Abstract Cratonic lithosphere is believed to have been chemically buoyant and mechanically resistant to destruction over billions of years. Yet the absence of cratonic roots at some Archean terrains casts doubt on the craton stability and longevity on a global scale. As unique mantle-derived melts at ancient continents, silica-poor, kimberlitic melts are ideal tools to constrain the temporal variation of lithosphere thickness and the processes affecting the lithosphere root. However, no reliable thermobarometer exists to date for strongly silica-undersaturated, mantle-derived melts. Here we develop a new thermobarometer for silica-poor, CO2-rich melts using high-temperature, high-pressure experimental data. Our barometer is calibrated based on a new observation of pressure-dependent variation of Al2O3 in partial melts saturated with garnet and olivine, while our thermometer is calibrated based on the well-known olivine-melt Mg-exchange. For applications to natural magmas, we also establish a correction scheme to estimate their primary melt compositions. Applying this liquid-based thermobarometer to the estimated primary melt compositions for a global kimberlite dataset, we show that the equilibration depths between primary kimberlite melts and mantle peridotites indicate a decrease of up to ∼150 km in cratonic lithosphere thickness globally during the past ∼2 Gyr. Together with the temporal coupling between global kimberlite frequency and cold subduction flux since ∼2 Gyr ago, our results imply a causal link between lithosphere thinning and supply of CO2-rich melts enhanced by deep subduction of carbonated oceanic crusts. While hibernating at the lithosphere root, these melts chemically metasomatize and rheologically weaken the rigid lithosphere and consequently facilitate destruction through convective removal in the ambient mantle or thermo-magmatic erosion during mantle plume activities.

中文翻译：

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富含 CO2、二氧化硅不饱和熔体的热气压测定法限制了金伯利岩岩浆活动地区克拉通岩石圈随时间变薄

摘要 克拉通岩石圈被认为在数十亿年的时间里一直具有化学浮力和机械抗破坏性。然而，在一些太古宙地形上没有克拉通根部，这使人们对全球范围内克拉通的稳定性和寿命产生怀疑。作为古代大陆独特的地幔衍生熔体，贫硅的金伯利岩熔体是限制岩石圈厚度随时间变化和影响岩石圈根部过程的理想工具。然而，迄今为止，还没有可靠的温度晴雨表来测量二氧化硅强烈不饱和的地幔衍生熔体。在这里，我们使用高温、高压实验数据开发了一种用于贫二氧化硅、富 CO2 熔体的新型温度气压计。我们的气压计是基于对用石榴石和橄榄石饱和的部分熔体中 Al2O3 的压力相关变化的新观察进行校准的，而我们的温度计是基于众所周知的橄榄石熔体镁交换校准的。对于天然岩浆的应用，我们还建立了一个校正方案来估计它们的主要熔体成分。将此基于液体的温度气压计应用于估计的全球金伯利岩数据集的原生熔体成分，我们表明原生金伯利岩熔体和地幔橄榄岩之间的平衡深度表明，在过去~2 期间，全球克拉通岩石圈厚度减少了约 150 公里。吉尔。连同全球金伯利岩频率和自~2 Gyr 以前以来的冷俯冲通量之间的时间耦合，我们的结果表明岩石圈变薄与碳酸化洋壳深俯冲增强的富含二氧化碳的熔体供应之间存在因果关系。在岩石圈根部冬眠时，这些熔体在化学上交代并在流变学上削弱了刚性岩石圈，从而通过地幔柱活动期间周围地幔中的对流去除或热岩浆侵蚀促进了破坏。