The Xiong'er Volcanic Belt () is a 1770 to 1800 million year-old group of

volcanic rock Volcanic rock (often shortened to volcanics in scientific contexts) is a rock formed from lava erupted from a volcano. In other words, it differs from other igneous rock by being of volcanic origin. Like all rock types, the concept of volcanic ...

s located on the southern edge of the North China craton (Figure 1). It covers an area of approximately 60,000 km² and varies from 3000 m to 7000 m thick. The perimeter of the

volcanic belt A volcanic belt is a large volcanically active region. Other terms are used for smaller areas of activity, such as volcanic fields. Volcanic belts are found above zones of unusually high temperature () where magma is created by partial melting ...

is composed of three faults: the Jianxian-Lintong fault to the northwest, the Luoyang-Baofeng fault to the northeast, and the Luonan-Luanchan fault to the south (Figure 2). The volcanic belt formed at a time in Earth's history when all of the continents were joined forming the Supercontinent Columbia, the earliest known

supercontinent In geology, a supercontinent is the assembly of most or all of Earth's continental blocks or cratons to form a single large landmass. However, some geologists use a different definition, "a grouping of formerly dispersed continents", which leav ...

. The Xiong'er Volcanic Belt is very important because it can provide valuable information to help piece together the formation and breakup of the Supercontinent Columbia and the North China craton by identifying what type of boundary was located on the southern edge of the North China craton. Xiong'er Simplified Geologic Map

Geologic formations

The Xiong'er Volcanic Belt is made up of four

geologic formations A geological formation, or simply formation, is a body of rock having a consistent set of physical characteristics (lithology) that distinguishes it from adjacent bodies of rock, and which occupies a particular position in the layers of rock expo ...

which include one

sedimentary Sedimentary rocks are types of rock that are formed by the accumulation or deposition of mineral or organic particles at Earth's surface, followed by cementation. Sedimentation is the collective name for processes that cause these particles ...

and three

volcanic A volcano is a rupture in the crust of a planetary-mass object, such as Earth, that allows hot lava, volcanic ash, and gases to escape from a magma chamber below the surface. On Earth, volcanoes are most often found where tectonic plat ...

units. Starting at the bottom is the sedimentary Daguish formation and above it are the three volcanic formations, which consist of the Xushan, Jidanping, and Majiahe. They unconformably overlie the

Archean The Archean Eon ( , also spelled Archaean or Archæan) is the second of four geologic eons of Earth's history, representing the time from . The Archean was preceded by the Hadean Eon and followed by the Proterozoic. The Earth during the Arc ...

Paleoproterozoic The Paleoproterozoic Era (;, also spelled Palaeoproterozoic), spanning the time period from (2.5–1.6 Ga), is the first of the three sub-divisions ( eras) of the Proterozoic Eon. The Paleoproterozoic is also the longest era of the Earth's ...

formations which make up the basement rock in the area, and they lie

unconformably An unconformity is a buried erosional or non-depositional surface separating two rock masses or strata of different ages, indicating that sediment deposition was not continuous. In general, the older layer was exposed to erosion for an interval ...

below the meso-

Neoproterozoic The Neoproterozoic Era is the unit of geologic time from 1 billion to 538.8 million years ago. It is the last era of the Precambrian Supereon and the Proterozoic Eon; it is subdivided into the Tonian, Cryogenian, and Ediacaran periods. It is prec ...

sedimentary rocks, which include sandstones and limestones. *Daguish Formation :The Daguish

formation Formation may refer to: Linguistics * Back-formation, the process of creating a new lexeme by removing or affixes * Word formation, the creation of a new word by adding affixes Mathematics and science * Cave formation or speleothem, a secondar ...

is the bottommost formation, with a maximum thickness of 212 m. It is composed of

sedimentary rock Sedimentary rocks are types of rock that are formed by the accumulation or deposition of mineral or organic particles at Earth's surface, followed by cementation. Sedimentation is the collective name for processes that cause these particles ...

s such as

breccia Breccia () is a rock composed of large angular broken fragments of minerals or rocks cemented together by a fine-grained matrix. The word has its origins in the Italian language, in which it means "rubble". A breccia may have a variety of ...

conglomerate Conglomerate or conglomeration may refer to: * Conglomerate (company) * Conglomerate (geology) * Conglomerate (mathematics) In popular culture: * The Conglomerate (American group), a production crew and musical group founded by Busta Rhymes ** ...

, and

mudstone Mudstone, a type of mudrock, is a fine-grained sedimentary rock whose original constituents were clays or muds. Mudstone is distinguished from '' shale'' by its lack of fissility (parallel layering).Blatt, H., and R.J. Tracy, 1996, ''Petrology.' ...

. *Xushan Formation :The Xushan

is the second formation from the bottom and is dominantly composed of the

s basalt andesite and

andesite Andesite () is a volcanic rock of intermediate composition. In a general sense, it is the intermediate type between silica-poor basalt and silica-rich rhyolite. It is fine-grained (aphanitic) to porphyritic in texture, and is composed predo ...

. *Jidanping Formation :The Jidanping

is the third formation from the bottom and is a mixture of

s which include

dacite Dacite () is a volcanic rock formed by rapid solidification of lava that is high in silica and low in alkali metal oxides. It has a fine-grained ( aphanitic) to porphyritic texture and is intermediate in composition between andesite and rhyo ...

rhyolite Rhyolite ( ) is the most silica-rich of volcanic rocks. It is generally glassy or fine-grained (aphanitic) in texture, but may be porphyritic, containing larger mineral crystals ( phenocrysts) in an otherwise fine-grained groundmass. The miner ...

, basalt andesite, and

. *Majiahe Formation :The Majiahe

is the top formation and is dominantly composed of basalt andesite and

but also contains

pyroclastic Pyroclastic rocks (derived from the el, πῦρ, links=no, meaning fire; and , meaning broken) are clastic rocks composed of rock fragments produced and ejected by explosive volcanic eruptions. The individual rock fragments are known as pyroc ...

and

s as well. Rift

Tectonic setting

Currently there are two proposed hypotheses for the

tectonic Tectonics (; ) are the processes that control the structure and properties of the Earth's crust and its evolution through time. These include the processes of mountain building, the growth and behavior of the strong, old cores of continents ...

setting in which the Xiong'er Volcanic Belt formed. One is in a continental

rift In geology, a rift is a linear zone where the lithosphere is being pulled apart and is an example of extensional tectonics. Typical rift features are a central linear downfaulted depression, called a graben, or more commonly a half-grabe ...

setting, an area where a continent is being pushed apart as shown in figure 3. While the other hypotheses suggest an

Andean The Andes, Andes Mountains or Andean Mountains (; ) are the longest continental mountain range in the world, forming a continuous highland along the western edge of South America. The range is long, wide (widest between 18°S – 20°S l ...

type continental margin, where an oceanic plate is

subducting Subduction is a geological process in which the oceanic lithosphere is recycled into the Earth's mantle at convergent boundaries. Where the oceanic lithosphere of a tectonic plate converges with the less dense lithosphere of a second plate, the ...

underneath a continental plate as shown in figure 4. Evidence for a continental rift setting comes from geochemical data and the presence of

mafic A mafic mineral or rock is a silicate mineral or igneous rock rich in magnesium and iron. Most mafic minerals are dark in color, and common rock-forming mafic minerals include olivine, pyroxene, amphibole, and biotite. Common mafic rocks in ...

dike swarms within the North China craton. The mafic dike swarms support the rift hypothesis because they are believed to have formed from a mantle plume and have been dated to the same age as the Xiong'er volcanic belt. While the geochemical data which includes elemental composition and mineralogy of the volcanic rocks is believed by some to be similar to other volcanic rocks from continental settings. Evidence for an Andean type continental margin comes from the

lithology The lithology of a rock unit is a description of its physical characteristics visible at outcrop, in hand or core samples, or with low magnification microscopy. Physical characteristics include colour, texture, grain size, and composition. Li ...

and geochemical data. The lithological evidence includes rock type, grain size, composition, and texture. While the geochemical data includes elemental composition which is believed by some to be similar to an Andean type continental margin. Each of these tectonic settings typically produces volcanic rocks with specific geochemical signatures such as being enriched or depleted in certain elements. However the Xiong'er volcanic belt does not match up well geochemically with either of these tectonic settings, but seems to have more of a mixture of the two which has caused much confusion about the origin of the belt.

Significance of tectonic setting

Understanding what type of tectonic setting the Xiong'er Volcanic Belt formed in is crucial for the reconstruction of the Supercontinent Columbia and for making models of plate movement in the Earth's past. If the Xiong'er Volcanic belt represents a rift, then that will indicate that the southern edge of the North China craton faced another continent while it was a part of the Supercontinent Columbia, but if it is an Andean type continental margin then that will indicate that the southern edge of the North China craton would have faced the open ocean at this time.

References

{{Coord missing, China Volcanism of China Proterozoic volcanism Volcanic belts