Wyoming Craton
The Wyoming craton (also Wyoming Province) is the American craton (old continental mainland core ) in the west-central United States. It extends across Montana, Wyoming and parts of northern Utah. With approximately 100,000 square kilometers size, it is an original fragment of the North American continental crust.
During the Trans -Hudson orogeny of the Wyoming craton was welded to the previously taken successive continental fragments Superior Craton and Hearne -Rae craton along Trans - Hudson suture zone.
In Wyoming craton are places 3600 - survived three billion years old gneisses, also can be assigned using isotope analysis that crustal parts of the same age were incorporated into younger plutons. This leads to the conclusion that the origins of the Wyoming craton dating back to the Paläoarchaikum, he magmatic and tectonic overprints in Neoarchaikum and finally was suspended in Mesoproterozoikum an expansion process that led to continental rifting.
Geological Overview
The Precambrian basement rocks of Wyoming consists of three major geologic terranes:
- The archaic Wyoming craton (or Wyoming Province)
- The Paleoproterozoic Trans -Hudson Orogen -
- And the Paleoproterozoic Colorado Orogen.
The Colorado Orogen collided with the Wyoming craton in the period 1780-1750 Ma. Due to the clash with the Colorado orogen and the Trans -Hudson Orogen - learned the archaic Wyoming craton at its south - eastern edge and a very strong tectonic overprint.
The Wyoming craton consists mainly of two rock complexes - one hand granitic plutons, which have an age of 2800 to 2550 million years ago and are associated with gneisses and migmatites, on the other hand supracrustal metavolcanics and metasediments, which account for less than 10%. The granitoids are in potassium usually and mainly come from older, ( 3100-2800 million years old ) recycled gneisses. The relatively strong magnetic contrast between the granitoids and gneisses allows the mapping of rock units in terrain sections where the bedrock is covered by sediments. The magnetic data suggest a nearly semicircular, to the north open arrangement of the archaic units recognize.
Subdivisions of the Wyoming Province
The Wyoming province can be divided into three provinces ( from young to old):
- Which accumulated in the south Terrane
- The Beartooth - Bighorn magmatic zone
- The Metasedimentprovinz of Montana.
The archaic rocks of the Metasedimentprovinz of Montana and the Beartooth - Bighorn magmatic zone are characterized by
Even before the 3000 - 2800 Ma were kratonisiert and thus an integral part of the Wyoming Province. More crustal growth through Kontinentalbogenmagmatismus was 2680-2500 Ma by the accumulated along the southern edge of the craton terrane. Towards the end of the Archean, all three provinces in present-day Wyoming craton were then firmly welded together.
Between 1900 and 1800 Ma the now consolidated crust area of Wyoming was attached to Laurentia.
Paläoproterozoische mobile belt crust ( turn from 2400 to 1700 million years old ) then besieged the Wyoming Province on its west and south sides and inevitably led to renewed tectonic movements that were accompanied by magmatic processes.
Chamberlain ( 2003) divided due to a different interpretation of the processes in the late Archean Wyoming province into five provinces:
- The Metasedimentprovinz of Montana
- The Bighorn sub-province
- The Sweetwater sub- province.
These three provinces formed the archaic core. As well as:
- The Sierra Madre and Medicine Bow - crustal block
- The Black Hills - Hartsville - crustal block.
The crustal blocks latter behaved possibly allochthonous with respect to the three billion years old craton.
With the analytical method " Deep Probe " was found that in the Bighorn sub-province, a thick lower crust is present, which has been pushed to 2700 Ma associated with mafic igneous activity. The Sweetwater sub- province is characterized by an east-west - trending tectonic structure forming that had arisen in at least three time- related tectonic episodes ( basin formation, narrowing phase and Inselbogenmagmatismus ). This structure (including the 2.62 billion years old Oregon Trail structure ) will have mapped out the location and orientation for the later held Proterozoic grave breach events and lara mix uplift processes.
The current Lithospärenstruktur the Wyoming Province is the result of billions of years of sustained cumulative crustal processes such as Crustal growth, tectonic deformations and contrasting Lithospärenaufbau. If since 3000 Ma ever a noticeable crustal growth does occur, it is probably based on a combination of Inselbogenmagmatismus with the planting of mafic lower crust.
Emergence of Laurentia
Already before 1860 million years ago on the west side of the Wyoming craton the annealing process of the Selway - Terrans. From around 1840 Ma led to the collision between the Hearne and the Superior craton during the Trans -Hudson orogeny in Canada. The first movements of the same orogeny taken then the Wyoming craton from 1810 Ma in the northern and eastern portion (western North and South Dakota, southeastern Montana). The final union of the eastern Wyoming Craton with Laurentia occurred in the period 1780-1740 Ma - at the southern edge of the growing continent took place, the accretion of a volcanic island arc - the Colorado orogen. The orogenic movements eventually found their conclusion in a post- tectonic magmatic phase, for example, the granite of Harney Peak in the Black Hills secreted.
Addition of the Colorado orogen
During the Paläoproterozoikums around 1760 Ma the Colorado orogen ran down the Wyoming craton along the 500- kilometer-wide Cheyenne belt, which was named after the city of Cheyenne in Wyoming and mainly consists of Proterozoic island arc rocks. This collision with the result that the Wyoming province itself was still within 75 km of the resulting suture intensely deformed and metamorphosed. The suture - a 5 km wide NW- vergenter Mylonitgürtel whose southern side was 10 km lifted - pervades the Laramie Mountains and divides them into two very different halves. But the earlier collision took place on the eastern edge of the craton with the Paleoproterozoic Trans -Hudson Orogen, was not without consequences - in prominent Hartsville - crustal block and in the Laramie Mountains, the archaic rocks were also very highly stressed tectonically.
In the Laramie Mountains and the neighboring Medicine Bow Mountains, the Colorado orogen of about 1400 million years old Mesoproterozoic anorthosites and syenites of the Laramie - Anorthositkomplexes and granites is ( the ilmenite - leading Sherman Granite like ) intruded. These intrusions enforce not only the Cheyenne belt, but also draw on crystalline rocks in the Wyoming Province on. Overall, however, they are only the northern portion of a very broad Intrusivgürtels that runs through the entire Colorado Orogen.
Lara mixer orogeny and Neogene tectonics
The Wyoming craton owes its spectacular mountain ranges essentially a compressive deformation phase, which took place during the mixing Lara orogeny to around 60 million years ago. The Precambrian rocks consisting of basement blocks were raised during this deformation in high crustal levels, the vertical offset of the basement can be up to 9250 meters! Subsequent erosion then created the current topography. The little earlier expired in western Wyoming - Sevier orogeny was tangential nature and had only relatively thin-layer thrusts brought forth - indicate that the bedrock in this region was slightly deformed and even slightly raised uninterrupted magnetic anomalies.
In the period Pliocene - Pleistocene it came to the last major tectonic break phase, it was, inter alia, the Teton Range tilted out of steeply dipping faults. The vertical offset on the east side of this chain is 7800 meters.