冈瓦纳

在地质学中，冈瓦那大陆（英语：Gondwana，/ɡɒndˈwɑːnə/，或Gondwanaland），也称冈瓦纳古陆、南方大陆，是存在于新元古代至侏罗纪前期（约5.73亿至1.8亿年前）的超大陆，它是从罗迪尼亚大陆分裂出来的两块超大陆之一（另一个超大陆为劳亚大陆），存在于南半球。冈瓦那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·修斯于是以此来起名冈瓦那大陆。由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、马达加斯加及非洲大陆，以及已经漂流到北半球的印度古陆、阿拉伯半岛。位于超大陆中心的南极洲与冈瓦那的其他板块都相邻。南美、非洲与南极洲之间最古老的磁异常发现于160 to 180 Ma的侏罗纪的威德尔海南部。超大陆破裂形成了地球上最大的大火成岩省。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。侏罗纪早期的冈瓦那超大陆开始破裂。 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. 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.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.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. The Indian Plate and the Australian Plate are now separated by the Capricorn Plate and its diffuse boundaries. During the opening of the Indian Ocean, the Kerguelen hotspot first formed the Kerguelen Plateau on the Antarctic Plate 约 118 to 95 Ma and then the Ninety East Ridge on the Indian Plate at 约 100 Ma. 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 Eocene 约 35.5 Ma global ocean temperature dropped significantly. 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 Antarctica 约 84 Ma.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 Trough 约 118 Ma. North of the Equator the rifting began after 120.4 Ma and continued until 约 100 to 96 Ma.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. This development is presumed to have been linked to the subduction of cold oceanic lithosphere. During the mid to Late Cretaceous (ca. 90 million years ago) the Andean orogeny changed significantly in character. 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. Plate tectonic reorganization since the mid-Cretaceous might also have been linked to the opening of the South Atlantic Ocean. 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. 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.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.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, 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.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.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.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. 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.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. 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.水龙类化石在非洲和南美都有发现，而它们不可能跨越海洋游到对岸。只能说明大陆本相连。很多动物起源于冈瓦那大陆，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。阿非利加洲（非洲）南极洲亚细亚洲（亚洲）大洋洲（澳洲）欧罗巴洲（欧洲）北亚美利加洲（北美洲）南亚美利加洲（南美洲）欧亚非大陆亚美利加洲（美洲）欧亚大陆大洋洲淹没的大陆 凯尔盖朗海台 · 西兰大陆 · 巽他古陆未来可能形成的超大陆 终极盘古大陆 · 阿美西亚大陆 · 新盘古大陆神话与猜测的大陆 库马里坎达姆大陆 · 雷姆利亚大陆 · 麦若普斯大陆 · 姆大陆 · 未知的南方大陆 · 亚特兰蒂斯