Centrifuge-assisted piston cylinder experiments were conducted on plagioclase in basaltic melt at 1140–1250 °C, 0.42–0.84 GPa and mostly 1000 g. One set of experiments assesses the settling velocity of a dilute plagioclase suspension; a second sinks or floats plagioclase in a MORB-type melt exploring conditions of neutral buoyancy; and a third set examines floatation of plagioclase from an evolved lunar magma ocean composition. A compaction rate for plagioclase cumulates is established. The experiments demonstrate that neutral density of plagioclase An₇₄ in a MOR-type tholeiitic basalt occurs at 0.59 ± 0.04 GPa (1200 °C), contrasting predictions by present models on melt density which yield a density inversion pressure at 0.10–0.15 GPa. In nature, the level of neutral buoyancy depends on melt composition; nevertheless, for the onset of plagioclase crystallization in dry tholeiitic basalts, our result is robust. As the molar volume of plagioclase is well known, the experimentally determined pressure of neutral buoyancy indicates a correction of -1.6% to previous density models for silicate melts. It follows that for (tholeiitic) layered mafic intrusions, plagioclase is negatively buoyant for early, relatively primitive, parent melts. In contrast, the extreme Fe enrichment of a fractionating lunar magma ocean leads to melt densities that let anorthite always float. Compaction φ/φ₀ of experimental plagioclase cumulates is quantified to φ/φ₀ = − 0.0582 log (Δρ·h·a·t) + 1.284, where φ₀ is the porosity after settling (67 ± 2%), h the cumulate pile height, a acceleration and φ porosity as a function of time t. Gravitational-driven compaction in tens of m-thick plagioclase cumulate in basaltic magmas reaches down to ~ 40% porosity within hundreds of years, a timescales competing with characteristic cooling times of cumulate layers of mafic intrusions. To achieve plagioclase modes > 80% due to compaction, an additional overload of ~ 100 m (layers) of mafic minerals would be required. Compaction of a lunar anorthosite crust of 35 km to 20% porosity (i.e. ~ 90% plagioclase after crystallization of the interstitial melt) would require 30 kyrs.

在玄武岩熔体中斜长石酶在1140–1250°C，0.42–0.84 GPa和大部分为1000 g的条件下，进行了离心辅助活塞缸实验。一组实验评估了稀斜长石悬浮液的沉降速度。第二个在MORB型熔体中下沉或漂浮斜长石，探索中性浮力的条件；第三组研究了演化的月球岩浆海洋成分中斜长石的漂浮。建立了斜长石堆积物的压实率。实验证明斜长石An _74的中性密度在MOR型的玄武岩中发生在0.59±0.04 GPa（1200°C），与目前模型对熔体密度的预测相反，熔体密度在0.10-0.15 GPa时产生密度反转压力。在自然界中，中性浮力的水平取决于熔体的成分。然而，对于干燥的玄武岩中斜长石结晶的开始，我们的结果是可靠的。由于斜长石的摩尔体积是众所周知的，通过实验确定的中性浮力压力表明，对硅酸盐熔体的先前密度模型的校正为-1.6％。因此，对于（厚生的）层状镁铁质侵入体而言，斜长石对于早期的，相对原始的母体熔体是负浮力的。相比之下，在月球岩浆分离海洋中极度的Fe富集导致融化密度，使钙长石始终漂浮。压实φ / φ ₀实验的斜长石进行累积量化为φ / φ ₀  = - 0.0582日志（Δ ρ · ħ ·一·吨）+ 1.284，其中φ ₀是沉降后的孔隙率（67±2％），ħ的累积绒头高度，一个加速度和φ孔隙率作为时间的函数吨。重力驱动的压实在几十米在数百年内，玄武岩浆中的厚斜长石孔隙率降低到了约40％的孔隙度，这个时间尺度与镁铁质侵入体的累积层的特征冷却时间相竞争。为使压实作用获得的斜长石模式> 80％，镁铁矿质会额外造成〜100 m（层）的超载。将35 km的月球原位硬壳压实到20％的孔隙度（即在间隙熔体结晶后〜90％斜长石）将需要30 kyrs。