Mafic volcanic rocks are typically formed by primitive magmas (MgO >8 wt.%) and are evidence of both a rapid magma ascent from the source and a negligible differentiation en route to the surface. Thus, mafic rocks on Earth are relatively close in composition to the primary magma. These rocks are common in intraplate and extensional tectonic environments, but not in subduction settings. At subduction zones, where magma differentiation is virtually inevitable, most magmas, if not all, evolve before reaching the surface. Hence it is difficult to approach primary compositions to understand, for instance, the percentage of partial melting in the mantle. This is the case in the northernmost Andean volcanic chain (~140 km) in Colombia. There, however, mafic rocks have been recently recognised, providing an opportunity to approach the composition of primitive magmas. The rocks are located at the south of the volcanic chain and are associated with the Quaternary Pijaos monogenetic volcanic field. The rocks are porphyritic, phenocryst-poor, and host two main mineral phases: olivine (Fo_71-90) and clinopyroxene (Wo_38-45, En_45-54, Fs_7-12), with plagioclase, pyroxene and Fe–Ti oxides as microlites. The products are basaltic to basaltic andesite, and have the typical sub-alkaline/high-K calc-alkaline chemical signature of subduction settings. Applied geothermobarometers indicate that olivine crystallised between 1325 and 1266 °C, while clinopyroxene between 1273 and 1117 °C. These values somehow constrain the partial melting temperatures not only below the field but also below the region. High-forsterite and high-CaO clinopyroxene evidenced in the rocks, also contribute to the comprehension of the magma evolution through deep fractional crystallisation in the complex magmatic plumbing system that dominates this region of the Andean volcanic chain.

镁铁质火山岩通常由原始岩浆（MgO> 8 wt。％）形成，既证明了从源头快速岩浆上升，也没有证据表明岩浆在到达地表的过程中存在明显的差异。因此，地球上的镁铁质岩石的成分与原生岩浆相对较近。这些岩石在板内和伸展构造环境中很常见，但在俯冲环境中却不常见。在几乎不可能发生岩浆分化的俯冲带，大多数岩浆（如果不是全部的话）在到达地表之前就已经演化了。因此，难以接近主要成分来理解例如地幔中部分熔融的百分比。哥伦比亚最北端的安第斯火山链（约140公里）就是这种情况。但是，在那里最近发现了镁铁质岩石，为探讨原始岩浆的组成提供了机会。这些岩石位于火山链的南部，并与第四纪的皮亚奥斯第四纪单生火山场有关。岩石是斑状的，稀晶岩的，并具有两个主要的矿物相：橄榄石（Fo_71-90）和Clinopyroxene（_{WO 38-45}，En _45-54，Fs _7-12），并有斜长石，辉石和Fe-Ti氧化物作为微晶石。该产品为玄武质至玄武安山岩，并具有典型的俯冲环境亚碱性/高钾钙碱性化学特征。应用的地热气压计表明，橄榄石在1325至1266°C之间结晶，而斜辉石在1273至1117°C之间结晶。这些值以某种方式不仅限制了田间以下，而且还限制了该区域以下的部分熔融温度。岩石中显示的高镁橄榄石和高CaO斜辉石也通过复杂的岩浆管道系统中占主导地位的安第斯火山链区域的复杂岩浆管道系统的深部分步结晶作用，有助于岩浆演化。