Abstract In this study, Sr isotopes combined with Nd isotopes of modern cold seep carbonates were studied to provide reliable proxies for sources and pathways of seep fluids. We presented Sr and Nd isotopes together with stable carbon and oxygen isotope data of cold seep carbonates recovered from the northern continental slope of the South China Sea (SCS). Based on the evidence for negligible detrital contamination and diagenetic alteration, carbonate samples are considered dependable archives which record Sr and Nd isotope signals of the original pore waters from which carbonates have precipitated. Excellent correlation between 87Sr/86Sr ratios and 1/Sr observed in carbonate samples indicates two end-members with distinct Sr isotopic signatures, including modern seawater as a major source and a lesser contribution from methane-rich seep fluid driven from a deep source. Besides these two end-members, release of Nd from organic matter and Fe–Mn oxyhydroxide is an additional contribution to pore water Nd. Furthermore, Sr and Nd isotopic compositions suggest water-rock interactions between upward seep fluid and detrital component in sediments, which resulted in the isotopic shift towards pronounced 143Nd depleted and slightly 87Sr enriched in the fluid phase. This study provides insight into the knowledge for tracing seepage fluid circulation by Sr–Nd isotope system at modern seep systems.

中文翻译：

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南海北部冷渗碳酸盐的 Sr 和 Nd 同位素作为流体来源的替代物

摘要 在这项研究中，研究了现代冷渗碳酸盐的 Sr 同位素与 Nd 同位素结合，为渗流流体的来源和途径提供可靠的替代物。我们提供了从南海北部大陆坡 (SCS) 回收的冷渗碳酸盐的 Sr 和 Nd 同位素以及稳定的碳和氧同位素数据。基于可忽略的碎屑污染和成岩蚀变的证据，碳酸盐样品被认为是可靠的档案，记录了碳酸盐沉淀的原始孔隙水的 Sr 和 Nd 同位素信号。在碳酸盐样品中观察到的 87Sr/86Sr 比率和 1/Sr 之间的极好相关性表明两个末端成员具有不同的 Sr 同位素特征，包括现代海水作为主要来源，而来自深源驱动的富含甲烷的渗流流体的贡献较小。除了这两个端元之外，从有机质和 Fe-Mn 羟基氧化物中释放 Nd 是对孔隙水 Nd 的额外贡献。此外，Sr 和 Nd 同位素组成表明向上渗流流体和沉积物中的碎屑成分之间的水-岩相互作用，导致同位素向显着的 143Nd 耗尽和流体相中略微富集的 87Sr 移动。这项研究提供了深入了解现代渗流系统中 Sr-Nd 同位素系统跟踪渗流流体循环的知识。Sr 和 Nd 同位素组成表明向上渗流流体和沉积物中碎屑成分之间的水-岩相互作用，导致同位素向显着的 143Nd 耗尽和流体相中的 87Sr 略微富集。这项研究提供了深入了解现代渗流系统中 Sr-Nd 同位素系统跟踪渗流流体循环的知识。Sr 和 Nd 同位素组成表明向上渗流流体和沉积物中碎屑成分之间的水-岩相互作用，导致同位素向显着的 143Nd 耗尽和流体相中的 87Sr 略微富集。这项研究提供了深入了解现代渗流系统中 Sr-Nd 同位素系统跟踪渗流流体循环的知识。