By comparing high-quality volcanic gas and whole rock compositions, we calculated the apparent (observed) mass partition coefficients Kd* for 58 elements on six basaltic volcanoes located in arc and rift/hotspot settings. The inferred Kd* vary from ∼1100 for sulfur to 0.0001 for zirconium, i.e., within seven orders of magnitude. Only 14 elements have Kd* > 1, including highly volatile S, Se, Te and halogens, as well as Tl, Re, Os, Bi, Cd, Au, In and As. Alkali metals have Kd* in the range from 0.1 for Cs to 0.01 for Na. Partition coefficients of other rock-forming elements are <0.001. The partition coefficients for elements depend on element speciation and concentrations of ligand-forming elements in the gas such as sulfur and chlorine. Elements transported in the gas predominantly as halides have higher partition coefficients in HCl-rich arc gases, whereas elements preferably forming sulfides, hydrides and free atoms, have higher Kd* in sulfur-rich, HCl-poor and reduced rift/hotspot gases. Degassing directly from the free melt surface is negligible; deep gas passing through the erupting vent is quickly overwhelmed by the signal of low-pressure degassing. Equilibration of rising bubbles with the surrounding melt almost eliminates the difference between Kd* calculated for degassing lava flows (no connection with deep magma) and for lava lakes and open-vent volcanoes (convective mass exchange with deep magma takes place). Diffusion does not strongly affect the apparent partitioning of magmas degassing at surface. Gas bubbles growing in near-surface silicate melts at atmospheric pressure have a large density difference compared to the surrounding melt of 12–15 thousand times. This leads to the rapid expansion of such bubbles and a decrease in the thickness of the diffusion boundary layer in the melt due to its stretching around the growing bubble, which sharply decreases diffusion fractionation. As a result, the apparent partition coefficients (Kd*) for degassing basaltic volcanoes are close to the equilibrium ones (Kd) for most of the elements. The partition coefficients of volatile elements (S and Cl) calculated from the comparison of volcanic gas and rock compositions are in agreement with the values determined previously via experiments or theoretical modeling.

通过比较高质量的火山岩气和整个岩石成分，我们计算了位于弧线和裂谷/热点环境中的六个玄武岩火山上58个元素的表观（观测）质量分配系数Kd *。推断的Kd *从硫的约1100变化到锆的0.0001，即在七个数量级之内。Kd *> 1的元素只有14个，包括高挥发性的S，Se，Te和卤素，以及T1，Re，Os，Bi，Cd，Au，In和As。碱金属有Kd*范围从Cs的0.1到Na的0.01。其他岩石形成元素的分配系数<0.001。元素的分配系数取决于元素的种类和气体中诸如硫和氯的配体形成元素的浓度。在气体中主要以卤化物形式传输的元素在富含HCl的电弧气体中具有更高的分配系数，而优选形成硫化物，氢化物和自由原子的元素在富含硫的，HCl贫乏且裂谷/热点气体中具有更高的Kd *。从自由熔体表面直接脱气可以忽略不计；通过喷口的深层气体很快就被低压脱气的信号所淹没。上升的气泡与周围熔体的平衡几乎消除了Kd之间的差异*计算用于对熔岩流进行脱气（与深部岩浆无关）以及为熔岩湖和开敞式火山（与深部岩浆进行对流物质交换）。扩散不会强烈影响岩浆在表面脱气的表观划分。在大气压力下，在近地表硅酸盐熔体中生长的气泡与周围的熔体相比有12.5万倍的密度差。这导致这种气泡的快速膨胀，并且由于熔体在生长的气泡周围的拉伸而导致熔体中扩散边界层的厚度减小，这急剧地降低了扩散分馏。其结果是，表观分配系数（的Kd脱气玄武火山*）是接近平衡的人（的Kd）的大部分元素。通过比较火山气体和岩石成分而计算出的挥发性元素（S和Cl）的分配系数与先前通过实验或理论模型确定的值一致。