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首页> 外文期刊>Contributions to Mineralogy and Petrology >Stable (C, O) and radiogenic (Sr, Nd) isotopes of carbonates as indicators of magmatic and post-magmatic processes of phoscorite-series rocks and carbonatites from Catalao I, central Brazil
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Stable (C, O) and radiogenic (Sr, Nd) isotopes of carbonates as indicators of magmatic and post-magmatic processes of phoscorite-series rocks and carbonatites from Catalao I, central Brazil

机译：碳酸盐的稳定（C，O）和放射成因（Sr，Nd）同位素，是巴西中部加泰罗一世的磷矿岩系岩石和碳酸盐岩岩浆和岩浆后过程的指示剂

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The Late-Cretaceous Catalao I contains stockworks of thin dykes of phoscorite-series rocks, which can be subdivided into P1 (olivine-bearing, phoscorites) and P2/P3 (olivine-lacking, nelsonites). Dolomite carbonatites (DC) are intimately associated with nelsonites, as pockets and dykes. The P2 apatite nelsonite, the P3 magnetite nelsonite, and, to a lesser extent DC, host the Catala?o I niobium mineralization. C–O isotopes signatures in carbonates reveal several distinct magmatic and post-magmatic processes. Limpid carbonates with stable isotopic mantle-like composition show Rayleigh fractionation and are interpreted as primary, while those with brittle-turbid aspect, and higher oxygen isotope composition, probably underwent recrystallization by interaction with H_2O-rich fluids. A group of samples shows higher oxygen compositions and lower carbon values, which could be explained by degassing of carbonatite magma during cooling. A degassing pattern, parallel to magmatic degassing but at higher oxygen and lower carbon compositions, observed in carbonate veins, may indicate degassing of fracture filling fluids. Furthermore, C–O isotopes of carbonate from monazite-bearing carbonatite have a positive correlation, indicating a distinct, late-stage carbo-hydrothermal event. Though the Catala?o I nelsonites and phoscorites are of igneous origin, they underwent several post-magmatic events, which sometimes overprinted partially or entirely the magmatic isotope signature.
机译：白垩纪晚期的卡塔劳一世包含薄薄的脉石系列岩石堤坝，可以将其细分为P1（含橄榄石的磷沸石）和P2 / P3（缺少橄榄石的新钠铁矿）。白云石碳酸盐岩（DC）与钠铝榴石密切相关，例如囊袋和堤坝。 P2磷灰石钠铁矿，P3磁铁矿钠铁矿，以及在较小范围内的DC中，容纳了Catala？o I铌矿化。碳酸盐中的C–O同位素特征揭示了几个不同的岩浆和后岩浆过程。具有稳定同位素地幔状成分的碳酸盐碳酸盐显示瑞利分馏并被解释为主要碳酸盐，而那些具有脆浊态和较高氧同位素组成的碳酸盐碳酸盐可能通过与富含H_2O的流体相互作用而重结晶。一组样品显示出较高的氧组成和较低的碳值，这可以通过在冷却过程中使碳酸盐岩岩浆脱气来解释。在碳酸盐岩脉中观察到的与岩浆脱气平行但在较高的氧气和较低的碳组成下的脱气模式可能表明压裂填充液已经脱气。此外，含独居石的碳酸盐岩中碳酸盐的碳氧同位素呈正相关，表明有明显的后期碳水热事件。尽管加泰罗尼亚I钠铁矿和辉绿岩都是火成岩成因，但它们经历了几次岩浆后事件，有时会部分或全部覆盖岩浆同位素特征。

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