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首页> 外文期刊>Earth and Planetary Science Letters: A Letter Journal Devoted to the Development in Time of the Earth and Planetary System >Isotopic constraints on the cooling of the continental lithosphere
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Isotopic constraints on the cooling of the continental lithosphere

机译：同位素对大陆岩石圈冷却的限制

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摘要

A new model of continuous diffusion of radiogenic isotopes was applied to mineral ~(147)Sm-~(143)Nd and ~(176)Lu-~(176)Hf data on low-temperature garnet-peridotite xenoliths from Cretaceous South African kimberlites. The radiometric ages are younger than the Archean whole-rock Re-Os and U-Pb ages and reflect that both the Sm-Nd and Lu-Hf chronometric systems remained open under the thermal conditions of the lithospheric mantle. The radiogenic character of Hf in garnets, however, indicates that even if essentially no pyroxene remained immune to the effects of metasomatic events, the core of many garnets may preserve memory of the long history of this mineral in the subcontinental lithosphere. The cooling rates deduced from the garnet Sm-Nd ages in the South African lithosphere are fairly low (40-105 ℃ Gy~(-1)), but compare well with values obtained on similar samples from different regions. These unexpectedly low values imply that the heat flow at the base of the subcontinental lithospheric mantle has changed only very slowly through time. They further support the recent suggestion that, as a result of viscous dissipation by plate bending, convection vigor and heat flow are to some extent decoupled, which argues against a thermal feedback on geodynamics. Modern convection may still be mining fossil heat stored in the lower mantle.
机译：一种新的放射性同位素连续扩散模型被应用于南非白垩纪金伯利岩低温石榴石-橄榄岩橄榄岩异岩的〜（147）Sm-〜（143）Nd和〜（176）Lu-〜（176）Hf数据。辐射时代比太古代完整岩石的Re-Os和U-Pb年龄要年轻，这反映出Sm-Nd和Lu-Hf计时系统在岩石圈地幔的热条件下都保持开放。然而，石榴石中Hf的放射源特征表明，即使基本上没有辉石对变质事件的影响保持免疫力，许多石榴石的核心仍可以保留该矿物在大陆下岩石圈的悠久历史。从南非岩石圈的石榴石Sm-Nd年龄推算出的降温速率相当低（40-105℃Gy〜（-1）），但与不同地区类似样品获得的降温效果相当。这些出乎意料的低值意味着，亚大陆岩石圈地幔底部的热流随时间的变化非常缓慢。他们进一步支持了最近的建议，即由于板弯曲引起的粘性耗散，对流活力和热流在某种程度上是分离的，这与地球动力学的热反馈相抵触。现代对流可能仍在开采下地幔中储存的化石热量。

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