Chemical and thermal evolution of the upper mantle; implications for Earth's climate and biosphere and the nature of mantle convection

大洋中脊玄武岩(MORB)的化学成分可用于推断上地幔的温度，而古老的海底熔岩保存了中生代以来地幔温度和地壳厚度变化的记录。现有的旧海底化学数据表明，在80 Ma之前，上地幔比今天高60℃。这种规模的地幔温度变化对全球气候和生物圈产生了影响。有人认为，白垩纪温室气候和海平面高位是由于地幔温度较高而导致洋壳产量高于正常水平所致。然而，目前关于较老洋壳的化学数据很少，而且大多数现有的分析都是在高度蚀变的、富含斑晶的全岩样品上进行的。我们将确定每个主要大洋盆地过去170 Ma以来MORB化学的变化，通过使用微量分析技术分析新鲜的玄武岩玻璃来避免蚀变的影响。在太平洋、大西洋和印度洋的古老洋壳上钻探的许多DSDP/ODP点都有适合进行这项研究的样品。这些结果将被用来研究地幔对流尺度的含义，以及在1-10 Ma的时间尺度上对海平面、海水化学和气候的影响。

The chemistry of mid-ocean ridge basalts (MORB) can be used to infer the temperature of the upper mantle, and ancient seafloor lavas preserve a record of mantle temperature and crustal thickness variations since the Mesozoic. Existing chemical data for old seafloor suggest that before 80 Ma the upper mantle was 60°C hotter than today. Mantle temperature variations on this scale impact on global climate and the biosphere. It has been argued that the Cretaceous greenhouse climate and sea-level highstand was triggered by higher than normal rates of oceanic crust production, due to higher mantle temperatures. However, there are presently very few chemical data for older oceanic crust, and most existing analyses were carried out on highly altered, phenocryst-rich, whole-rock samples. We will determine the changes in MORB chemistry over the past 170 Ma in each of the major ocean basins, avoiding the effects of alteration by analysing fresh basaltic glass using microanalytical techniques. Suitable samples for this study are available from the numerous DSDP/ODP sites drilled on old oceanic crust in the Pacific, Atlantic and Indian Oceans. The results will be used to examine the implications for the scale of mantle convection, and effects on sea-level, seawater chemistry and climate on timescales of 1-10 Ma.