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. [1] It is located in northeast China, Inner Mongolia, the Yellow Sea, and North Korea. [1] The term craton designates this as a piece of continent that is stable, buoyant and rigid. [1] [3] [4] Basic properties of the cratonic crust include being thick (around 200 km), relatively cold when compared to other regions, and low density. [1] [3] [4] The North China Craton is an ancient craton, which experienced a long period of stability and fitted the definition of a craton well. [1] However, the North China Craton later experienced destruction of some of its deeper parts (decratonization), which means that this piece of continent is no longer as stable. [3] [4]
The North China Craton was at first some discrete, separate blocks of continents with independent tectonic activities. [5] 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. [5] The exact process of how the craton was formed is still under debate. After the craton was formed, it stayed stable until the middle of the Ordovician period (480 million years ago). [4] 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 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. [6]
The North China Craton covers approximately 1,500,000 km2 in area [7] and its boundaries are defined by several mountain ranges (orogenic belts), the Central Asian Orogenic Belt to the north, the Qilianshan Orogen to the west, Qinling Dabie Orogen to the south and Su-Lu Orogen to the east. [2] The intracontinental orogen Yan Shan belt ranges from east to west in the northern part of the craton. [1]
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, [2] which is also called Central Orogenic Belt [1] or Jin yu Belt. [8] 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 the Phanerozoic. The Eastern Block is defined by high heat flow, thin lithosphere and a lot of earthquakes. [1] It experienced a number of earthquakes with a magnitude of over 8 on the Richter scale, claiming millions of lives. [1] The thin mantle root, which is the lowest part of lithosphere, is the reason for its instability. [1] The thinning of the mantle root caused the craton to destabilize, weakening the seismogenic layer, which then allows earthquakes to happen in the crust. [1] 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. [1] The Western Block is located in Helanshan-Qianlishan, Daqing-Ulashan, Guyang-Wuchuan, Sheerteng and Jining. [1] It is stable because of the thick mantle root. [1] Little internal deformation occurred here since Precambrian. [1]
The rocks in 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. [5] The Precambrian rocks were then overlain by Phanerozoic (539 million years ago to present) sedimentary rocks or igneous rocks. [9] The Phanerozoic rocks are largely not metamorphosed. [9] The Eastern Block 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. [9] These are overlain by Paleoproterozoic rocks which were formed in rift basins. [9] 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. [9] The Archean basement is overlain unconformably by Paleoproterozoic khondalite belts, which consist of different types of metamorphic rocks, such as graphite-bearing sillimanite garnet gneiss. [9] 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 a shallow lake environment in the Early to Middle Triassic. [4] Apart from sedimentation, there were six major stages of magmatism after the Phanerozoic decratonization. [4] In Jurassic to Cretaceous (100-65 million years ago) sedimentary rocks were often mixed with volcanic rocks due to volcanic activities. [4]
The North China Craton experienced complex tectonic events throughout the Earth's history. The most important deformation events are how 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. [9] In Mesozoic to Cenozoic time (146-2.6 million years ago), the Precambrian basement rocks were extensively reworked or reactivated. [9]
The Precambrian tectonics of the North China Craton is complicated. Different scholars have proposed different models to explain the tectonics of the Craton, with two dominant schools of thought coming from Kusky (2003, [13] 2007, [1] 2010 [12] ) and Zhao (2000, [14] [9] 2005, [2] and 2012 [5] ). 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 the amalgamation of the Craton from their ancient blocks, [1] [13] [12] while Zhao [2] [5] [9] [14] 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. [13] [15] First, in the Archean time (4.6-2.5 billion years ago), the lithosphere of the craton started to develop. [13] [15] Some ancient micro-blocks amalgamated to form the Eastern and Western Blocks 3.8 to 2.7 billion years ago. [13] [15] The formation time of the blocks is determined based on the age of the rocks found in the craton. [13] [15] 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. [13] [15] Then, the Eastern Block underwent deformation, rifting at the Western Edge of the Block 2.7 to 2.5 billion years ago. [12] Evidences for a rift system have been found in the Central Orogenic Belt and they were dated 2.7 billion years old. [13] These included ophiolite and remnants of a rift system. [13] [15]
Collision and amalgamation started to occur in Paleoproterozoic time (2.5–1.6 billion years ago). [13] [15] 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. [1] [12] The boundary of the Central Orogenic Belt is defined by Archean geology which is 1600 km from west Liaoning to west Henan. [13] Kusky proposed that the tectonic setting of the amalgamation is an island arc, in which a westward dipping subduction zone was formed. [13] [15] The two blocks then combined through a westward subduction of the Eastern Block. [13] The timing of the collision event is determined based on the age of crystallisation of the igneous rocks in the region and the age of metamorphism in the Central Orogenic Belt. [13] 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. [13] After the amalgamation of the North China Craton, Inner Mongolia–Northern Hebei Orogen in the Western Block was formed by the collision of an arc terrane and the northern margin of the craton 2.3 billion years ago. [13] The arc terrane was formed in an ocean developed during post-collisional extension in the amalgamation event 2.5 billion years ago. [13]
Apart from the deformation event in a local scale, the craton also interacted and deformed in a regional scale. [13] [15] It interacted with the Columbia Supercontinent after its formation. [12] The northern margin of the whole craton collided with another continent during the formation of Columbia Supercontinent from 1.92 to 1.85 billion years ago. [12] [13] Lastly, the tectonic setting of the craton became extensional, and therefore began to break out of the Columbia Supercontinent 1.8 billion years ago. [12]
Zhao proposed another model suggesting the amalgamation of the Eastern and Western Blocks occurred 1.85 billion years ago instead. [9] [14] [16] [17] The Archean time (3.8-2.7 billion years ago) was a time of major crustal growth. [9] [14] [16] [17]
Continents started to grow in volume globally during this period, and so did the North China Craton. [2] [5] 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. [2] [5] He suggested that the Neoarchean (2.8–2.5 billion years ago) crust of the North China Craton, which accounts for 85% of 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. [2] [5] Zhao suggested a pluton model to explain the formation of metamorphic rocks 2.5 billion years ago. [2] [5] Neoarchean (2.8–2.5 Ma) mantle upwelled and heated up the upper mantle and lower crust, resulting in metamorphism. [9]
In 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. [5] [9] Based on the metamorphic ages in the Trans North China Orogen, the assembly and the formation process of the North China Craton is determined. [5] [9] Zhao proposed that the North China Craton was formed from 4 blocks, the Yinshan Block, the Ordos Block, the Longgang Block and the Langrim Block. [5] [9] The Yinshan and Ordos Blocks collided and formed the Western Block, creating the Khondalite Belt 1.95 billion years ago. [5] [9] 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. [5] [9] A rifting system is proposed because of how the rocks were metamorphosed in the belt and symmetrical rocks have been found on both side of the Belt. [5] [9] Around 1.9 billion years ago, the rift system at the Jiao-Liao-Ji Belt switched to a subductional and collisional system. [5] [9] The Longgang Block and the Langrim Block then combined, forming the Eastern Block. [5] [9] 1.85 billion years ago, the Trans North China Orogen was formed by the collision of the Eastern and Western Blocks in an eastward subduction system, with probably an ocean between the 2 blocks subducted. [2] [5] [9] [14]
Zhao also proposed model about the interaction of the North China Craton with the Columbia Supercontinent. [17] [18] He suggested that the craton's formation event 1.85 billion years ago was part of the formation process of the Columbia Supercontinent. [17] [18] The craton also recorded outward accretion event of the Columbia Supercontinent after it was formed. [17] [18] 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. [18] 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. [18]
Time [a] | The 2.5Ga Amalgamation Model (Kusky) | The 1.8Ga Amalgamation Model (Zhao) |
---|---|---|
3.8–2.7Ga | Ancient micro blocks amalgamated to form the Western and Eastern Block [13] | Crust grew and formed, with plutons upwell in the region, causing extensive metamorphism [2] [5] [9] [14] |
2.7–2.5Ga | Eastern Block deformation (rifting in the western edge) [12] | |
2.5–2.3Ga | The Western and Eastern Block collided, and formed the N-S trending Central Orogenic Belt between where the 2 blocks are amalgamated [1] [12] | |
2.3Ga | Arc Terrane collision to for Inner Mongolia- Northern Hebei Orogen in the North of the Craton [13] | |
2.2–1.9Ga | Rifting and collision of the Eastern Block along the Jiao-Liao-Ji Belt [5] [9] | |
1.95Ga | Northern margin collided with continents in the Columbia Supercontinent [12] [13] | Yinshan and Ordos Block collided and formed the Western Block and the Khondalite Belt [5] [9] |
1.85Ga | Collision of the Eastern and Western Blocks leading to their amalgamation and the formation of Trans North China Orogen [5] [9] | |
1.8Ga | The tectonic setting of the craton became extensional where the craton broke out from Columbia Supercontinent [12] [13] |
Kusky and Zhao proposed arguments against each other's model. Kusky argued that 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. [12] The collision event with the Columbia Supercontinent also replaced lithosphere with new mantle, which would affect the dating. [12] Another argument is that the metamorphic rocks found 1.8 billion years ago is not confined to the Central Orogenic Belt (or Trans-North China Orogenic Belt). [12] They are also found in the Western Block, indicating that the metamorphic events was a craton-wide event. [12] 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. [5] [17] Therefore, they would have been separated at that time. [5] [17] The pluton upwelling may explain the metamorphic event 2.5 billion years ago. [5] [17] Zhao also argued that Kusky has not provided sufficient isotopic evidence regarding the metamorphic data. [5] [17] 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. [5] [17]
Apart from 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. [19] [20] [21] He agreed with Kusky on the time frame of deformational events occurred in the North China Craton. [19] 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 the Columbia Supercontinent. [19] The mechanism behind these tectonic events is rift and subduction system, which is similar to the two models proposed by Kusky and Zhao. [19] 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. [19] [20] [21] Zhai found that 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. [19] [20] [21] 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 a strong deformation event that created a high pressure and high temperature environment. [19] [20] [21]
Faure and Trap proposed another model based on the dating and structural evidences they found. [22] [23] [24] 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 [22] [23] [24] The timing of final amalgamation in their model 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. [22] [23] [24] The division of micro-blocks deviated from Zhao's model. [22] [23] [24] 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 the Trans-North China Orogen in Zhao's model. [22] [23] [24] The 3 blocks were separated by two oceans, which were the Taihang Ocean and the Lüliang Ocean. [22] [23] [24] They have also proposed the sequence and timing of the events occurred. [22] [23] [24] Around 2.1 billion years ago, the Taihang Ocean closed with the Eastern Block and Fuping Block amalgamated through the Taihang Suture. [22] [23] [24] From 1.9 to 1.8 billion years ago, the Lüliang Ocean closed, promoting the amalgamation of the Eastern and Western Blocks. [22] [23] [24]
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. [11] [26] For the time frame of the deformational events, he generally agreed with Zhao's model based on metamorphic data. [11] [26] He provided a new insight to explain 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. [11] [26] He did an extensive seismic mapping over the craton, making use of P-waves and S-waves. [11] [26] He discovered traces of a subducted plate in the mantle, which indicated the possible direction of subduction of the ancient plate. [11] [26] 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)., [11] [26] in which the Yinshan block subducted eastward towards the Yanliao block. [11] [26] The Yinshan block further subducted to the south to the Ordos block. [11] [26] The Ordos Block was therefore experiencing double subduction, facilitating the amalgamation of different blocks of the craton and its interactions with the Columbia Supercontinent. [11] [26]
Zhao's Model (1.85Ga Amalgamation model) | Kusky's Model (2.5Ga Amalgamation Model) | Zhai's Model (7 Blocks Model) | Faure's Model (3 Blocks Model) | Santosh's Model (Double subduction model) | |
---|---|---|---|---|---|
Timing of amalgamation | 1.85Ga [2] [5] [17] | 2.5–2.3 Ga [1] [12] [13] [15] | 2.5–2.3 Ga [19] [20] [21] | Final amalgamation at 1.8–1.9Ga, but an additional amalgamation event of the Fuping Block with the Eastern Block [22] [23] [24] | 1.85Ga [11] [26] |
Constituent Microblocks of the North China Craton | The Eastern and Western Blocks, separated by Trans-North China Orogen [2] [5] [17] | The Eastern and Western Blocks, separated by Central Orogenic Belt [1] [12] [13] [15] | 7 microblocks (Qianhuai Block, Jiaoliao Block, Jining Block, Xuchang Block, Xuhuai Block, Alashan Block) separated by belts of metamorphic rocks [19] [20] [21] | The Eastern and Western Blocks with Fuping Block in between [22] [23] [24] | The Eastern and Western Blocks, separated by Trans-North China Orogen [11] [26] |
Direction of subduction | Eastward subduction [2] [5] [17] | Westward subduction [1] [12] [13] [15] | (Not mentioned) | Westward subction [22] [23] [24] | Double subduction, both westward and eastward subduction [11] [26] |
The North China Craton remained stable for a long time after the amalgamation of craton. [1] [4] There were thick sediments deposited from Neoproterozoic (1000 to 539 million years ago). [1] [4] The flat-lying Palaeozoic sedimentary rocks recorded extinction and evolution. [27] [4] The center of the craton remained stable until mid-Ordovician (467-458 million years ago), due to the discovery of xenoliths in the older lithosphere in kimberlite dykes. [4] Since then, the North China Craton entered period of craton destruction, meaning that the craton was no longer stable. [1] [4] Most scientists defined destruction of a craton as thinning of lithosphere, thus losing rigidity and stability. [1] [4] [28] A large-scale lithosphere thinning event took place especially in the Eastern Block of the craton, resulting in large-scale deformations and earthquakes in the region. [1] [4] [28] Gravity gradient showed that the Eastern Block remains thin up till present day. [1] [29] 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), [1] [4] late Triassic collision of the Yangtze Craton and North China Craton (240-210 million years ago), [29] [30] [31] [32] [33] [34] [35] Jurassic subduction of the Paleo-Pacific Plate (200-100 million years ago) [28] [36] [37] and Cretaceous collapse of orogens (130-120 million years ago). [1] [4] [38] [39] [40] [41] As for the destabilisation mechanism, 4 models could be generalised. They are the subduction model, [1] [28] [32] [37] [29] [30] the extension model [4] [33] [38] [41] the magma underplating mode, [39] [40] [42] [43] [44] and the lithospheric folding model. [32]
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.
Geological Event | Geological Structure Resulted | |
---|---|---|
Carboniferous to Middle Jurassic (324-236 million years ago) | Subduction and closure of Paleo-Asian Ocean, with phases of magmatism observed. [1] [4] | Solonker Suture (North of the Craton) [1] [4] |
Late Triassic (240-210 million years ago) | Suture between the North China Craton and the Yang Tze Craton by deep subduction and continental collision. Isotopic data showed that at least part of the craton root was destroyed. [1] [4] [32] | Qinling-Dabie Orogen (South to Southwest of the Craton) [1] [4] [32] |
Jurassic (200-100 million years ago) | The Pacific Plate was subducted westward in an active continental margin setting. This result in new magmatic material (as shown by isotopic age) being aligned with the subduction zone, proving craton destruction. [1] [4] [28] [36] [37] | Tan-Lu Fault (East of the Craton) [1] [4] [28] [36] [37] |
Cretaceous (130-120 million years ago) | Mode of tectonic switched to extension. The orogenic belt and plateau (Hubei collisional plateau and Yanshan belt) started to collapse, which also result in the replacement of magmatic material in the mantle root. [1] [4] | Bohai Bay Basin [1] [4] |
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 is very important in terms of understanding biostratigraphy and evolution. [27] [6] 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. [27] [6] The North China platform was formed in early Palaeozoic. [27] [6] It had been relatively stable during Cambrian and the limestone units are therefore deposited with relatively few interruptions. [27] [6] The limestone units were deposited in underwater environment in Cambrian. [27] [6] It was bounded by faults and belts for example Tanlu fault. [27] [6] The Cambrian and Ordovician carbonate sedimentary units can be defined by six formations: Liguan, Zhushadong, Mantou, Zhangxia, Gushan, Chaomidian. [27] [6] Different trilobite samples can be retrieved in different strata, forming biozones. [27] [6] For example, lackwelderia tenuilimbata (a type of trilobite) zone in Gushan formation. [27] [6] The trilobite biozones can be useful to correlate and identify events in different places, like identifying unconformity sequences from a missing biozones or correlates events happening in a neighbouring block (like Tarim block). [27] [6]
The carbonate sequence can also be of evolutionary significance because it indicates extinction events like the biomeres in the Cambrian. [51] Biomeres are small extinction events defined by the migration of a group of trilobite, family Olenidae, which had lived in deep sea environment. [51] Olenidae trilobites migrated to shallow sea regions while the other trilobite groups and families died out in certain time periods. [51] This is speculated to be due to a change in ocean conditions, either a drop in ocean temperature, or a drop in oxygen concentration. [51] They affected the circulation and living environment for marine species. [51] The shallow marine environment would change dramatically, resembling a deep sea environment. [51] The deep sea species would thrive, while the other species died out. The trilobite fossils actually records important natural selection processes. [51] The carbonate sequence containing the trilobite fossils hence important to record paleoenvironment and evolution. [51]
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 is affected by atmospheric and hydrosphere interaction and the evolution from primitive tectonics to modern plate tectonics. [52] Ore formation is related to supercontinent fragmentation and assembly. [52] 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. [52] Therefore, the formation of a certain type of ore is restricted to a specific period and the minerals are formed in relation with tectonic events. [52] 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. [2] [52]
Banded iron formations (BIFs) belong to granulite facies and are widely distributed in the metamorphosed units. The age of the ore is defined by isotopic analysis of hafnium dating]. [53] They are interlayered with volcanic-sedimentary rocks. [52] They can also occur as some other features: dismembered layers, lenses and boudins. [52] All the iron occurrences are in oxide form, rarely in silicate or carbonate form. [52] By analysing their oxygen isotope composition, it is suggested that the iron was deposited in an environment of weakly oxidized shallow sea environment. [52] [53] There are four regions where extensive iron deposits are found: Anshan in northeast China, eastern Hebei, Wutai and Xuchang-Huoqiu. [52] 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. [52]
Copper- zinc (Cu-Zn) deposits were deposited in the Hongtoushan greenstone belt, which was located in the northeastern part of the North China Craton. [52] They are typical volcanogenic massive sulfide ore deposits and were formed under rift environment. [52] The formation of the Cu-Zn deposits might not be under modern tectonics, so the formation process might be different from modern rift system. [52]
Neoarchean greenstone belt gold deposits are located in Sandaogou (northeastern side of The North China Craton). [52] [54] The greenstone belt type gold deposits are not commonly found in the craton because most of them were reworked in the Mesozoic, so they appeared to be in some other form. [52] However, from other cratonic examples in the world, the greenstone belt gold deposits should be abundant in the first place. [52]
Ultra high temperature metamorphic rocks found in the Paleoproterozoic Period indicate the start of modern tectonics. [52] [55] Great oxygenation events (GOE) also occurred in this period and it marked the start of a shift from an oxygen poor to an oxygen rich environments. [52] [55] There are two types of minerals commonly found from this period. [52] [55] 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. [55] Copper deposits are found in the Zhongtiaoshan area of Shanxi province. [52] [55] The khondalite sequence, which are high temperature metamorphic rocks, and graphite are often found together with the ore deposits. [52] There are a few types of ore deposits found and each of them correspond to a different formation environment. [52] 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. [52] [55]
Magnesite – boron deposits were formed in sedimentary sequences under rift related shallow sea lagoon settings. [52] It was a response to the great oxidation event as seen from its isotopic content. [52] In the Jiaoliao mobile belt, the GOE changed the isotopic ratio of 13C and 18O as the rock underwent recrystallization and mass exchange. [52] The ore also allows people to further understand the Global Oxidation Event system, for example, showing the exact atmospheric chemical change during that period. [52]
A rare-earth element-iron-lead-zinc (REE-Fe-Pb-Zn) system was formed from extensional rifting with upwelling of mantle, and therefore magma fractionation. [56] [52] 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. [56] [52] The REE-Fe-Pb-Zn system occurs in an alternating volcanic and sedimentary succession. [56] [52] Apart from REE, LREE (light rare earth elements) are also found in carbonatite dykes. [56] [52] Rare earth elements have important industrial and political implications in China. [56] [52] China is close to monopolising the export of rare earth elements in the whole world. [56] [52] Even the United States relies heavily on rare earth elements imported from China, [56] [52] while rare earth elements are essential in technologies. [57] [58] 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. [57] [58]
A copper-molybdenum (Cu-Mo) system originated in both the Central Asian Orogenic Belt (North) and the Qinling Orogenic Belt (South). [52]
The Central Asian Orgenic belt ore deposits occurred in arc complexes. [52] They formed from the closure of Paleo-Asian ocean. [52] The subduction generated copper and molybdenum Cu-Mo mineralization in the lithosphere block margins. [52] [59] [60] Duobaoshan Cu and Bainaimiao Cu-Mo deposits are found in granodiorite. [52] [59] Tonghugou deposits occur with the copper ore chalcopyrite. [52] North China hosted a large reserve of molybdenum with more than 70 ore bodies found in the Northern margin of the craton. [52]
Mineral deposits in southern margin of the North China Craton are next to the Qinling orogenic belt. [52] [59] Some deposits were formed during the amalgamation of the North and South China blocks. [52] A rifting-subduction-collision processes in Danfeng suture zone generated VMS deposits (Cu-Pb-Zn) in the arc area and a marginal fault basin. [52] [59]
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. [52] [59]
Gold (Au) deposits in the Mesozoic are very abundant. [52] [61] The formation environment of the gold includes intercontinental mineralization, craton destruction and mantle replacement. [52] The origin of the gold is from Precambrian basement rocks of the Jiaodong Complex and underlying mantle which underwent high grade metamorphism when intruded with Mesozoic granitoids. [52] [61] The largest cluster of gold deposits in China is found in the Jiaodong peninsula (east of Shandong Province). [52] [61] The area yielded one-fourth of the country's gold production but consisted only of 0.2% of the area of China. [52] The three sub-clusters of gold deposits in northern China are Linglong, Yantai and Kunyushan respectively. [52]
China has been producing diamonds for over 40 years in the North China Craton. [62] At first, diamonds were produced from alluvial deposits, but later on technology improved and the diamonds are now produced from kimberlitic sources. [62] 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. [62] The former operated for 34 years and produced 90,000 carats of diamonds per year. [62] The latter produced 60,000 carats per year, but its mining activity ceased in 2002. [62]
Diamond bearing kimberlite pipes and dykes were emplaced during the Ordovician in the Archean crust between 450–480 million years ago and again in the Tertiary. [62] Uplifting events caused the kimberlite to be exposed. [62] The two mines exist along narrow and discontinuous dykes around the Tan Lu fault. [62] Porphyritic kimberlites often occur with a matrix of other materials, such as serpentinized olivine and phlogopite or biotite, and breccia fragments. [62] The occurrence of diamonds with different materials caused a difference in diamond grade, diamond size distribution and quality. [62] For example, the diamonds from the China Diamond Corps' 701 Changma Mine worth US$40 per carat, while the diamonds from the Wafangdian Mine worth up to US$125 per carat. [62]
Orogeny is a mountain-building process that takes place at a convergent plate margin when plate motion compresses the margin. An orogenic belt or orogen develops as the compressed plate crumples and is uplifted to form one or more mountain ranges. This involves a series of geological processes collectively called orogenesis. These include both structural deformation of existing continental crust and the creation of new continental crust through volcanism. Magma rising in the orogen carries less dense material upwards while leaving more dense material behind, resulting in compositional differentiation of Earth's lithosphere. A synorogenic process or event is one that occurs during an orogeny.
Columbia, also known as Nuna or Hudsonland, is a hypothetical ancient supercontinent. It was first proposed by John J.W. Rogers and M. Santosh in 2002 and is thought to have existed approximately 2,500 to 1,500 million years ago (Ma), in the Paleoproterozoic era. The assembly of the supercontinent was likely completed during global-scale collisional events from 2,100 to 1,800 Ma.
The Grenville orogeny was a long-lived Mesoproterozoic mountain-building event associated with the assembly of the supercontinent Rodinia. Its record is a prominent orogenic belt which spans a significant portion of the North American continent, from Labrador to Mexico, as well as to Scotland.
The Pan-African orogeny was a series of major Neoproterozoic orogenic events which related to the formation of the supercontinents Gondwana and Pannotia about 600 million years ago. This orogeny is also known as the Pan-Gondwanan or Saldanian Orogeny. The Pan-African orogeny and the Grenville orogeny are the largest known systems of orogenies on Earth. The sum of the continental crust formed in the Pan-African orogeny and the Grenville orogeny makes the Neoproterozoic the period of Earth's history that has produced most continental crust.
The Kaapvaal Craton, along with the Pilbara Craton of Western Australia, are the only remaining areas of pristine 3.6–2.5 Ga crust on Earth. Similarities of rock records from both these cratons, especially of the overlying late Archean sequences, suggest that they were once part of the Vaalbara supercontinent.
The geology of China consists of three Precambrian cratons surrounded by a number of orogenic belts. The modern tectonic environment is dominated by the continued collision of India with the rest of Asia starting 40–50 million years ago. This has formed the Himalayas and continues to deform most of China. China has vast mineral reserves, a significant earthquake risk in its western regions and rare isolated active volcanoes throughout the country.
The Trans-Hudson orogeny or Trans-Hudsonian orogeny was the major mountain building event (orogeny) that formed the Precambrian Canadian Shield and the North American Craton, forging the initial North American continent. It gave rise to the Trans-Hudson orogen (THO), or Trans-Hudson Orogen Transect (THOT), which is the largest Paleoproterozoic orogenic belt in the world. It consists of a network of belts that were formed by Proterozoic crustal accretion and the collision of pre-existing Archean continents. The event occurred 2.0–1.8 billion years ago.
The West African Craton (WAC) is one of the five cratons of the Precambrian basement rock of Africa that make up the African Plate, the others being the Kalahari craton, Congo craton, Saharan Metacraton and Tanzania Craton. Cratons themselves are tectonically inactive, but can occur near active margins, with the WAC extending across 14 countries in Western Africa, coming together in the late Precambrian and early Palaeozoic eras to form the African continent. It consists of two Archean centers juxtaposed against multiple Paleoproterozoic domains made of greenstone belts, sedimentary basins, regional granitoid-tonalite-trondhjemite-granodiorite (TTG) plutons, and large shear zones. The craton is overlain by Neoproterozoic and younger sedimentary basins. The boundaries of the WAC are predominantly defined by a combination of geophysics and surface geology, with additional constraints by the geochemistry of the region. At one time, volcanic action around the rim of the craton may have contributed to a major global warming event.
The geology of Russia, the world's largest country, which extends over much of northern Eurasia, consists of several stable cratons and sedimentary platforms bounded by orogenic (mountain) belts.
The Svecofennian orogeny is a series of related orogenies that resulted in the formation of much of the continental crust in what is today Sweden and Finland plus some minor parts of Russia. The orogenies lasted from about 2000 to 1800 million years ago during the Paleoproterozoic Era. The resulting orogen is known as the Svecofennian orogen or Svecofennides. To the west and southwest the Svecofennian orogen limits with the generally younger Transscandinavian Igneous Belt. It is assumed that the westernmost fringes of the Svecofennian orogen have been reworked by the Sveconorwegian orogeny just as the western parts of the Transscandinavian Igneous Belt has. The Svecofennian orogeny involved the accretion of numerous island arcs in such manner that the pre-existing craton grew with this new material from what is today northeast to the southwest. The accretion of the island arcs was also related to two other processes that occurred in the same period; the formation of magma that then cooled to form igneous rocks and the metamorphism of rocks.
The Aravalli Mountain Range is a northeast-southwest trending orogenic belt in the northwest part of India and is part of the Indian Shield that was formed from a series of cratonic collisions. The Aravalli Mountains consist of the Aravalli and Delhi fold belts, and are collectively known as the Aravalli-Delhi orogenic belt. The whole mountain range is about 700 km long. Unlike the much younger Himalayan section nearby, the Aravalli Mountains are believed much older and can be traced back to the Proterozoic Eon. They are arguably the oldest geological feature on Earth. The collision between the Bundelkhand craton and the Marwar craton is believed to be the primary mechanism for the development of the mountain range.
The Huangling Anticline or Complex represents a group of rock units that appear in the middle of the Yangtze Block in South China, distributed across Yixingshan, Zigui, Huangling, and Yichang counties. The group of rock involves nonconformity that sedimentary rocks overlie the metamorphic basement. It is a 73-km long, asymmetrical dome-shaped anticline with axial plane orientating in the north-south direction. It has a steeper west flank and a gentler east flank. Basically, there are three tectonic units from the anticline core to the rim, including Archean to Paleoproterozoic metamorphic basement, Neoproterozoic to Jurassic sedimentary rocks, and Cretaceous fluvial deposit sedimentary cover. The northern part of the core is mainly tonalite-trondhjemite-gneiss (TTG) and Cretaceous sedimentary rock called the Archean Kongling Complex. The middle of the core is mainly the Neoproterozoic granitoid. The southern part of the core is the Neoproterozoic potassium granite. Two basins are situated on the western and eastern flanks of the core, respectively, including the Zigui basin and Dangyang basin. Both basins are synforms while Zigui basin has a larger extent of folding. Yuanan Graben and Jingmen Graben are found within the Dangyang Basin area. The Huangling Anticline is an important area that helps unravel the tectonic history of the South China Craton because it has well-exposed layers of rock units from Archean basement rock to Cretaceous sedimentary rock cover due to the erosion of the anticline.
The Qinling orogenic belt is a tectonic feature that evolved throughout the Proterozoic and Phanerozoic eons due to a variety of tectonic activities. It is a part of the Central China Orogenic Belt, aligned in an east–west orientation across Central China, and spans portions of Shaanxi, Henan and Gansu provinces along the Qinling Mountains which are one of the greatest mountain ranges in China. The first materials involved in the Qinling orogenic belt formed around 2.5 billion years ago, whereas the main morphology of the belt now largely reflects the Triassic collision between the North China Plate and the South China Plate and Cenozoic extension across China. During these 2.5 billion years, various types of rocks have been formed here due to different tectonic processes and chemical reactions between rocks. Therefore, geologists are able to reconstruct the evolution of mountain belt based on evidence preserved in these rocks.
The Eastern Block of the North China Craton is one of the Earth's oldest pieces of continent. It is separated from the Western Block by the Trans-North China Orogen. It is situated in northeastern China and North Korea. The Block contains rock exposures older than 2.5 billion years. It serves as an ideal place to study how the crust was formed in the past and the related tectonic settings.
The South China Craton or South China Block is one of the Precambrian continental blocks in China. It is traditionally divided into the Yangtze Block in the NW and the Cathaysia Block in the SE. The Jiangshan–Shaoxing Fault represents the suture boundary between the two sub-blocks. Recent study suggests that the South China Block possibly has one more sub-block which is named the Tolo Terrane. The oldest rocks in the South China Block occur within the Kongling Complex, which yields zircon U–Pb ages of 3.3–2.9 Ga.
The Western Block of the North China Craton is an ancient micro-continental block mainly composed of Neoarchean and Paleoproterozoic rock basement, with some parts overlain by Cambrian to Cenozoic volcanic and sedimentary rocks. It is one of two sub-blocks within the North China Craton, located in east-central China. The boundaries of the Western Block are slightly different among distinct models, but the shapes and areas are similar. There is a broad consensus that the Western Block covers a large part of the east-central China.
The Yavapai orogeny was an orogenic (mountain-building) event in what is now the Southwestern United States that occurred between 1710 and 1680 million years ago (Mya), in the Statherian Period of the Paleoproterozoic. Recorded in the rocks of New Mexico and Arizona, it is interpreted as the collision of the 1800-1700 Mya age Yavapai island arc terrane with the proto-North American continent. This was the first in a series of orogenies within a long-lived convergent boundary along southern Laurentia that ended with the ca. 1200–1000 Mya Grenville orogeny during the final assembly of the supercontinent Rodinia, which ended an 800-million-year episode of convergent boundary tectonism.
The Central Asian Orogenic Belt (CAOB), also called the Altaids, is one of the world's largest Phanerozoic accretionary orogens, and thus a leading laboratory of geologically recent crustal growth. The orogenic belt is bounded by the East European Craton and the North China Craton in the Northwest-Southeast direction, as well as Siberia Craton and Tarim Craton in the Northeast-Southwest direction. It formed by ocean closures during Neoproterozoic to the late Phanerozoic time, from around 750 to 150 Ma. Like many other accretionary orogenic belts, the Central Asian Orogenic Belt consists of a huge amount of magmatic arcs, arc-related basins, accretionary complexes, seamounts, continental fragments and ophiolites. It is also considered a relatively distinctive collisional orogenic belt because widespread subduction-accretion complexes and arc magmatic rocks can be found in the region, but collision-related foreland basins are not common.
The geology of the Kimberley, a region of Western Australia, is a rock record of the early Proterozoic eon that includes tectonic plate collision, mountain-building (orogeny) and the joining (suturing) of the Kimberley and Northern Australia cratons, followed by sedimentary basin formation.
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