1. AN INTRODUCTION TO THE SCIENTIFIC RESULTS OF LEG 168 1
1. AN INTRODUCTION TO THE SCIENTIFIC RESULTS OF LEG 168 1
复制标题
1. LEG 168 的科学结果简介 1
DOI：
--
复制
发表时间：
2000
期刊：
影响因子：
--
通讯作者：
Juan de Fuca
中科院分区：
文献类型：
--
作者：
A. Fisher;E. Davis;Juan de Fuca
众所周知，通过海洋地壳的热液循环携带了很大一部分来自冷却的岩石圈板块的热量，对海洋的化学成分产生了强烈的影响，并在海洋地壳被俯冲再循环之前改变了海洋地壳的成分。海洋钻探计划（ODP）第168条的目标包括：(1)阐明山脊侧翼热液环流的基本物理和流体化学，(2)记录在年轻的山脊侧翼环境中主导流动的上部火成岩地壳和沉积物的后续变化。这是通过在Juan de Fuca Ridge北部东侧翼的样带上钻探0.8至3.6 Ma的地壳来完成的（图1）。在大多数海洋盆地中，火成岩地壳的埋藏和由此产生的可渗透基底的水文隔离发生了数千万年；在胡安德富卡山脊的东侧，由于山脊靠近邻近的北美大陆边缘在更新世期间脱落的大量浊积岩沉积物，因此埋藏速度加快。Leg 168钻探点沿东向西样带的布置跨越了一系列地壳年龄、沉积物厚度、基底的热化学状态（图1），从而可以评估当前条件以及条件如何随时间变化。样带西端最靠近扩张轴和沉积物/火成岩基底上覆位置，热液冷却程度最大，岩石和流体蚀变最小。相比之下，样带东端的地点显示出更大的岩石和流体蚀变。在第168号立法期间，对沉积物下面的地下室部分的渗透故意很浅；主要关注的是基底流体成分、地层温度、流体压力和蚀变的横向变化。更深的穿透和实验留作以后钻探的目标。基于Leg 168船载研究的结果在Leg 168初始报告卷（船上科学党，1997年）和一篇简短的总结文章（Davis et al.， 1997年）中进行了总结。由于最近ODP出版政策的变化，许多包含Leg 168结果的论文出现在期刊上，而不是本卷。在本介绍的其余部分中，我们强调了后巡航研究的结果，重点是水文地质过程和出现在本卷之外的论文。
Hydrothermal circulation through the oceanic crust is known to carry a significant portion of the heat from cooling lithospheric plates, to exert a strong influence on the chemistry of the oceans, and to modify the composition of oceanic crust before it is recycled by subduction. Among the objectives of Ocean Drilling Program (ODP) Leg 168 were (1) elucidation of the fundamental physics and fluid chemistry of ridge flank hydrothermal circulation and (2) documentation of consequent alteration of the upper igneous crust and sediments that host the flow in a young ridge flank setting. This was accomplished with a transect of sites on the eastern flank of the northern Juan de Fuca Ridge drilled into crust ranging in age from 0.8 to 3.6 Ma (Fig. 1). In most ocean basins, burial of the igneous crust and the resultant hydrologic isolation of permeable basement takes place over tens of millions of years; on the eastern Juan de Fuca Ridge flank, burial is accelerated as a consequence of the proximity of the ridge to the abundant supply of turbidite sediments shed from the adjacent North American continental margin during the Pleistocene. The arrangement of Leg 168 drill sites along an east-to-west transect spanned a range of crustal ages, sediment thicknesses, and thermal and chemical states in basement (Fig. 1), allowing an assessment of current conditions and how conditions may have changed over time. Sites at the western end of the transect were closest to the spreading axis and the position of sediment/igneous-basement onlap and showed the greatest extent of hydrothermal cooling and the least amount of rock and fluid alteration. In contrast, sites at the eastern end of the transect revealed considerably greater rock and fluid alteration. Penetration into the basement section beneath the sediments was intentionally shallow during Leg 168; primary attention was given to lateral variations in basement fluid composition, formation temperatures, fluid pressures, and alteration. Deeper penetration and experiments were reserved as goals for later drilling. Results based on Leg 168 shipboard studies are summarized in the Leg 168 Initial Reports volume (Shipboard Scientific Party, 1997) and in a short summary article (Davis et al., 1997). Because of recent changes in ODP publications policy, many papers containing results from Leg 168 appear in journals rather than this volume. In the rest of this introduction we highlight results of post-cruise research, with an emphasis on hydrogeologic processes and papers that appear outside this volume.