澳大利亚昆士兰科技大学Kamber, Balz S.研究组的一项最新研究提出深部超热熔残余物是地幔金刚石的摇篮。相关论文发表在2023年3月15日出版的《自然》杂志上。

研究小组展示了在足够高温度下熔融产生克拉通根的镁质橄榄石的热力学和地球化学模拟的结果。新的封闭系统和开放系统模型通过深层熔融(约200km)和极热熔融(≥1800 °C)，再现了观察到的克拉通地幔矿物组成，消除了浅层熔融和堆积的需要。如在克拉通化石表面的绿岩带中观察到的那样，模拟的高镁质液体(科马提岩)演化为富铝和贫钛的形式。贫钛的科马提岩的缺乏表明，先进的封闭系统等化学熔融(＞1825°C)远不如开放系统深层液体与现有难熔地幔之间的相互作用常见。金刚石包裹体矿物的高耐熔成分可能意味着金刚石优先生长在克拉通根部还原程度较高的部分，由于来自较深的前边界层(该边界层在太古宙末期消失)的热柱影响，这些部分受超热高温熔融耗尽。

研究人员表示，古老的稳定大陆深达250km，其根基延伸到金刚石稳定区。这些克拉通的机械强度归因于它们的冷却和坚硬，这些特征是从广泛的熔体重继承而来。最突出的模型预测，在金刚石稳定层以上相对较浅的深度(50-100 km)形成克拉通，随后是通过鱼鳞状叠置形成较深的根。

附：英文原文

Title: Deep, ultra-hot-melting residues as cradles of mantle diamond

Author: Walsh, Carl, Kamber, Balz S., Tomlinson, Emma L.

Issue&Volume: 2023-03-15

Abstract: The ancient stable continents are up to 250km deep, with roots extending into the diamond stability field. These cratons owe their mechanical strength to being cool and rigid, features inherited from extensive melt extraction. The most prominent model for craton formation anticipates dominant melting at relatively shallow depth (50-100km) above diamond stability, followed by later imbrication to form the deeper roots. Here we present results from thermodynamic and geochemical modelling of melting at sufficiently high temperatures to produce the very magnesian olivine of cratonic roots. The new closed-system and open-system modelling reproduces the observed cratonic mantle mineral compositions by deep (about 200km) and very hot melting (≥1,800°C), obviating the need for shallow melting and stacking. The modelled highly magnesian liquids (komatiites) evolve to Al-enriched and Ti-depleted forms, as observed in the greenstone belts at the fossil surface of cratons. The paucity of Ti-depleted komatiite implies that advanced closed-system isochemical melting (>1,825°C) was much less common than open-system interaction between deeper liquids and melting of existing refractory mantle. The highly refractory compositions of diamond inclusion minerals could imply preferential diamond growth in the more reducing parts of the cratonic root, depleted by ultra-hot melting in response to heat plumes from a deeper former boundary layer that vanished at the end of the Archaean.

DOI: 10.1038/s41586-022-05665-2

Source: https://www.nature.com/articles/s41586-022-05665-2