地球深處的巨大岩石團塊握有關於我們星球的重大資訊

原文網址：www.sciencedaily.com/releases/2016/06/160624155000.htm

Giant Blobs of Rock, Deep Inside the Earth, Hold Important Clues About Our Planet

地球深處的巨大岩石團塊握有關於我們星球的重大資訊

Two massive blob-like structures lie deep within Earth, roughly on opposite sides of the planet. The two structures, each the size of a continent and 100 times taller than Mount Everest, sit on the core, 1,800 miles deep, and about halfway to the center of Earth.

在地球深處有兩個巨大團塊狀構造，大致位於地球相對兩側。這兩個構造的大小都跟一個陸塊差不多，且厚度是聖母峰的100倍之上。它們位處距地表深1800哩(約2900公里)離地核不遠處，差不多是地表至地球中心距離的一半。

Arizona State University scientists Edward Garnero, Allen McNamara and Sang-Heon (Dan) Shim, of the School of Earth and Space Exploration, suggest these blobs are made of something different from the rest of Earth's mantle. The scientists' work appears in the June issue of Nature Geoscience.

亞利桑納州立大學地球與宇宙探索學院的科學家Edward Garnero、 Allen McNamara和Sang-Heon (Dan) Shim提出這些團塊是由跟地函其他部分截然不同的物質組成。這些科學家的研究成果刊登於六月號的《自然—地質科學》(Nature Geoscience)。

"While the origin and composition of the blobs are yet unknown," said Garnero, "we suspect they hold important clues as to how Earth was formed and how it works today."

「雖然這些團塊的成分和起源仍然不太清楚。」 Garnero說。「我們猜想它們握有地球如何形成以及地球現今如何運作的重大線索。」

The blobs, he says, may also help explain the plumbing that leads to some massive volcanic eruptions, as well as the mechanism of plate tectonics from the convection, or stirring, of the mantle. This is the geo-force that drives earthquakes.

他說這些團塊或許有助於解釋導致大型火山噴發的岩漿系統，以及地函對流或擾動藉由何種機制促成板塊構造運動。後者同時也是驅動地震發生的地質作用力。

Deep stirring

來自深層的擾動

Earth is layered like an onion, with a thin outer crust, a thick viscous mantle, a fluid outer core and a solid inner core. The two blobs sit in the mantle on top of Earth's core, under the Pacific Ocean on one side and beneath Africa and the Atlantic Ocean on the other.

地球就像洋蔥一樣可分成數層，最外面是薄薄的地殼，接著是又厚又黏稠的地函，最後則是液狀的外核和固態的內核。這兩個團塊位於地函中距地核不遠處，其中一個位於太平洋下方，另一個則在非洲和大西洋之下。

Waves from earthquakes passing through Earth's deep interior have revealed that these blobs are regions where seismic waves travel slowly. The mantle materials that surround these regions are thought to be composed of cooler rocks, associated with the downward movement of tectonic plates.

穿過地球深處的地震波顯示這些團塊是會讓地震波通過時減慢的區域。一般認為包圍這些區域的物質是由溫度較低，跟板塊下沉有關的岩石組成。

The blobs, also called thermochemical piles, have long been depicted as warmer-than-average mantle materials, pushed upward by a slow churning of hot mantle rock. The new paper argues they are also chemically different from the surrounding mantle rock, and may partly contain material pushed down by plate tectonics. They might even be material left over from Earth's formation, 4.5 billion years ago.

這些又稱作「熱化學堆」(thermochemical pile)的團塊長久以來被描述成溫度高於地函平均的物質，並且受炙熱地函岩石的攪動而往上湧。這篇新論文聲稱它們在化學性質上也跟周圍的地函岩石不同，並且含有一部分由板塊構造運動下推至此的物質。它們甚至可能是自地球45億年前形成時殘存至今的物質。

Much is yet to be learned about these blobs. But the emerging view from seismic and geodynamic information is that they appear denser than the surrounding mantle materials, are dynamically stable and long-lived, and have been shaped by the mantle's large-scale flow. The scientists expect that further work on the two deep-seated anomalies will help clarify the picture and tell of their origin.

對於這些團塊還有很多尚待瞭解之處。但從地震學以及地球動力學得到的新觀點認為它們的密度跟周遭地函相較而言比較高，在動力學上則處於長期穩定的狀態，且形狀會受到地函大尺度流動的影響。科學家希冀未來對這兩個地球深處異常帶的研究可以幫助科學家闡明它們的樣貌和起源。

"If a neuroscientist found an unknown structure in the human brain, the whole community of brain scientists, from psychologists to surgeons, would actively pursue understanding its role in the function of the whole system," Garnero said.

「如果有位神經學家在人腦中找到一塊前所未知的區域，那整個腦科學界，從心理學家至外科醫生都會熱切地去瞭解這個新區域在整個系統當中扮演何種腳色。」 Garnero說。

"As the thermochemical piles come into sharper focus, we hope other Earth scientists will explore how these features fit into the big puzzle of planet Earth."

「隨著熱化學堆越來越受到注目，我們希望其他地球科學家來探索這些特殊構造應該嵌合在地球這幅大拼圖中的何處。」

引用自：Arizona State University (ASU). "Giant Blobs of Rock, Deep Inside the Earth, Hold Important Clues About Our Planet." ScienceDaily. ScienceDaily, 24 June 2016.