We investigated olivine minette dykes from the Rio Colan Valley of the Julian Alps (NE Italy) to provide new constraints on the mantle geochemistry underneath this extreme sector of the Italian Southern Alps. Petrographic observations, high Mg#s, high Cr and Ni contents, low Dy/YbCN ratios and flat heavy rare earth element (REE) profiles imply these are primary magmas derived from a depleted peridotite with olivine and garnet as possible residual phases. However, high K2O and incompatible trace element contents, coupled with superchondritic Nb/Ta ratios, suggest that the source was modified into a rutile–phlogopite-bearing carbonated peridotite by multiple metasomatic events such as recycling of crustal material and carbonatitic metasomatism related to an old orogenic event and rutile-rich metasomatism linked to the Pangaea break-up. Laser ablation – multi-collector – inductively coupled plasma – mass spectrometer (LA-MC-ICP-MS) U–Pb geochronology of apatites from two dykes yielded differences between unforced and forced discordia ages up to ∼45 Ma, likely due to the initial 207Pb/206Pb correction adopted. Nonetheless, because forced discordia and 206Pb/238U weighted mean ages are overall similar within the uncertainty, our preferred interpretation is that olivine minettes intruded and crystallized at ∼67 Ma. The age and anorogenic signature of these magmas are consistent with the regional extensional tectonics in the Julian Alps due to the advance of the external Dinaric front following Adria plate eastward subduction. Eventually, we show also that Rio Colan magmas are geochemically hybrid products between lamprophyres and lamproites compared with similar Italian and Western Mediterranean volcanics.

我们调查了朱利安阿尔卑斯山（意大利东北部）里奥科兰山谷的橄榄石尖岩脉，为意大利南阿尔卑斯山这一极端区域下方的地幔地球化学提供了新的限制。岩相观察、高 Mg#s、高 Cr 和 Ni 含量、低 Dy/Yb CN比和平坦的重稀土元素 (REE) 剖面表明这些是源自贫化橄榄岩的原生岩浆，可能含有橄榄石和石榴石作为残余相。然而，高 K 2O 和不相容的微量元素含量，加上超球粒陨石 Nb/Ta 比率，表明该源头通过多种交代事件，例如地壳物质的循环和与古老造山活动相关的碳酸盐交代作用，被改质为含金红石-金云母的碳化橄榄岩。富含金红石的交代作用与盘古大陆的分裂有关。激光烧蚀 - 多接收器 - 电感耦合等离子体 - 质谱仪 (LA-MC-ICP-MS) 对两个岩堤中的磷灰石进行 U-Pb 地质年代学研究，得出非受迫和受迫的不和谐年龄之间的差异高达约 45 Ma，这可能是由于最初的采用207 Pb/ 206 Pb 校正。尽管如此，因为强迫性的不和谐和206 Pb/ 238U加权平均年龄在不确定性范围内总体相似，我们首选的解释是橄榄石尖晶石在~67 Ma侵入并结晶。这些岩浆的年龄和造山特征与朱利安阿尔卑斯山的区域伸展构造一致，这是由于阿德里亚板块向东俯冲后外部迪那拉锋的推进。最终，我们还表明，与类似的意大利和西地中海火山岩相比，里约科兰岩浆是煌斑岩和煌斑岩之间的地球化学混合产物。