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Primary carbonatite melt from deeply subducted oceanic crust

机译：深层俯冲洋壳中的一次碳酸盐岩融化

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Partial melting in the Earth's mantle plays an important part in generating the geochemical and isotopic diversity observed in volcanic rocks at the surface. Identifying the composition of these primary melts in the mantle is crucial for establishing links between mantle geochemical 'reservoirs' and fundamental geo-dynamic processes. Mineral inclusions in natural diamonds have provided a unique window into such deep mantle processes. Here we provide experimental and geochemical evidence that silicate mineral inclusions in diamonds from Juina, Brazil, crystallized from primary and evolved carbonatite melts in the mantle transition zone and deep upper mantle. The incompatible trace element abundances calculated for a melt coexisting with a calcium-titanium-silicate perovskite inclusion indicate deep melting of carbonated oceanic crust, probably at transition-zone depths. Further to perovskite, calcic-majorite garnet inclusions record crystallization in the deep upper mantle from an evolved melt that closely resembles estimates of primitive carbonatite on the basis of volcanic rocks. Small-degree melts of subducted crust can be viewed as agents of chemical mass-transfer in the upper mantle and transition zone, leaving a chemical imprint of ocean crust that can possibly endure for billions of years.
机译：地球地幔的部分融化在产生地表火山岩中观察到的地球化学和同位素多样性方面起着重要作用。确定地幔中这些主要熔体的成分对于在地幔地球化学“储层”与基本地球动力学过程之间建立联系至关重要。天然钻石中的矿物质夹杂物为此类深部地幔过程提供了独特的窗口。在这里，我们提供了实验和地球化学证据，证明了来自巴西Juina的钻石中的硅酸盐矿物包裹体是从地幔过渡带和上地幔深部的原生和演化的碳酸盐熔岩中结晶出来的。对于与钙钛硅酸盐钙钛矿夹杂物共存的熔体计算出的不相容的痕量元素丰度表明，可能在过渡带深度，碳酸盐化洋壳发生了深层熔融。除钙钛矿外，钙镁铁榴石石榴石包裹体还记录了在深部上地幔中从演化的熔体中结晶的现象，该熔体非常类似于根据火山岩估算的原始碳酸盐岩。俯冲的地壳的小规模熔体可以看作是上地幔和过渡带中化学物质传递的媒介，留下了可能持续数十亿年的海洋地壳化学烙印。

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