地球上最大的火山群如何誕生

原文網址：www.sciencedaily.com/releases/2017/05/170503131933.htm

地球上最大的火山群如何誕生

由澳洲國立大學主持的研究解決了懸宕168年的謎題：世界上體積最大也最活躍的夏威夷火山如何誕生。

研究發現夏威夷的火山之所以會沿著成雙的軌跡形成，是因為300萬年前太平洋板塊的移動方向發生變化。

主要研究人員，澳洲國立大學的Tim Jones表示自1849年以來，科學家就已經知道夏威夷雙生火山鏈的存在，但直到現在它們的成因仍然是個未解之謎。

「這項發現有助於科學家更精確地重建地球歷史，也讓我們對這處萬眾矚目的地方有更多瞭解。」澳洲國立大學地球科學研究院(RSES)的博士生Jones表示。

「我們對太平洋板塊如何移動進行的分析，是首度有研究能指出它的移動方向在300萬年前曾發生一起重大變化。這有助我們解釋夏威夷――地球最大的火山熱點以及世上最受歡迎的旅遊景點之一的起源為何。」

包括薩摩亞在內，太平洋其他地方也有雙生火山鏈存在，而此研究發現它們也是在300萬年前出現。

Jones表示火山大多數發現於板塊邊界，因此這類遠離板塊邊界的火山活動便相當令人感到驚訝。

他說：「地核產生的熱能使得稱作『地函熱柱』(mantle plume)的高溫岩石柱往上升至板塊下方，而在地表產生火山活動。」

「地函熱柱在大滅絕事件、鑽石的形成以及陸地的分裂中，都佔有一席之地。」

共同作者，RSES的Rhodri Davies博士表示雙生火山鏈會出現，是因為地函熱柱跟板塊移動的方向變得不在同一直線上。

Davies博士表示：「我們的假說預測板塊和地函熱柱在未來某個時期將會重新排成一直線，到時候這兩道軌跡將會再次融合為一。」

「在整部地球歷史中，板塊總是不停移動，卻無依循特定規則。我們探討久遠以前的過去，發現在年輕的夏威夷火山中出現的雙重火山鏈並非單一事件――實際上，它們跟過往板塊運動出現的改變相當一致。」

夏威夷坐落在由火山和海底山組成的火山鏈的東南端，越往西北則年代越老。

研究人員運用澳洲國立大學的國家計算機基地來模擬太平洋板塊的運動方向，以及通過夏威夷的雙生火山鏈是如何形成。

Hawaii: How the world's biggest volcanoes formed

A study led by The Australian National University (ANU) has solved the 168-year-old mystery of how the world's biggest and most active volcanoes formed in Hawaii.

The study found that the volcanoes formed along twin tracks due to a shift in the Pacific Plate's direction three million years ago.

Lead researcher Tim Jones from ANU said scientists had known of the existence of the twin volcanic tracks since 1849, but the cause of them had remained a mystery until now.

"The discovery helps to better reconstruct Earth's history and understand part of the world that has captivated people's imagination," said Mr Jones, a PhD student from the ANU Research School of Earth Sciences (RSES).

"The analysis we did on past Pacific Plate motions is the first to reveal that there was a substantial change in motion 3 million years ago. It helps to explain the origin of Hawaii, Earth's biggest volcanic hotspot and one of the most popular tourist destinations in the world."

Twin volcanic tracks exist in other parts of the Pacific, including Samoa, and the study found that these also emerged three million years ago.

Mr Jones said this kind of volcanic activity was surprising because it occurred away from tectonic plate boundaries, where most volcanoes are found.

"Heat from the Earth's core causes hot columns of rock, called mantle plumes, to rise under tectonic plates and produce volcanic activity on the surface," he said.

"Mantle plumes have played a role in mass extinctions, the creation of diamonds and the breaking up of continents."

Co-researcher Dr Rhodri Davies from RSES said the twin volcanic tracks emerged because the mantle plume was out of alignment with the direction of the plate motion.

"Our hypothesis predicts that the plate and the plume will realign again at some stage in the future, and the two tracks will merge to form a single track once again," Dr Davies said.

"Plate shifts have been occurring constantly, but irregularly, throughout Earth's history. Looking further back in time we find that double tracks are not unique to young Hawaiian volcanism -- indeed, they coincide with other past changes in plate motion."

Hawaii sits at the south-eastern limit of a chain of volcanoes and submerged seamounts which get progressively older towards the north west.

The researchers worked with the National Computational Infrastructure at ANU to model the Pacific Plate's change in direction and formation of the twin volcanic tracks through Hawaii.

原始論文：T. D. Jones, D. R. Davies, I. H. Campbell, G. Iaffaldano, G. Yaxley, S. C. Kramer, C. R. Wilson. The concurrent emergence and causes of double volcanic hotspot tracks on the Pacific plate. Nature, 2017; DOI: 10.1038/nature22054

引用自：Australian National University. "Hawaii: How the world's biggest volcanoes formed." ScienceDaily. ScienceDaily, 3 May 2017.