Geochemical evolution of Juan de Fuca Ridge flank hydrothermal fluids: evidence from veins and porefluids, IODP Leg 301.

IODP摘要(9月04日型)NE/C513242/1-Teagle地球表面(地壳)由构造板块组成，板块运动非常缓慢。在大洋中央，板块正在相互分离，随着火山喷发用熔岩填补缺口，新的地壳形成。这些水下火山在海洋下形成了被称为大洋中脊的链条。当这些火山在水下喷发时，海水会迅速冷却熔岩。当岩石迅速冷却时，它们就会破裂。海水能够穿过裂缝，向下深入地壳，那里的岩石仍然很热。当这种情况发生时，冷海水也会冷却这些岩石，结果海水变热。如果水变得足够热，它就会膨胀，密度变小，因此它会升回海底。沿着大洋中脊，人们发现高达400摄氏度的海水从岩石的裂缝中冒出来。这些炽热的流体被称为“热液流体”，但它们并不只是从岩石上带走热量。它们还可以与岩石交换化学物质。有些元素会留在岩石里，比如镁。其他的则从岩石中溶解，进入水中，并被输送到海洋中，如二氧化硅。这一过程可能会导致海洋和岩石的化学成分发生重大变化，如果我们想知道海洋的化学成分自形成以来是如何变化的，这是非常重要的。当高温海水穿过岩石留下的元素时，它们通常以矿物“矿脉”的形式存在，填补了流体通过的缝隙。常见的脉状矿物包括粘土、碳酸盐和石英。静脉的化学成分取决于它们所形成的流体的化学成分。可以测量静脉的化学成分，并将结果用于计算流体的化学成分。综合海洋钻探计划(IODP)是一个国际科学项目，它使用一艘名为“JOIDES决议”的钻井船在海底钻探岩石。2004年6月，IODP将把这艘船带到一个大洋中脊：加拿大以西太平洋上的胡安德富卡山脊。它将钻探沿山脊形成的火山岩，这些火山岩被热液冷却。我们将研究这些岩石的化学成分，以及它们内部形成的矿脉。这将使我们能够了解热流体的化学成分，以及随着岩石冷却和老化它是如何变化的。从我们对蚀变岩石和矿物的分析中，我们将能够估计这些热液如何影响海洋的化学成分。

IODP ABSTRACT (typed Sep 04) NE/C513242/1 - Teagle The earth's surface (crust) is made up of tectonic plates, which move around very slowly. Under the middle of the oceans the plates are moving away from each other, and new crust forms as volcanic eruptions fill the gap with molten rock. These underwater volcanoes form chains under the oceans known as mid-ocean ridges. As these volcanoes erupt underwater the seawater cools the lava very quickly. When rocks cool quickly they crack. Seawater is able to pass through the cracks, down deeper into the crust where the rocks are still hot. As this happens the cold seawater cools these rocks as well, and the seawater heats up as a result. If the water gets hot enough it expands and becomes less dense, so it rises back to the seafloor. Along mid-ocean ridges seawater as hot as 400 degrees Celsius has been found coming out of cracks in the rock. These hot fluids are known as 'hydrothermal fluids', but they don't only remove heat from the rock. They can also exchange chemicals with the rock. Some elements are left behind in the rock, such as magnesium. Others are dissolved out of the rock, into the water, and transported into the ocean, such as silica. This process can produce major changes in the chemistry of the oceans and the rocks, which are very important if we want to know how the chemistry of the oceans has changed since they formed. When elements are left behind by the hot seawater passing through the rock they are often left as mineral 'veins' that fill the cracks the fluids passed through. Common vein minerals include clay, carbonate and quartz. The chemistry of the veins depends on the chemistry of the fluid they formed from. The chemistry of the veins can be measured, and the results are used to calculate the chemistry of the fluids. The Integrated Ocean Drilling Program (IODP) is an international scientific project that uses a drill ship, the 'JOIDES Resolution', to drill rocks from beneath the oceans. In June 2004 IODP is taking the ship to a mid-ocean ridge: the Juan de Fuca Ridge, in the Pacific, west of Canada. It will drill volcanic rocks that formed along the ridge and were cooled by hydrothermal fluids. We will investigate the chemistry of these rocks, and the mineral veins that formed within them. This will allow us to understand the chemistry of the hot fluid, and how it changes as the rocks cool and get older. From our analyses of the altered rocks and minerals we will be able to estimate how these hydrothermal fluids affect the chemistry of the oceans.