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New Earth dawns: supercontinent slowly takes shape

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New Earth dawns: supercontinent slowly takes shape

Сообщение автор Б&П в Чт 30 Апр 2015, 8:32 am

New Earth dawns: supercontinent slowly takes shape
(«The Sydney Morning Herald», Australia)

Peter Spinks

The weekend earthquake in Nepal reminds that planet Earth is in the process of forming one monumental supercontinent, not unlike the ancient one known as Rodinia.

The 7.8-magnitude earthquake that devastated Nepal at the weekend is a stark reminder that the Earth-moving forces that shape continents are as active today as they were 4.5 billion years ago when our planet was in the throes of being formed.

"We were near the quake's epicentre the day before it happened – and were near the epicentre of a major aftershock the day after," says Curtin University geologist Zheng-Xiang Li, speaking from Lhasa. "We were here to study how the India-Eurasian collision had driven the uplift of the Tibetan Plateau and the rise of the Himalayas."

Our island continent of Australia is set to join Amasia – in that we’re shifting by about seven centimetres a year towards Asia.

Professor Zheng-Xiang Li.

Professor Li was in Nepal to collect evidence in support of his theory that the Earth's seven major continents are in the process of re-forming to ultimately yield one giant supercontinent. "The speculated future supercontinent has been named Amasia, by Canadian scientist Professor Paul Hoffman," he explains.

The shift towards Amasia has become apparent over the past hundred million years or so, Professor Li points out. "It would take at least tens of millions more years – perhaps several hundred million years – before the new supercontinent is fully formed."

The evidence is compelling: GPS measurements show that the Atlantic Ocean is widening by a few centimetres a year. The Pacific Ocean, on the other hand, is narrowing at a similar rate.

"If this trend continues, within the next one or two hundred million years, the Pacific will have closed up – resulting in a collision between the American and the Eurasian continents," Professor Li notes. "Australia, meanwhile, is set to join Amasia – in that we're slowly but surely shifting by about seven centimetres a year towards Asia."


Supercontinents form by gathering most or all continents together. The India-Eurasia collision signifies the addition of India to the core of the future supercontinent, Professor Li says.

"India actually joined Eurasia some 50 million years ago," he explains. "The tectonic force kept driving India to move northward, causing the Indian continent to subduct – or slide – underneath the Himalayas and southern Tibet."

The weekend earthquake occurred at about 20 kilometres beneath the Himalayas. This where the two crustal plates slide against each other and build stresses that lead to countless quakes.

Professor Li is working with colleagues abroad to demonstrate that what he calls the "new revolution in plate tectonics" is underway. "By revolution, I mean the theoretical revolution similar to the development of plate tectonics theory in the 1960s," Professor Li explains.

The theory is based on the premise that Earth's outer shell is divided into several brittle sections, called crustal plates, which glide over the mantle, the rocky inner layer above the planet's core. There are seven main plates and numerous smaller ones, all moving and shoving against each other as they slide across the hot mantle.

"This time, we are about to understand what drives plate tectonics," says Professor Li. His major International Geoscience Programme project, dubbed "Supercontinent Cycles and Global Geodynamics", will investigate the hypothesis that Earth's plates, and its deep mantle, evolve in super-cycles.

The project, sponsored by UNESCO and the International Union for Geological Sciences, involves a multidisciplinary team of hundreds of scientists and research students from around the world. "Our team will address perhaps the most fundamental geoscience question – how Earth works," he explains.

Among other things, the project co-leaders Professor David Evans of Yale University, Professor Shijie Zhong of Colorado and Professor Bruce Eglington of Saskatchewan will study the evolution of a series of supercontinents through Earth's history. This will include the break-up of the last such supercontinent, Pangea, which led to the formation of the Atlantic, Indian and Southern oceans.

"We'll also research how the Earth's inner engine has driven the supercontinent cycles and establish new concepts, tools, maps and global databases to assist with modelling global changes and the discovery of new Earth resources."

This is the first time that such a diverse team has been brought together at such a scale to investigate this topic. "We'll use state-of-the-art expertise and facilities in paleo-magmatism, geo-tectonics, computer modelling and database management, including those at Curtin's Institute for Geoscience Research," Professor Li adds.

Plate tectonics

"When introduced, the theory of plate tectonics broke away from the century-old beliefs that Earth's movements were dominantly vertical ones with little or no lateral shift," Professor Li says. "The theory has a major drawback: there's no satisfactory explanation for the driving mechanisms of plate movements: things like ridge push, slab pull, slab suction and mantle convection."

Complicating matters further was the discovery of mantle plumes – hot rocks that have risen from the Earth's deep mantle. "Although some researchers argued for an active, driving role of plumes in plate dynamics, most researchers consider plumes as an independent factor," he points out. "The lack of clear understanding of how the Earth engine works hinders our ability to understand how our continents evolved."

New technologies

The advent of new geo-technologies is about to change all that. Three areas in particular spring to mind.

First, the introduction of high-resolution seismic tomography allows scientists to scrutinise the internal structure of Earth's mantle. "It's shown us that subducted oceanic plates can descend to over 2800 kilometres – all the way to the core-mantle boundary," Professor Li says.

Second, new techniques – involving palaeo-magnetic and geographical information systems – have extended knowledge of the changing configuration of continents from just the last 540 million years to more than 1 billion years ago.

Finally, rapid increases in computing power and the development of sophisticated modelling codes allowed geodynamic processes to be modelled at global to regional scales in three and even four dimensions.

"These advances have allowed us to link present-day plate tectonics on Earth's surface to dynamic processes deep in the mantle – and to link these to ancient records of geology," Professor Li says.

"This has fundamental implications: from the formation and evolution of the continental crust, and the distribution of Earth resources, to the oxygenation of our atmosphere, major climate changes and even the evolution of life."

Earth undressed

New fracture zones – points of weakness in the ocean floor – open up in the crust from time to time. These zones are essentially 'train-tracks' showing the direction of plate motion; their magnetic peculiarities are used to calculate the speed at which plates move away from each other.

Based on these and other clues, scientists have deduced that a relatively new fracture zone seems to be opening up as the Indo-Australian plate, on which India and Australia lies, cracks up. The suspected break crosses the equator near northern Sumatra and extends south-west beneath the Indian Ocean, seismologists say, with the two continents beginning to shift independently of one another.

Both continents are moving in roughly the same direction, north to north-east, with Australia travelling a fraction faster than India, says University of Tasmania geoscientist Jo Whittaker, also a member of Professor Li's team. This is causing a vast area near the centre of the Indo-Australian plate to buckle.

The breakup of the Earth's tectonic plates, a mind-numbingly lengthy process, has been affecting the Indo-Australian plate for about 15 million years. "Our understanding of how the forces from deformation processes such as these accumulate in the ocean crust, and are released by means of earthquakes, is not well understood," Dr Whittaker explains.

New boundary

On longer time scales, the breakup zone is likely to lead to the birth of a new plate boundary, where the two giant plates edge towards each other and one plate plunges beneath the other.

This would result in more earthquakes in the region – possibly with devastating effect, despite the new fracture zone being far from land. Over the next few tens of thousands of years, the break-up region, south-west of northern Sumatra, will probably experience more earthquakes, says Melbourne University seismologist Gary Gibson.

"The horizontal motion of the shallow crustal events will not lead to large tsunamis, as sometimes generated by subduction earthquakes," Mr Gibson explains. Such quakes occur when one tectonic plate is forced beneath another, producing vertical motion that causes uplift or subsidence of the sea floor.

The development of a new plate boundary could affect tectonic stresses inside the Australian continent, slightly increasing earthquake activity on some faults while reducing the likelihood of quakes on others, Mr Gibson believes.

But fear not: Australia will not be greatly affected by this ongoing tectonic activity. This, scientists say, is because the new plate boundary is thousands of kilometres from the continent.


The break-up is along a well-defined fault, with its north-east end near two major earthquakes that occurred west of Sumatra in April 2012. These quakes, measuring 8.6 and 8.1 on the Richter scale, occurred on a fracture zone. (Seismic events that large usually occur at plate boundaries – yet these were at least 100 kilometres from such zones.)

The 2012 quakes were caused by what is known as strike-slip faults, in which surfaces on opposite sides of the fault plane move horizontally and parallel to the fault. The breakup seems to be happening over a widespread region of fracture.

Meanwhile, research reported in the British journal Nature reveals that, in addition to the Indo-Australian Plate, there could already be another, known as the Capricorn plate, in place.

"The Capricorn plate has been suggested but is not yet proven," Mr Gibson points out. "It is a region delineated by above-average levels of earthquake activity and may involve a widespread fracture zone."

More evidence

A classic example of a fragmented tectonic plate is the breakup of the African plate along the famed Rift Valley, which runs north-south through eastern Africa. "That breakup has progressed much further than the one involving the Indo-Australia Plate," Mr Gibson says.

Evidence for the breakup of the Indo-Australian plate comes from a range of sources. Although no GPS receivers are located on the Capricorn plate, there are several in India and Australia.

"When data are compared, there are significant differences in the speed and direction of motion that suggests the Capricorn plate lies in the Indian Ocean between India and Australia," Dr Whittaker notes.

More supporting evidence comes from detailed maps of the sea floor and X-rays of sediments. These show reactivation of fracture zones, compression in certain areas of the Indian Ocean and stretching in other places.

Original: http://smh.com.au/

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Re: New Earth dawns: supercontinent slowly takes shape

Сообщение автор Б&П в Чт 30 Апр 2015, 8:34 am

Заря "Новой Земли": суперконтинент постепенно формируется
(«The Sydney Morning Herald», Австралия)

Питер Спинкс

Недавнее землетрясение в Непале - напоминание о том, что на Земле идет процесс формирования единого колоссального суперконтинента, вроде древнего материка Родиния, утверждает обозреватель The Sydney Morning Herald Питер Спинкс.

Силы, которые формируют континенты, сегодня не менее активны, чем 4,5 млрд лет назад.

"Мы находились вблизи эпицентра землетрясения за день до того, как оно случилось. А на следующий день после землетрясения мы находились вблизи эпицентра одного из крупных повторных толчков, - сказал в интервью геолог Чжен-Сян Ли (университет Кёртин, Австралия), который сейчас находится в Лхасе. - Мы приехали изучать, как столкновение Индостанской и Евразийской плит в свое время привело к подъему Тибетского нагорья и росту Гималаев".

В Непале Ли собирал данные в подтверждение своей теории, что основные континенты Земли находятся в процессе перегруппировки и в итоге образуют единый гигантский суперконтинент. Ученый Пол Хоффмен нарек этот предполагаемый суперконтинет "Амазия".

По мнению Ли, формирование Амазии стало заметным в последние 100 млн лет, а завершится оно еще через несколько десятков - или сотен - миллионов лет.

Данные GPS демонстрируют, что Атлантический океан каждый год расширяется на несколько сантиметров, а Тихий становится уже.

"Если эта тенденция продолжится, через сто-двести миллионов лет Тихий океан исчезнет, а американский и евразийский континенты столкнутся", - утверждает Ли. По его словам, Австралия смещается в сторону Азии на 7 см в год.

Ли и его зарубежные коллеги намерены проверить гипотезу, что тектонические плиты и мантия Земли развиваются по модели "суперциклов". Они изучат эволюцию суперконтинентов в прошлом, в том числе распад Пангеи, повлекший за собой образование Атлантического, Индийского и Южного (условное название вод Тихого, Атлантического и Индийского океанов, окружающих Антарктиду. - Прим. ред.) океанов.

Ли указал, что современная теория тектоники литосферных плит не может убедительно объяснить механизмы, которые стоят за движением плит. Картину еще более осложняют мантийные плюмы - горячие камни, всплывающие из мантии Земли.

Ученые надеются на новые геотехнологии, отмечает автор статьи. Это сейсмическая томография высокого разрешения, позволяющая изучать внутреннюю структуру мантии, новые методы, которые расширили наши познания об изменчивой конфигурации континентов, а также компьютерное моделирование геодинамических процессов на глобальном или региональном уровне.

"Время от времени в земной коре разверзаются новые зоны разломов - слабые места в океанском дне. По сути, это "железнодорожные ветки", указывающие направление движения плит", - говорится в статье.

Ученые заключили, что в Индо-Австралийской плите, по-видимому, возникает относительно новая зона разлома.

Предполагаемый разлом пересекает экватор вблизи севера Суматры и тянется на юго-запад под Индийским океаном.

И Индия, и Австралия смещаются на северо-северо-восток, но Австралия движется чуть быстрее, чем Индия, говорит Джо Уиттакер (Тасманийский университет). В результате огромная область близ центра Индо-Австралийской плиты изгибается.

Вероятно, в итоге возникнет новая граница плит: зона, где две плиты сближаются и край одной наползает на другую, передает корреспондент.

В ближайшие несколько десятков тысячелетий в зоне разлома - местах к юго-западу от северной Суматры - вероятно, участятся землетрясения, говорит сейсмолог Гэри Гибсон (Мельбурнский университет).

Оригинал публикации: http://www.smh.com.au/national/education/new-earth-dawns-supercontinent-slowly-takes-shape-20150426-1mqa1q.html
Источник перевода: http://www.inopressa.ru/

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