Phosphorus and aluminum zoning in olivine: contrasting behavior of two nominally incompatible trace elements
Phosphorus and aluminum zoning in olivine: contrasting behavior of two nominally incompatible trace elements
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橄榄石中磷和铝的分区：两种名义上不相容的微量元素的对比行为
DOI：
10.1007/s00410-019-1618-y
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发表时间：
2019
影响因子：
3.5
通讯作者：
Melnik, Oleg
中科院分区：
文献类型：
--
作者：
Shea, Thomas;Hammer, Julia E.;Hellebrand, Eric;Mourey, Adrien J.;Costa, Fidel;First, Emily C.;Lynn, Kendra J.;Melnik, Oleg
橄榄石中的磷分带因其保存有关晶体生长速率和机制的关键信息的能力而受到相当大的关注。它的浓度在亚微米空间范围内变化很大，并形成复杂的雪花状图案，通常归因于晶体的快速生长。还观察到了表面上相似的铝浓缩模式，这表明这两种元素的合并和分配行为类似。我们在原始Kī劳厄玄武岩上进行了1atm结晶实验，以考察橄榄石生长过程中P和Al分带的形成与过冷− ΔT(−ΔT=Tiquidus−T)的关系。在T初始= 1290°C(高于橄榄石稳定性10°C)下花费24小时后，电荷被迅速冷却到最终温度T最终= 1220-1270°C，对应于过冷度− ΔT= 10-60°C(其中T= 1280°C)。实验橄榄石的成分X射线图显示，只需要一个小的过冷度(≤ 25°C)就可以产生与骨骼生长相关的细微尺度的P和Al富集物。浓度分布表明，尽管在橄榄石中具有相似的富集型式，但P和Al的表观晶体/熔体质量分配系数分别为= 0.002-1和= 0.002-0.006。在同一晶体中，磷的富集率为 >； 的40倍，而铝的富集率永远不会超过2倍。合成橄榄石和天然橄榄石附近的玻璃通常富含铝，但在分析不确定的情况下，不富含磷。因此，我们没有找到直接证据表明，存在富含磷的成分边界层，足以在天然和合成橄榄石中产生富磷。结合生长和扩散的数值模型解决了富铝边界层产生观测到的橄榄石中的富集型模式的条件。相比之下，相同的模型未能再现观测到的磷的富集量，这与我们的观察结果一致，即富磷边界层并不显著。如果取而代之的是，橄榄石/熔体的分配依赖于生长速度，则模型充分地再现了我们在没有边界层形成的情况下观察到的40倍的浓缩。我们推测，P的近无分割行为(接近1)与橄榄石晶格在快速结晶过程中容纳P的硬度可能较低有关，和/或与快速生长过程中空位缺陷的加速形成有关。我们的结果证实，P是初始快速增长的一个强有力的标志，但揭示了诱导这些浓缩所需的过冷度并不是特别大。例如，火山下几乎无处不在的岩浆混合过程可能足以导致骨骼生长所需的低到中等程度的过冷。
Phosphorus zoning in olivine is receiving considerable attention for its capacity to preserve key information about rates and mechanisms of crystal growth. Its concentration can vary significantly over sub-micron spatial scales and form intricate, snowflake-like patterns that are generally attributed to fast crystal growth. Ostensibly similar aluminum enrichment patterns have also been observed, suggesting comparable incorporation and partitioning behavior for both elements. We perform 1-atm crystallization experiments on a primitive Kīlauea basalt to examine the formation of P and Al zoning as a function of undercooling − ΔT(−ΔT=Tliquidus−Tcrystallization) during olivine growth. After 24 h spent atTinitial= 1290 °C (10 °C above olivine stability), charges are rapidly cooled to final temperaturesTfinal= 1220–1270 °C, corresponding to undercoolings − ΔT= 10–60 °C (withTliquidus= 1280 °C). Compositional X-ray maps of experimental olivine reveal that only a small undercooling (≤ 25 °C) is required to produce the fine-scale enrichments in P and Al associated with skeletal growth. Concentration profiles indicate that despite qualitatively similar enrichment patterns in olivine, P and Al have contrasting apparent crystal/melt mass distribution coefficients of= 0.01‒1 and= 0.002‒0.006. Phosphorus can be enriched by a factor > 40-fold in the same crystal, whereas Al enrichment never exceed factors of 2. Glass in the vicinity of synthetic and natural olivine is usually enriched in Al, but, within analytical uncertainty, not in P. Thus, we find no direct evidence for a compositional boundary layer enriched in P that would suffice to produce P enrichments in natural and synthetic olivine. Numerical models combining growth and diffusion resolve the conditions at which Al-rich boundary layers produce the observed enrichment patterns in olivine. In contrast, the same models fail to reproduce the observed P enrichments, consistent with our observation that P-rich boundary layers are insignificant. If instead, P olivine/melt partitioning is made to depend on growth rate, models adequately reproduce our observations of 40-fold enrichment without boundary layer formation. We surmise that near-partitionless behavior (close to 1) of P is related to the olivine lattice being perhaps less stiff in accommodating P during rapid crystallization, and/or to enhanced formation of vacancy defects during fast growth. Our results confirm that P is a robust marker of initial rapid growth, but reveal that the undercooling necessary to induce these enrichments is not particularly large. The near-ubiquitous process of magma mixing under volcanoes, for instance, is likely sufficient to induce low-to-moderate degrees of undercooling required for skeletal growth.
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影响因子：
3.5
作者：
I. Zhukova;H. O’Neill;I. Campbell
通讯作者：
I. Zhukova;H. O’Neill;I. Campbell
影响因子：
2.9
作者：
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橄榄石、斜长石斑晶与宿主岩浆之间的阴离子和阳离子分配：离子微探针研究的新应用
DOI：
--
发表时间：
1984
期刊：
影响因子：
--
作者：
H. Yurimoto;S. Sueno
通讯作者：
S. Sueno
Hf、Lu、Ti 和 Mn 在橄榄石、单斜辉石和玄武岩液体之间的分配
DOI：
--
发表时间：
1987
期刊：
影响因子：
--
作者：
T. Dunn
通讯作者：
T. Dunn
影响因子：
2.8
作者：
J. Donovan;T. Tingle
通讯作者：
J. Donovan;T. Tingle