Petrologic Studies of the Australian-Antarctic Discordance

澳大利亚-南极不协调带（AAD）是现今在澳大利亚和南极洲之间的一个低重力和异常深海底区域的发散板块边界上的表现。AAD还包含太平洋型和印度型全球尺度同位素省的分界线。在不一致的扩展轴显示一个不寻常的，圆齿偏移模式，并在恒定（中等）扩展速率下，几乎全谱的轴脊形态。与这种形态和构造的多样性相结合的是异常广泛的地球化学多样性，这似乎需要广泛的原始岩浆成分，而这反过来又需要熔化条件的广泛变化。1988年，首席研究员成功地对该地区进行了一次巡航，并获得了15天的SeaMARC II侧扫描覆盖范围和26条新的疏浚拖船。这项工作的目标是：尽可能详细地确定同位素边界的性质和位置；全面定义AAD熔岩的地球化学和岩石学多样性，并从构造和MORB成因方面了解这种多样性的潜在成因；并定义和评估沿山脊某一段熔岩的多样性根据它们独特的不同演化过程。

The Australian-Antarctic Discordance (AAD) is the parsent-day manifestation, at a divergent plate boundary, of a region of low gravity and anomalously deep ocean floor between Australia and Antarctica. The AAD also contains the boundary between Pacific- type and Indian-type global-scale isotopic provinces. The spreading axis within the discordance displays an unusual, crenulate offset pattern and, at constant (medium) spreading rate, almost the full spectrum of axial ridge morphologies. Coupled with this morphologic and tectonic diversity is an unusually broad geochemical diversity that appears to require a broad range of primary magma compositions which require, in turn, a broad variation in conditions of melting. The principal investigator led a successful cruise to the area in 1988 and obtained 15 days of SeaMARC II side-scan coverage and 26 new dredge hauls. The objectives of this work are to: determine, in as fine detail as possible, the nature and location of the isotopic boundary; fully define the geochemical and petrologic diversity of AAD lavas and to understand the underlying petrogenetic causes for this diversity in relation to tectonics and MORB genesis in general; and define and evaluate the diversity of lavas along one section of the ridge in terms of distinctively different processes by which they evolved.