Download Geological settings of Coal-bearing Basins of Mongolia - IGCP-589

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2012 年 10 月
第 33 卷 增刊 1: 43-44
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报
Oct. 2012
Acta Geoscientica Sinica
球
学
Vol.33 Supp.1: 43-44
www.地球学报.com
doi: 10.3975/cagsb.2012.s1.23
蒙古国含煤盆地的地质背景
Geological Settings of Coal-bearing Basins of Mongolia
Minjin CHULUUN1), Batbayar MINJIN2)
1) Mongolian University of Science and Technology;
2) Genie Energy International Co.
Abstract: Mongolia is located within the Central Asian Orogenic Belt. The belt is consist of numerous tectonic
blocks or terranes, which resulted from collisions during the Early Paleozoic (Caledonian orogeny), Late Paleozoic
(Hercynian orogeny) and partly in Early Mesozoic (Indosinian orogeny) (Sengör et al., 1993; Heubeck, 2001;
Badarch et al., 2003). These collisions had a profound effect on the coal-bearing sedimentary basins in
Carboniferous, Permian, Jurassic and Cretaceous periods of Mongolia. A total of more than 200 coal occurrences
and deposits are known, of which about 70 have been explored.
Key words: Coal-bearing basin; Mongolia
1
Carboniferous coal basins
Pennsylvanian coal basins developed in western
Mongolia, within Mongolian Altai Mountains. Basement of these basins is the Lake island arc terrain,
which developed during the Cambrian to Early Ordovician periods. Post accretion assemblages include
Silurian, Devonian and Mississippian marine sedimentary and some volcanic rocks, and Ordovician and
Devonian plutons (Badarch et al, 2002). Due to the
closure of Carboniferous arc system, the Mongolian
Altai basins were uplifted, consequently foreland
structure was formed and thick coal seams with complicated seam splitting and low sulfur contents accumulated. Such type seam is typical in rapidly subsiding
foreland setting. Low sulfur content is a main characteristic reflecting a scant hydrological connection to
the sea (Diessel, 1992).
2
Permian coal basins
Permian coal deposits in Mongolia are known in
the South Gobi area and the Southern Khangai Mnt.
South Mongolia is geologically subdivided into several terranes, including island arc terranes, and
fore/back arc basins. The Devonian and Carboniferous
periods represent a time of continental growth and
accretion within a long lived volcanic arc systems.
Amalgamation was completed by the Permian period,
except for the Sulankheer terrane, located in the south
easternmost part of Mongolia (Lemb and Badarch,
1997, 2001). In South Gobi coal-bearing upper Permian Tavantolgoi group deposits fill several
sub-basins and are folded and faulted by normal and
E-mail: [email protected].
thrust faults. In the Permian, the Paleoasian Ocean
between southern Mongolia and northern China closed
(Lamb et al., 2008). Because of this collision predominant structures of the South Gobi basin were
formed with peat accumulation in the foreland troughs.
Southern Khangai Permian basins are situated in the
northern part on the east-west oriented Valley of Lakes,
which was formed as foreland settings during the
Carboniferous, was influenced by the collision and
accommodated Permian coal measures accumulation
3
Jurassic coal basins
Mongolia’s coal deposits of Jurassic age were
formed in 2 stages and developed in several different
basins, such as Basin of Great Lakes in Western Mongolia, Valley of Lakes in Central Mongolia, the Orkhon-Selenge rivers area in north Mongolia, and minor
coal strata in east Mongolia.
In western Mongolia, coal-bearing Lower-Middle
Jurassic Jargalant Formation in Basin of Great Lakes
unconformably rests on the Vendian-Lower Cambrian
rocks and is represented by conglomerate, interbedded
with sandstone, siltstone and mudstone, with coal at
the top of the formation. In Valley of Lakes in Central
Mongolia and in south-southeast, Early-Middle Jurassic coal-bearing sediments are known in the rift-graben,
which covered by upper Cretaceous and Cenozoic
continental sediments.
The north-south directed contractile deformation
in north and northwest China and south Mongolia occurred during the Triassic and Jurassic periods. This
contractile deformation is known in coal-bearing
sediments of above mentioned Jurassic basins.
44
Acta Geoscientica Sinica
In north Mongolia the basement consists of Precambrian metamorphic complexes overlain by Paleozoic sedimentary rocks with marine fossils and volcano-plutonic rocks of active continental margin. In
this area many small graben are filled with Middle-Upper Jurassic coal-bearing sediments. The tectonic setting of this area is unclear due to lack of geological documentation. There are several possible
mechanisms such as the closure of the Mongol-Okhotsk Ocean which had north-south directed
regional contractile deformation, and extension in
eastern Mongolia that started in the Late Jurassic.
4
Cretaceous coal basins
After closure of the Mongol-Okhotsk Ocean, terrestrial conditions dominated Mongolia. At the end of
the Jurassic, in eastern and central Mongolia, tectonic
condition changed from compressional to extensional.
In eastern Mongolia, rifting began prior to 155 Ma and
ended after 126 Ma (Graham et al., 2001). The extension may be proposed including back arc extension
due to subduction of the paleo-Pacific plate (Watson et
al., 1987), and the collapse of overthickened crust
(Johnson et al., 2001). According to Graham et al.
(2001), the Zuunbayan Group falls into rift valleys.
Within the troughs, relatively large lakes formed
where thick mud and oil shales accumulated. With
decreasing subsidence rates, water levels decreased
and
paleoenvironmental condition became more
suitable for peat accumulation. The shallow lakes were
filled with Khukhteeg coal-bearing and Baruunbayan
sandy-conglomerate formations.
Carboniferous (Mongolian-Altai basin), Permian
(South Gobi and Southern Khangai basins) and Jurassic coal-bearing basins (West Mongolian and Valley of
Lakes basins) are foreland basins formed under compressional tectonic conditions. Cretaceous coals (Eastern Mongolian) and may be Middle-Upper Jurassic
coals (North Mongolia) accumulated within the rift
valleys created by extensional tectonics.
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