Abstract The Amaga basin between the Western and Central Cordilleras of the Northern Andes of Colombia hosts the Neogene volcanic and volcaniclastic Combia Formation. Deposition of the Combia Formation in relation to Nazca plate subduction and arc volcanism is still a matter of debate. Therefore, the timing, petrography and geochemical characteristics of Combia Formation rocks were studied in the western and eastern parts of the Amaga basin, in order to gain more information on the type of magma generation and volcanic activity that led to the deposition of the Combia Formation. Apatite and zircon fission-track dating largely confirm a 12-6 Ma age for the deposition of the Combia Formation. Petrographic and major element analyses show that mainly trachy-andesite ignimbrites with a calc-alkaline composition were deposited in the western Amaga basin, whereas the volcanic rocks of the eastern Amaga basin are lavas flow and fall-out deposits of basaltic andesites of tholeiitic affinity. Trace element and isotopic analyses show that slab dehydration and sediment melting/decarbonation were important in primary magma generation in the mantle wedge, but the primary magma was mixed with lower continental crustal melts (e.g. High-Pb radiogenic), resulting in characteristic isotope signatures in the western and eastern Amaga basin. Then, the hot-zone developed a high Pb-radiogenic, garnet-bearing lower continental crustal (LCC) level as a consequence of the quantity of dehydration of the subducting slab and of changes in the tectonic regime. An extensional pull-apart event (12- 9 Ma), likely facilitated rapid magma ascend to the uppermost crust along a subvertical magma plumbing system throughout the Romeral Fault zone in the eastern Amaga basin, and calc-alkaline magmas with adakite-like signature, which may indicate contractile tectonics that allow the formation of middle-to upper-crustal magma chambers with a garnet fractionation at depth and the evolution of silicate melts into the hot zone mainly related to the amount of water (>4 wt %) present.

中文翻译：

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哥伦比亚阿马加盆地 Combia 组的热年代学、岩石学和地球化学特征

摘要 哥伦比亚北部安第斯山脉西部和中部山脉之间的 Amaga 盆地拥有新近纪火山和火山碎屑 Combia 地层。Combia 地层的沉积与纳斯卡板块俯冲和弧形火山作用有关，仍然是一个有争议的问题。因此，在阿马加盆地西部和东部对 Combia 组岩石的时间、岩石学和地球化学特征进行了研究，以获取更多有关导致 Combia 组沉积的岩浆生成类型和火山活动的信息。 . 磷灰石和锆石裂变径迹测年在很大程度上证实了 Combia 组沉积的 12-6 Ma 年龄。岩相学和主要元素分析表明，主要具有钙碱性成分的粗安山岩熔凝岩沉积在阿马加盆地西部，而阿马加盆地东部的火山岩是熔岩流和拉斑玄武岩安山岩的沉降沉积物。微量元素和同位素分析表明，板片脱水和沉积物熔化/脱碳在地幔楔中的原生岩浆生成中很重要，但原生岩浆与较低的大陆地壳熔体（例如高铅放射成因）混合，导致在地幔楔中产生特征同位素特征。阿马加盆地西部和东部。然后，由于俯冲板片的脱水量和构造制度的变化，热区形成了高铅放射性、含石榴石的下大陆地壳（LCC）水平。一次拉伸拉开事件（12-9 Ma），