Carbon and oxygen isotopic exchange between external and internal fluids of carbonate minerals can reset the clumped isotope composition (Δ) of paleotemperature archives. Understanding the nature of this exchange during carbonate diagenetic alterations is essential for correctly interpreting the paleoenvironmental significance of Δ-derived temperatures. Through batch hydrothermal experiments on aragonitic coral carbonates, we examine the kinetic signatures of clumped isotope fractionation from the initial disequilibrium to final equilibrium states during the dolomitization of the aragonite. By analyzing oxygen isotope fractionation and Sr partitioning between carbonate and fluid, we simulate the effect of exchange reactions on the Δ values. As the resetting feature of Δ values in our aragonite samples disagrees with the fractionation pattern observed in previous aragonite solid-state reordering experiment, we rule out the effect of the solid-state reordering. Our findings demonstrate that isotope exchanges with internal or external fluids coexist, particularly during the early stage of aragonite self-recrystallization. The results of this study indicate that the Δ value of coral aragonite is susceptible to internal exchange reactions in Mg-bearing solutions at 160–220 °C. Additionally, by modeling the bulk recrystallization and internal fluid-mineral exchange and evaluating their relative importance, we determine that the internal exchange reaction results in a nonlinear correlation between δO and Δ values. Importantly, we highlight the previously unrecognized diagenetic scenario in which the internal fluid-mineral exchange effect on the Δ value can outweigh the bulk recrystallization effect with external fluid coexisting. Consequently, our findings emphasize the need for a comprehensive assessment on the reaction kinetics for different types of recrystallization effects, to support the application of clumped isotope proxies for altered carbonate samples in diagenetic environments.

中文翻译：

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流体介导的交换反应诱导团块同位素重置：文石白云石化实验的见解

碳酸盐矿物的外部和内部流体之间的碳和氧同位素交换可以重置古温度档案的聚集同位素组成（Δ）。了解碳酸盐岩成岩变化过程中这种交换的性质对于正确解释 Δ 衍生温度的古环境意义至关重要。通过文石珊瑚碳酸盐的批量水热实验，我们研究了文石白云石化过程中从初始不平衡状态到最终平衡状态的团块同位素分馏的动力学特征。通过分析氧同位素分馏和碳酸盐与流体之间的 Sr 分配，我们模拟了交换反应对 Δ 值的影响。由于文石样品中Δ值的重置特征与之前文石固态重排序实验中观察到的分馏模式不一致，因此我们排除了固态重排序的影响。我们的研究结果表明，同位素交换与内部或外部流体共存，特别是在文石自重结晶的早期阶段。本研究结果表明，珊瑚文石的 Δ 值在 160-220 °C 的含镁溶液中容易受到内部交换反应的影响。此外，通过对本体重结晶和内部流体-矿物交换进行建模并评估它们的相对重要性，我们确定内部交换反应会导致 δ18O 和 Δ 值之间的非线性相关性。重要的是，我们强调了以前未被认识到的成岩作用情景，其中内部流体-矿物交换对 Δ 值的影响可以超过外部流体共存时的本体再结晶效应。因此，我们的研究结果强调需要对不同类型的重结晶效应的反应动力学进行全面评估，以支持在成岩环境中改变碳酸盐样品的簇同位素代理的应用。