Constraints on diamond formation and craton evolution from S isotopes and trace element contents in diamond sulfides

硫化金刚石中S同位素和微量元素含量对金刚石形成和克拉通演化的制约

• 批准号: 185165593
• 负责人: Dr. Sonja Aulbach
• 金额: --
• 依托单位: Abteilung Petrologie und Geochemie
• 依托单位国家: 德国
• 项目类别: Research Grants
• 财政年份: 2010
• 资助国家: 德国
• 起止时间: 2009-12-31 至 2012-12-31
• 项目状态: 已结题
• 来源: https://gepris.dfg.de/gepris/projekt/185165593?language=en
• 关键词: Constraints; diamond; formation; craton; evolution

Diamonds are rare accessory mantle minerals sampling deep mantle lithologies including cratonic eclogites. These are indicative of major processes affecting lithosphere evolution, i.e. whether they were emplaced via subduction of oceanic crust or crystallized from mafic melts within the mantle. Diamond dating studies have revealed many eclogitic diamond suites to be ancient (Proterozoic or Archaean). This, combined with the chemically inert nature of diamond, which prevents its mineral content from being modified by post-formation mantle metasomatic events, makes the study of inclusions in diamonds particularly exciting. Since sulfide minerals are a frequent inclusion type in diamonds that contain high abundances of chalcophile and siderophile elements in addition to sulfur, they lend themselves to in situ analytical techniques. Eclogitic sulfide inclusions, isolated from diamonds sampling the deep lithosphere in the central Slave Craton, have previously been dated to ca 1.9 Ga, a time corresponding to subduction at the Slave craton margin, but also close to a major dike formation episode leading to the crystallization of mafic components in the mantle. I propose to determine multiple S isotopes on sulfide inclusions by ion microprobe to constrain a crustal vs deep formation origin (S isotopes can be fractionated in the shallow lithosphere including the oceanic slab but not in the deep mantle). Additional investigation of the trace-element abundances, which are fractionated during fluid release and partial melting, by laser ablation ICPMS, promises insights on the origin of the sulfides, conditions of diamond formation and evolution of the associated lithospheric mantle.

钻石是稀有的副地幔矿物，采样于深层地幔岩性，包括克拉通榴辉岩。这些表明了影响岩石圈演化的主要过程，即它们是通过洋壳俯冲而形成的，还是由地幔内镁铁质熔体结晶而成的。钻石测年研究表明，许多榴辉岩钻石套件都是古老的（元古代或太古宙）。再加上钻石的化学惰性，可以防止其矿物含量被形成后地幔交代事件改变，使得对钻石内含物的研究特别令人兴奋。由于硫化物矿物是钻石中常见的内含物类型，除了硫之外，还含有大量的亲铜元素和亲铁元素，因此它们适合于原位分析技术。 榴辉硫化物包裹体是从从属克拉通中部深层岩石圈取样的钻石中分离出来的，此前已测得的年代为约 1.9 Ga，该时间对应于从属克拉通边缘的俯冲作用，但也接近导致结晶的主要岩脉形成事件。地幔中的镁铁质成分。我建议通过离子微探针测定硫化物包裹体上的多种硫同位素，以限制地壳与深层地层起源（硫同位素可以在包括海洋板片在内的浅层岩石圈中进行分馏，但不能在深部地幔中进行分馏）。通过激光烧蚀 ICPMS 对微量元素丰度进行进一步研究，这些微量元素丰度在流体释放和部分熔化过程中被分馏，有望深入了解硫化物的起源、钻石形成的条件以及相关岩石圈地幔的演化。