NEOARCHEAN STRONGLY PERALUMINOUS GRANITES OF THE WYOMING PROVINCE RECORD MODERN CRUSTAL COMPOSITIONS AND MELT-FORMING PROCESSES

2020 ◽  
Author(s):  
Fabio Da Prat ◽  
◽  
Carol D. Frost ◽  
Darrell J. Henry ◽  
David W. Mogk ◽  
...  
Keyword(s):  
Peraluminous Granites ◽  
Wyoming Province

scholarly journals Precambrian Geological Evolution of the Teton Range, Western Wyoming

1999 ◽  
Vol 23 ◽  
pp. 85-87
Author(s):  
Kevin Chamberlain ◽  
B. Frost ◽  
Carol Frost
Keyword(s):  
National Park ◽  
Plate Tectonics ◽  
Crustal Growth ◽  
Ongoing Research ◽  
Grand Teton National Park ◽  
Basement Rocks ◽  
First Case ◽  
Peraluminous Granites ◽  
Teton Range ◽  
Wyoming Province

The crystalline rocks that form the core of the Teton Range are part of the Wyoming Province, which is one of the oldest portions of North America. Study of the basement of the Tetons, coupled with the results of ongoing research in similar-aged rocks exposed elsewhere in Wyoming, will provide information on how the crust evolved in the early Earth in general and in the Wyoming province in particular. In 1999 the project involved two weeks of fieldwork in Grand Teton National Park and regions to the east, including the Gros Ventre Range, deep canyons of the Buffalo Fork River near Togwotee Pass, and outcrops of basement near Dubois, Wyoming. The main goals of the fieldwork were to complete the sampling of key units in Grand Teton National Park, and to determine whether or not the next nearest outcrops of basement (Gros Ventre, Togwotee Pass and Dubois regions) share the early geologic history preserved in the rocks of Teton National Park. This field work involved four faculty members from UW and a graduate student, who is doing the study as part of her MS thesis. Several months of laboratory analysis at UW have characterized the rocks through thin section, stained slabs, and whole rock geochemical and Nd, Sr, and Ph isotopic methods and produced preliminary U-Pb dates. The principal results from this year 's efforts are that the Teton basement rocks consist of large proportions of juvenile crust, the majority of the rocks formed over a relatively narrow time span from ~2.74 to 2.68 Ga, they were deformed at about 2.67 Ga, and that rocks exposed in the Buffalo Fork River to the east are shallow level equivalents to the deep rocks exposed in the Tetons. Based on these observations and measurements, we hypothesize that the basement rocks of the Tetons formed in an off­shore, island arc setting between 2.74-2.68 Ga, and they were accreted to the Wyoming province at about 2.67 Ga. Post-tectonic intrusion of distinctive peraluminous granites in both the Teton's (Mt. Owens quartz monzonite) and elsewhere in the Wyoming province at 2.55 Ga strengthens our interpretation of a shared history after 2.67 Ga. If this model for the basement rocks in the Teton's holds up, it will be the first case of crustal growth by lateral accretion for the Archean Wyoming province, and one of the earliest examples of plate tectonics style crustal growth documented from anywhere in the world. Plate tectonic growth has dominated the Earth 's evolution from ~2.5 Ga to the present, but it is unclear whether or not analogous processes operated before 2.5 Ga.

Lithospheric roots beneath western Laurentia: the geochemical signal in mantle garnets

2003 ◽  
Vol 40 (8) ◽  
pp. 1027-1051 ◽  
Author(s):  
D Canil ◽  
D J Schulze ◽  
D Hall ◽  
B C Hearn Jr. ◽  
S M Milliken
Keyword(s):  
Rare Earth ◽  
North America ◽  
Trace Element ◽  
Earth Element ◽  
Geochemical Data ◽  
Trace Element Data ◽  
Mantle Lithosphere ◽  
Western North America ◽  
Wyoming Province ◽  
Thick Mantle

This study presents major and trace element data for 243 mantle garnet xenocrysts from six kimberlites in parts of western North America. The geochemical data for the garnet xenocrysts are used to infer the composition, thickness, and tectonothermal affinity of the mantle lithosphere beneath western Laurentia at the time of kimberlite eruption. The garnets record temperatures between 800 and 1450°C using Ni-in-garnet thermometry and represent mainly lherzolitic mantle lithosphere sampled over an interval from about 110–260 km depth. Garnets with sinuous rare-earth element patterns, high Sr, and high Sc/V occur mainly at shallow depths and occur almost exclusively in kimberlites interpreted to have sampled Archean mantle lithosphere beneath the Wyoming Province in Laurentia, and are notably absent in garnets from kimberlites erupting through the Proterozoic Yavapai Mazatzal and Trans-Hudson provinces. The similarities in depths of equilibration, but differing geochemical patterns in garnets from the Cross kimberlite (southeastern British Columbia) compared to kimberlites in the Wyoming Province argue for post-Archean replacement and (or) modification of mantle beneath the Archean Hearne Province. Convective removal of mantle lithosphere beneath the Archean Hearne Province in a "tectonic vise" during the Proterozoic terminal collisions that formed Laurentia either did not occur, or was followed by replacement of thick mantle lithosphere that was sampled by kimberlite in the Triassic, and is still observed there seismically today.

Geologic Map of the Park Reservoir Quadrangle, Sheridan County, Wyoming

2020 ◽  
Vol 57 (4) ◽  
pp. 375-388
Author(s):  
Ryan Bessen ◽  
Jennifer Gifford ◽  
Zack Ledbetter ◽  
Sean McGuire ◽  
Kyle True ◽  
...  
Keyword(s):  
Structural Features ◽  
Geologic Mapping ◽  
Rock Types ◽  
Basement Rocks ◽  
Geologic Maps ◽  
Geologic Map ◽  
Tear Fault ◽  
Mapping Techniques ◽  
Wyoming Province ◽  
Bighorn Mountains

This project involved the construction of a detailed geologic map of the Park Reservoir, Wyoming 7.5-Minute Quadrangle (Scale 1:24,000). The Quadrangle occurs entirely in the Bighorn National Forest, which is a popular recreation site for thousands of people each year. This research advances the scientific understanding of the geology of the Bighorn Mountains and the Archean geology of the Wyoming Province. Traditional geologic mapping techniques were used in concert with isotopic age determinations. Our goal was to further subdivide the various phases of the 2.8–3.0 Ga Archean rocks based on their rock types, age, and structural features. This research supports the broader efforts of the Wyoming State Geological Survey to complete 1:24,000 scale geologic maps of the state. The northern part of the Bighorn Mountains is composed of the Bighorn batholith, a composite complex of intrusive bodies that were emplaced between 2.96–2.87 Ga. Our mapping of the Park Reservoir Quadrangle has revealed the presence of five different Archean quartzofeldspathic units, two sets of amphibolite and diabase dikes, a small occurrence of the Cambrian Flathead Sandstone, two Quaternary tills, and Quaternary alluvium. The Archean rock units range in age from ca. 2.96–2.75 Ga, the oldest of which are the most ancient rocks yet reported in the Bighorn batholith. All the Archean rocks have subtle but apparent planar fabric elements, which are variable in orientation and are interpreted to represent magmatic flow during emplacement. The Granite Ridge tear fault, which is the northern boundary of the Piney Creek thrust block, is mapped into the Archean core as a mylonite zone. This relationship indicates that the bounding faults of the Piney Creek thrust block were controlled by weak zones within the Precambrian basement rocks.

Archean geochronological framework of the Bighorn Mountains, Wyoming

2006 ◽  
Vol 43 (10) ◽  
pp. 1399-1418 ◽  
Author(s):  
Carol D Frost ◽  
C Mark Fanning
Keyword(s):  
Ion Microprobe ◽  
Entire Area ◽  
Wind River Range ◽  
Gneiss Complex ◽  
Granitic Intrusion ◽  
Northern Portion ◽  
Tonalitic Gneiss ◽  
Archean Crust ◽  
Wyoming Province ◽  
Bighorn Mountains

The Bighorn Mountains of the central Wyoming Province expose a large tract of Archean crust that has been tectonically inactive and at relatively high crustal levels since ~2.7 Ga. Seven sensitive high-resolution ion microprobe (SHRIMP) U–Pb zircon and titanite age determinations on samples of the main lithologic units provide a geochronological framework for the evolution of this area. The oldest, precisely dated magmatic event occurred at 2950 ± 5 Ma, when diorite to granite dykes and sills intruded an older gneiss complex exposed in the central and southern Bighorn Mountains. Rocks as old as 3.25 Ga may be present in this gneissic basement, as indicated by the oldest dates obtained on areas of zircon grains that are interpreted as inherited cores. A tonalitic gneiss was intruded into the gneiss complex at 2886 ± 5 Ma. Deformation of the central and southern gneisses preceded the intrusion of the Bighorn batholith, a tonalitic to granitic intrusion that occupies the northern portion of the uplift. This composite batholith was intruded over the period 2.86–2.84 Ga. Ca. 3.0–2.8 Ga crust is also present in the Beartooth Mountains, the Washakie block of the northeastern Wind River Range, the Owl Creek Mountains, and the northern Granite Mountains, but late Archean deformation and plutonism has obscured much of the earlier history in the southern portion of this area. The entire area, referred to as the Beartooth–Bighorn Magmatic Zone, has been undeformed since 2.6 Ga. Proterozoic extension was focused in those parts of the Wyoming Province outside of this domain.

scholarly journals Geological archive of the onset of plate tectonics

2018 ◽  
Vol 376 (2132) ◽  
pp. 20170405 ◽  
Author(s):  
Peter A. Cawood ◽  
Chris J. Hawkesworth ◽  
Sergei A. Pisarevsky ◽  
Bruno Dhuime ◽  
Fabio A. Capitanio ◽  
...  
Keyword(s):  
Plate Tectonics ◽  
Foreland Basin ◽  
Sea Floor ◽  
Palaeomagnetic Data ◽  
Peraluminous Granites ◽  
Lithospheric Plates ◽  
Crustal Reworking ◽  
Sea Floor Spreading ◽  
Back Arc ◽  
Earth Dynamics

Plate tectonics, involving a globally linked system of lateral motion of rigid surface plates, is a characteristic feature of our planet, but estimates of how long it has been the modus operandi of lithospheric formation and interactions range from the Hadean to the Neoproterozoic. In this paper, we review sedimentary, igneous and metamorphic proxies along with palaeomagnetic data to infer both the development of rigid lithospheric plates and their independent relative motion, and conclude that significant changes in Earth behaviour occurred in the mid- to late Archaean, between 3.2 Ga and 2.5 Ga. These data include: sedimentary rock associations inferred to have accumulated in passive continental margin settings, marking the onset of sea-floor spreading; the oldest foreland basin deposits associated with lithospheric convergence; a change from thin, new continental crust of mafic composition to thicker crust of intermediate composition, increased crustal reworking and the emplacement of potassic and peraluminous granites, indicating stabilization of the lithosphere; replacement of dome and keel structures in granite-greenstone terranes, which relate to vertical tectonics, by linear thrust imbricated belts; the commencement of temporally paired systems of intermediate and high dT/dP gradients, with the former interpreted to represent subduction to collisional settings and the latter representing possible hinterland back-arc settings or ocean plateau environments. Palaeomagnetic data from the Kaapvaal and Pilbara cratons for the interval 2780–2710 Ma and from the Superior, Kaapvaal and Kola-Karelia cratons for 2700–2440 Ma suggest significant relative movements. We consider these changes in the behaviour and character of the lithosphere to be consistent with a gestational transition from a non-plate tectonic mode, arguably with localized subduction, to the onset of sustained plate tectonics. This article is part of a discussion meeting issue ‘Earth dynamics and the development of plate tectonics'.

scholarly journals The Medicine Hat Block and the Early Paleoproterozoic Assembly of Western Laurentia

Geosciences ◽  
2020 ◽  
Vol 10 (7) ◽  
pp. 271
Author(s):  
Jennifer N. Gifford ◽  
Shawn J. Malone ◽  
Paul A. Mueller
Keyword(s):  
Ocean Basin ◽  
Geochemical Data ◽  
Drill Core ◽  
Tectonic Zone ◽  
Aggregation Model ◽  
Wyoming Craton ◽  
Crystalline Crust ◽  
Wyoming Province ◽  
Crustal Xenoliths ◽  
Complex Block

The accretion of the Wyoming, Hearne, and Superior Provinces to form the Archean core of western Laurentia occurred rapidly in the Paleoproterozoic. Missing from Hoffman’s (1988) original rapid aggregation model was the Medicine Hat block (MHB). The MHB is a structurally distinct, complex block of Precambrian crystalline crust located between the Archean Wyoming Craton and the Archean Hearne Province and overlain by an extensive Phanerozoic cover. It is distinguished on the basis of geophysical evidence and limited geochemical data from crustal xenoliths and drill core. New U-Pb ages and Lu-Hf data from zircons reveal protolith crystallization ages from 2.50 to 3.28 Ga, magmatism/metamorphism at 1.76 to 1.81 Ga, and εHfT values from −23.3 to 8.5 in the Archean and Proterozoic rocks of the MHB. These data suggest that the MHB played a pivotal role in the complex assembly of western Laurentia in the Paleoproterozoic as a conjugate or extension to the Montana Metasedimentary Terrane (MMT) of the northwestern Wyoming Province. This MMT–MHB connection likely existed in the Mesoarchean, but it was broken sometime during the earliest Paleoproterozoic with the formation and closure of a small ocean basin. Closure of the ocean led to formation of the Little Belt arc along the southern margin of the MHB beginning at approximately 1.9 Ga. The MHB and MMT re-joined at this time as they amalgamated into the supercontinent Laurentia during the Great Falls orogeny (1.7–1.9 Ga), which formed the Great Falls tectonic zone (GFTZ). The GFTZ developed in the same timeframe as the better-known Trans-Hudson orogen to the east that marks the merger of the Wyoming, Hearne, and Superior Provinces, which along with the MHB, formed the Archean core of western Laurentia.

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