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

大西洋中脊一段形成的海洋岩石圈：2000万年的历史

• 批准号: 0328217
• 负责人: Enrico Bonatti
• 金额: --
• 依托单位: Columbia University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2003
• 资助国家: 美国
• 起止时间: 2003-09-01 至 2007-06-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0328217&HistoricalAwards=false
• 关键词: Oceanic; Lithosphere; Created; Segment; Mid

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.

在这笔资金的资助下，PIS将研究Vema岩石圈部分的样品，Vema岩石圈是一片弯曲的、隆起的大洋岩石圈，沿着大西洋中部Vema断裂带附近的流线暴露了300多公里，代表着山脊轴线上20 My的沉积时间间隔。这项工作建立在一个发现的基础上，即上升地幔经历的熔融程度随时间发生了显著变化，短波(~3-4My)振荡叠加在长期(~20My)稳定增加上，与地壳厚度变化相关。PI将：(A)测定橄榄岩中地幔平衡相斜方辉石、单斜辉石和尖晶石的主量元素和微量元素，以完善熔融度随时间变化的模式。(B)测定来自VLS上地壳单元的一套玄武岩玻璃和非玻璃玄武岩的主量元素和微量元素组成，以获得熔融程度变化的独立估计。(C)完成对橄榄岩和玄武岩玻璃中cpx的锶-钕-铅同位素组成的研究，以确定熔融程度与同位素组成之间的可能关系，并帮助解决地幔橄榄岩和地壳玄武岩之间的遗传联系问题，因为初步数据表明，玄武岩的同位素比橄榄岩更“丰富”。(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，估计山脊之下地幔的上涌速度。对于区分岩石圈形成的“被动”模型和浮力起作用的模型，了解地幔上升速度相对于扩散半速率是至关重要的。