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ReversePetrogen: A Multiphase Dry Reverse Fractional Crystallization-Mantle Melting Thermobarometer Applied to 13,589 Mid-Ocean Ridge Basalt Glasses
Journal of Geophysical Research: Solid Earth ( IF 3.9 ) Pub Date : 2021-07-29 , DOI: 10.1029/2020jb021292
S. Brown Krein 1 , Z. J. Molitor 1 , T. L. Grove 1
Affiliation  

We present a new algorithm, ReversePetrogen (RevPet), to infer mantle melting conditions (pressure, temperature, source composition) using evolved basalts that have experienced multiphase fractional crystallization. RevPet measures and minimizes the compositional distance between experimentally predicted phase saturation boundaries and an erupted basalt and the more primitive liquids that return it to a primary melt. We use RevPet to investigate mantle melting conditions at mid-ocean ridges (MORs) using a global data set of 13,589 basaltic glasses. We find that their average apparent mantle potential temperature (TP*) is 1322°C ± 56°C with melting pressures of 13.0 ± 5 kbars. Inferring the true initial (pre-melted) TP from TP* requires knowing the style and degree of melting of the input basalts. If MORB glasses were entirely produced by near-fractional melting of a homogenous source, they would record the cooling of the mantle during melting from an initial TP = ∼1380°C (ΔTP = 0°C) down to TP = ∼1270°C. If, instead, they were all fully pooled near-fractional melts of the same source, they would record variations in ambient MOR TP from ∼1300°C to 1450°C (ΔTP = 150°C). However, because MOR basalts are thought to be both near-fractional and variably pooled melts of variable sources, MOR TP must be intermediate between these two extremes. Our best estimate, consistent with MOR crustal thickness, is that ambient MOR TP is homogenous (∼1350°C–1400°C) except near hotspots where TP reaches ∼1600°C. Some primitive glasses found near slow-spreading ridges and back-arcs record very low temperatures (TP* < 1250°C) and pressures of melting (<10 kbar) and reflect mantle cooling during melting and melt equilibration in the mantle lithosphere.

中文翻译:

ReversePetrogen:应用于 13,589 大洋中脊玄武岩玻璃的多相干式反向分数结晶-地幔熔化温度计

我们提出了一种新算法ReversePetrogen (RevPet),使用经历了多相分结晶的演化玄武岩来推断地幔熔融条件(压力、温度、源成分)。RevPet测量并最小化实验预测的相饱和边界与喷发的玄武岩以及使其返回初级熔体的更原始液体之间的组成距离。我们使用RevPet使用包含 13,589 个玄武岩玻璃的全球数据集来研究大洋中脊 (MOR) 的地幔熔化条件。我们发现它们的平均表观地幔位温(T P *)为 1322°C ± 56°C,熔化压力为 13.0 ± 5 kbars。推断真正的初始(预熔)牛逼P牛逼P *需要知道的风格和输入玄武岩熔融程度。如果 MORB 玻璃完全是由同质源的近分数熔化产生的,它们将记录从初始T P  = ∼1380°C (Δ T P  = 0°C) 到T P  =熔化过程中地幔的冷却~1270℃。相反,如果它们都是相同来源的完全汇集的近分数熔体,它们将记录环境 MOR T P从~1300°C 到 1450°C(Δ T P  = 150°C)的变化。然而,由于 MOR 玄武岩被认为是不同来源的近分数和可变汇集熔体,MORT P必须介于这两个极端之间。我们与 MOR 地壳厚度一致的最佳估计是,环境 MOR T P是均质的(~1350°C–1400°C),除了靠近热点的T P达到~1600°C。一些原始眼镜附近发现低速扩张脊和背弧记录非常低的温度(Ť P * <1250℃)和熔化(<10千巴)的压力下和反映地幔熔化期间冷却和熔体在地幔岩石圈平衡。
更新日期:2021-07-30
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