碳酸岩岩浆与地壳反应综述

Carbonatite magma and crustal metasomatism:A review

碳酸岩是地表出露较少的地幔来源的岩石,其地幔交代作用已被广泛研究,而碳酸岩岩浆与地壳的反应过程却研究较少,目前已在中国草滩和丰镇地区、德国Kaiserstuhl地区、俄罗斯Petyayan-Vara地区和澳大利亚Nolans Bore矿床等各地被报道。碳酸岩岩浆与地壳反应的特征是可能形成大量富铁云母、辉石、榍石、钡冰长石等硅酸盐矿物并造成C-O和Sr-Nd同位素体系的扰动。实验岩石学研究发现碳酸岩岩浆在地幔与橄榄岩反应形成异剥橄榄岩,对应的在中下地壳反应形成反夕卡岩。碳酸岩岩浆与围岩的反应会造成局部Si的富集促使REE在早期岩浆阶段进入磷灰石,从而抑制稀土成矿。深部地壳的碳酸岩-硅酸岩反应在相同构造背景下通常不像浅部热液系统容易出露地表,并且其反应产物容易被误认为是夕卡岩矿物组合。因此,更多的高温高压实验研究以及对硅酸盐流体来源不是很清楚的高温夕卡岩矿物组合进行重新评估,将是揭示地壳深部反夕卡岩过程,特别是相关成矿作用的关键。

Carbonatite is a mantle-derived rock with minimal surface exposure.Carbonatite mantle metasomatism has received much attention,but the reaction between carbonate magma and the crust is little studied.Such reaction has been reported in China’s Caotan-Fengzhen regions,Germany’s Kaiserstuhl region,Russia’s Petyayan-Vara region,and Australia’s Nolans Bore deposit.The reaction is characterized by the formations of large quantities of iron-rich mica,pyroxene,sphene,hyalophane,and other silicate minerals,and disruptions to the C-O and Sr-Nd isotope systems.In the mantle,carbonatite magma reacts with peridotite to produce meta-exfoliated peridotite;in the middle and lower crust,such reaction produces antiskarn.The reaction between carbonatite magma and wall-rock can result in local Si enrichment,which encourages REE entry into apatite in the early magmatic stage and prevents REE mineralization.Carbonatite-silicate reactions in the deep crust are typically not exposed to the surface as shallow hydrothermal systems do under the same structural context,and reaction products are easily misidentified as skarn mineral assemblages.Therefore,it is critical to uncover the anti-skarn processes in the deep crust—particularly its associated mineralization,through high-temperature,high-pressure experimental research,along with re-evaluation of high-temperature skarn mineral assemblages whose sources of silicate fluids are unknown.