted terranes that lie to the north and west of the

Wyoming craton The Wyoming Craton is a craton in the west-central United States and western Canada – more specifically, in Montana, Wyoming, southern Alberta, southern Saskatchewan, and parts of northern Utah. Also called the Wyoming Province, it is the init ...

, including the Farmington Canyon Complex (<2.5 Ga), the Selway terrane (2.4-1.6 Ga), the Medicine Hat block (2.6-3.3 Ga) and the Priest River complex (>2.6-1.5 Ga). Together, these terranes comprise part of the basement rock of the North American continent and have been critical to studies of crustal accretion in the Precambrian. Ongoing study of the Grouse Creek block will contribute to understanding the

paleogeography Palaeogeography (or paleogeography) is the study of historical geography, generally physical landscapes. Palaeogeography can also include the study of human or cultural environments. When the focus is specifically on landforms, the term pal ...

of the Wyoming craton prior to its incorporation into the

supercontinent In geology, a supercontinent is the assembly of most or all of Earth's continental blocks or cratons to form a single large landmass. However, some geologists use a different definition, "a grouping of formerly dispersed continents", which leav ...

Laurentia Laurentia or the North American Craton is a large continental craton that forms the ancient geological core of North America. Many times in its past, Laurentia has been a separate continent, as it is now in the form of North America, althoug ...

approximately 1.86 billion years ago. The name was proposed by David Foster and others.

Geographic and geologic boundaries

The location of the Grouse Creek block has been determined at some points by determining the age when minerals were metamorphosed through isotopic analysis of

uranium Uranium is a chemical element with the symbol U and atomic number 92. It is a silvery-grey metal in the actinide series of the periodic table. A uranium atom has 92 protons and 92 electrons, of which 6 are valence electrons. Uranium is weak ...

, strontium,

neodymium Neodymium is a chemical element with the symbol Nd and atomic number 60. It is the fourth member of the lanthanide series and is considered to be one of the rare-earth metals. It is a hard, slightly malleable, silvery metal that quickly tarnishe ...

and

lead Lead is a chemical element with the symbol Pb (from the Latin ) and atomic number 82. It is a heavy metal that is denser than most common materials. Lead is soft and malleable, and also has a relatively low melting point. When freshly cu ...

. The ages matched characteristic outcropping Archean orthogneisses. Outcrops have been sampled in the Pioneer Mountains, the Albion Range,Armstrong, R.L.; and Hills, F.A. "Rb–Sr and K–Ar geochrono- logic studies of mantled gneiss domes, Albion Range, southern Idaho, USA." Earth and Planetary Science Letters, 3: 114–124 (1967). the

East Humboldt Range The East Humboldt Range is a mountain range in Elko County, Nevada, United States. It is located along the eastern edge of the upper watershed of the Humboldt River, which flows to the southwest from its source just north of the range. The ra ...

, and the Grouse Creek Range. Results indicate that while surface exposures of the Grouse Creek block are rare, the extent of the block is large, reaching from southern Idaho to northeastern Nevada and northwestern Utah (Fig. 1).Fleck, R.J.; and Wooden, J.L. "Isotopic identification of the Archean/Proterozoic lithosphere." Geological Society of America, Abstracts with Programs, 29:70-71 (1997).Wolf, D.E.; Leeman, W.P.; and Vervoort, J.D. "U–Pb zircon geochronology of crustal xenoliths confirms presence of Archean basement beneath the central and eastern Snake River Plain." Geological Society of America, Abstracts with Programs, 37: 60 (2005). The boundaries of the block remain a topic of significant study. : ''North Boundary'': North of the Snake River Plain to at least the Pioneer Core Complex.Durk, K.M.; Fanning, C.M.; and Link, P.K. "SHRIMP U-Pb ages for Archean orthogneiss, Mesoproterozoic paragneiss, and Eocene Boulder Creek Pluton, Pioneer Mountains, south-central Idaho, part of the 2600 Ma Grouse Creek Block." Geological Society of America, Abstracts with Programs, 39: 613 (2007).Fanning, C.M.; and Link, Paul K. "Age and provenance of Precambrian metamorphic rocks in the Pioneer metamorphic core complex, south-central Idaho; the southern edge of the lower Belt Supergroup, the Grouse Creek Block, and hints of a proximal Grenville source in the Northe." Geological Society of America, Abstracts with Programs, 41: 271 (2009). : ''East Boundary'': It is generally accepted that the eastern edge is separated from the Wyoming craton by

Paleoproterozoic The Paleoproterozoic Era (;, also spelled Palaeoproterozoic), spanning the time period from (2.5–1.6 Ga), is the first of the three sub-divisions ( eras) of the Proterozoic Eon. The Paleoproterozoic is also the longest era of the Earth's ...

rocks of the Farmington Canyon ComplexFoster, D.A.; Mueller, P.A.; Kamenov, G.D.; and Stroud, M. "Isotopic analyses of the Grouse Creek Block; A link to the Wyoming Craton?" Geological Society of America, Abstracts with Programs, 41: 270 (2009). in the

Wasatch Range The Wasatch Range ( ) or Wasatch Mountains is a mountain range in the western United States that runs about from the Utah-Idaho border south to central Utah. It is the western edge of the greater Rocky Mountains, and the eastern edge of the G ...

of Utah.Nelson, S.; Harris, R.; Dorais, M.; Heizler, M.; Constenius, K.; and Barnett, D. "Basement complexes in the Wasatch fault, Utah, provide new limits on crustal accretion." ''Geology.'' 30:831–834 (2002).Bryant, B. 1988. "Geology of the Farmington Canyon complex, Wasatch Mountains, Utah." US. Geological Survey Professional Paper 1476. : ''South Boundary'': May occur between the East Humboldt Range and

Ruby Mountains The Ruby Mountains are a mountain range, primarily located within Elko County with a small extension into White Pine County, in Nevada, United States. Most of the range is included within the Humboldt-Toiyabe National Forest. The range reache ...

in Nevada where U-Pb geochronology and Sr, Nd and Pb isotope analysis of intrusive rocks indicate Archean basement is truncated by Proterozoic basement of the

Cheyenne Belt The Cheyenne Belt is the plate tectonics, tectonic suture zone between the Archean-age Wyoming craton to the north and the Paleoproterozoic-age Yavapai province to the south. It runs through the southeastern quadrant of the state of Wyoming, United ...

.Wright, J.E.; and Snoke, A.W. "Tertiary magmatism and mylonitization in the Ruby – East Humboldt metamorphic core complex, northeastern Nevada; U–Pb geochronology and Sr, Nd, and Pb isotope geochemistry." Geological Society of America Bulletin, 105: 935–952 (1993).Premo, W.R.; Howard, K.A.; and Castineiras, P. "New SHRIMP U–Pb zircon ages and Nd isotopic signatures for plutonism in the northern Ruby – East Humboldt Ranges of NE Nevada: implications for the timing of Tertiary core complex formation." Geological Society of America, Abstracts with Programs, 37: 359 (2005). : ''West Boundary'': Not well defined largely due to a lack of outcropping rock, though it has been hypothesized that the block could extend to the Neoproterozoic Cordilleran rift margin.

History of study

Initial geochronology of the Grouse Creek block in 1967 provided age dates identical to those of the Wyoming craton, causing the margin between the two to be blurred. The Grouse Creek block was later proposed as a separate terrane following the discovery of outcropping 2.45 to 1.6 billion year old Paleoproterozoic metasedimentary rocksBarnett, D.; Bowman, J.; and Smith, H. "Petrologic and geo- chronologic studies in the Farmington Canyon complex, Wasatch Mountains, Utah." Utah Geological Survey Contract Report 93-5 (1993). of the Farmington Canyon Complex in the Wasatch Range of Utah separating the block from the Wyoming craton. There is still debate as to whether the Grouse Creek block is distinct from the Wyoming Craton at depth.Mueller, P.; Foster, D.; Mogk, D.; and Wooden, J. "New insights into the Proterozoic evolution of the western margin of Laurentia and their tectonic implications." Geological Society of America, Abstracts with Programs, 36: 404 (2004). Geologists proposed three hypotheses for the provenance of the Grouse Creek block: #The Grouse Creek block could be an accreted Archean block. #It may be a re-accreted rifted fragment of the Wyoming craton. #Or the block could be a part of the Wyoming craton separated by a younger intracratonic rift. Geo- and thermochronologic data indicates mountain building and magmatism in the Farmington Canyon Complex at 2.45 and 1.8 billion years ago can be attributed to accretion of the Grouse Creek block to the Wyoming craton in the Paleoproterozoic. The Wyoming craton can be differentiated from other Archean terranes by an enriched ²⁰⁷Pb/²⁰⁴Pb ratio that is hypothesized to represent early crustal extraction, as well as

samarium Samarium is a chemical element with symbol Sm and atomic number 62. It is a moderately hard silvery metal that slowly oxidizes in air. Being a typical member of the lanthanide series, samarium usually has the oxidation state +3. Compounds of samar ...

and neodymium ratios providing rock ages of up to 4.0 Ga. Investigation of lead and neodymium isotope ratios in the Grouse Creek block provide evidence that it is chemically unique with respect to the Wyoming craton, corroborating past studies indicating the accretion of the terrane to the western margin of the Wyoming craton in the Paleoproterozoic (Fig. 2). AccreWedge

References

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