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.

金刚石是一种罕见的地幔副矿物，可从地幔深部岩石（包括榴辉岩）中取样。这些都是影响岩石圈演化的主要过程的指示，即它们是否是通过洋壳俯冲或从地幔内的镁铁质熔体结晶。金刚石测年研究表明，许多榴辉岩金刚石套是古老的（元古代或侏罗纪）。这与金刚石的化学惰性性质相结合，防止其矿物含量被形成后的地幔交代事件改变，使得金刚石中包裹体的研究特别令人兴奋。由于硫化物矿物是金刚石中常见的包裹体类型，除了硫之外，还含有高丰度的亲铜和亲铁元素，因此它们适合于原位分析技术。 榴辉岩硫化物包裹体，从钻石采样深岩石圈中的中央奴隶克拉通，以前被约会到约1.9 Ga，对应于俯冲在奴隶克拉通边缘的时间，但也接近一个主要的岩脉形成情节，导致在地幔中的镁铁质成分的结晶。我建议用离子探针测定硫化物包裹体上的多种S同位素，以限制地壳与深部地层的起源（S同位素可以在包括大洋板片在内的浅岩石圈中分馏，但不能在深部地幔中分馏）。通过激光烧蚀ICPMS对流体释放和部分熔融过程中分馏的微量元素丰度的进一步研究，有望深入了解硫化物的起源、金刚石形成的条件和相关岩石圈地幔的演化。