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The geology of Thailand includes deep crystalline metamorphic basement rocks, overlain by extensive sandstone, limestone, turbidites and some volcanic rocks. The region experienced complicated tectonics during the Paleozoic, long-running shallow water conditions and then renewed uplift and erosion in the past several million years ago. [1]
Medium- and high-grade metamorphic rocks form the basement of Thailand and geologists have debated based on radiometric dating whether metamorphism took place during the Precambrian or Mesozoic (if during the Mesozoic, it likely overprinted and recrystallized older rocks). In the northwest, many rocks near Chiang Mai and Kanchanaburi are metamorphosed to amphibolite or epidote grade on the sequence of metamorphic facies. The region has a paragneiss-schist and anatectic-migmatic sequence.
Early Paleozoic rocks are only known in western Thailand, such as sandstones on Tarutao Island in the Andaman Sea with Cambrian and Ordovician trilobite fossils. Together with non-fossil bearing strata on the mainland, they make up the Tarutao Group. Primarily sandstones, some make direct contact visible at the surface with underlying gneiss.
Limestone commonly deposited in the Ordovician and Silurian, forming the Thung Song Group, with a large component of argillite in the upper and lower part of the group. There is also a shale horizon called the Ban Na Shale, interbedded with Ordovician limestone. The presence of shale suggests a deeper water environment in the Silurian. The Thong Pha Phum Group conformably overlies the Thung Song Group in the west with a thick sequence of non-fossil bearing clastic marine sedimentary rocks that likely deposited in a forearc basin. Volcanic activity was common in the Devonian and Carboniferous as limestone accumulated on a western facing continental margin (exposures of these rocks are visible at Petchabun-Loei in east-central Thailand).
Carboniferous and Permian turbidite sequences overlie these groups in south, west and central Thailand. Thick sequences of clastic sediment in the Kaeng Krachan Formation extends from the center-west into Myanmar. Some geologists have interpreted pebbly diamictite mudstone and turbidites in the Mergui Group as glacial sediments, with possible origin in India or northwest Australia. One interpretation holds that the Mergui Group was thrust on top of the Shan-Thai Block from the west during the Mesozoic, forming a nappe. Extensional tectonics in the north led to mafic volcanic activity within the Shan-Thai Block in the Carboniferous, continuing into the Permian. Some red beds also formed during the same period.
During the Permian, almost the entire region was submerged during a major marine transgression. Carbonates deposited in shallow, shelf seas and today form dramatic karst landscapes. The warm water Saraburi Group in the east has numerous fossils, while the Ratburi Group in the west does not. In peninsular Thailand, sandstone is predominant interfingered with Ratburi Group limestones. Along the western edge of the Khorat Plateau, a limestone dominated shelf sequence abuts turbidites and pyroclastic flow deposits. A magmatic arc around a west-dipping subduction zone produced intermediate and felsic volcanic rocks in the north around Lampang to the east of Chiang Mai. [2]
During the Triassic, a major marine transgression flooded Thailand. Conglomerate is common at the base of units from this time period, overlain by limestone that thickens to the westward. East of Chiang Mai, the Lampang Group has marine shale, sandstone, limestone and conglomerate three kilometers thick, overlain by an additional two kilometers of flysch. Geologists have interpreted it as shallow-water deposition in a forearc basin over a west-dipping subduction zone.
Marine conditions lasted into the Norian, or as late as the Jurassic in the west. The Mae Moei Group is a major limestone unit in the northwest equivalent to the Lampang Group with Jurassic strata at the top and overlain by Cretaceous red beds.
By contrast to the patterns of marine deposition, the Khorat Plateau in the northeast is underlain by Triassic-Cretaceous continental deposits. Offshore islands and the Cambodian border have numerous sandstones related to the plateau. With calc-alkaline volcanic rock at its base, the Khorat Plateau is diachronous giving the appearance that basin deposition moved further west through the Mesozoic. The Khorat Group is five kilometers thick in the northeast and holds occasional dinosaur, plant and bivalve fossils. Much of the deposition took place in a lake environment. The Khorat Group begins with 2.5 kilometers of red beds, overlain by light-colored sandstones, red beds and evaporites such as carnallite, tachyhydrite, halite and sylvite. The carnallite zone is up to 95 meters thick and the halite deposit is one of the thickest on Earth. [3]
Thailand has intrusive granitoid everywhere but the Khorat Plateau. I- and S-type plutons are dominant along the border with Myanmar and extending to the Phuket Island. Typically, they are small and isolated with biotite and muscovite-rich granite as well as potassium feldspar megacrysts, hornblende and large mica-tourmaline or lepidolite pegmatites. S-type granites in this belt commonly have tin-tungsten mineralization. Triassic S-type granitoid batholiths, often associated with orthogneiss and migmatite, form a central belt in western Thailand the peninsula.
Cenozoic sedimentary rocks are mainly found in low-lying areas in the north and west, but also at several areas in the south. In the north, graben formations filled with sediment two kilometers thick. For much of the Cenozoic, Thailand was comparatively flat until rapid uplift began in the north, accompanied by block faulting and horst and graben formation in the Pliocene and Pleistocene, leaving valley floors to fill with gravel and sand. Large quantities of natural gas and some petroleum have been found in the blended terrestrial and marine sedimentary strata along the Andaman Sea coast, ranging in age from Oligocene to Pliocene. Marine influence is modest and common later in the sequence, which is up to eight kilometers thick.
The Chao Paya Basin around Bangkok and Pitsanulok Basin in the north both have extensive Quaternary sedimentary cover from the last 2.5 million years. Based on aerial magnetic surveys and boreholes, geologists have inferred that the Chao Paya Basin is believed to be a composite graben with uneven underlying topography.
Throughout the Quaternary, as uplift continued sediments eroded off the rising highlands and deposited in low-lying areas. During the Pleistocene ice ages, the Gulf of Thailand resembled its present geography, although sea levels did rise and extend more than 100 kilometers north of Bangkok, leaving behind the 20 meter thick Bangkok Clay in the Holocene. An alkaline basalt province erupted across northern Thailand and into Cambodia and Vietnam, leaving behind small vents, plugs and flows. [4]
Thailand is a leading global producer of tin, almost exclusively from cassiterite. In a few locations, very small occurrences of malayaite and stannite—other examples of tin minerals—have been found.
Cassiterite is found in quartz veins, skarn deposits, aplite, pegmatite and greisenized granite intrusions, often with accessory minerals such as fluorite, muscovite, wolframite, columbite, tantalite, tourmaline, topaz, zircon and beryl. Sulfide minerals like chalcopyrite, pyrite, arsenopyrite, sphalerite, galena and bismuthinite are found in association with cassiterite in the north and south. Virtually all deposits display some form of hydrothermal formation. In the west and along the Malaysian border are tin-bearing granites. In fact, the Ranong-Phuket area near the Andaman Sea coast and the southern peninsula of Thailand produces 85 percent of its tin output. Onshore and offshore placer deposits are the key tin source.
Additionally, Thailand has some production of gypsum, limestone, kaolin, sapphire, zircon, tantalite, columbite, antimony, lead, zinc, barite and fluorite. Examples include Jurassic sandstones with copper-uranium mineralization or Ordovician limestones with lead-zinc sulfides. Onshore and offshore Cenozoic basins have lignite, oil shale and some petroleum. [5]
The geology of Nigeria formed beginning in the Archean and Proterozoic eons of the Precambrian. The country forms the Nigerian Province and more than half of its surface is igneous and metamorphic crystalline basement rock from the Precambrian. Between 2.9 billion and 500 million years ago, Nigeria was affected by three major orogeny mountain-building events and related igneous intrusions. Following the Pan-African orogeny, in the Cambrian at the time that multi-cellular life proliferated, Nigeria began to experience regional sedimentation and witnessed new igneous intrusions. By the Cretaceous period of the late Mesozoic, massive sedimentation was underway in different basins, due to a large marine transgression. By the Eocene, in the Cenozoic, the region returned to terrestrial conditions.
The geology of Cambodia is the study of the nation's rocks, minerals, water and landforms. Cambodia's ancient geologic history in the Precambrian is poorly understood. The region experienced tectonic activity and low-grade metamorphic rock formation throughout the Paleozoic, which a shift to marine conditions and fossil formation during the Permian and through much of the Mesozoic. Few rocks remain from the Cenozoic. Cambodia has comparatively few natural resources, although there is bauxite formed from laterite weathering, as well as phosphorite, iron, gems, limestone and other materials.
The geology of Georgia is the study of rocks, minerals, water, landforms and geologic history in Georgia. The country is dominated by the Caucasus Mountains at the junction of the Eurasian Plate and the Afro-Arabian Plate, and rock units from the Mesozoic and Cenozoic are particularly prevalent. For much of its geologic history, until the uplift of the Caucasus, Georgia was submerged by marine transgression events. Geologic research for 150 years by Georgian and Russian geologists has shed significant light on the region and since the 1970s has been augmented with the understanding of plate tectonics.
The geology of Bosnia & Herzegovina is the study of rocks, minerals, water, landforms and geologic history in the country. The oldest rocks exposed at or near the surface date to the Paleozoic and the Precambrian geologic history of the region remains poorly understood. Complex assemblages of flysch, ophiolite, mélange and igneous plutons together with thick sedimentary units are a defining characteristic of the Dinaric Alps, also known as the Dinaride Mountains, which dominate much of the country's landscape.
The geology of Sweden is the regional study of rocks, minerals, tectonics, natural resources and groundwater in the country. The oldest rocks in Sweden date to more than 2.5 billion years ago in the Precambrian. Complex orogeny mountain building events and other tectonic occurrences built up extensive metamorphic crystalline basement rock that often contains valuable metal deposits throughout much of the country. Metamorphism continued into the Paleozoic after the Snowball Earth glaciation as the continent Baltica collided with an island arc and then the continent Laurentia. Sedimentary rocks are most common in southern Sweden with thick sequences from the last 250 million years underlying Malmö and older marine sedimentary rocks forming the surface of Gotland.
The geology of Moldova encompasses basement rocks from the Precambrian dating back more than 2.5 billion years, overlain by thick sequences of Proterozoic, Paleozoic, Mesozoic and Cenozoic sedimentary rocks.
The geology of Utah, in the western United States, includes rocks formed at the edge of the proto-North American continent during the Precambrian. A shallow marine sedimentary environment covered the region for much of the Paleozoic and Mesozoic, followed by dryland conditions, volcanism, and the formation of the basin and range terrain in the Cenozoic.
The geology of Kazakhstan includes extensive basement rocks from the Precambrian and widespread Paleozoic rocks, as well as sediments formed in rift basins during the Mesozoic.
The geology of Laos includes poorly defined oldest rocks. Marine conditions persisted for much of the Paleozoic and parts of the Mesozoic, followed by periods of uplift and erosion. The country has extensive salt, gypsum and potash, but very little hydrocarbons and limited base metals.
The geology of Afghanistan includes nearly one billion year old rocks from the Precambrian. The region experienced widespread marine transgressions and deposition during the Paleozoic and Mesozoic, that continued into the Cenozoic with the uplift of the Hindu Kush mountains.
The geology of Kyrgyzstan began to form during the Proterozoic. The country has experienced long-running uplift events, forming the Tian Shan mountains and large, sediment filled basins.
The geology of Uzbekistan consists of two microcontinents and the remnants of oceanic crust, which fused together into a tectonically complex but resource rich land mass during the Paleozoic, before becoming draped in thick, primarily marine sedimentary units.
The geology of North Korea has been studied by the Central Geological Survey of Mineral Resources, rare international research and by inference from South Korea's geology.
The geology of Bulgaria consists of two major structural features. The Rhodope Massif in southern Bulgaria is made up of Archean, Proterozoic and Cambrian rocks and is a sub-province of the Thracian-Anatolian polymetallic province. It has dropped down, faulted basins filled with Cenozoic sediments and volcanic rocks. The Moesian Platform to the north extends into Romania and has Paleozoic rocks covered by rocks from the Mesozoic, typically buried by thick Danube River valley Quaternary sediments. In places, the Moesian Platform has small oil and gas fields. Bulgaria is a country in southeastern Europe. It is bordered by Romania to the north, Serbia and North Macedonia to the west, Greece and Turkey to the south, and the Black Sea to the east.
The geology of Slovakia is structurally complex, with a highly varied array of mountain ranges and belts largely formed during the Paleozoic, Mesozoic and Cenozoic eras.
The geology of Lithuania consists of ancient Proterozoic basement rock overlain by thick sequences of Paleozoic, Mesozoic and Cenozoic marine sedimentary rocks, with some oil reserves, abundant limestone, dolomite, phosphorite and glauconite. Lithuania is a country in the Baltic region of northern-eastern Europe.
Geology of Latvia includes an ancient Archean and Proterozoic crystalline basement overlain with Neoproterozoic volcanic rocks and numerous sedimentary rock sequences from the Paleozoic, some from the Mesozoic and many from the recent Quaternary past. Latvia is a country in the Baltic region of Northern Europe.
The geology of Greece is highly structurally complex due to its position at the junction between the European and African tectonic plates.
The geology of Denmark includes 12 kilometers of unmetamorphosed sediments lying atop the Precambrian Fennoscandian Shield, the Norwegian-Scottish Caledonides and buried North German-Polish Caledonides. The stable Fennoscandian Shield formed from 1.45 billion years ago to 850 million years ago in the Proterozoic. The Fennoscandian Border Zone is a large fault, bounding the deep basement rock of the Danish Basin—a trough between the Border Zone and the Ringkobing-Fyn High. The Sorgenfrei-Tornquist Zone is a fault-bounded area displaying Cretaceous-Cenozoic inversion.
The geology of Yukon includes sections of ancient Precambrian Proterozoic rock from the western edge of the proto-North American continent Laurentia, with several different island arc terranes added through the Paleozoic, Mesozoic and Cenozoic, driving volcanism, pluton formation and sedimentation.
