This work evaluates an exceptionally complex natural laboratory, the Middle Triassic Latemar isolated platform in the northern Italian Dolomite Mountains and explores spatial and temporal gradients in processes and products related to contact metamorphism, dolomitization and dedolomitization of marine limestones. The relation between petrographic change and re-equilibration of geochemical proxy data is evaluated from the perspective of carbonate-archive research. Hydrothermal dolomitization of the limestone units is triggered by dykes and associated hydrothermal fluids radiating from the nearby Predazzo Intrusion. Detailed petrography, fluid inclusion analysis, δ¹³C and δ¹⁸O data and ⁸⁷Sr/⁸⁶Sr isotope ratios shed light on the extreme textural and geochemical complexity. Metamorphic and diagenetic patterns include: (i) peak-metamorphic and retrograde-metamorphic phases including three dolomite marbles, two dedolomite marbles, brucite, magnesium silicates and late-stage meteoric/vadose cement at the contact aureole; (ii) four spatially defined episodes of dolomitization, authigenic quartz, low magnesium calcite and late-stage meteoric cement at the Latemar isolated platform; and (iii) kilometre-scale gradients in δ¹³C values from the contact aureole towards the platform interior. Results shown here are relevant for two reasons: first, the spatial analysis of alteration products ranging from high-grade metamorphic overprint of marbles at temperatures of 700°C in the contact aureole to moderately altered limestones in the platform interior at temperatures <100°C, allows the observation of processes that commonly occur along vertical (prograde) gradients from shallow burial to metamorphism at depths >20 km. Second, under rock-buffered conditions, and irrespective of metamorphic to diagenetic fluid−rock interactions, both marbles, and low-temperature hydrothermal dolomites have conservative marine δ¹³C and δ¹⁸O values. The fact that metamorphism and hydrothermal dolomitization of precursor limestones and early diagenetic dolostones did not per se reset environmental proxy data is of interest for those concerned with carbonate archive research in Earth’s deep time.

中文翻译：

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碳酸盐档案中代理数据保存的限制——从海洋石灰岩到大理石横断面的经验教训，意大利拉特马尔

这项工作评估了一个异常复杂的自然实验室，即意大利北部白云岩山脉中三叠纪晚期孤立平台，并探索与海洋石灰岩的接触变质作用、白云石化和去白云石化相关的过程和产品的时空梯度。从碳酸盐档案研究的角度评估了岩石学变化与地球化学代理数据重新平衡之间的关系。石灰岩单元的热液白云石化是由附近 Predazzo 侵入体辐射的堤坝和相关热液引发的。详细的岩相学、流体包裹体分析、δ ¹³ C 和 δ ¹⁸ O 数据以及⁸⁷ Sr/ ⁸⁶Sr 同位素比率揭示了极端的结构和地球化学复杂性。变质和成岩模式包括： (i) 峰变质阶段和逆行变质阶段，包括接触光环处的三个白云岩大理岩、两个白云岩大理岩、水镁石、硅酸镁和晚期流星/渗流胶结物；(ii) 在 Latemar 孤立平台的四个空间定义的白云石化、自生石英、低镁方解石和晚期流星胶结物事件；^{(iii) δ 13}中的千米级梯度从接触光环到平台内部的 C 值。这里显示的结果有两个相关性：首先，蚀变产物的空间分析，范围从接触光环中 700°C 温度下大理石的高级变质叠印到温度 <100°C 时平台内部中度蚀变的石灰岩，允许观察通常沿垂直（前进）梯度从浅埋藏到深度> 20 km的变质作用的过程。其次，在岩石缓冲条件下，无论变质到成岩流体-岩石相互作用如何，大理岩和低温热液白云岩都具有保守的海相 δ ¹³ C 和 δ ¹⁸O 值。前体石灰岩和早期成岩白云岩的变质作用和热液白云石化本身并没有重置环境代理数据这一事实对于那些关注地球深处碳酸盐档案研究的人来说是有意义的。