Migration of the Pacific-Indian Isotopic Boundary and Evolution of the Australian-Antarctic Discordance: A Drilling Site Survey

在固体地球物理学中，提高对地幔环流系统的认识是一个高度优先的科学问题。通过绘制海底关键区域地壳成分的面积分布图，可以获得地幔储层的大小、组成和分布、地幔温度变化、地幔对流搅拌效率和单个地幔储层寿命的定量信息。这种类型的一个非常重要的问题是印度洋上地幔独特的同位素和地球化学特征的起源和演化，可以通过地表取样和地壳钻探来解决。在印度洋扩张中心喷发的熔岩在同位素上不同于太平洋的熔岩。在沿扩展脊的澳大利亚-南极不协调区内，太平洋和同位素省之间已经确定了一条独特而尖锐的边界。本项目的目标是绘制远离脊顶的边界图，因为有限的现有数据往往表明边界随着时间的推移向西移动。将于1996年初进行为期40天的研究巡航，在离轴地区收集地震反射、重力和磁力数据和疏浚样本。这些数据还将提供现场调查信息，以支持海洋钻探计划的一项提议，即对旧地壳进行取样，试图绘制边界的历史。该项目涉及来自华盛顿大学、俄勒冈州立大学和伍兹霍尔海洋研究所的科学家。＊＊＊

9527462 Pyle An improved understanding of the systematics of mantle circulation is a high scientific priority in solid earth geophysics. By mapping the areal distribution of crustal compositions over key areas of ocean floor, quantitative information about the size, composition, and distribution of mantle reservoirs, variations in mantle temperatures, the efficiency of convective stirring in the mantle, and the longevity of individual mantle reservoirs can be obtained. One very important problem of this type, which can be addressed by surficial sampling and crustal drilling, concerns the origin and evolution of the distinctive isotopic and geochemical signature of the Indian Ocean upper mantle. Lavas erupted at Indian Ocean spreading centers are isotopically distinct from those of the Pacific. A unique and sharp boundary between Pacific and isotopic provinces has been identified within the Australian-Antarctic Discordance along the spreading ridge. The objective of the present project is to map this boundary away from the ridge crest, since limited available data tends to indicate a westward migration of the boundary over time. Seismic reflection, gravity and magnetic data and dredge samples will be collected in the off-axis area during a 40 day research cruise in early 1996. These data will also provide site-survey information in support of a proposal to the Ocean Drilling Program to sample old crust in an attempt to map the history of the boundary. The project involves scientists from the University of Washington, Oregon State University, and Woods Hole Oceanographic Institution. ***