中国中东部早白垩纪埃达克质岩Mo同位素组成研究

钼同位素在氧化还原相关的水热液和地表过程中可以发生分馏。不同储层钼同位素特征的不同，使钼同位素成为地壳物质循环以及亲S元素富集成矿的潜在示踪剂。本文报告了61个早白垩世高钾钙碱性岩（定义为埃达克质岩）的钼同位素组成，其来源与中国中东部有着明显的亲缘关系，其中包括大别造山带低镁埃达克质岩，沿南郯庐断裂带分布的高镁埃达克质岩和长江下游高镁含矿埃达克质岩。低镁埃达克质岩具有最轻δ98 MONIST3134，0.48‰～-0.03‰，不含矿和含矿高镁埃达克质岩同位素组成较重，变化较大，分别为-0.38‰～0.41‰、0.58‰～1.39‰。岩浆演化（例如角闪石结晶）主导着低镁埃达克质岩中的钼同位素变化，但不能解释高镁埃达克质岩中的钼同位素变化。Ce/Mo与Mo、δ98Mo和εNd（t）的混合趋势表明，不含矿和含矿的埃达克质岩具有一个共同的富集地幔端元（低Ce/Mo比，低εNd（t）和δ98Mo）。同时，不含矿和含矿的埃达克质岩还具有两个不同的端元组成，都具有高Ce/Mo比，但是这两个端元δ98Mo明显不同。对于不含矿埃达克质岩的高Ce/Mo端元，具有低δ98Mo，以及中-高富集的εNd（t）和低放射成因Pb，代表了与低镁埃达克质岩来源相似的大陆下地壳。相比之下，含矿的高镁埃达克质岩的高Ce/Mo端元具有极高的δ98Mo（>1.5‰），表明俯冲还原性沉积物的加入。另一方面，我们认为，它们共同的富集地幔端元是地幔交代的结果，交代流体源于俯冲氧化沉积物。本研究表明，钼同位素有助于了解地幔中的埃达克岩起源和相关的铜-金-钼成矿作用，强调了氧化沉积物的加入是地幔中亲硫金属初步富集的因素。Molybdenum (Mo) isotopes undergo fractionation during redox-related hydrothermal and surficial processes. The distinct Mo isotopic signatures of different geochemical reservoirs make Mo isotopes a potential tracer for crustal material recycling and chalcophile element enrichment and mineralization. Here we report molybdenum isotopic compositions of 61 Early Cretaceous high-K calc-alkaline rocks (defined as adakites), whose sources show clear affinities to those in central-eastern China, including low-Mg adakites from the Dabie Orogenic Belt, high-Mg adakites distributed along the southern Tan-Lu Fault Zone, and ore-bearing high-Mg adakites in the lower Yangtze River region. Low-Mg adakites exhibit the lightest δ98Mo values, ranging from 0.48‰ to -0.03‰, while non-ore-bearing and ore-bearing high-Mg adakites have heavier and more variable isotopic compositions, with ranges of -0.38‰ to 0.41‰ and 0.58‰ to 1.39‰, respectively. Magmatic evolution (e.g., amphibole crystallization) dominates Mo isotopic variations in low-Mg adakites, but fails to explain the Mo isotopic changes in high-Mg adakites. Mixing trends between Ce/Mo ratio, Mo concentrations, δ98Mo and εNd(t) indicate that both non-ore-bearing and ore-bearing adakites share a common enriched mantle endmember with low Ce/Mo ratios, low εNd(t) values and low δ98Mo. Meanwhile, non-ore-bearing and ore-bearing adakites also have two distinct endmembers with high Ce/Mo ratios, but their δ98Mo values differ significantly. For the high Ce/Mo endmember of non-ore-bearing adakites, which has low δ98Mo, moderate-to-high enriched εNd(t) values and low radiogenic Pb isotopes, it represents a continental lower crustal source similar to that of low-Mg adakites. In contrast, the high Ce/Mo endmember of ore-bearing high-Mg adakites has extremely high δ98Mo (>1.5‰), indicating the input of subducted reducing sediments. On the other hand, we propose that their common enriched mantle endmember results from mantle metasomatism, where the metasomatic fluid is derived from subducted oxidizing sediments. This study demonstrates that molybdenum isotopes can aid in constraining the origin of adakites in the mantle and associated Cu-Au-Mo mineralization, emphasizing that the input of oxidizing sediments is a critical factor for the initial enrichment of chalcophile metals in the mantle.

搜集汇总

背景与挑战

背景概述

该数据集聚焦于中国中东部早白垩纪埃达克质岩的钼同位素组成研究，包含61个岩石样本数据，分为低镁埃达克质岩、不含矿高镁埃达克质岩和含矿高镁埃达克质岩三类，揭示了钼同位素在示踪地壳物质循环和铜-金-钼成矿作用中的关键作用。研究通过分析同位素变化，探讨了岩浆演化和不同地幔端元对岩石成因的影响，为理解埃达克岩起源及相关矿产资源形成提供了地球化学依据。