Oceanic Lithosphere Created at a Segment of the Mid Atlantic Ridge: A 20 Million Year History

在这笔资金的资助下，pi将研究来自维玛岩石圈剖面的样本，这是一个弯曲的，凸起的海洋岩石圈，沿着大西洋中部维玛断裂带附近的一条流线暴露了300多公里，在脊轴上代表了20英里的时间间隔。这项工作建立在这样的发现之上：上涌的地幔所经历的融化程度随着时间的推移发生了显著的变化，短波长（~3- 4毫微米）振荡叠加在与地壳厚度变化相关的长范围（~ 20毫微米）稳定增长上。pi将：(a)测定来自橄榄岩的地幔平衡相正辉石、斜辉石和尖晶石的主要和微量元素，以细化熔融程度随时间变化的模式。(b)确定VLS上部地壳单元的一组玄武岩玻璃质和非玻璃质玄武岩的主要元素和微量元素组成，以获得对熔融程度变化的独立估计。(c)完成对来自橄榄岩和玄武岩玻璃的cpx的Sr-Nd-Pb同位素组成的研究，以便确认熔化程度和同位素组成之间可能存在的关系，并帮助解决地幔橄榄岩和地壳玄武岩之间的成因联系问题，因为初步数据显示玄武岩在同位素上比橄榄岩更“富集”。(d)通过将地幔橄榄岩的熔融程度曲线与玄武岩的熔融程度曲线或由重力推断的地壳厚度曲线进行比较，估计洋脊下地幔的上涌速度。对于区分岩石圈形成的“被动”模型和浮力起作用的模型来说，地幔上涌速度相对于扩张半速率的知识是至关重要的。

Under this funding, the PIs will study samples from the Vema lithospheric section, a flexured, uplifted sliver of oceanic lithosphere, exposed for over 300 km along a flow line near the Vema fracture zone in the central Atlantic, and representing a time interval of 20 my of accretion at a ridge axis. This effort builds on the finding that the degree of melting undergone by the upwelling mantle has changed significantly through time, with short-wavelength (~3- 4 my) oscillations superimposed on a long range (~ 20 my) steady increase, correlated with crustal thickness variations. The PIs will: (a) Determine the major and trace elements of mantle equilibrated phases orthopyroxene, clinopyroxene and spinel from peridotites to refine the pattern of variations of degree of melting with time. (b) Determine the major and trace elements composition of a set of basaltic glasses and non-glassy basalts from the upper crustal unit of the VLS to obtain an independent estimate of variations of extent of melting. (c) Complete the study of Sr-Nd-Pb isotopic composition of cpx from the peridotites and of the basaltic glasses, in order to confirm a possible relationship between degree of melting and isotopic composition and to help solve the issue of the genetic link between mantle peridotites and crustal basalts, given that preliminary data show the basalts to be isotopically more "enriched" than the peridotites. (d) Estimate the upwelling velocity of the mantle beneath the Ridge will by comparing the mantle peridotites degree of melting curve with that derived from the basalts or with a crustal thickness curve inferred from gravity. Knowledge of mantle upwelling velocity relative to spreading half-rate is critical to discriminate between "passive" models of creation of lithosphere, and models where buoyant forces play a role.