East Antarctic Shield

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Figure 1. Map of East and West Antarctica separated by the Transantarctic Mountain Range Map of the McMurdo-South Pole highway.jpg
Figure 1. Map of East and West Antarctica separated by the Transantarctic Mountain Range

The East Antarctic Shield or Craton is a cratonic rock body that covers 10.2 million square kilometers or roughly 73% of the continent of Antarctica. [1] The shield is almost entirely buried by the East Antarctic Ice Sheet that has an average thickness of 2200 meters but reaches up to 4700 meters in some locations. East Antarctica is separated from West Antarctica by the 100–300 kilometer wide Transantarctic Mountains, which span nearly 3,500 kilometers from the Weddell Sea to the Ross Sea. [2] The East Antarctic Shield is then divided into an extensive central craton (Mawson craton) that occupies most of the continental interior and various other marginal cratons that are exposed along the coast.

Contents

Background

The blue line represents the path traveled by the East Antarctic Shield over the past 550 million years. Red numbers indicate the time (millions of years ago); the yellow dot represents the south pole. Map of motion of the East Antarctic Shield.svg
The blue line represents the path traveled by the East Antarctic Shield over the past 550 million years. Red numbers indicate the time (millions of years ago); the yellow dot represents the south pole.

Over the past 1 billion years, East Antarctica has traveled from tropical (to subtropical) southerly latitudes to its current location with the entire East Antarctic Shield positioned south of the Antarctic Circle. [2] Despite its relative lack of motion over the past 75 million years, the East Antarctic Shield has played a significant role in the arrangement and motion of its surrounding plates during the amalgamation and separation of the supercontinents, Rodinia, Gondwana, and Pangea. Because the surface of the shield is covered by ice and therefore not directly accessible, the information about its tectonic history comes primarily from seismic and core-sample data. Geologists have used this data to define the rock types present, age the rocks using radioactive dating techniques, unveil the climate history from isotope ratios, and trace the shield's motion based on varying magnetic properties. Unfortunately, there are only a few places where data can be collected directly from the basement rock, and even at these locations, the exposed areas of the central craton can be misleading due to factors such as reworking during high-grade late Neoproterozoic to Cambrian deformation, variable overprinting by Cambrian tectonics, and the presence of younger metasediments. [2] However, it has been determined that the East Antarctic Shield has a Precambrian to Ordovician basement of igneous and sedimentary rocks that are deformed and metamorphosed to varying degrees, and intruded by syn- to post-tectonic granites. [3] The basement is locally overlain by undeformed Devonian to Jurassic sediments, and intruded by Jurassic tholeiitic plutonic and volcanic rocks. [1] This knowledge of the shield's structural features and compositions leads to the development of a tectonic history. The traditional models of East Antarctic Shield geology typically involve a three-stage tectonic history that includes:

Interaction with supercontinents

Rodinia: 1100–750 Ma

East Antarctica comprises Archean and Proterozoic-Cambrian terranes that amalgamated during Precambrian and Cambrian times. [4] [5] In the time of the supercontinent Rodinia, western Australia and East Antarctica were linked by the two-stage Albany-Fraser-Wilkes orogen, which occurred between 1350 and 1260 Ma and 1210-1140 Ma, and also the older, Mawson craton. [6] It is estimated that Rodinia formed between 1100 Ma and 1000 Ma. [2] During this time, there was tectonism occurring from Coats Land to the Windmill Islands of East Antarctica. This was taken as evidence for a continuous, late Mesoproterozoic to early Neoproterozoic mobile belt skirting across the coast of the East Antarctic Shield. [7] This Grenville-age belt is commonly called the Wegener-Mawson Mobile Belt, or the Circum East Antarctic Mobile Belt, and can be extended to formerly adjacent continents. The Maud Province correlates with the Namaqua-Natal Province of South Africa. Rocks in the Rayner Complex and northern Prince Charles Mountains are an extension of the Eastern Ghats of India. Lastly, relationships in the Bunger Hills-Windmill Islands correspond closely to those in the Albany-Fraser Orogen of western Australia. [3] [7] This region of Grenville-age tectonism is interpreted as a suture between the Central Antarctic-South Australian craton (the Mawson continent) and the marginal cratons that make up most of southern Africa, India and western Australia. [3] This tectonism continued until 900 Ma and by 750 Ma, the supercontinent Rodinia had begun to break up. The rupture might have resulted from the opening of an equatorial ocean basin between West Laurentia and West Australia-East Antarctica. [2]

Gondwana: 550–320 Ma

The configuration of the continents during the time of Gondwana. The location of the Pan-African Orogeny, Lutzow Holm belt and many other features caused by the interaction between the East Antarctic Shield and the surrounding plates. Kuunga2.png
The configuration of the continents during the time of Gondwana. The location of the Pan-African Orogeny, Lutzow Holm belt and many other features caused by the interaction between the East Antarctic Shield and the surrounding plates.

Then came Gondwana. The amalgamation of East and West Gondwana occurred by the closure of the Mozambique Ocean. This collision occurred between 700 and 500 Ma and resulted in the East African Orogeny. [8] The protracted Pan-African tectonic period was one of the most spectacular mountain building episodes in Earth's history. Gondwana incorporated all of Africa, Madagascar, Seychelles, Arabia, India and East Antarctica along with most of South America and Australia. [2] In the late Cambrian, Gondwana stretched from polar (NW Africa) to subtropical southerly latitudes with East Antarctica around the equator. The Pan-African orogenies that stabilized the East Antarctic Shield took place in two main zones; a broad region between the Shackleton Mountain Range, caused by the collision with South Africa, and India, and along the Transantarctic Mountains (Ross Orogeny). [2]

The Ross Orogen comprises a deformed sequence of Neoproterozoic to Cambrian sediments. [9] These sediments were deposited at a passive margin that likely developed during the rifting of North America from the East Antarctic Shield, and were subsequently deformed and metamorphosed at a low- to medium-grade and intruded by syn- and post-tectonic granitoids. [3] Plutonism and metamorphism commenced at about 550 Ma with peak metamorphism at 540-535 Ma. [10] At this time, two more high-grade Cambrian mobile belts formed in East Antarctica, the Lutzow Holm Belt and the Prydz Belt. Tectonism was relatively synchronous between the two from 550 to 515 Ma and both belts overprinted late Mesoproterozoic to early Neoproterozoic, Grenville-age magmatic and metamorphosed rocks. The Lutzow Holm Belt separates the Grenville-age Maud and Rayner Provinces and is the southernmost segment of the East African Orogeny, which extended from East Africa to the Shackleton Range. [3] Evidence for ocean closure is well-documented in the East African Orogen and this is supported by the occurrence of ophiolite material in the Shackleton Range. [11] Further evidence for ocean closure along the Lutzow Holm Belt is provided by the different ages of Grenville-age tectonism in the Maud and Rayner Provinces of either side of the inferred suture. The climax of activity in both the Lutzow Holm and Prydz Belts was at 530 Ma, but the possibility of two-near-simultaneous collisions cannot be discounted and would mean that East Antarctica comprise three major crustal fragments that did not combine until the Cambrian. [12]

Pangea: 320–160 Ma

Animation of the rifting of Pangaea Pangea animation 03.gif
Animation of the rifting of Pangaea

From 320 Ma onward, Gondwana, Laurussia, and intervening terranes merged to form the supercontinent Pangea. [2] Pangea's main amalgamation occurred during the Carboniferous but continents continued to be added and rifted away in the Late Paleozoic to Early Mesozoic. [13] Pangea ruptured during the Jurassic, preceded by and associated with widespread magmatic activity, including the Karoo flood basalts and related dyke swarms in South Africa and the Ferrar Province in East Antarctica. [14]

Post Pangea: 160 Ma–present

In the Late Jurassic and Early Cretaceous, the East Antarctic Shield began to move southward at a faster rate than Africa and South America, resulting in seafloor spreading between the two sub-blocks of Gondwana in the Weddell Sea, Riiser-Larsen Sea, Mozambique and Somali basins. [2] A long phase of extension and rifting took place in the southern Weddell Sea before the onset of seafloor spreading, dated around 147 Ma. [15] During the mid-Cretaceous, seafloor spreading propagated eastward from the Riiser-Larsen Sea to the Enderby basin between East Antarctica and India. [16] At 50 Ma, the inception of rapid northward drift of the Australian plate caused rapid accretion of oceanic crust on the East Antarctic Shield. [17] Relative extension between West Australia and East Antarctica commenced in the Late Cretaceous to Early Tertiary, but oceanic crust between these two plates was formed only between 45 and 30 Ma in the Adare Trough of the Ross Sea. [18]

See also

Related Research Articles

Rodinia was a Mesoproterozoic and Neoproterozoic supercontinent that assembled 1.26–0.9 billion years ago (Ga) and broke up 750–633 million years ago (Ma). Valentine & Moores 1970 were probably the first to recognise a Precambrian supercontinent, which they named "Pangaea I." It was renamed "Rodinia" by McMenamin & McMenamin 1990 who also were the first to produce a reconstruction and propose a temporal framework for the supercontinent.

<span class="mw-page-title-main">Laurasia</span> Northern landmass that formed part of the Pangaea supercontinent

Laurasia was the more northern of two large landmasses that formed part of the Pangaea supercontinent from around 335 to 175 million years ago (Mya), the other being Gondwana. It separated from Gondwana 215 to 175 Mya during the breakup of Pangaea, drifting farther north after the split and finally broke apart with the opening of the North Atlantic Ocean c. 56 Mya. The name is a portmanteau of Laurentia and Asia.

<span class="mw-page-title-main">Columbia (supercontinent)</span> Ancient supercontinent of approximately 2,500 to 1,500 million years ago

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.

<span class="mw-page-title-main">Arctica</span> Ancient continent in the Neoarchean era

Arctica, or Arctida is a hypothetical ancient continent which formed approximately 2.565 billion years ago in the Neoarchean era. It was made of Archaean cratons, including the Siberian Craton, with its Anabar/Aldan shields in Siberia, and the Slave, Wyoming, Superior, and North Atlantic cratons in North America. Arctica was named by Rogers 1996 because the Arctic Ocean formed by the separation of the North American and Siberian cratons. Russian geologists writing in English call the continent "Arctida" since it was given that name in 1987, alternatively the Hyperborean craton, in reference to the hyperboreans in Greek mythology.

<span class="mw-page-title-main">Pannotia</span> Hypothesized Neoproterozoic supercontinent

Pannotia, also known as the Vendian supercontinent, Greater Gondwana, and the Pan-African supercontinent, was a relatively short-lived Neoproterozoic supercontinent that formed at the end of the Precambrian during the Pan-African orogeny, during the Cryogenian period and broke apart 560 Ma with the opening of the Iapetus Ocean, in the late Ediacaran and early Cambrian. Pannotia formed when Laurentia was located adjacent to the two major South American cratons, Amazonia and Río de la Plata. The opening of the Iapetus Ocean separated Laurentia from Baltica, Amazonia, and Río de la Plata. A 2022 paper argues that Pannotia never fully existed, reinterpreting the geochronological evidence: "the supposed landmass had begun to break up well before it was fully assembled". However, the assembly of the next supercontinent Pangaea is well established.

<span class="mw-page-title-main">Congo Craton</span> Precambrian craton that with four others makes up the modern continent of Africa

The Congo Craton, covered by the Palaeozoic-to-recent Congo Basin, is an ancient Precambrian craton that with four others makes up the modern continent of Africa. These cratons were formed between about 3.6 and 2.0 billion years ago and have been tectonically stable since that time. All of these cratons are bounded by younger fold belts formed between 2.0 billion and 300 million years ago.

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.

<span class="mw-page-title-main">Geology of Antarctica</span> Geologic composition of Antarctica

The geology of Antarctica covers the geological development of the continent through the Archean, Proterozoic and Phanerozoic eons.


SWEAT is the hypothesis that the Southwestern United States was at one time connected to East Antarctica.

<span class="mw-page-title-main">Gondwana</span> Neoproterozoic to Cretaceous landmass

Gondwana was a large landmass, sometimes referred to as a supercontinent. The remnants of Gondwana make up around two-thirds of today's continental area, including South America, Africa, Antarctica, Australia, Zealandia, Arabia, and the Indian Subcontinent.

<span class="mw-page-title-main">Ur (continent)</span> Hypothetical Archaean supercontinent from about 3.1 billion years ago

Ur is a hypothetical supercontinent that formed in the Archean eon around 3.1 billion years ago (Ga). In a reconstruction by Rogers, Ur is half a billion years older than Arctica and, in the early period of its existence, probably the only continent on Earth, making it a supercontinent despite probably being smaller than present-day Australia. In more recent works geologists often refer to both Ur and other proposed Archaean continental assemblages as supercratons. Ur can, nevertheless, be half a billion years younger than Vaalbara, but the concepts of these two early cratonic assemblages are incompatible.

<span class="mw-page-title-main">Laurentia</span> Craton forming the geological core of North America

Laurentia or the North American Craton is a large continental craton that forms the ancient geological core of North America. Many times in its past, Laurentia has been a separate continent, as it is now in the form of North America, although originally it also included the cratonic areas of Greenland and the Hebridean Terrane in northwest Scotland. During other times in its past, Laurentia has been part of larger continents and supercontinents and consists of many smaller terranes assembled on a network of early Proterozoic orogenic belts. Small microcontinents and oceanic islands collided with and sutured onto the ever-growing Laurentia, and together formed the stable Precambrian craton seen today.

<span class="mw-page-title-main">East African Orogeny</span> Main stage in the Neoproterozoic assembly of East and West Gondwana

The East African Orogeny (EAO) is the main stage in the Neoproterozoic assembly of East and West Gondwana along the Mozambique Belt.

A paleocontinent or palaeocontinent is a distinct area of continental crust that existed as a major landmass in the geological past. There have been many different landmasses throughout Earth's time. They range in sizes, some are just a collection of small microcontinents while others are large conglomerates of crust. As time progresses and sea levels rise and fall more crust can be exposed making way for larger landmasses. The continents of the past shaped the evolution of organisms on Earth and contributed to the climate of the globe as well. As landmasses break apart, species are separated and those that were once the same now have evolved to their new climate. The constant movement of these landmasses greatly determines the distribution of organisms on Earth's surface. This is evident with how similar fossils are found on completely separate continents. Also, as continents move, mountain building events (orogenies) occur, causing a shift in the global climate as new rock is exposed and then there is more exposed rock at higher elevations. This causes glacial ice expansion and an overall cooler global climate. The movement of the continents greatly affects the overall dispersal of organisms throughout the world and the trend in climate throughout Earth's history. Examples include Laurentia, Baltica and Avalonia, which collided together during the Caledonian orogeny to form the Old Red Sandstone paleocontinent of Laurussia. Another example includes a collision that occurred during the late Pennsylvanian and early Permian time when there was a collision between the two continents of Tarimsky and Kirghiz-Kazakh. This collision was caused because of their askew convergence when the paleoceanic basin closed.

<span class="mw-page-title-main">Terra Australis Orogen</span>

The Terra Australis Orogen (TAO) was a late Neoproterozoic- to Paleozoic-age accretionary orogen that ringed the ancient, active southern margin of the supercontinents Rodinia and later Pannotia. This vast orogenic belt stretched for c. 18,000 km (11,000 mi) along-strike and involved, from west to east, landmasses belonging to the modern-day Andean margin of South America, the South African Cape, West Antarctica, Victoria Land in East Antarctica, Eastern Australia, Tasmania, and New Zealand. The formation of the Terra Australis Orogen is associated with the breakup of Rodinia at the end of the Neoproterozoic Era and the creation of Panthalassa, the paleo-Pacific Ocean, and it was succeeded by the Gondwanide orogeny with the formation of the supercontinent Pangea in the middle Paleozoic Era.

<span class="mw-page-title-main">Tectonic evolution of Patagonia</span>

Patagonia comprises the southernmost region of South America, portions of which lie on either side of the Argentina-Chile border. It has traditionally been described as the region south of the Rio, Colorado, although the physiographic border has more recently been moved southward to the Huincul fault. The region's geologic border to the north is composed of the Rio de la Plata craton and several accreted terranes comprising the La Pampa province. The underlying basement rocks of the Patagonian region can be subdivided into two large massifs: the North Patagonian Massif and the Deseado Massif. These massifs are surrounded by sedimentary basins formed in the Mesozoic that underwent subsequent deformation during the Andean orogeny. Patagonia is known for its vast earthquakes and the damage they cause.

<span class="mw-page-title-main">South China Craton</span> Precambrian continental block located in China

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.

<span class="mw-page-title-main">Yavapai orogeny</span> Mountain building event 1.7 billion years ago in the southwestern United States

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.

<span class="mw-page-title-main">Geology of the Ellsworth Mountains</span> Geology of the Ellsworth Mountains, Antarctica

The geology of the Ellsworth Mountains, Antarctica, is a rock record of continuous deposition that occurred from the Cambrian to the Permian periods, with basic igneous volcanism and uplift occurring during the Middle to Late Cambrian epochs, deformation occurring in the Late Permian period or early Mesozoic era, and glacier formation occurring in the Cretaceous period and Cenozoic era. The Ellsworth Mountains are located within West Antarctica at 79°S, 85°W. In general, it is made up of mostly rugged and angular peaks such as the Vinson Massif, the highest mountain in Antarctica.

References

  1. 1 2 Drewry, David J. (November 1976). "Sedimentary basins of the east antarctic craton from geophysical evidence". Tectonophysics. 36 (1–3): 301–314. Bibcode:1976Tectp..36..301J. doi:10.1016/0040-1951(76)90023-8.
  2. 1 2 3 4 5 6 7 8 9 Torsvik, T. H.; Gaina, C.; Redfield, T. F. (2008). "Antarctica and Global Paleogeography: From Rodinia, Through Gondwanaland and Pangea, to the Birth of the Southern Ocean and the Opening of Gateways". Antarctica: A Keystone in a Changing World. pp. 125–140. doi:10.17226/12168. ISBN   978-0-309-11854-5.
  3. 1 2 3 4 5 6 Fitzsimons, I. C. W. (2000). "A review of tectonic events in the East Antarctic Shield and their implications for Gondwana and earlier supercontinents". Journal of African Earth Sciences. 31 (1): 3–23. Bibcode:2000JAfES..31....3F. doi:10.1016/S0899-5362(00)00069-5.
  4. ↑ Boger, S. D.; Fanning, C. J. L.; Fanning, C. M. (2001). "Early Paleozoic tectonism within the East Antarctic craton: The final suture between east and west Gondwana?". Geology. 29 (5): 463–466. Bibcode:2001Geo....29..463B. doi:10.1130/0091-7613(2001)029<0463:EPTWTE>2.0.CO;2.
  5. ↑ Harley, S. C. (2003). "Archaean-Cambrian crustal development of East Antarctica: Metamorphic characteristics and tectonic implication". Geological Society of London, Special Publications. Proterozoic East Gondwana: Supercontinent Assembly and Breakup (206): 203–230. Bibcode:2003GSLSP.206..203H. doi:10.1144/GSL.SP.2003.206.01.11. S2CID   128667053.
  6. ↑ Fitzsimons, I. C. E. (2003). "Proterozoic basement provinces of southern and southwestern Australia, and their correlations with Antarctica". Geological Society of London, Special Publications. Proterozoic East Gondwana: Supercontinent Assembly and Breakup (206): 93–130. Bibcode:2003GSLSP.206...93F. doi:10.1144/GSL.SP.2003.206.01.07. S2CID   129929345.
  7. 1 2 Kamanev, E. N. (1993). "Structure and evolution of the Antarctic shield in Precambrian". Gondwana Eight: Assembly, Evolution and Dispersal: 141–151.
  8. ↑ Shackleton, R. M. (1986). "Precambrian collision tectonics in Africa". Geological Society of London, Special Publications. Collision Tectonics (19): 329–349. Bibcode:1986GSLSP..19..329S. doi:10.1144/GSL.SP.1986.019.01.19. S2CID   131080096.
  9. ↑ Stump, E. (1995). The Ross Orogen of the Transantarctic Mountains. Cambridge University Press. p. 284. ISBN   9780521019996.
  10. ↑ Goodje, J. W.; Walker, N. W.; Hansel, V. L. (1993). "Neoproterozoic-Cambrian basement-involved orogenesis within the Antarctic margin of Gondwana". Geology. 21 (1): 37–40. Bibcode:1993Geo....21...37G. doi:10.1130/0091-7613(1993)021<0037:NCBIOW>2.3.CO;2.
  11. ↑ Stern, R. J. (1994). "Arc assembly and continental collision in the Neoproterozoic East African Orogen: implications for the consolidation of Gondwanaland". Annual Review of Earth and Planetary Sciences. 22: 319–351. Bibcode:1994AREPS..22..319S. doi:10.1146/annurev.ea.22.050194.001535. S2CID   4999945.
  12. ↑ Grunow, A.; Hanson, R.; Wilson, T. (1996). "Were aspects of Pan-African deformation linked to lapetus opening?". Geology. 24 (12): 1063–1066. Bibcode:1996Geo....24.1063G. doi:10.1130/0091-7613(1996)024<1063:WAOPAD>2.3.CO;2.
  13. ↑ Torsvik, T. H.; Cocks, L. R. M. (2004). "Earth geography from 400–250 million years: A paleomagnetic, faunal and facies review". Journal of the Geological Society of London. 161 (4): 555–572. doi:10.1144/0016-764903-098. S2CID   128812370.
  14. ↑ Torsvik, T. H.; Smethurst, M. A.; Burke, K.; Steinberg, B. (2006). "Large Igneous Provinces generated from the margins of the Large Low Velocity Provinces in the deep mantle". Geophysical Journal International . 167 (3): 1447–1460. Bibcode:2006GeoJI.167.1447T. doi: 10.1111/j.1365-246X.2006.03158.x .
  15. ↑ König, M.; Jokat, W. (2006). "The Mesozoic breakup of the Weddell Sea". Journal of Geophysical Research. 111 (B12): 12102. Bibcode:2006JGRB..11112102K. doi: 10.1029/2005JB004035 .
  16. ↑ Gaina, C.; Müller, R. D.; Brown, B.; Ishihara, T.; Ivanov, K.S. (2007). "Breakup and early seafloor spreading between India and Antarctica". Geophysical Journal International. 170 (1): 151–169. Bibcode:2007GeoJI.170..151G. doi: 10.1111/j.1365-246X.2007.03450.x .
  17. ↑ Whittaker, J. M.; Müller, R. D.; Laitchenkov, G.; Stagg, H.; Sdrolias, M.; Gaina, C.; Goncharov, A. (2007). "Major Australia-Antarctica plate reorganization at Hawaiian-Emperor bend time". Science. 318 (5847): 83–87. Bibcode:2007Sci...318...83W. doi:10.1126/science.1143769. PMID   17916729. S2CID   129191964.
  18. ↑ Cande, S. C.; Stock, J.; Müller, R. D.; Ishihara, T. (2000). "Cenozoic motion between East and West Antarctica". Nature. 404 (6774): 145–150. Bibcode:2000Natur.404..145C. doi:10.1038/35004501. PMID   10724159. S2CID   4399729.
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