Misplaced Pages

#881118

27-584: The Wyoming Craton was sutured together with the Superior and Hearne - Rae cratons in the mountain-building episode that created the Trans-Hudson Suture Zone to form the core of North America ( Laurentia ). It was incorporated into southwest Laurentia approximately 1.86 billion years ago. Local preservation of 3.6–3.0 Ga gneisses and widespread isotopic evidence for crust of this age incorporated into younger plutons indicates that

54-587: A larger plate, and is relatively buoyant due to thickness or low density. When the plate of which it was a part subducted under another plate, the terrane failed to subduct, detached from its transporting plate, and accreted onto the overriding plate. Therefore, the terrane transferred from one plate to the other. Typically, accreting terranes are portions of continental crust which have rifted off another continental mass and been transported surrounded by oceanic crust, or they are old island arcs formed at some distant subduction zones. A tectonostratigraphic terrane

81-629: Is 50–60 million years younger than that reported for the Hearne-Superior collision of the Trans-Hudson orogeny in Canada. Younger metamorphic dates (1.81–1.71 Ga) also typify the eastern and northern Wyoming province peripheries in the western Dakotas and southeastern Montana . The final assembly of the eastern Wyoming Craton as part of the continent Laurentia began during the ca. 1.78–1.74 Ga interval of island-arc accretion along

108-422: Is a stub . You can help Misplaced Pages by expanding it . Terrane accretion In geology , a terrane ( / t ə ˈ r eɪ n , ˈ t ɛr eɪ n / ; in full, a tectonostratigraphic terrane ) is a crust fragment formed on a tectonic plate (or broken off from it) and accreted or " sutured " to crust lying on another plate. The crustal block or fragment preserves its distinctive geologic history, which

135-436: Is a fault-bounded package of rocks of at least regional extent characterized by a geologic history that differs from that of neighboring terranes. The essential characteristic of these terranes is that the present spatial relations are incompatible with the inferred geologic histories. Where terranes that lie next to each other possess strata of the same age, they are considered separate terranes only if it can be demonstrated that

162-407: Is also an older usage of the term terrane , which described a series of related rock formations or an area with a preponderance of a particular rock or rock group. A tectonostratigraphic terrane did not necessarily originate as an independent microplate , since it may not contain the full thickness of the lithosphere . It is a piece of crust that has been transported laterally, usually as part of

189-427: Is different from the surrounding areas—hence the term "exotic" terrane. The suture zone between a terrane and the crust it attaches to is usually identifiable as a fault . A sedimentary deposit that buries the contact of the terrane with adjacent rock is called an overlap formation . An igneous intrusion that has intruded and obscured the contact of a terrane with adjacent rock is called a stitching pluton . There

216-653: Is often represented on the surface by an orogen or mountain range. In plate tectonics, sutures are the remains of subduction zones , and the terranes that are joined are interpreted as fragments of different palaeocontinents or tectonic plates . Outcrops of sutures can vary in width from a few hundred meters to a couple of kilometers . They can be networks of mylonitic shear zones or brittle fault zones, but are usually both. Sutures are usually associated with igneous intrusions and tectonic lenses with varying kinds of lithologies from plutonic rocks to ophiolitic fragments. An example from Great Britain

243-529: Is the Iapetus Suture which, though now concealed beneath younger rocks, has been determined by geophysical means to run along a line roughly parallel with the Anglo-Scottish border and represents the joint between the former continent of Laurentia to the north and the former micro-continent of Avalonia to the south. Avalonia is in fact a plain which dips steeply northwestwards through

270-643: The 2.62 Ga Oregon Trail structure, controlled the locations and orientations of Proterozoic rifting and uplifts related to the Laramide orogeny . If there has been any net crustal growth of the Wyoming Province since 3.0 Ga, it has involved a combination of mafic underplating and arc magmatism. During the Paleoproterozoic , island-arc terrane associated with the Colorado orogeny accreted to

297-732: The 3.0 Ga craton), (4) the Sierra Madre – Medicine Bow block, and (5) the Black Hills – Hartville block. Based on imaging by the "Deep Probe" analysis, a thick lower crustal layer corresponds geographically with the Bighorn subprovince and may be an underplate associated with ca. 2.70 Ga mafic magmatism. The Sweetwater subprovince is characterized by an east–west-tending tectonic grain that was established by three or more roughly contemporaneous late Archean, pulses of basin development, shortening, and arc magmatism. This tectonic grain, including

SECTION 10

#1732764829882

324-590: The Archean craton produced strong structural overprinting along the southern and eastern margins of the Wyoming craton. The Wyoming Craton consists mainly of two gross rock units—granitoid plutons (2.8–2.55 Ga) and gneiss and migmatite —together with subordinate (<10 percent) supracrustal metavolcanic-metasedimentary rocks. The granitoid rocks are mainly potassic granite and were derived principally from reworked older (3.1–2.8 Ga) gneiss. Magnetic contrast between

351-801: The Hartville uplift. Mesoproterozoic (~1.4 Ga) anorthosite and syenites of the Laramie Anorthosite Complex and granite ( ilmenite -bearing Sherman Granite) intrude into rocks of the Colorado orogen in the Laramie and adjacent Medicine Bow Mountains . Both the anorthosite and granite transect the Cheyenne belt in the Laramide Mountains, and intrude crystalline rocks of the Wyoming province. These intrusions comprise

378-675: The Montana metasedimentary province, the Beartooth–Bighorn magmatic zone, and the Southern accreted terranes. Archean rocks of the Montana metasedimentary province and the Beartooth-Bighorn magmatic zone are characterized by (1) their antiquity (rock ages to 3.5 Ga, detrital zircon ages up to 4.0 Ga, and Nd model ages exceeding 4.0 Ga); (2) a distinctly enriched Pb / Pb isotopic signature, which suggests that this part of

405-422: The Southern accreted terranes along the southern margin of the province at 2.68–2.50 Ga. By the end of the Archean, the three subprovinces were joined as part of what is now the Wyoming craton. Subsequent to amalgamation of the Wyoming crust to Laurentia at ca. 1.8–1.9 Ga, Paleoproterozoic crust (1.7–2.4 Ga) was juxtaposed along the southern and western boundaries of the province. Subsequent tectonism and magmatism in

432-739: The Wyoming Craton along the Cheyenne belt , a 500-km-wide belt of Proterozoic rocks named for Cheyenne, Wyoming . As a result of the collision, older, Archean rocks of the Wyoming province were intensely deformed and metamorphosed for at least 75 km inboard from the suture, which is marked today by the Laramie Mountains. Along the east margin of the craton, collision with the Paleoproterozoic Trans-Hudson orogen intensely deformed Archean cratonic rocks in

459-551: The Wyoming Craton originated as a 100,000 km middle Archean craton that was modified by late Archean volcanic magmatism and plate movements and Proterozoic extension and rifting . The Wyoming, Superior and Hearne-Ray cratons were once sections of separate continents, but today they are all welded together. The collisions of these cratons began before ca. 1.77 Ga , with post- tectonic magmatism at ca. 1.715 Ga (the Harney Peak granite ). This tectonic-magmatic interval

486-596: The Wyoming region are concentrated in the areas underlain by these Proterozoic mobile belts. An analysis by Kevin Chamberlain et al. (2003), on the basis of differences in late Archean histories, subdivides the Wyoming Province into five subprovinces: three in the Archean core, (1) the Montana metasedimentary province, (2) the Bighorn subprovince, and (3) the Sweetwater subprovince, and two Archean terrains that may have originated elsewhere (that is, allochthonous to

513-413: The ability of crustal fragments to "drift" thousands of miles from their origin and attach themselves, crumpled, to an exotic shore. Such terranes were dubbed " accreted terranes " by geologists . Geologist J. N. Carney writes: It was soon determined that these exotic crustal slices had in fact originated as "suspect terranes" in regions at some considerable remove, frequently thousands of kilometers, from

540-575: The basement rocks were little disturbed and not significantly uplifted during the thrusting. Even younger high-angle faulting of Pliocene – Pleistocene age has formed the Teton Range . Vertical relief on the east face of the mountains is about 25,000 ft. (7800 m). Suture (geology) In structural geology , a suture is a joining along a major fault zone, of separate terranes , tectonic units that have different plate tectonic , metamorphic and paleogeographic histories. The suture

567-504: The crust, underthrusting Laurentia. When used in paleontology , suture can also refer to fossil exoskeletons , as in the suture line, a division on a trilobite between the free cheek and the fixed cheek; this suture line allowed the trilobite to perform ecdysis (the shedding of its skin). Heron, P., Pysklywec, R. & Stephenson, R. Lasting mantle scars lead to perennial plate tectonics. Nat Commun 7, 11834 (2016). https://doi.org/10.1038/ncomms11834 This tectonics article

SECTION 20

#1732764829882

594-463: The deformation, and subsequent erosion has molded the uplifted rocks into the rugged present-day topography. Vertical displacement of the basement surface was as much as 30,000 ft. (9250 m). By contrast, in western Wyoming thrust faulting , associated with the Sevier orogeny of approximately the same age, was thin-skinned, and the lack of disruption of magnetic anomalies in the region indicates that

621-428: The geologic evolutions are different and incompatible. There must be an absence of intermediate lithofacies that could link the strata. The concept of tectonostratigraphic terrane developed from studies in the 1970s of the complicated Pacific Cordilleran orogenic margin of North America , a complex and diverse geological potpourri that was difficult to explain until the new science of plate tectonics illuminated

648-548: The granitoid rocks and gneiss provides a means to map these gross rock units in covered areas. The overall structural pattern of the Archean units shown by magnetic data is crudely semi-circular and open to the north. The present-day lithospheric architecture of the Wyoming Province is the result of cumulative processes of crustal growth, tectonic modification, and lithospheric contrasts that have apparently persisted for billions of years. The Wyoming province can be subdivided into three subprovinces, namely, from oldest to youngest,

675-407: The northernmost segment of a wide belt of 1.4 Ga granitic intrusions that occur throughout the Colorado orogen. Long after its assembly, the Wyoming Craton owes its spectacular mountainous terranes mainly to a regional episode of compressional deformation during the Laramide orogeny (ca.60 Ma). The basement blocks composed of Precambrian rocks were uplifted locally to high levels in the crust during

702-513: The province was not produced by the amalgamation of already-formed exotic terranes; and (3) a distinctively thick (15–20 km), mafic lower crust. The Montana metasedimentary province and Beartooth–Bighorn magmatic zone were established as cratons by about 3.0–2.8 Ga. Crustal growth occurred through a combination of continental-arc magmatism resulting from oceanic crust subducted beneath continental crust on an adjacent plate, creating an arc-shaped mountain belt, together with terrane accretion in

729-698: The southern margin of the growing craton. The Precambrian basement of Wyoming consists mainly of three major geologic terranes , the Archean Wyoming Craton or Province, the Paleoproterozoic Trans-Hudson orogen, and the Paleoproterozoic Colorado orogeny . The Colorado orogen collided with the Wyoming Craton at 1.78–1.75 Ga. Collision of the Colorado orogen and the Trans-Hudson orogen with

#881118