The only Late Cretaceous-Paleocene intraplate magmatic unit of southern Patagonia, known as the Las Mercedes basalt, is petrogenetically studied in its geodynamic context. The outcrops of this unit are thin ridges located in a narrow 50 km wide latitudinal strip (∼48 °S) of the central region of the Deseado Massif, generated by pahoeoe-type lava flows that probably covered large ancient streams and rivers. Compositionally the rocks are metaluminous basanites and alkaline and subalkaline basalts uninfluenced by slab-derived components with Mg# ranging from 53.9–65. The origin of this intraplate igneous manifestation would have been related to the opening of a Late Cretaceous-Paleocene trench-perpendicular slab tear of the Aluk subducting plate. This event induced the decompression melting of the sub-slab silica-deficient garnet pyroxenite asthenosphere causing the extrusion of a discrete volume of basalts. The slab anisotropy was generated by the slab-dip change in a transition region from a flattened sector (north of ∼48 °S) related to a large flat-slab (Nalé flat-slab) to one with steeper subduction angle (south of ∼48 °S). Also, this slab tearing would be responsible for the anomalous occurrence of intraplate magmatism located in the same latitudinal strip of the Las Mercedes basalt but in the Andean magmatic arc region, which together represent the only Late Cretaceous igneous activity unrelated to the magmatic arc in central-southern Patagonia and southern Andean region.

巴塔哥尼亚南部唯一的晚白垩世-古新世板内岩浆单元，被称为拉斯梅赛德斯玄武岩，在其地球动力学背景下进行了岩石成因研究。该单元的露头是位于 Deseado 地块中部地区 50 公里宽的狭窄纬度带 (~48 °S) 中的细山脊，由可能覆盖大型古老溪流和河流的 pahoeoe 型熔岩流产生。从成分上讲，岩石是金属铝质玄武岩和碱性和亚碱性玄武岩，不受板坯衍生成分的影响，Mg# 范围为 53.9-65。这种板内火成岩表现的起源可能与 Aluk 俯冲板块的晚白垩世-古新世海沟垂直板块撕裂的开口有关。这一事件引起了下板坯缺乏二氧化硅的石榴石辉石岩软流圈的减压熔化，从而导致了离散体积的玄武岩的挤压。板坯各向异性是由与大平板相关的扁平扇形（约 48°S 以北）的过渡区域中的板坯倾角变化产生的（Nalé 平板）到具有更陡俯冲角（约 48°S 以南）的平板。此外，这种板片撕裂将导致位于 Las Mercedes 玄武岩同一纬度带但位于安第斯岩浆弧区域的板内岩浆活动异常发生，它们共同代表了唯一与中部岩浆弧无关的晚白垩世火成岩活动。 -巴塔哥尼亚南部和安第斯地区南部。