地函柱引發板塊運動？

原文網址：www.sciencedaily.com/releases/2015/11/151111143225.htm

Plate tectonics thanks to plumes?

地函柱引發板塊運動？

"Knowing what a chicken looks like and what all the chickens before it looked like doesn't help us to understand the egg," says Taras Gerya. The ETH Professor of Geophysics uses this metaphor to address plate tectonics and the early history of the Earth. The Earth's lithosphere is divided into several plates that are in constant motion, and today's geologists have a good understanding of what drives these plate movements: heavier ocean plates are submerged beneath lighter continental plates along what are known as subduction zones. Once the movement has begun, it is perpetuated due to the weight of the dense subducting plate.

「知道一隻雞以及牠列祖列宗的長相並不能讓我們認識雞蛋的模樣。」Taras Gerya說。這名蘇黎世聯邦理工學院(ETH)地球物理學系的教授以此比喻板塊運動和地球早期的歷史。地球岩石圈分裂成好幾塊會不斷運動的板塊。現今的地質學家對驅動板塊移動的作用力已有相當瞭解：密度較高的海洋板塊沿著隱沒帶沉沒至較輕的大陸板塊之下。一旦此運動開始進行，隱沒板塊的重量便會使之維持下去。

But just as in the past, earth scientists still do not understand what triggered plate tectonics in the first place, nor how the first subduction zone was formed. A weak spot in the Earth's lithosphere was necessary in order for parts of the Earth's crust to begin their descent into the Earth's mantle. Was this weak spot caused by a gigantic meteorite that effectively smashed a hole in the Earth's lithosphere? Or did mantle convection forces shatter the lithosphere into moving parts?

但跟過去的地球科學家一樣，我們現在仍然不瞭解一開始是什麼觸發了板塊運動，而隱沒帶又是如何形成。我們所知的是地球岩石圈必然出現了一個軟弱區域，才能使部分的地球地殼開始沉入地函。這個軟弱區域會是因為一次巨型隕石撞擊，在地球岩石圈重重擊出一個大坑而形成嗎？或者是地函對流將岩石圈碎裂成好幾塊能自由移動的碎片？

Venus as a model

以金星作為模型

Gerya is not satisfied with any of these potential explanations. "It's not trivial to draw conclusions about what set the tectonic movements in motion," he says. The ETH professor therefore set out to find a new, plausible explanation.

Gerya對這些可能的解釋都不甚滿意。「得出是什麼開啟了能夠持續運作的板塊運動可是件至關重要的事。」他說。這位ETH的教授因此計畫要找出一套可行的新解釋。

Among other things, he found inspiration in studies about the surface of the planet Venus, which has never had plate tectonics. Gerya observed (and modelled) huge, crater-like circles (coronae) on Venus that may also have existed on the Earth's surface in the early period (Precambrian) of the Earth's history before plate tectonics even began. These structures could indicate that mantle plumes once rose from Venus' iron core to the outer layer, thus softening and weakening the planet's surface. Plumes form in the deep interior of the planet. They rise up to the lithosphere, bringing with them hot partially molten mantle material that causes the lithosphere to weaken and deform. Halted by the resistance of the hard lithosphere, the material begins to spread, taking on a mushroom-like shape.

除了其他方面之外，他也從關於金星地表的研究中得到了不少啟發。Gerya觀察到(並模擬)金星上有著像隕石坑般的巨大圓形構造(冕狀物，coronae)。由於這顆星球從未發生板塊運動，因此在板塊運動發生前的早期(前寒武紀)地球地表，也可能存在著類似構造。這種構造象徵著有地函柱(plume)從金星的鐵質地核往上升至星球外層，因而軟化並弱化了行星地表。地函柱在金星深處形成，往上移動而與岩石圈接觸。它們攜帶的炙熱部分熔融地函會弱化岩石圈並使其變形。在被堅硬的岩石圈阻擋之後，這些熱物質會往外擴散，而形成蘑菇狀的外觀。

Such plumes also likely existed in the Earth's interior and could have created the weaknesses in the Earth's lithosphere needed to initiate plate tectonics on Earth.

這種地函柱也可能會存在於地球內部，並形成啟動板塊運動所需，存在於岩石圈之內的軟弱區域。

Mantle plumes create weaknesses

地函柱創造軟弱區域

The ETH geophysicist worked with his team to develop new computer models that he then used to investigate this idea for the first time in high resolution and in 3D. The corresponding publication has recently been published in Nature.

ETH的地球物理學家與他的團隊發展出一套新的電腦模型，讓他首度能在3D高解析度系統下探討上述想法。相關結果近日發表於期刊《自然》(Nature)之中。

The simulations show that mantle plumes and the weaknesses they create could have actually initiated the first subduction zones.

模擬結果顯示出地函柱與其造成的軟弱區域真的能夠促使第一個隱沒帶形成。

In the simulations, the plume weakens the overlying lithosphere and forms a circular, thinning weak point with a diameter of several dozen to hundreds of kilometres. This is stretched over time by the supply of hot material from the deep mantle. "In order to make a ring larger, you have to break it," explains the researcher. This also applies to the Earth's surface: the ring-shaped weaknesses can (in the model) only be enlarged and subducted if the margins are torn.

在模擬過程當中，地函柱會弱化上覆的岩石圈，並在其中形成一層薄薄的環形軟弱區域，直徑可從數十至數百公里不等。隨著深部地函不斷提供熱物質，它會開始往外擴展。「若要將一個環拉得更大，你非得扯斷它不可。」研究人員解釋。此觀點也能套用在地球表面：(模擬中)唯有這道環形弱點的邊緣被撕裂後，它才能往外擴張並且發生隱沒。

Water lubricates the plate margin

水分潤滑了板塊邊緣

The tears spread throughout the lithosphere, large slabs of the heavier rigid lithosphere plunge into the soft mantle, and the first plate margins emerge. The tension created by the plunging slabs ultimately sets the plates in motion. They plunge, well lubricated by the buried seawater of the ocean above. Subduction has begun -- and with it, plate tectonics. "Water acts as a lubricant and is an absolute necessity in the initiation of a self-sustaining subduction," says Gerya.

這些裂縫會延伸至岩石圈各處，造成密度較高的堅硬岩石圈斷塊往下沉至柔軟的地函當中。第一道板塊邊界就此誕生。而下沉板塊造成的拉力最後會使得整個板塊跟著移動。在下沉的過程當中，上方海水會隨之埋入而達到潤滑效果，使整個過程進行得更加順利。隱沒作用於焉開始，隨之而來的是板塊運動開始運作。「在啟動可以永續運作的隱沒作用的過程中，水的潤滑絕對是項不可或缺的要素。」

In their simulations, the researchers compare different temperature conditions and lithosphere states. They came to the conclusion that plume-induced plate tectonics could plausibly develop under the conditions that prevailed in the Precambrian around three billion years ago. Back then the Earth's lithosphere was already thick and cool, but the mantle was still very hot, providing enough energy to significantly weaken the lithosphere above the plumes.

研究人員在模擬過程當中，比較不同溫度條件和岩石圈狀態會有何差異。他們得出的結論顯示30億年前前寒物紀時期的地球，可以達到發生由地函柱引發的板塊運動所需的條件。那時地球岩石圈雖然已經達到一定厚度且冷卻下來，然而地函仍然相當熾熱，能夠提供使地函柱之上的岩石圈弱化至一定程度需要的能量。

Had the lithosphere instead being thin and warm, and therefore soft, the simulations show that a ring-shaped rapidly descending structure called drip would simply have formed around the plume head. While this would have steadily sunk into the mantle, it would not have caused the soft lithosphere to subduct and tear and therefore would not have produced plate margins. Likewise, the computer simulations showed that under today's conditions, where there is less temperature difference between lithosphere and plume material, plume-induced subduction is hard to initiate because the lithosphere is already too rigid and the plumes are barely able to weaken it sufficiently.

模擬結果顯示假如岩石圈的厚度較薄、溫度較高，因此較為軟弱， 則僅會在地函柱頭附近形成一種會迅速下沉，稱作drip的環狀構造。由於這種構造會穩定地往下沉入地函，因此它不會撕裂軟弱的岩石圈並造成隱沒作用，板塊邊界也不會形成。同樣地，電腦模擬也顯示在目前岩石圈以及地函柱物質之間溫差較小的狀態下，由於岩石圈已經太過堅硬使得地函柱不足以大幅弱化它，因此難以發生由地函柱引發的隱沒作用。

Dominant mechanism

主要機制

"Our new models explain how plate tectonics came about," says the geophysicist. Plume activity was enough to give rise to today's plate mosaic. He calls the power of the plumes the dominant trigger for global plate tectonics.

「我們的新模型解釋了板塊運動如何開始。」這名地球物理學家說。他聲稱地函柱的力量便是啟動地球板塊運動的主因，也造就了今日我們所見的片片板塊。

The simulations can also explain how so-called triple junctions, i.e. zones in which three plates come together, are nucleated by multi-directional stretching of the lithosphere induced by plumes. One such example of a triple junction can be found in the Horn of Africa where Ethiopia, Eritrea and Djibouti meet.

這項模擬也能解釋三向聯結構造(triple junction，三個板塊交接的地區)是如何因為地函柱造成岩石圈往多重方向拉伸，使得不同板塊交接而形成。在衣索比亞、厄利垂亞、吉布地三國交界的非洲之角即可看到三向聯結構造中的一例。

A possible plume-weakened zone analogous to a starting point for global plate tectonics likely exists in the modern world: the researchers see such a zone in the Caribbean plate. Its shape, location and spread correspond largely to the new model simulations.

今日，在世界上可能還存在著類似地球板塊運動的起始地點，由地函柱產生的軟弱帶。研究人員在加勒比板塊中看到一個這樣的區域，它的形狀、位置以及逐漸擴張都相當符合這個新模型的模擬結果。

Indeed it is arguably impossible to prove how global plate tectonics started on Earth based solely on observations: there is no geophysical and only a small amount of geological data from the Earth's early years, and laboratory experiments are not possible for extremely large-scale and very long-term tectonic processes, says the ETH researcher. "Computer models are therefore the only way we can reproduce and understand the events of the Earth's early history."

我們的確能說幾乎不可能僅靠觀察來證明地球上的板塊運動是如何開始。我們無法得到地球早年歲月時的地球物理資料，而地質證據也是吉光片羽。同樣地，實驗室試驗不可能重現如此大規模且極度長期的構造運動過程。「因此電腦模擬是我們僅剩的唯一方法，可以重現並瞭解地球早期究竟有何事件發生。」這位ETH的研究人員說。

引用自：ETH Zurich. "Plate tectonics thanks to plumes?." ScienceDaily. ScienceDaily, 11 November 2015. 

原文網址：www.sciencedaily.com/releases/2015/11/151103140444.htm

Diamonds may not be so rare as once thought

鑽石或許並不如之前認為的那般稀有

Chemical model shows a simpler deep Earth formation

化學模型顯示出鑽石在地球深處的簡易形成方法

Diamonds may not be as rare as once believed, but this finding in a new Johns Hopkins University research report won't mean deep discounts at local jewelry stores.

鑽石也許並不像之前咸信的如此稀有，然而這起約翰·霍普金斯大學新研究報告中的發現，並不代表你家附近珠寶店的鑽石價格會暴跌。

"Diamond formation in the deep Earth, the very deep Earth, may be a more common process than we thought," said Johns Hopkins geochemist Dimitri A. Sverjensky, whose article co-written with doctoral student Fang Huang appears today in the online journal Nature Communications. The report says the results 'constitute a new quantitative theory of diamond formation,' but that does not mean it will be easier to find gem-quality diamonds and bring them to market.

「鑽石於地球深處，非常非常深處形成的過程也許比我們認為得更常發生。」約翰·霍普金斯大學的地球化學家Dimitri A. Sverjensky說。他和他的博士班學生Fang Huang合撰的文章今日刊登於期刊《自然通訊》(Nature Communications)線上版。這篇報告寫道他們的結果「建構了一套可用來解釋鑽石如何形成的新型數量化理論」，但這並不代表找到並銷售寶石等級的鑽石會變得易如反掌。

For one thing, the prevalence of diamonds near the Earth's surface -- where they can be mined -- still depends on relatively rare volcanic magma eruptions that raise them from the depths where they form. For another, the diamonds being considered in these studies are not necessarily the stuff of engagement rings, unless the recipient is equipped with a microscope. Most are only a few microns across and are not visible to the unaided eye.

一方面來說，要在地表附近形成鑽石含量豐富而能供人類開採的礦藏，仍然要靠某些相當罕見，能將鑽石從它們形成的地球深處帶至地表的火山爆發事件。另一方面，這篇研究中所指的鑽石並不全然像訂婚鑽戒上的那般光彩奪目，除非收下的人配有顯微鏡。這些鑽石大都只有幾微米的大小，絕非肉眼可見。

Using a chemical model, Sverjensky and Huang found that these precious stones could be born in a natural chemical reaction that is simpler than the two main processes that up to now have been understood to produce diamonds. Specifically, their model -- yet to be tested with actual materials -- shows that diamonds can form with an increase in acidity during interaction between water and rock.

利用化學模擬方法，Sverjensky 和Huang發現這些珍稀的寶石能在某種自然發生的化學反應中形成，這種反應遠較目前為止所知，另外兩種形成鑽石的主要機制簡單許多。準確來說，雖然還未經實物驗證，他們的模型顯示水與岩石反應的過程中，酸度提高會使鑽石形成。

The common understanding up to now has been that diamonds are formed in the movement of fluid by the oxidation of methane or the chemical reduction of carbon dioxide. Oxidation results in a higher oxidation state, or a gain of electrons. Reduction means a lower oxidation state, and collectively the two are known as 'redox' reactions.

迄今，一般我們認為鑽石是由於液體流動的過程中，發生甲烷氧化或者二氧化碳還原而形成。氧化會提高物質的氧化態，或者可說是讓它失去電子；還原則會降低氧化碳，兩者通常合稱為氧化還原反應。

"It was always hard to explain why the redox reactions took place," said Sverjensky, a professor in the Morton K. Blaustein Department of Earth and Planetary Sciences in the university's Krieger School of Arts and Sciences. The reactions require different types of fluids to be moving through the rocks encountering environments with different oxidation states.

「要解釋氧化還原反應為何發生總是一件很難的事。」Sverjensky說，他是約翰·霍普金斯大學克里格藝術科學學院，地球與行星科學系的教授。這類反應需要不同流體在岩石中流動時，遇到氧化態有所差異的環境才會發生。

The new research showed that water could produce diamonds as its pH falls naturally -- that is, as it becomes more acidic -- while moving from one type of rock to another, Sverjensky said.

Sverjensky說，這項新研究顯示水在不同種類岩石之間流動時，在pH值自然下降(也就是變得更加酸性)的過程中，鑽石就會從中產生。

The finding is one of many in about the last 25 years that expands scientists' understanding of how pervasive diamonds may be, Sverjensky said.

Sverjensky說，包含此發現，科學家過去25年來已經從許多研究中愈加瞭解鑽石的分布其實是多麼廣泛。

"The more people look, the more they're finding diamonds in different rock types now," Sverjensky said. "I think everybody would agree there's more and more environments of diamond formation being discovered."

「人們愈去探討，他們就在愈多種岩石中發現鑽石。」Sverjensky說。「我想現在大家都同意會有愈來愈多的環境被發現有鑽石形成於其中。」

Nobody has yet put a number on the greater abundance of diamonds, but Sverjensky said scientists are working on that with chemical models. It's impossible to physically explore the great depths at which diamonds are created: roughly 90 to 120 miles below the Earth's surface at intense pressure and at temperatures about 1,650 to 2,000 degrees Fahrenheit.

雖然尚未有人發現由此成因而形成的豐富鑽石礦藏，Sverjensky說科學家可以利用化學模型來進行相關研究。目前人類還無法實際去探索鑽石形成的深度，它們位於地表之下140至200公里，在那裏壓力相當地大，而溫度可高達900至1100℃。

The deepest drilling exploration ever made was about 8 or 9 miles below the surface, he said.

他說，人類曾鑽到最深的地方也只不過是地表之下13至15公里。

If the study doesn't shake the diamond markets, it promises to help shed light on fluid movement in the deep Earth, which helps account for the carbon cycle on which all life on the planet depends.

即使這篇研究並沒有撼動鑽石市場，至少它肯定會讓我們對液體在地球深部是如何流動有更多的瞭解，而這與地球上所有生物依存的碳循環息息相關。

"Fluids are the key link between the shallow and the deep Earth," Sverjensky said. "That's why it's important."

「液體是連結地球深部和淺部的關鍵角色。」Sverjensky說。「這就是它為何如此重要的原因。」

This research was supported by grants from the Sloan Foundation through the Deep Carbon Observatory (Reservoirs and Fluxes and Extreme Physics and Chemistry programs) and by a U.S. Energy Department grant, DE-FG-02-96ER-14616.

本研究的贊助來自於斯隆基金會的深碳觀測計畫(Deep Carbon Observatory)下的子計畫，「儲量與通量」以及「極端物理化學條件」；另外一份則來自美國能源局計畫編號DE-FG-02-96ER-14616。

引用自：Johns Hopkins University. "Diamonds may not be so rare as once thought: Chemical model shows a simpler deep Earth formation." ScienceDaily. ScienceDaily, 3 November 2015. 

深海熱泉會移除海洋中的碳

原文網址：www.sciencedaily.com/releases/2015/11/151102143735.htm

Deep-sea hydrothermal vents have carbon-removing properties

深海熱泉會移除海洋中的碳

University of Georgia Skidaway Institute of Oceanography scientist Aron Stubbins joined a team of researchers to determine how hydrothermal vents influence ocean carbon storage. The results of their study were recently published in the journal Nature Geoscience.

喬治亞大學斯基德维海洋研究所的科學家Aron Stubbins參與的研究團隊探討深海熱泉對海洋碳儲量會有何影響。他們的結果近日發表於期刊《自然－地質科學》之上。

Hydrothermal vents are hotspots of activity on the otherwise dark, cold ocean floor. Since their discovery, scientists have been intrigued by these deep ocean ecosystems, studying their potential role in the evolution of life and their influence upon today's ocean.

深海熱泉(hydrothermal vent)為既暗又冷的海床上少數活動劇烈的熱點。自從發現它們以來，科學家便對熱泉周邊的深海生態系統深感興趣，進行了無數研究以瞭解它們在生物演化上的地位，以及對現今海洋的影響。

Stubbins and his colleagues were most interested in the way the vents' extremely high temperatures and pressure affect dissolved organic carbon. Oceanic dissolved organic carbon is a massive carbon store that helps regulate the level of carbon dioxide in the atmosphere -- and the global climate.

Stubbins和他的同僚最感興趣的是極端高溫高壓的熱泉環境會如何影響溶解性有機碳。海洋的溶解性有機碳是座巨大的碳儲存庫，因此有助於調控大氣中的二氧化碳濃度，進一步影響全球氣候。

Originally, the researchers thought the vents might be a source of the dissolved organic carbon. Their research showed just the opposite.

起初，研究人員預計熱泉可能會是溶解性有機碳的來源之一，但研究結果呈現出來的卻恰好相反。

Lead scientist Jeffrey Hawkes, currently a postdoctoral fellow at Uppsala University in Sweden, directed an experiment in which the researchers heated water in a laboratory to 380 degrees Celsius (716 degrees Fahrenheit) in a scientific pressure cooker to mimic the effect of ocean water passing through hydrothermal vents.

現為瑞典烏普薩拉大學博士後研究員的Jeffrey Hawkes為此研究的主要研究人員，他於實驗室中利用高壓鍋具將海水加熱至380℃，來模擬海水經過熱泉系統時的情境，並觀察過程中會發生何種效應。

The results revealed that dissolved organic carbon is efficiently removed from ocean water when heated. The organic molecules are broken down and the carbon converted to carbon dioxide.

結果顯示海水加熱後會從中移除大多數的溶解性有機碳。這些有機分子被分解掉之後，其中的碳元素會轉變成二氧化碳。

The entire ocean volume circulates through hydrothermal vents about every 40 million years. This is a very long time, much longer than the timeframes over which current climate change is occurring, Stubbins explained. It is also much longer than the average lifetime of dissolved organic molecules in the ocean, which generally circulate for thousands of years, not millions.

若要讓所有海水都流經熱泉系統大約要花費4000萬年。Stubbins解釋說這是一段耗時甚久的歷程，跟眼下正發生的氣候變遷時間尺度相比而言要長得多。而這跟海洋中溶解性有機分子平均存在的時間相比也長了許多，它們通常以數千年的時間尺度循環，而非數百萬年。

"However, there may be extreme survivor molecules that persist and store carbon in the oceans for millions of years," Stubbins said. "Eventually, even these hardiest of survivor molecules will meet a fiery end as they circulate through vent systems."

「然而，或許海洋中存在有某些可稱作終極生存者的分子，它們能夠持有並儲存碳原子長達數百萬年。」Stubbins說。「然而，即便是所有分子中最頑強的倖存者，最終它們還是會在流經熱泉系統時燃燒殆盡。」

Hawkes conducted the work while at the Research Group for Marine Geochemistry, University of Oldenburg, Germany. The study's co-authors also included Pamela Rossel and Thorsten Dittmar, University of Oldenburg; David Butterfield, University of Washington; Douglas Connelly and Eric Achterberg, University of Southampton, United Kingdom; Andrea Koschinsky, Jacobs University, Germany; Valerie Chavagnac, Université de Toulouse, France; and Christian Hansen and Wolfgang Bach, University of Bremen, Germany.

Hawkes於他在參與德國奧爾登堡大學海洋地質化學研究團隊時進行了這項研究計畫。共同作者包括Pamela Rossel和Thorsten Dittmar(奧爾登堡大學)、David Butterfield(美國華盛頓大學)、Douglas Connelly和Eric Achterberg(英國南安普敦大學)、Andrea Koschinsky(雅德國各布大學)、Valerie Chavagnac(法國土魯斯大學)、Christian Hansen和Wolfgang Bach(德國不來梅大學)。

引用自：University of Georgia. "Deep-sea hydrothermal vents have carbon-removing properties." ScienceDaily. ScienceDaily, 2 November 2015. 

研究人員對山區集水區有更進一步的了解

原文網址：www.sciencedaily.com/releases/2015/10/151029190848.htm

Researchers advance understanding of mountain watersheds

研究人員對山區集水區有更進一步的了解

University of Wyoming geoscientists have discovered that the underground water-holding capacity of mountain watersheds may be controlled by stresses in Earth's crust. The results, which may have important ramifications for understanding streamflow and aquifer systems in upland watersheds, appears Oct. 30 in Science, one of the world's leading scientific journals.

懷俄明大學的地球科學家發現於山區集水區，土地的保水能力可能受控於當地地殼應力。此結果於10/30發表在世上頂尖的科學期刊《科學》(Science)，對我們了解山區集水區的地表和地下水系統來說可能有相當深遠的影響。

The scientists conducted geophysical surveys to estimate the volume of open pore space in the subsurface at three sites around the country. Computer models of the state of stress at those sites showed remarkable agreement with the geophysical images. The surprising implication, says Steve Holbrook, a UW professor in the Department of Geology and Geophysics, is that scientists may be able to predict the distribution of pore space in the subsurface of mountain watersheds by looking at the state of stress in Earth's crust. That state of stress controls where subsurface fractures are opening up -- which, in turn, creates the space for water to reside in the subsurface, he says.

科學家分別在美國三個不同地點進行地球物理探測，以估算它們地下的開放孔隙體積。各地得出的地球物理探測影像，和以電腦模型計算出的當地應力狀態互相比較，皆顯示兩者之間的關聯十分密切。懷俄明大學地質與地球物理系的教授Steve Holbrook說，這項驚人的發現代表科學家或許能利用地殼的應力狀態，來預測山區集水區的地下孔隙是如何分佈。他說應力狀態控制了哪些地下裂隙會連通，進一步確立了地下水應位於何處。

"I think this paper is important because it proposes a new theoretical framework for understanding the large-scale porosity structure of watersheds, especially in areas with crystalline bedrock (such as granite or gneiss)," Holbrook says. "This has important implications for understanding runoff in streams, aquifer recharge and the long-term evolution of landscapes."

「我認為這篇論文的重要性不言而喻，因為它提出了一套新的理論框架讓我們去了解大尺度下集水區的孔隙結構，尤其是在岩床為結晶岩層(如花崗岩或片麻岩)的地區。」Holbrook說。「這對河川流量、地下水含水層補注和地貌長期演化的研究皆有很大的啟發。」

James St. Clair, a UW doctoral student, is lead author of the paper, titled "Geophysical Imaging Reveals Topographic Stress Control of Bedrock Weathering." Holbrook, Cliff Riebe, a UW associate professor of geology and geophysics; and Brad Carr, a research scientist in geology and geophysics; are co-authors of the paper.

此篇題名為「地球物理影像法顯示地形應力控制了岩盤風化」(Geophysical Imaging Reveals Topographic Stress Control of Bedrock Weathering)的論文第一作者為懷俄明大學的博士生James St. Clair。共同作者則有Holbrook、Cliff Riebe(懷俄明大學地質與地球物理系的副教授)以及Brad Carr(地質與地球物理系的研究員)。

Researchers from MIT, UCLA, the University of Hawaii, Johns Hopkins University, Duke University and the Colorado School of Mines also contributed.

來自麻省理工學院、加州大學洛杉磯分校、夏威夷大學、約翰霍普金斯大學、杜克大學和科羅拉多礦業學院的研究人員也參與了此研究。

Weathered bedrock and soil together make up the life-sustaining layer at Earth's surface commonly referred to as the "critical zone." Two of the three study sites were part of the national Critical Zone Observatory (CZO) network -- Gordon Gulch in Boulder Creek, Colo., and Calhoun Experimental Forest, S.C. The third study site was Pond Branch, Md., near Baltimore.

風化岩床和土壤共同組成了位於地球表層，能供養生物生存的地帶，一般稱作「關鍵區」(critical zone)。三個研究地區中有兩個即屬於國家關鍵區觀測站網路的一部分，分別為科羅拉多州柏爾德河的Gordon峽谷，和南卡羅來納州的Calhoun實驗林。第三個地點則是馬里蘭州巴爾的摩附近的Pond河。

"The paper provides a new framework for understanding the distribution of permeable fractures in the critical zone (CZ). This is important because it provides a means for predicting where in the subsurface there are likely to be fractures capable of storing water and/or supporting groundwater flow," St. Clair says. "Since we cannot see into the subsurface without drilling holes or performing geophysical surveys, our results provide the means for making first order predictions about CZ structure as a function of the local topography and knowledge (or an estimate) of the regional tectonic stress conditions."

「這篇論文提供研究人員一條新的脈絡來瞭解關鍵區(CZ)的可通透裂隙會如何分佈。其重要性在於這讓我們有方法可以預測地底下可儲存地下水，且/或可供其流動的裂隙可能位於何處。」St. Clair說。「在沒有進行鑽井或地球物理探勘的情況下，我們是不可能看進地底深處的。但我們的研究結果讓我們有方法可以從當地地貌，以及對區域大地應力作用情形的認知(或估計)來建立方程式而初步預測CZ的構造。」

The research included a combination of geophysical imaging of the subsurface -- conducted by UW's Wyoming Center for Environmental Hydrology and Geophysics (WyCEHG) -- and numerical models of the stress distribution in the subsurface, work that was done at MIT and the University of Hawaii, Holbrook says.

Holbrook說此研究由兩部分結合而成，分別為地球物理影像技術及地下應力分佈的數值模型。前者由懷俄明大學的環境水文學與地球物理中心進行，後者則由麻省理工學院和夏威夷大學共同建立。

The team performed seismic refraction and electrical resistivity surveys to determine the depth of bedrock at the three sites, which were chosen due to varying topography and ambient tectonic stress. At the two East Coast sites, the bedrock showed a surprising mirror-image relationship to topography; at the Rocky Mountain site, the bedrock was parallel to topography. In each case, the stress models successfully predicted the bedrock pattern.

研究團隊選擇這三處地貌和環境大地應力皆有所差異的三個地點，並分別進行折射震測(seismic refraction)和地電阻探測以得知岩盤深度。結果顯示位於東岸的兩處(Calhoun實驗林和Pond河)，岩盤深度分佈與地貌呈現出令人驚訝的鏡像關係；而在洛磯山脈(Gordon峽谷)，兩者則幾近平行。另外，在每個案例之中，應力模型皆成功預測了岩盤分佈模式。

"We found a remarkable agreement between the predictions of those stress models and the images of the porosity in the subsurface with geophysics at a large scale, at the landscape scale," Holbrook says. "It's the first time anyone's really looked at this at the landscape scale."

「我們發現在大尺度，也就是以地景整體為尺度下，應力模型的預測結果，跟地球物理方法得出的地下孔隙分佈影像之間的關聯十分顯著。」Holbrook說。「這是第一次有人真正地從地景尺度出發來縱觀全局。」

St. Clair says he was fortunate to work with a talented group of scientists with an extensive amount of research experience. He adds the experience improved his ability to work with a group of people with diverse backgrounds and improve his writing.

St. Clair說他很幸運能與這群富含研究經驗且才華洋溢的科學家合作。他還說這次經歷增加了他與來自各式各樣背景的人們合作的能力，同時也增進了他撰寫論文的技巧。

"Our results may be important to hydrologists, geomorphologists and geophysicists," St. Clair says. "Hydrologists, because it provides a means for identifying where water may be stored or where the flow rates are likely to be high; geomorphologists, because our results predict where chemical weathering rates are likely to be accelerated due to increased fluid flow along permeable fractures; and geophysicists, because it points out the potential influence of shallow stress fields on the seismic response of the CZ."

「我們的結果對水文學家、地形學家和地球物理學家來說或許都相當重要。」St. Clair說。「對於水文學家，這提供了一套方法讓他們能辨識出地下水可能儲存於哪，或者地下水在哪裡會流得比較快；對於地形學家，由於液體會沿著可通透裂隙流動，故我們的結果能預測出化學風化速率可能會因此而在哪些地方增加；對於地球物理學家，這也許能說明淺層應力場變化在CZ對地震的反應中扮演了何種角色。」

Despite the discovery, Holbrook says there is still much work to be done to test this model in different environments.

儘管已經有了這項發現，Holbrook說還有許多研究工作尚待完成，以驗證這個模型能否運用在不同環境當中。

"But, now we have a theoretical framework to guide that work, as well as unique geophysical data to suggest that the hypothesis has merit," he says.

「但現在我們已經有個理論框架可以依循，而且這些特別的地球物理數據也顯示這項假說極富潛力。」他說。

引用自：University of Wyoming. "Researchers advance understanding of mountain watersheds." ScienceDaily. ScienceDaily, 29 October 2015.