The lead isotope composition of the Earth´s mantle from double-spike analysis of abyssal peridotites

深海橄榄岩双尖峰分析的地幔铅同位素组成

• 批准号: 200181798
• 负责人: Privatdozent Dr. Marcel Regelous
• 金额: --
• 依托单位: Max-Planck-Institut für Chemie (Otto-Hahn-Institut)
• 依托单位国家: 德国
• 项目类别: Research Grants
• 财政年份: 2011
• 资助国家: 德国
• 起止时间: 2010-12-31 至 2014-12-31
• 项目状态: 已结题
• 来源: https://gepris.dfg.de/gepris/projekt/200181798?language=en
• 关键词: lead; isotope; composition; Earth; mantle

Oceanic basalts are widely used as probes of mantle composition, however this approach assumes that mantle melts inherit the isotopic composition of their source. Recent Pb isotope data for peridotites presumed to represent melting residues of the upper oceanic mantle extend to much less radiogenic compositions than observed in oceanic basalts. Incomplete extraction of Pb from an unradiogenic component in the mantle during melting could potentially explain the paradox that the bulk Earth apparently has a Pb isotope composition that is more radiogenic than is predicted if the Earth accreted from chondritic material. It could also explain the Pb isotope systematics of mid-ocean ridge basalts, which apparently reflect mixing between enriched and depleted mantle components. Reliable existing Pb isotope data for abyssal peridotites - residues of mantle melting at mid-ocean ridges - are too few (3 analyses) to test this hypothesis. Our proposed study will use a combination of new and existing methods to obtain some of the first reliable Pb isotope data for abyssal peridotites. We will analyse clinopyroxene and spinel separates, and use sequential dissolution methods to selectively dissolve different mineral phases within bulk-rock powders. Pb isotope compositions will be measured to high precision using a 202Pb-205Pb double-spike method. Our results will be used to test the hypothesis that a 'hidden' unradiogenic Pb component, which can balance the Earth's Pb budget, is present in the upper mantle.

海洋玄武岩被广泛用于探测地幔成分，但这种方法假定地幔熔体继承了其来源的同位素组成。最近的橄榄岩Pb同位素数据被认为代表了上大洋地幔的熔融残余物，其放射性成因成分比在海洋玄武岩中观察到的少得多。在熔融过程中，从地幔的非放射性成分中提取的Pb不完全可能解释这样一个悖论，即如果地球是由球粒陨石物质吸积的，那么地球的整体显然具有比预测的更强的放射性同位素组成。这也可以解释洋中脊玄武岩的Pb同位素系统，它明显反映了富、贫地幔组分的混合。深海橄榄岩——大洋中脊地幔熔融的残留物——的可靠的现有Pb同位素数据太少（3项分析），无法检验这一假设。我们提出的研究将结合新的和现有的方法来获得一些可靠的深海橄榄岩的Pb同位素数据。我们将分析斜辉石和尖晶石分离物，并使用顺序溶解方法选择性地溶解大块岩石粉末中的不同矿物相。采用202Pb-205Pb双尖峰法对铅同位素组成进行高精度测量。我们的研究结果将用于验证“隐藏”的非放射性成因铅成分的假设，该成分可以平衡地球的铅收支，存在于上地幔中。