Impurity ion and isotope partitioning into carbonate minerals provide a window into the molecular processes occurring at the fluid-mineral interface during crystal growth. Here, we employ calcium isotope fractionation together with process-based modeling to elucidate the mechanisms by which two divalent cations with starkly contrasting compatibility, magnesium and manganese, inhibit calcite growth and incorporate into the mineral lattice. Calcite growth inhibition by Mg²⁺ is log-linear and K_Mg is on the order of 0.02-0.03 throughout the range of {Mg²⁺}/{Ca²⁺} studied here (0.01-2.6). Mn²⁺ exhibits much stronger log-linear growth rate inhibition at low Mn²⁺ concentrations (fluid {Mn²⁺}/{Ca²⁺} = 0.001–0.02). Mn²⁺ is readily incorporated into the calcite lattice to form a calcite-rhodochrosite solid solution, with large partition coefficients (K_Mn 4.6-15.6) inversely correlated to growth rate. For both Mn²⁺ and Mg²⁺, calcium isotope fractionation is found to be invariant with {Me²⁺}/{Ca²⁺} despite more than an order of magnitude decline in growth rate. This invariant Δ^44/40Ca suggests that the presence of Mn²⁺ or Mg²⁺ does not significantly change the relative rates of Ca²⁺ attachment and detachment at kink sites during growth, indicative of a dominantly kink blocking inhibition mechanism. Because the partitioning behavior dictates that Mn²⁺ must attach to the surface significantly faster than Ca²⁺, attachment of Mn²⁺ is likely to be as a non-monomer species such as an ion pair or possibly a larger polynuclear cluster. We propose that calcite growth rate inhibition by Mn is determined by the kinetics of carbonate attachment at Mn-occupied kink sites, potentially due to slow re-orientation kinetics of carbonate ions that have formed an inner-sphere complex with Mn²⁺ at the surface but must reorient to incorporate into the lattice. We demonstrate that patterns in Mg²⁺ partitioning and inhibition behavior are broadly consistent with growth inhibition driven by slow Mg²⁺-aquo complex dehydration relative to Ca²⁺ but argue that this mechanism likely represents one endmember scenario, seen in Mg-calcite growth at low supersaturations and net precipitation rates. During growth at faster net precipitation rates, some portion of Mg²⁺ is likely incorporated as a partially hydrated or otherwise complexed species, but calcite growth remains significantly inhibited by the kinetics of CO₃^2- attachment at Mg²⁺ kink sites. These findings suggest a hybrid classical/nonclassical growth mechanism whereby Ca²⁺ incorporates largely as a free ion at kink sites while Mn²⁺ and some portion of Mg²⁺ are incorporated via non-monomer attachment. This pattern may be generalizable; trace constituent cations with aquo-complex desolvation rates significantly slower than the mineral growth rate preferentially incorporate as a non-monomer species during otherwise classical crystal growth.

杂质离子和同位素分配到碳酸盐矿物中为晶体生长过程中流体-矿物界面发生的分子过程提供了一个窗口。在这里，我们采用钙同位素分馏和基于过程的建模来阐明两种具有截然不同相容性的二价阳离子镁和锰抑制方解石生长并结合到矿物晶格中的机制。^{Mg 2+}对方解石生长的抑制是对数线性的，并且在此处研究的 {Mg ²⁺ }/{Ca ²⁺ } 范围内 (0.01-2.6) ，K _Mg约为 0.02-0.03 。Mn ²⁺在低 Mn ²⁺浓度（流体 {Mn²⁺ }/{Ca ²⁺ } = 0.001–0.02)。Mn ²⁺很容易掺入方解石晶格中，形成方解石-菱锰矿固溶体，其分配系数大（K _Mn 4.6-15.6）与生长速率成反比。对于 Mn ²⁺和 Mg ^{2+ ，发现钙同位素分馏对于 {Me 2+} }/{Ca ²⁺ }是不变的，尽管增长率下降了一个数量级以上。这种不变的 Δ ^44/40 Ca 表明 Mn ²⁺或 Mg ²⁺的存在不会显着改变 Ca ^{2+的相对比率}生长过程中扭结部位的附着和脱离，表明主要是扭结阻断抑制机制。因为分配行为表明 Mn ²⁺必须比 Ca ²⁺快得多地附着在表面上，所以Mn ²⁺的附着很可能是作为非单体物质，例如离子对或可能是更大的多核簇。我们提出，Mn 对方解石生长速率的抑制是由 Mn 占据的扭结位点的碳酸盐附着动力学决定的，这可能是由于碳酸盐离子的缓慢重新定向动力学，这些离子在表面与 Mn ²⁺形成了内球络合物但必须重新定向以合并到晶格中。我们证明了 Mg ^{2+中的模式分配和抑制行为与由相对于 Ca 2+的缓慢 Mg 2+} -aquo 复合物脱水驱动的生长抑制大致一致，但认为这种机制可能代表一种端元情景，见于低过饱和度和净沉淀率下的 Mg-方解石生长。在以更快的净沉淀速率生长期间，Mg ^{2+的某些部分可能以部分水合或其他络合物质的形式掺入，但方解石的生长仍然受到在 Mg 2+}扭结点处的 CO ₃ ^2-附着动力学的显着抑制。这些发现表明了一种混合的经典/非经典生长机制，其中 Ca ^{2+Mn 2+}和一部分Mg ²⁺通过非单体结合主要作为自由离子结合。这种模式可能是可推广的；水络合物去溶剂化速率明显慢于矿物生长速率的痕量成分阳离子在其他经典晶体生长过程中优先作为非单体物质结合。