Two models have been proposed to explain the early Andean evolution of the southwestern margin of Gondwana; a model that assumes continuous subduction-related magmatism since the Carboniferous and a second involving subduction cessation during the pre-Andean stage (~280–200 Ma) followed by subsequent reactivation at ca. 200 Ma. Here we provide new constraints regarding the onset of the Andean tectonic cycle and the transition between pre-Andean and early Andean stages (210–100 Ma) by performing a comprehensive study of the geochronology and petrogenesis of plutonic complexes from the Coastal Cordillera of northern Chile. We present the first zircon U-Pb geochronology and trace element dataset of intrusive rocks combined with whole-rock geochemistry for the early Andean stage. The oldest unit identified is a syenogranite dated at 246.7 ± 3.9 Ma with a subduction signature, i.e., slightly peraluminous, enriched in LILE over HFSE, negative Nb-Ta and positive Pb anomalies, and strong REE fractionation, but also shows anorogenic features with an alkali-rich composition and high enrichment in rare earth and HFS elements compared to chondritic values. These characteristics are interpreted as representing a transitional, anorogenic event from the pre-Andean stage. In contrast, the second oldest magmatic event was dated at 211.4 ± 1.2 Ma and has a chemical composition consistent with Andean-related magmatism and its zircon composition is similar to those from Late Triassic-Early Cretaceous units. Consequently, we conclude that the Andean orogeny started at ca. 210 Ma, before earlier estimates. Our study also supports works that indicate episodic high-flux magmatism and the eastward migration of the magmatic arc during the Mesozoic. Furthermore, the whole-rock Th/Yb and zircon U/Yb ratios show a trend from the Late Triassic to Late Jurassic of increasing depletion of the mantle source. However, during the Early Cretaceous more variable and enriched signatures are observed, possibly related to changes in the tectonic regime.

已经提出了两种模型来解释冈瓦纳西南缘的安第斯山脉的早期演化。该模型假定自石炭纪以来一直存在与俯冲有关的岩浆作用，第二次涉及安第斯前期（〜280–200 Ma）内的俯冲停止，随后在大约200 km重新激活。200毫安 在这里，我们通过对智利北部沿海山脉山脉古生代复合体的地质年代学和岩石成因进行了全面研究，从而为安第斯构造周期的开始以及安第斯山脉早期和安第斯早期阶段（210–100 Ma）之间的过渡提供了新的约束条件。 。我们提出了安第斯早期的第一个锆石U-Pb地质年代学和侵入岩结合全岩石地球化学的痕量元素数据集。识别出的最古老的单元是正长花岗岩，日期为246.7±3。9 Ma具有俯冲特征，即略带高铝质，在HFSE之上富含LILE，Nb-Ta负和Pb异常呈负值，且REE分级很强，但还显示出具有厌碱的特征，其成分富含碱，稀土和稀土元素富集度高。 HFS元素与软骨素值的比较。这些特征被解释为代表安第斯前期以来的过渡性食源性事件。相比之下，第二最古老的岩浆事件的年代为211.4±1.2 Ma，其化学成分与安第斯山脉相关的岩浆作用一致，其锆石成分与晚三叠纪-早白垩纪单元的锆石成分相似。因此，我们得出结论，安第斯造山运动始于约。210 Ma，之前未作估算。我们的研究还支持表明中生代偶发性高通量岩浆作用和岩浆弧向东迁移的工作。此外，从晚三叠世到晚侏罗世，整个岩石的Th / Yb和锆石U / Yb比率显示出地幔源耗竭增加的趋势。然而，在白垩纪早期，观察到更多的变化和丰富的特征，可能与构造机制的变化有关。