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94-601: The Hearne Craton is a craton in northern Canada which, together with the Rae Craton , forms the Western Churchill Province . Hearne is one of the six Archaean cratons of the Canadian Shield (the other being Slave , Rae , Wyoming , Superior , Nain ) that are bound together by Palaeoproterozoic orogenic belts . Before being merged these six cratons formed independent microcontinents . The Hearne Craton

188-400: A rising plume of molten material from the deep mantle. This would have built up a thick layer of depleted mantle underneath the cratons. A third model suggests that successive slabs of subducting oceanic lithosphere became lodged beneath a proto-craton, underplating the craton with chemically depleted rock. A fourth theory presented in a 2015 publication suggests that the origin of

282-461: A central strip to which the Slave , Superior , Sask , and Wyoming cratons were accreted. This strip is bounded by a series of orogens : the 1.92–1.69 Ga Trans-Hudson to the south, the 2.0–1.9 Ga Taltson–Thelon and the 1.97–1.84 Ga Wopmey to the west. Hearne and Rae were extensively reworked during the assembly of Laurentia and overlain by Palaeoproterozoic cover sequences. On Hearne

376-454: A continental shield , in which the basement rock crops out at the surface, and a platform which overlays the shield in some areas with sedimentary rock . The word craton was first proposed by the Austrian geologist Leopold Kober in 1921 as Kratogen , referring to stable continental platforms, and orogen as a term for mountain or orogenic belts . Later Hans Stille shortened

470-495: A missing biozones or correlates events happening in a neighbouring block (like Tarim block). The carbonate sequence can also be of evolutionary significance because it indicates extinction events like the biomeres in the Cambrian. Biomeres are small extinction events defined by the migration of a group of trilobite, family Olenidae , which had lived in deep sea environment. Olenidae trilobites migrated to shallow sea regions while

564-555: A piece of continent that is stable, buoyant and rigid. Basic properties of the cratonic crust include being thick (around 200 km), relatively cold when compared to other regions, and low density. The North China Craton is an ancient craton, which experienced a long period of stability and fitted the definition of a craton well. However, the North China Craton later experienced destruction of some of its deeper parts (decratonization), which means that this piece of continent

658-622: A rift system have been found in the Central Orogenic Belt and they were dated 2.7 billion years old. These included ophiolite and remnants of a rift system. Collision and amalgamation started to occur in Paleoproterozoic time (2.5–1.6 billion years ago). From 2.5 to 2.3 billion years ago, the Eastern and Western Blocks collided and amalgamated, forming the North China Craton with the Central Orogenic Belt in between. The boundary of

752-604: A shallow lake environment in the Early to Middle Triassic . Apart from sedimentation, there were six major stages of magmatism after the Phanerozoic decratonization. In Jurassic to Cretaceous (100-65 million years ago) sedimentary rocks were often mixed with volcanic rocks due to volcanic activities. The North China Craton experienced complex tectonic events throughout the Earth's history. The most important deformation events are how

846-457: A solid residue very close in composition to Archean lithospheric mantle, but continental shields do not contain enough komatiite to match the expected depletion. Either much of the komatiite never reached the surface, or other processes aided craton root formation. There are many competing hypotheses of how cratons have been formed. Jordan's model suggests that further cratonization was a result of repeated continental collisions. The thickening of

940-468: A strong deformation event that created a high pressure and high temperature environment. Faure and Trap proposed another model based on the dating and structural evidences they found. They used Ar-Ar and U-Pb dating methods and structural evidences including cleavages, lineation and dip and strike data to analyse the Precambrian history of the craton The timing of final amalgamation in their model

1034-526: Is affected by atmospheric and hydrosphere interaction and the evolution from primitive tectonics to modern plate tectonics. Ore formation is related to supercontinent fragmentation and assembly. For example, copper and lead deposited in sedimentary rocks indicated rifting and therefore fragmentation of a continent; copper, volcanogenic massive sulfide ore deposits (VMS ore deposits) and orogenic gold deposits indicated subduction and convergent tectonics, meaning amalgamation of continents. Therefore,

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1128-552: Is close to monopolising the export of rare earth elements in the whole world. Even the United States relies heavily on rare earth elements imported from China, while rare earth elements are essential in technologies. Rare earth elements can make high quality permanent magnets , and are therefore irreplaceable in the production of electrical appliances and technologies, including televisions, phones, wind turbines and lasers. A copper- molybdenum (Cu-Mo) system originated in both

1222-454: Is in-line with the timing proposed by Zhao, also around 1.8 to 1.9 billion years ago, but another time of significant deformation (2.1 billion years ago) have also been suggested. The division of micro-blocks deviated from Zhao's model. Faure and Trap identified 3 ancient continental blocks, the Eastern and Western Blocks, same as Zhao's model, as well as the Fuping Block, differing from

1316-580: Is made up of early to late Archean (3.8-3.0 billion years ago) tonalite-trondhjemite-granodiorite gneisses , granitic gneisses , some ultramafic to felsic volcanic rocks and metasediments with some granitoids which formed in some tectonic events 2.5 billion years ago. These are overlain by Paleoproterozoic rocks which were formed in rift basins . The Western Block consists of an Archean (2.6–2.5 billion years ago) basement which comprises tonalite-trondhjemite-granodiorite, mafic igneous rock, and metamorphosed sedimentary rocks. The Archean basement

1410-404: Is no longer as stable. The North China Craton was at first some discrete, separate blocks of continents with independent tectonic activities. In the Paleoproterozoic (2.5-1.8 billion years ago) the continents collided and amalgamated and interacted with the supercontinent, creating belts of metamorphic rocks between the formerly separate parts. The exact process of how the craton was formed

1504-450: Is overlain unconformably by Paleoproterozoic khondalite belts, which consist of different types of metamorphic rocks, such as graphite -bearing sillimanite garnet gneiss. Sediments were widely deposited in the Phanerozoic with various properties, for example, carbonate and coal bearing rocks were formed in the late Carboniferous to early Permian (307-270 million years ago), when purple sand-bearing mudstones were formed in

1598-698: Is proposed because of how the rocks were metamorphosed in the belt and symmetrical rocks have been found on both side of the Belt. Around 1.9 billion years ago, the rift system at the Jiao-Liao-Ji Belt switched to a subductional and collisional system. The Longgang Block and the Langrim Block then combined, forming the Eastern Block. 1.85 billion years ago, the Trans North China Orogen was formed by

1692-637: Is separated from the Rae Craton by the 2,000 km (1,200 mi)-long Snowbird Tectonic Zone (STZ). During the Neoarchaean and Palaeoproterozoic the STZ played a major role when the Western Churchill Province was first assembled and then reworked. The STZ is a record of Neoarchaean plate tectonics similar in scale to modern orogenic belts. When Laurentia formed at 2.0–1.7 Ga Hearne and Rae formed

1786-509: Is still under debate. After the craton was formed, it stayed stable until the middle of the Ordovician period (480 million years ago). The roots of the craton were then destabilised in the Eastern Block and entered a period of instability. The rocks formed in the Archean and Paleoproterozoic eons (4.6–1.6 billion years ago) were significantly overprinted during the root destruction. Apart from

1880-452: Is strongly influenced by the inclusion of moisture. Craton peridotite moisture content is unusually low, which leads to much greater strength. It also contains high percentages of low-weight magnesium instead of higher-weight calcium and iron. Peridotites are important for understanding the deep composition and origin of cratons because peridotite nodules are pieces of mantle rock modified by partial melting. Harzburgite peridotites represent

1974-546: Is very important in terms of understanding biostratigraphy and evolution. In Cambrian and Ordovician time, the units of limestone and carbonate kept a good record of biostratigraphy and therefore they are important for studying evolution and mass extinction . The North China platform was formed in early Palaeozoic. It had been relatively stable during Cambrian and the limestone units are therefore deposited with relatively few interruptions. The limestone units were deposited in underwater environment in Cambrian. It

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2068-636: The Baltic Shield had been eroded into a subdued terrain already during the Late Mesoproterozoic when the rapakivi granites intruded. North China Craton The North China Craton is a continental crustal block with one of Earth's most complete and complex records of igneous , sedimentary and metamorphic processes. It is located in northeast China, Inner Mongolia , the Yellow Sea , and North Korea . The term craton designates this as

2162-693: The Hongtoushan greenstone belt , which was located in the northeastern part of the North China Craton. They are typical volcanogenic massive sulfide ore deposits and were formed under rift environment. The formation of the Cu-Zn deposits might not be under modern tectonics, so the formation process might be different from modern rift system. Neoarchean greenstone belt gold deposits are located in Sandaogou (northeastern side of The North China Craton). The greenstone belt type gold deposits are not commonly found in

2256-636: The Ordos Block , the Longgang Block and the Langrim Block. The Yinshan and Ordos Blocks collided and formed the Western Block, creating the Khondalite Belt 1.95 billion years ago. For the Eastern Block, there was a rifting event in the Jiao-Liao-Ji Belt, which separated the Longgang Block and the Langrim Block with an ocean before the block was formed 2.1 to 1.9 billion years ago. A rifting system

2350-611: The Ordovician in the Archean crust between 450–480 million years ago and again in the Tertiary . Uplifting events caused the kimberlite to be exposed. The two mines exist along narrow and discontinuous dykes around the Tan Lu fault. Porphyritic kimberlites often occur with a matrix of other materials, such as serpentinized olivine and phlogopite or biotite , and breccia fragments. The occurrence of diamonds with different materials caused

2444-462: The Paleoproterozoic time (2.5–1.6 billion years ago), the North China Craton amalgamated in three steps, with the final amalgamation took place 1.85 billion years ago. Based on the metamorphic ages in the Trans North China Orogen, the assembly and the formation process of the North China Craton is determined. Zhao proposed that the North China Craton was formed from 4 blocks, the Yinshan Block,

2538-461: The Phanerozoic . The Eastern Block is defined by high heat flow, thin lithosphere and a lot of earthquakes . It experienced a number of earthquakes with a magnitude of over 8 on the Richter scale , claiming millions of lives. The thin mantle root, which is the lowest part of lithosphere , is the reason for its instability. The thinning of the mantle root caused the craton to destabilize, weakening

2632-582: The seismogenic layer , which then allows earthquakes to happen in the crust. The Eastern Block may once have had a thick mantle root, as shown by xenolith evidence, but this seems to have been thinned during the Mesozoic . The Western Block is located in Helanshan - Qianlishan , Daqing - Ulashan , Guyang - Wuchuan , Sheerteng and Jining . It is stable because of the thick mantle root. Little internal deformation occurred here since Precambrian . The rocks in

2726-406: The "cratonic regime". It involves processes of pediplanation and etchplanation that lead to the formation of flattish surfaces known as peneplains . While the process of etchplanation is associated to humid climate and pediplanation with arid and semi-arid climate, shifting climate over geological time leads to the formation of so-called polygenetic peneplains of mixed origin. Another result of

2820-483: The 1.8 billion years ago metamorphic events found by Zhao to prove the amalgamation event is just the overprint of the collision event with the Columbia Supercontinent 1.85 billion years ago. The collision event with the Columbia Supercontinent also replaced lithosphere with new mantle, which would affect the dating. Another argument is that the metamorphic rocks found 1.8 billion years ago is not confined to

2914-549: The Central Asian Orogenic Belt (North) and the Qinling Orogenic Belt (South). The Central Asian Orgenic belt ore deposits occurred in arc complexes. They formed from the closure of Paleo-Asian ocean. The subduction generated copper and molybdenum Cu-Mo mineralization in the lithosphere block margins. Duobaoshan Cu and Bainaimiao Cu-Mo deposits are found in granodiorite . Tonghugou deposits occur with

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3008-479: The Central Orogenic Belt (or Trans-North China Orogenic Belt). They are also found in the Western Block, indicating that the metamorphic events was a craton-wide event. Zhao, on the opposite, argued that based on the lithological evidences, for example, the Eastern and Western Blocks must have been formed in settings different from the central part 2.6 to 2.5 billion years ago. Therefore, they would have been separated at that time. The pluton upwelling may explain

3102-401: The Central Orogenic Belt is defined by Archean geology which is 1600 km from west Liaoning to west Henan . Kusky proposed that the tectonic setting of the amalgamation is an island arc , in which a westward dipping subduction zone was formed. The two blocks then combined through a westward subduction of the Eastern Block. The timing of the collision event is determined based on

3196-603: The Columbia Supercontinent after it was formed. The Xiong'er Volcanic Belt located in the Southern Margin of the craton recorded the accretion event of the Supercontinent in terms of a subduction zone. The North China Craton broke away from the Supercontinent 1.6 to 1.2 billion years ago via a rift system called Zhaertai Bayan Obo rift zone where mafic sills found is an evident of such event. Kusky and Zhao proposed arguments against each other's model. Kusky argued that

3290-436: The Columbia Supercontinent. The mechanism behind these tectonic events is rift and subduction system, which is similar to the two models proposed by Kusky and Zhao. There is a major difference of Zhai's theory with the above-mentioned models: he proposed that the North China Craton, instead of simply amalgamated and formed from the Eastern and Western Blocks, was amalgamated from a total of 7 ancient blocks. Zhai found that

3384-543: The Eastern and Western Blocks 3.8 to 2.7 billion years ago. The formation time of the blocks is determined based on the age of the rocks found in the craton. Most rocks in the craton were formed at around 2.7 billion years ago, with some small outcrops found to have formed 3.8 billion years ago. Then, the Eastern Block underwent deformation, rifting at the Western Edge of the Block 2.7 to 2.5 billion years ago. Evidences for

3478-709: The Kiyuk Group overlie the Hurwitz Group. Both groups are covered by a thick cover of thrusts and folds. The Manikewan Ocean, a palaeocean named by Stauffer 1984 , started to open along the south-east margin of Hearne at 2.075 Ga and had reached a width of 5,000 km (3,100 mi) after a hundred million years. Intra-oceanic arc collision resulted in the Amisk Collage and the Flin Flon – Glennie Complex around 1.92–1.88 Ga. Today these Palaeoproterzoic structures in

3572-849: The North China Craton. At first, diamonds were produced from alluvial deposits, but later on technology improved and the diamonds are now produced from kimberlitic sources. There are two main diamond mines in China, the China Diamond Corps' 701 Changma Mine in Shandong province and the Wafangdian Mine in Liaoning Province . The former operated for 34 years and produced 90,000 carats of diamonds per year. The latter produced 60,000 carats per year, but its mining activity ceased in 2002. Diamond bearing kimberlite pipes and dykes were emplaced during

3666-473: The North China craton consist of Precambrian (4.6 billion years ago to 539 million years ago) basement rocks, with the oldest zircon dated 4.1 billion years ago and the oldest rock dated 3.8 billion years ago. The Precambrian rocks were then overlain by Phanerozoic (539 million years ago to present) sedimentary rocks or igneous rocks. The Phanerozoic rocks are largely not metamorphosed. The Eastern Block

3760-450: The Permian basement, was formed in two distinct periods. First is from 2.8 to 2.7 billion years ago, and later from 2.6 to 2.5 billion years ago, based on zircon age data. Zhao suggested a pluton model to explain the formation of metamorphic rocks 2.5 billion years ago. Neoarchean (2.8–2.5 Ma) mantle upwelled and heated up the upper mantle and lower crust, resulting in metamorphism. In

3854-817: The Trans-Hudson Orogen welds the Archaean Hearne and the Superior cratons. As the ocean continued to close, an Andean-style arc pluton known as the Wathaman Batholith formed 1.86–1.85 Ga. The subduction of the Manikewan Ocean stopped when the La Ronge Arc collided with Hearne. The final closure of the ocean around 1.83 Ga, when Hearne, Superior, and Sask cratons merged with the Flin Flon – Glennie Complex,

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3948-717: The Trans-North China Orogen in Zhao's model. The 3 blocks were separated by two oceans, which were the Taihang Ocean and the Lüliang Ocean. They have also proposed the sequence and timing of the events occurred. Around 2.1 billion years ago, the Taihang Ocean closed with the Eastern Block and Fuping Block amalgamated through the Taihang Suture. From 1.9 to 1.8 billion years ago, the Lüliang Ocean closed, promoting

4042-536: The Western Block was formed by the collision of an arc terrane and the northern margin of the craton 2.3 billion years ago. The arc terrane was formed in an ocean developed during post-collisional extension in the amalgamation event 2.5 billion years ago. Apart from the deformation event in a local scale, the craton also interacted and deformed in a regional scale. It interacted with the Columbia Supercontinent after its formation. The northern margin of

4136-518: The Yangtze Craton and North China Craton (240-210 million years ago), Jurassic subduction of the Paleo-Pacific Plate (200-100 million years ago) and Cretaceous collapse of orogens (130-120 million years ago). As for the destabilisation mechanism, 4 models could be generalised. They are the subduction model, the extension model the magma underplating mode, and

4230-434: The age of crystallisation of the igneous rocks in the region and the age of metamorphism in the Central Orogenic Belt. Kusky also believed that the collision happened right after the rifting event, as seen from examples from orogens in other parts of the world, deformation events tend to happen closely with each other in terms of timing. After the amalgamation of the North China Craton, Inner Mongolia–Northern Hebei Orogen in

4324-484: The amalgamation of different blocks of the craton and its interactions with the Columbia Supercontinent. The North China Craton remained stable for a long time after the amalgamation of craton. There were thick sediments deposited from Neoproterozoic (1000 to 539 million years ago). The flat-lying Palaeozoic sedimentary rocks recorded extinction and evolution . The center of the craton remained stable until mid-Ordovician (467-458 million years ago), due to

4418-454: The amalgamation of the Craton from their ancient blocks, while Zhao argued that the later event was responsible for the amalgamation. Kusky's model proposed a sequence of events showing the microblocks amalgamating 2.5 billion years ago. First, in the Archean time (4.6-2.5 billion years ago), the lithosphere of the craton started to develop. Some ancient micro-blocks amalgamated to form

4512-400: The amalgamation of the Eastern and Western Blocks. Santosh proposed a model to explain the rapid pace of amalgamation of the continental blocks, thus providing a better picture of the mechanisms of cratonization of the North China Craton. For the time frame of the deformational events, he generally agreed with Zhao's model based on metamorphic data. He provided a new insight to explain

4606-755: The ancient plate. He finds that the Yinshan block (part of the Western Block) and the Yanliao block (part of the Eastern Block) subducted towards the centre around the Ordos Block (part of the Western Block)., in which the Yinshan block subducted eastward towards the Yanliao block. The Yinshan block further subducted to the south to the Ordos block. The Ordos Block was therefore experiencing double subduction, facilitating

4700-505: The arc area and a marginal fault basin. During the opening of Paleo-Qinling oceans in this period, nickel -copper deposits formed with peridotite gabbro bodies and the ores can be found in Luonan . Gold (Au) deposits in the Mesozoic are very abundant. The formation environment of the gold includes intercontinental mineralization, craton destruction and mantle replacement. The origin of

4794-443: The collision of the Eastern and Western Blocks in an eastward subduction system, with probably an ocean between the 2 blocks subducted. Zhao also proposed model about the interaction of the North China Craton with the Columbia Supercontinent. He suggested that the craton's formation event 1.85 billion years ago was part of the formation process of the Columbia Supercontinent. The craton also recorded outward accretion event of

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4888-650: The copper ore chalcopyrite . North China hosted a large reserve of molybdenum with more than 70 ore bodies found in the Northern margin of the craton. Mineral deposits in southern margin of the North China Craton are next to the Qinling orogenic belt . Some deposits were formed during the amalgamation of the North and South China blocks. A rifting-subduction-collision processes in Danfeng suture zone generated VMS deposits (Cu-Pb-Zn) in

4982-497: The craton because most of them were reworked in the Mesozoic, so they appeared to be in some other form. However, from other cratonic examples in the world, the greenstone belt gold deposits should be abundant in the first place. Ultra high temperature metamorphic rocks found in the Paleoproterozoic Period indicate the start of modern tectonics. Great oxygenation events (GOE) also occurred in this period and it marked

5076-502: The craton from sinking into the deep mantle. Cratonic lithosphere is much older than oceanic lithosphere—up to 4 billion years versus 180 million years. Rock fragments ( xenoliths ) carried up from the mantle by magmas containing peridotite have been delivered to the surface as inclusions in subvolcanic pipes called kimberlites . These inclusions have densities consistent with craton composition and are composed of mantle material residual from high degrees of partial melt. Peridotite

5170-559: The craton, resulting in large-scale deformations and earthquakes in the region. Gravity gradient showed that the Eastern Block remains thin up till present day. The mechanism and timing of craton destruction is still under debate. Scientists proposed four important deformation events that could possibly lead to or contributed to craton destruction, namely subduction and closure of Paleo-Asian Ocean in Carboniferous to Jurassic (324-236 million years ago), late Triassic collision of

5264-413: The cratons is similar to crustal plateaus observed on Venus, which may have been created by large asteroid impacts. In this model, large impacts on the Earth's early lithosphere penetrated deep into the mantle and created enormous lava ponds. The paper suggests these lava ponds cooled to form the craton's root. The chemistry of xenoliths and seismic tomography both favor the two accretional models over

5358-399: The crust associated with these collisions may have been balanced by craton root thickening according to the principle of isostacy . Jordan likens this model to "kneading" of the cratons, allowing low density material to move up and higher density to move down, creating stable cratonic roots as deep as 400 km (250 mi). A second model suggests that the surface crust was thickened by

5452-427: The crystalline residues after extraction of melts of compositions like basalt and komatiite . The process by which cratons were formed is called cratonization . There is much about this process that remains uncertain, with very little consensus in the scientific community. However, the first cratonic landmasses likely formed during the Archean eon. This is indicated by the age of diamonds , which originate in

5546-426: The depleted "lid" formed by the first layer. The impact origin model does not require plumes or accretion; this model is, however, not incompatible with either. All these proposed mechanisms rely on buoyant, viscous material separating from a denser residue due to mantle flow, and it is possible that more than one mechanism contributed to craton root formation. The long-term erosion of cratons has been labelled

5640-405: The discovery of xenoliths in the older lithosphere in kimberlite dykes . Since then, the North China Craton entered period of craton destruction, meaning that the craton was no longer stable. Most scientists defined destruction of a craton as thinning of lithosphere, thus losing rigidity and stability. A large-scale lithosphere thinning event took place especially in the Eastern Block of

5734-538: The formation of a certain type of ore is restricted to a specific period and the minerals are formed in relation with tectonic events. Below the ore deposits are explained based on the period they were formed. All deposits in this period are found in greenstone belts , which is a belt full of metamorphic rocks. This is consistent with the active tectonic activity in the Neoarchean . Banded iron formations (BIFs) belong to granulite facies and are widely distributed in

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5828-1158: The former term to Kraton , from which craton derives. Examples of cratons are the Dharwar Craton in India, North China Craton , the East European Craton , the Amazonian Craton in South America, the Kaapvaal Craton in South Africa, the North American Craton (also called the Laurentia Craton), and the Gawler Craton in South Australia. Cratons have thick lithospheric roots. Mantle tomography shows that cratons are underlain by anomalously cold mantle corresponding to lithosphere more than twice

5922-563: The gold is from Precambrian basement rocks of the Jiaodong Complex and underlying mantle which underwent high grade metamorphism when intruded with Mesozoic granitoids. The largest cluster of gold deposits in China is found in the Jiaodong peninsula (east of Shandong Province ). The area yielded one-fourth of the country's gold production but consisted only of 0.2% of the area of China. The three sub-clusters of gold deposits in northern China are Linglong, Yantai and Kunyushan respectively. China has been producing diamonds for over 40 years in

6016-406: The high-grade metamorphic rocks, a good indicator of amalgamation events, has been observed all over the craton, not just restricted to the Trans-North China Orogen or the Central Orogenic Belt. He then proposed that there must have been more blocks that participated in the amalgamation process in order to explain the presence of belts of high-grade metamorphic rocks, which must have been formed in

6110-445: The iron was deposited in an environment of weakly oxidized shallow sea environment. There are four regions where extensive iron deposits are found: Anshan in northeast China, eastern Hebei , Wutai and Xuchang -Huoqiu. The North China Craton banded iron formation contains the most important source of iron in China. It consists of more than 60–80% of the nations iron reserves. Copper - zinc (Cu-Zn) deposits were deposited in

6204-471: The late Archean, accompanied by voluminous mafic magmatism. However, melt extraction alone cannot explain all the properties of craton roots. Jordan notes in his paper that this mechanism could be effective for constructing craton roots only down to a depth of 200 kilometers (120 mi). The great depths of craton roots required further explanation. The 30 to 40 percent partial melting of mantle rock at 4 to 10 GPa pressure produces komatiite magma and

6298-455: The lithospheric folding model. There were several major tectonic events occurring in the Phanerozoic , especially in the margins of the Eastern Block. Some of them were hypothesized to have caused the destruction of the craton. The causes of the craton destruction event and the thinning of the Eastern Block lithosphere are complicated. Four models can be generalized from the different mechanisms proposed by scientists. The North China Craton

6392-405: The longevity of cratons is that they may alternate between periods of high and low relative sea levels . High relative sea level leads to increased oceanicity, while the opposite leads to increased inland conditions . Many cratons have had subdued topographies since Precambrian times. For example, the Yilgarn Craton of Western Australia was flattish already by Middle Proterozoic times and

6486-452: The metamorphic event 2.5 billion years ago. Zhao also argued that Kusky has not provided sufficient isotopic evidence regarding the metamorphic data. In contrast with Kusky's argument that deformation events should follow tight with each other rather than staying still for 700 million years, Zhao argued that there are a lot of orogens in the world that have stayed still for a long period of time without any deformation events. Apart from

6580-403: The metamorphosed units. The age of the ore is defined by isotopic analysis of hafnium dating. They are interlayered with volcanic-sedimentary rocks. They can also occur as some other features: dismembered layers, lenses and boudins . All the iron occurrences are in oxide form, rarely in silicate or carbonate form. By analysing their oxygen isotope composition, it is suggested that

6674-441: The micro continental blocks collided and almagamated to form the craton, and different phases of metamorphism during Precambrian time from around 3 to 1.6 billion years ago. In Mesozoic to Cenozoic time (146-2.6 million years ago), the Precambrian basement rocks were extensively reworked or reactivated. The Precambrian tectonics of the North China Craton is complicated. Different scholars have proposed different models to explain

6768-481: The models which Kusky and Zhao proposed, there are some other models available to explain the tectonic evolution of the North China Craton. One of the models is proposed by Zhai. He agreed with Kusky on the time frame of deformational events occurred in the North China Craton. He also proposed that the continent grew from around 2.9 to 2.7 billion years ago, amalgamating 2.5 billion years ago and deforming around 2.0 to 1.8 billion years ago due to its interactions with

6862-410: The most extensive such cover sequence is a series of continental and marine deposits known as the Hurwitz Group, a series of north-east-trending belts that cover 150,000 km (58,000 sq mi). A synclinoria infolded with Archaean basement in central Hearne has a fold-train with a wavelength of 35–45 km (22–28 mi). In the south-western Hearne continental siliciclastic rocks known as

6956-420: The ore deposits. There are a few types of ore deposits found and each of them correspond to a different formation environment. Cu-Pb-Zn formed in metamorphosed VMS deposits, Cu-Mo deposits formed in accreted arc complexes, while copper-cobalt Cu-Co deposits formed in an intrusive environment. Magnesite – boron deposits were formed in sedimentary sequences under rift related shallow sea lagoon settings. It

7050-507: The other species died out. The trilobite fossils actually records important natural selection processes. The carbonate sequence containing the trilobite fossils hence important to record paleoenvironment and evolution. The North China Craton contains abundant mineral resources which are very important economically. With the complex tectonic activities in The North China Craton, the ore deposits are also very rich. Deposition of ore

7144-417: The other trilobite groups and families died out in certain time periods. This is speculated to be due to a change in ocean conditions, either a drop in ocean temperature, or a drop in oxygen concentration. They affected the circulation and living environment for marine species. The shallow marine environment would change dramatically, resembling a deep sea environment. The deep sea species would thrive, while

7238-420: The plume model. However, other geochemical evidence favors mantle plumes. Tomography shows two layers in the craton roots beneath North America. One is found at depths shallower than 150 km (93 mi) and may be Archean, while the second is found at depths from 180 to 240 km (110 to 150 mi) and may be younger. The second layer may be a less depleted thermal boundary layer that stagnated against

7332-537: The records of tectonic activities, the craton also contains important mineral resources, such as iron ores and rare earth elements , and fossils records of evolutionary development. The North China Craton covers approximately 1,500,000 km in area and its boundaries are defined by several mountain ranges (orogenic belts), the Central Asian Orogenic Belt to the north, the Qilianshan Orogen to

7426-489: The roots of cratons, and which are almost always over 2 billion years and often over 3 billion years in age. Rock of Archean age makes up only 7% of the world's current cratons; even allowing for erosion and destruction of past formations, this suggests that only 5 to 40 percent of the present continental crust formed during the Archean. Cratonization likely was completed during the Proterozoic . Subsequent growth of continents

7520-600: The start of a shift from an oxygen poor to an oxygen rich environments. There are two types of minerals commonly found from this period. They are copper-lead zinc deposits and magnesite – boron deposits. Copper-lead-zinc (Cu-Pb-Zn) deposits were deposited in collisional setting mobile belts, which were in a rift and subduction system. Copper deposits are found in the Zhongtiaoshan area of Shanxi province. The khondalite sequence, which are high temperature metamorphic rocks, and graphite are often found together with

7614-417: The subduction direction of the plates during amalgamation, where the 2.5 Ga craton amalgamation model suggested westward subduction, and the 1.85Ga craton amalgamation model suggested eastern subduction. He did an extensive seismic mapping over the craton, making use of P-waves and S-waves . He discovered traces of a subducted plate in the mantle, which indicated the possible direction of subduction of

7708-515: The surrounding hotter, but more chemically dense, mantle. In addition to cooling the craton roots and lowering their chemical density, the extraction of magma also increased the viscosity and melting temperature of the craton roots and prevented mixing with the surrounding undepleted mantle. The resulting mantle roots have remained stable for billions of years. Jordan suggests that depletion occurred primarily in subduction zones and secondarily as flood basalts . This model of melt extraction from

7802-438: The tectonics of the Craton, with two dominant schools of thought coming from Kusky (2003, 2007, 2010 ) and Zhao (2000, 2005, and 2012 ). The major difference in their models is the interpretation of the two most significant Precambrian metamorphic events, occurring 2.5 billion years ago and 1.8 billion years ago respectively, in the North China Craton. Kusky argued that the metamorphic event 2.5 billion years ago corresponded to

7896-503: The typical 100 km (60 mi) thickness of mature oceanic or non-cratonic, continental lithosphere. At that depth, craton roots extend into the asthenosphere , and the low-velocity zone seen elsewhere at these depths is weak or absent beneath stable cratons. Craton lithosphere is distinctly different from oceanic lithosphere because cratons have a neutral or positive buoyancy and a low intrinsic density. This low density offsets density increases from geothermal contraction and prevents

7990-455: The upper mantle has held up well with subsequent observations. The properties of mantle xenoliths confirm that the geothermal gradient is much lower beneath continents than oceans. The olivine of craton root xenoliths is extremely dry, which would give the roots a very high viscosity. Rhenium–osmium dating of xenoliths indicates that the oldest melting events took place in the early to middle Archean. Significant cratonization continued into

8084-658: The west, Qinling Dabie Orogen to the south and Su-Lu Orogen to the east. The intracontinental orogen Yan Shan belt ranges from east to west in the northern part of the craton. The North China Craton consists of two blocks, the Western Block and the Eastern Block, separated by the 100–300 km wide Trans North China Orogen, which is also called Central Orogenic Belt or Jin yu Belt. The Eastern Block covers areas including southern Anshan - Benxi , eastern Hebei , southern Jilin , northern Liaoning , Miyun - Chengdu and western Shandong . Tectonic activities, such as earthquakes, increased since craton root destruction started in

8178-470: The whole craton collided with another continent during the formation of Columbia Supercontinent from 1.92 to 1.85 billion years ago. Lastly, the tectonic setting of the craton became extensional, and therefore began to break out of the Columbia Supercontinent 1.8 billion years ago. Zhao proposed another model suggesting the amalgamation of the Eastern and Western Blocks occurred 1.85 billion years ago instead. The Archean time (3.8-2.7 billion years ago)

8272-608: Was a response to the great oxidation event as seen from its isotopic content. In the Jiaoliao mobile belt, the GOE changed the isotopic ratio of C and O as the rock underwent recrystallization and mass exchange. The ore also allows people to further understand the Global Oxidation Event system, for example, showing the exact atmospheric chemical change during that period. A rare-earth element -iron-lead-zinc (REE-Fe-Pb-Zn) system

8366-488: Was a time of major crustal growth. Continents started to grow in volume globally during this period, and so did the North China Craton. Pre-Neoarchean (4.6–2.8 billion years ago) rocks are just a small portion of the basement rocks, but zircon as old as 4.1 billion years old was found in the craton. He suggested that the Neoarchean (2.8–2.5 billion years ago) crust of the North China Craton, which accounts for 85% of

8460-578: Was bounded by faults and belts for example Tanlu fault. The Cambrian and Ordovician carbonate sedimentary units can be defined by six formations: Liguan, Zhushadong, Mantou, Zhangxia, Gushan, Chaomidian. Different trilobite samples can be retrieved in different strata, forming biozones . For example, lackwelderia tenuilimbata (a type of trilobite) zone in Gushan formation. The trilobite biozones can be useful to correlate and identify events in different places, like identifying unconformity sequences from

8554-469: Was by accretion at continental margins. The origin of the roots of cratons is still debated. However, the present understanding of cratonization began with the publication in 1978 of a paper by Thomas H. Jordan in Nature . Jordan proposes that cratons formed from a high degree of partial melting of the upper mantle, with 30 to 40 percent of the source rock entering the melt. Such a high degree of melting

8648-433: Was followed by a period of metamorphism that peaked around 1.82–1.8 Ga. The Manikewan Mobile Belt now covers an area of 600,000 km (230,000 sq mi) but is overlain by Middle Proterozoic Athabasca sandstone. Craton The term craton is used to distinguish the stable portion of the continental crust from regions that are more geologically active and unstable. Cratons are composed of two layers:

8742-544: Was formed from extensional rifting with upwelling of mantle, and therefore magma fractionation. There were multiple rifting events resulting in the deposition of iron minerals and the occurrence rare earth element was closely related to the iron and carbonatite dykes . The REE-Fe-Pb-Zn system occurs in an alternating volcanic and sedimentary succession. Apart from REE, LREE (light rare earth elements) are also found in carbonatite dykes. Rare earth elements have important industrial and political implications in China. China

8836-423: Was possible because of the high mantle temperatures of the Archean. The extraction of so much magma left behind a solid peridotite residue that was enriched in lightweight magnesium and thus lower in chemical density than undepleted mantle. This lower chemical density compensated for the effects of thermal contraction as the craton and its roots cooled, so that the physical density of the cratonic roots matched that of

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