Origin of geochemical heterogeneity in mid-ocean ridge upper mantle, ODP Leg 209

大洋钻探计划（ODP）第209航次预计将在15° 20 'N（佛得角）断裂带的北部和南部沿大西洋中脊（MAR）沿着钻探6至7个100米规模的地幔橄榄岩岩心。全球范围的疏浚已经证明了热点和扩张速率对地幔橄榄岩化学的影响。远离这些热点的地幔异常的重要性才刚刚开始被充分认识到。然而，与熔体输送相关的熔体岩石反应的程度仍然存在激烈的争论。不同的模型，在一定程度上刺激了腿209共同首席彼得·克莱门的工作，范围从部分熔融与孤立（通道）熔体运输全球多孔流，后者意味着所有橄榄岩已受到熔体岩石反应。辉石岩、纯橄榄岩、剪切带和橄榄岩宿主模态相位变化的丰度变化可以在岩心中很好地确定，并且是指示熔体-岩石反应的可变程度的主要候选者。我们建议选择两个合适的岩心剖面（长度20-30米），显示岩性和应变的变化，并要求进行详细取样。通过获得一个完整的地球化学数据集，这些样品，我们希望更好地约束的程度，和反应的管理，熔融岩石反应和多孔流动，并限制什么样的过程控制典型的“噪音”或背景变化的一部分，在原地海洋地幔。重要的是，建议的调查规模弥补了目前大洋橄榄岩调查中的空白，与任何蛇绿岩剖面相比，所选地点的构造情况是众所周知的。

Ocean Drilling Program (ODP) Leg 209 expects drilling six to seven, 100 m scale cores of mantle peridotite along the Mid Atlantic Ridge (MAR) north and south of the 15°20'N (Capo Verde) Fracture Zone. Global scale dredging has demonstrated the influence of hot spots and spreading rate on mantle peridotite chemistry. The importance of mantle anomalies away from such hot spots is just beginning to be fully realized. The extent of melt rock reaction as associated with melt transport remains, however, fiercely debated. Diverse models, in part stimulated by the work of Leg 209 co-chief Peter Kelemen, range from fractional melting linked with isolated (channeled) melt transport to global porous flow, the latter implying that all peridotites have been affected by melt-rock reaction. Variations in the abundance of pyroxenites, dunites, shear zones and modal phase variation in peridotite hosts can be well determined in drill core and are the prime candidates to indicate variable extents of melt-rock reaction. We propose to select two suitable sections of core (length scale 20-30 m) showing variations in lithology and strain and request their detailed sampling. By obtaining a complete geochemical data set on these samples, we expect to better constrain the extent of, and the reactions governing, melt rock reaction and porous flow and to constrain what processes control the typical "noise" or background variation in a section of in-situ oceanic mantle. Importantly, the suggested scale of investigation bridges a current gap in the investigations of oceanic peridotite and the tectonic situation of the chosen site is, in contrast to any ophiolitic section, well known.