冈瓦纳大陆

(重定向自冈瓦那大陆
5.5亿年前形成后的冈瓦纳大陆
4.2億年前的冈瓦纳大陸,此視角下中心對準地理南極

地質學中,冈瓦纳大陆(英語:Gondwana/ɡɒndˈwɑːnə/[1][2],或Gondwanaland),也称冈瓦那大陆冈瓦纳古陆南方大陆,是存在於新元古代侏羅紀前期(約5.73亿至1.8亿年前)的超大陸,它是從罗迪尼亚大陸分裂出來的兩塊超大陸之一(另一個超大陸為劳亚大陆),存在于南半球

名字的由来编辑

冈瓦纳本是印度的一个地名。在这个地方发现了岩石与南半球其他大陆的共性,爱德华·修斯於是以此來起名冈瓦纳大陆。

大陆漂移过程编辑

罗迪尼亚大陆的南部分裂而成。进一步分裂成:新西兰岛屿、澳洲大陆南美大陆南极大陆馬達加斯加非洲大陆,以及已經漂流到北半球的印度古陆、阿拉伯半島

走向分裂编辑

中生代编辑

位于超大陆中心的南极洲与冈瓦纳的其他板块都相邻。南美、非洲与南极洲之间最古老的磁异常发现于160 to 180 Ma侏罗纪威德尔海南部。[3]超大陆破裂形成了地球上最大的大火成岩省

西印度洋的初始编辑
非洲与马达加斯加之间的洋底形成150 Ma (左),以及印度与马达加斯加之间洋底形成c. 70 Ma (右).

卡鲁-费拉大火成岩省英语Karoo-Ferrar洪流玄武岩(南非、南极洲、南美洲、印度、澳洲、新西兰,1.84亿年前)对应普林斯巴赫阶-托阿尔阶灭绝事件(托阿尔阶大洋缺氧)。导致大量海洋物种相继死光。二氧化碳浓度急剧上升,全球突然变暖5~10℃,地球上出现严重缺氧局面,很多生物因此走向灭绝。侏罗纪早期的冈瓦纳超大陆开始破裂。 Before the Karoo plume initiated rifting between Africa and Antarctica, it separated a series of smaller continental blocks from Gondwana's southern, Proto-Pacific margin (along what is now the 横贯南极山脉): the Antarctic Peninsula, Marie Byrd Land, 西兰大陆, and 瑟斯顿岛; the Falkland Islands and Ellsworth–Whitmore Mountains (in Antarctica) were rotated 90° in opposite directions; and South America south of the Gastre Fault (often referred to as Patagonia) was pushed westward.[4] The history of the Africa-Antarctica break-up can be studied in great detail in the fracture zones and magnetic anomalies flanking the Southwest Indian Ridge.[5]

The Madagascar block and the Mascarene Plateau, stretching from the Seychelles to Réunion, were broken off India; elements of this breakup nearly coincide with the Cretaceous–Paleogene extinction event. The India–Madagascar–Seychelles separations appear to coincide with the eruption of the Deccan basalts, whose eruption site may survive as the Réunion hotspot. The Seychelles and the Maldives are now separated by the Central Indian Ridge.

During the initial break-up in the Early Jurassic a marine transgression swept over the Horn of Africa covering Triassic planation surfaces with sandstone, limestone, shale, marls and evaporites.[6][7]

Opening of eastern Indian Ocean编辑

The first ocean floor formed between India and Antarctica c. 120 Ma (left). The Kerguelen LIP began to form the Ninety East ridge c. 80 Ma (centre). The Indian and Australian plates merged c. 40 Ma (right).

East Gondwana, comprising Antarctica, Madagascar, India, and Australia, began to separate from Africa. East Gondwana then began to break up 约 132.5 to 96 Ma when India moved northwest from Australia-Antarctica.[8] The Indian Plate and the Australian Plate are now separated by the Capricorn Plate and its diffuse boundaries.[9] During the opening of the Indian Ocean, the Kerguelen hotspot first formed the Kerguelen Plateau on the Antarctic Plate118 to 95 Ma and then the Ninety East Ridge on the Indian Plate at 约 100 Ma.[10] The Kerguelen Plateau and the Broken Ridge, the southern end of the Ninety East Ridge, are now separated by the Southeast Indian Ridge.

Separation between Australia and East Antarctica began 约 132 Ma with sea-floor spreading occurring 约 96 Ma. A shallow seaway developed over the South Tasman Rise during the Early Cenozoic and as oceanic crust started to separate the continents during the Eocene35.5 Ma global ocean temperature dropped significantly.[11] A dramatic shift from arc- to rift magmatism 约 100 Ma separated Zealandia, including New Zealand, the Campbell Plateau, Chatham Rise, Lord Howe Rise, Norfolk Ridge, and New Caledonia, from West Antarctica84 Ma.[12]

Opening of South Atlantic Ocean编辑

At c. 126 Ma (left) the Falkland Plateau began to slide past southern Africa and the Paraná-Etendeka LIP had opened the Mid-Atlantic Ridge. At c. 83 Ma (right) the South Atlantic was fully opened and the Romanche Fracture Zone was forming near the Equator.

The opening of the South Atlantic Ocean divided West Gondwana (South America and Africa), but there is a considerable debate over the exact timing of this break-up. Rifting propagated from south to north along Triassic–Early Jurassic lineaments, but intra-continental rifts also began to develop within both continents in Jurassic–Cretaceous sedimentary basins; subdividing each continent into three sub-plates. Rifting began 约 190 Ma at Falkland latitudes, forcing Patagonia to move relative to the still static remainder of South America and Africa, and this westward movement lasted until the Early Cretaceous 126.7 Ma. From there rifting propagated northward during the Late Jurassic 约 150 Ma or Early Cretaceous 约 140 Ma most likely forcing dextral movements between sub-plates on either side. South of the Walvis Ridge and Rio Grande Rise the Paraná and Etendeka magmatics resulted in further ocean-floor spreading 约 130 to 135 Ma and the development of rifts systems on both continents, including the Central African Rift System and the Central African Shear Zone which lasted until 约 85 Ma. At Brazilian latitudes spreading is more difficult to assess because of the lack of palaeo-magnetic data, but rifting occurred in Nigeria at the Benue Trough118 Ma. North of the Equator the rifting began after 120.4 Ma and continued until 约 100 to 96 Ma.[13]

Early Andean orogeny编辑

The first phases of Andean orogeny in the Jurassic and Early Cretaceous were characterized by extensional tectonics, rifting, the development of back-arc basins and the emplacement of large batholiths.[14][15] This development is presumed to have been linked to the subduction of cold oceanic lithosphere.[15] During the mid to Late Cretaceous (ca. 90 million years ago) the Andean orogeny changed significantly in character.[14][15] Warmer and younger oceanic lithosphere is believed to have started to be subducted beneath South America around this time. Such kind of subduction is held responsible not only for the intense contractional deformation that different lithologies were subject to, but also the uplift and erosion known to have occurred from the Late Cretaceous onward.[15] Plate tectonic reorganization since the mid-Cretaceous might also have been linked to the opening of the South Atlantic Ocean.[14] Another change related to mid-Cretaceous plate tectonic changes was the change of subduction direction of the oceanic lithosphere that went from having south-east motion to having a north-east motion at about 90 million years ago.[16] While subduction direction changed it remained oblique (and not perpendicular) to the coast of South America, and the direction change affected several subduction zone-parallel faults including Atacama, Domeyko and Liquiñe-Ofqui.[15][16]

Cenozoic编辑

The Indian subcontinent began to collide with Asia circa 70 Ma, since which more than 1,400 km(870 mi) of crust has been absorbed by the Himalayan-Tibetan orogen. During the Cenozoic the orogen resulted in the construction of the Tibetan Plateau between the Tethyan Himalayas in the south and the Kunlun and Qilian mountains in the north.[17]

Later, South America was connected to North America via the Isthmus of Panama, cutting off a circulation of warm water and thereby making the Arctic colder,[18] as well as allowing the Great American Interchange.

The breakup of Gondwana can be said to continue in eastern Africa at the Afar Triple Junction, which separates the Arabian, Nubian, and Somali plates, resulting in rifting in the Red Sea and East African Rift.[19]

Australia–Antarctica separation编辑

In the Early Cenozoic Australia was still connected to Antarctica 约 35–40° south of its current location and both continents were largely unglaciated. A rift between the two developed but remained an embayment until the Eocene-Oligocene boundary when the Circumpolar Current developed and the glaciation of Antarctica began.[20]

Australia was warm and wet during the Palaeocene and dominated by rainforest. The opening of the Tasman Gateway at the Eocene-Oligocene boundary (33 Ma) resulted in abrupt cooling but the Oligocene became a period of high rainfall with swamps in southeast Australia. During the Miocene a warm and humid climate developed with pockets of rainforests in central Australia but before the end of the period colder and drier climate severely reduced this rainforest. A brief period of increased rainfall in the Pliocene was followed by drier climate which favoured grassland. Since then the fluctuation between wet interglacial periods and dry glacial periods has developed into the present arid regime. Australia has thus experienced various climate changes over a 15 million year period with a gradual decrease in precipitation.[21]

The Tasman Gateway between Australia and Antarctica began to open 约 40 to 30 Ma. Palaeontological evidences indicate the Antarctic Circumpolar Current (ACC) was established in the Late Oligocene 约 23 Ma with the full opening of the Drake Passage and the deepening of the Tasman Gateway. The oldest oceanic crust in the Drake Passage, however, is 34 to 29 Ma-old which indicates spreading between the Antarctic and South American plates began near the Eocene/Oligocene boundary.[22] Deep sea environments in Tierra del Fuego and the North Scotia Ridge during the Eocene and Oligocene indicate a "Proto-ACC" opened during this period. Later, 26 to 14 Ma, a series of events severally restricted the Proto-ACC: change to shallow marine conditions along the North Scotia Ridge; closure of the Fuegan Seaway, the deep sea that existed in Tierra del Fuego; and uplift of the Patagonian Cordillera. This, together with the reactivated Iceland plume, contributed to global warming. During the Miocene, the Drake Passage began to widen and as water flow between South America and the Antarctic Peninsula increased, the renewed ACC resulted in cooler global climate.[23]

Since the Eocene the northward movement of the Australian Plate has resulted in an arc-continent collision with the Philippine and Caroline plates and the uplift of the New Guinea Highlands.[24] From the Oligocene to the late Miocene, the climate in Australia, dominated by warm and humid rainforests before this collision, began to alternate between open forest and rainforest before the continent became the arid or semiarid landscape it is today.[25]

证据编辑

水龙类化石非洲南美都有发现,而它们不可能跨越海洋游到对岸。只能说明大陆本相连。

  • 岩石证据
  • 其他证据

对动物地理的影响编辑

很多动物起源于冈瓦纳大陆,如长鼻类(大象)、古腭类(鸵鸟等),解释了南亚和非洲,非洲和南美之间动物区系的类似性。解释了新西兰没有土生哺乳动物(蝙蝠除外)的原因等。

参考文献编辑

  1. ^ gondwana. Dictionary.com. Lexico Publishing Group. [2010-01-18]. 
  2. ^ Gondwanaland. Merriam-Webster Online Dictionary. [2010-01-18]. 
  3. ^ Jokat 等人 2003,Introduction, pp. 1–2
  4. ^ Encarnación 等人 1996,Early rifting and Gondwana breakup, pp. 537–538
  5. ^ Royer 等人 1988,Figg. 7 a–j, pp. 248–257
  6. ^ Abbate, Ernesto; Bruni, Piero; Sagri, Mario. Geology of Ethiopia: A Review and Geomorphological Perspectives. (编) Billi, Paolo. Landscapes and Landforms of Ethiopia. World Geomorphological Landscapes. 2015: 33–64. ISBN 978-94-017-8026-1. doi:10.1007/978-94-017-8026-1_2. 
  7. ^ Coltorti, M.; Dramis, F.; Ollier, C.D. Planation surfaces in Northern Ethiopia. Geomorphology. 2007, 89 (3–4): 287–296. Bibcode:2007Geomo..89..287C. doi:10.1016/j.geomorph.2006.12.007. 
  8. ^ Powell,Roots & Veevers(1988),Abstract
  9. ^ DeMets,Gordon & Royer(2005),Introduction; Fig. 1, p. 446
  10. ^ Müller,Royer & Lawver(1993),Model results, pp. 277–278
  11. ^ McLoughlin 2001,East Antarctica–Australia, p. 280
  12. ^ McLoughlin 2001,West Antarctica–Tasmantia, p. 280
  13. ^ Seton 等人 2012,South Atlantic, pp. 217–218
  14. ^ 14.0 14.1 14.2 Ramos 2009,Abstract
  15. ^ 15.0 15.1 15.2 15.3 15.4 Charrier,Pinto & Rodríguez(2006),第45–46页
  16. ^ 16.0 16.1 Hoffmann-Rothe 等人 2006
  17. ^ Yin & Harrison 2000,Abstract
  18. ^ Luyendyk,Forsyth & Phillips(1972),Abstract
  19. ^ Jestin,Huchon & Gaulier(1994),Abstract
  20. ^ Martin 2006,Palaeogeography, pp. 538–539
  21. ^ Martin 2006,Conclusions, pp. 557–558
  22. ^ Lagabrielle 等人 2009,Timing of opening of the Drake Passage region, pp. 198–199
  23. ^ Lagabrielle 等人 2009,Conclusions, p. 210
  24. ^ Hill & Hall 2003,Abstract
  25. ^ Travouillon 等人 2009,Abstract

参见编辑