Unconventional hydrocarbon resources such as shale oil/gas and coal-bed methane have become an increasingly important source of energy over the past decade. The Vaca Muerta Shale (Neuquén Basin, Argentina) contains the second largest technically recoverable quantity of shale gas in the world. Exploitation of the play has been complicated by elevated concentrations of CO₂ in several fields, the origin of which is currently poorly understood. Elevated CO₂ levels are consistently encountered when deep-rooted faults in the Auquilco Evaporite Formation, present below the Vaca Muerta Shale, overlap with shallower faults that propagate from the top of evaporites into the shale, indicating a sub-evaporate origin of the CO₂. Here we report new isotopic analysis of CO₂-rich gases from two producing fields. CO₂ concentrations increase with C₁/(C₂ + C₃) values (4.8–33.5) and fractionation of δ¹³C_CO2 (−0.9 to −7.7‰), suggest that CH₄ have been displaced by CO₂ which entered the shale after hydrocarbon maturation. The noble gas composition (³He/⁴He of 3.43–3.95 R_A, where R_A is the atmospheric ratio of 1.399 × 10⁻⁶, ²¹Ne/²²Ne of 0.0310–0.0455, ²⁰Ne/²²Ne of 9.89–10.52, ⁴⁰Ar/³⁶Ar of 2432–3674 and CO₂/³He 6.8–20.2 × 10⁷) of the gases is consistent with mixing of magmatic CO₂ with crustal hydrocarbon-rich gases and provides evidence for the loss of significant CO₂. Using inverse modelling techniques, we determine that the magmatic gas has a ³He/⁴He of 3.95–4.08 R_A, CO₂/³He of 8.8–16 × 10⁸ and ²⁰Ne/²²Ne of 12.13_−0.10^+0.08, ²¹Ne/²²Ne of 0.074_−0.003^+0.004. Based on the radiogenic He and Ne this is consistent with a depleted asthenosphere mantle source, which has been trapped in the crust since 6.0–22.8 Ma. This is significantly younger than Late Cretaceous maturation of the hydrocarbon source rocks. Mantle melting as a result of asthenosphere upwelling induced by the collision of the South Chile Ridge and the Chile Trench at ~14 Ma is the most likely source of the CO₂. Gases from below the shale contain two air saturated water-derived noble gas components, distinguished on the basis of ²⁰Ne^†/³⁶Ar, ⁸⁴Kr/³⁶Ar, ¹³²Xe/³⁶Ar ratios. These are consistent with early and late stage open system Rayleigh fractionation of groundwater-derived noble gases. We find evidence that these mix with the magmatic component prior to entering the Vaca Muerta and mixing with an adsorption derived gas retained in the source kerogen.

在过去十年中，非常规碳氢化合物资源（如页岩油/天然气和煤层气）已成为越来越重要的能源。Vaca Muerta页岩（阿根廷Neuquén盆地）包含世界上第二大技术上可回收的页岩气。由于在几个领域中CO ₂浓度的升高，对该剧的开采变得复杂，目前对该领域的起源知之甚少。当存在于瓦卡穆尔塔页岩下方的Auquilco蒸发岩层中的深层断层与从蒸发岩顶部传播到页岩中的浅层断层重叠时，始终遇到CO ₂升高的水平，这表明CO ₂的亚蒸发源。在这里，我们报告了新的一氧化碳同位素分析来自两个生产领域的富含_2的气体。CO ₂浓度为C增加₁ /（C ₂  + C ₃）的值（4.8-33.5）和δ的分馏¹³ Ç _CO2（-0.9至-7.7‰），表明CH ₄已经由CO移位₂，其输入的碳氢化合物成熟后的页岩。该稀有气体组成（³他/ ⁴赫3.43-3.95的R_甲，其中R_阿是1.399×10大气压比^-6，²¹ NE / ²²的0.0310-0.0455 NE，²⁰ NE / ²²的9.89-10.52 NE，⁴⁰的Ar / ³⁶的2432-3674 Ar和CO ₂ / ³他6.8-20.2×10 ⁷）的气体的是符合岩浆CO的混合₂地壳富烃气体，并提供证据为大量CO _2的损失。使用逆建模技术，我们确定该火山气体具有³ /赫⁴ He的3.95-4.08ř_甲，CO ₂ / ³的8.8-16×10赫⁸和²⁰ NE / ²²的12.13氖_-0.10 ^0.08，²¹ Ne /²²氖0.074 _-0.003 ^+0.004。根据放射性的氦和氖，这与流失的软流圈地幔源一致，该源自6.0-22.8 Ma以来一直被困在地壳中。这比烃源岩的晚白垩纪成熟要年轻得多。由于南智利山脊和智利海沟在约14 Ma发生碰撞而导致的软流层上升，地幔融化是最有可能的CO ₂来源。页岩下方的气体包含两种源自空气的饱和水稀有气体成分，以²⁰ Ne ^† / ³⁶ Ar，⁸⁴ Kr / ³⁶ Ar，¹³² Xe / ³⁶为基础进行区分Ar比率。这些与地下水衍生的稀有气体的早期和晚期开放系统瑞利分馏是一致的。我们发现证据表明，这些物质在进入瓦卡穆尔塔火山之前与岩浆成分混合，并与保留在源干酪根中的吸附衍生气体混合。