Geochronology of Proterozoic basement inliers in the Colombian Andes: tectonic history of remnants of a fragmented Grenville belt

Basement inliers of high-grade metamorphic rocks within the eastern Colombian Andes record a Grenvillian history. Among them, the Garzón Complex and the Dibulla, Bucaramanga and Jojoncito gneisses were studied using different geochronological methods to produce better correlations in the context of the reconstruction of the Grenville belt and of the supercontinent of Rodinia. The dynamic evolution of all of these units includes a final collisional event with exhumation of high-grade rocks. Such a tectonic history bears strong similarities with the Grenville Province in Canada and seems to confirm that these domains took part in the aggregation of Rodinia. Mesoproterozoic U-Pb zircon ages indicate heritage from magmatic protoliths, and the Sm-Nd model ages, as well as the ε_Nd values, suggest derivation from an evolved continental domain, such as the Amazonian craton, with some mixing with juvenile Neoproterozoic material. When these continental fragments are correlated with similar terrains in Mexico and the Central Andes, a large crustal fragment is implied; very probably it made up the southern portion of the Grenville belt within Rodinia, which was disrupted when Laurentia separated from Gondwana forming the Iapetus Ocean, leaving behind cratonic fragments that were later accreted to the South American Platform.

哥伦比亚安第斯山脉东部的高级变质岩基底残露头（Basement inliers）留存有格林威尔造山史（Grenvillian history）的完整记录。其中，研究人员采用多种地质年代学方法对加尔松杂岩（Garzón Complex）、迪武拉片麻岩（Dibulla gneiss）、布卡拉曼加片麻岩（Bucaramanga gneiss）和约洪西托片麻岩（Jojoncito gneiss）开展系统研究，以期在重建格林威尔造山带（Grenville belt）与罗迪尼亚超大陆（Rodinia）的框架下实现更可靠的地层对比。上述所有地质单元的动力学演化过程均包含一期最终碰撞造山事件，伴随高级变质岩的折返抬升（exhumation）。该构造演化轨迹与加拿大格林威尔省（Grenville Province）的特征高度相似，这一证据证实了上述地质单元曾参与罗迪尼亚超大陆的聚合拼合过程。中元古代锆石U-Pb年龄（Mesoproterozoic U-Pb zircon ages）指示其源区为岩浆成因原岩（magmatic protoliths）；Sm-Nd模式年龄（Sm-Nd model ages）与ε_Nd值则表明，其物质来源于演化成熟的大陆地块，例如亚马逊克拉通（Amazonian craton），并混入了部分新元古代新生地壳物质（juvenile Neoproterozoic material）。若将这些大陆碎块与墨西哥及安第斯中部的同类地块进行对比，则可推断存在一块大型地壳碎块：该碎块极有可能曾是罗迪尼亚超大陆内部格林威尔造山带的南部区段，后随劳伦大陆（Laurentia）与冈瓦纳大陆（Gondwana）分离形成伊阿珀托斯洋（Iapetus Ocean）时发生裂解，其残留的克拉通碎块最终被增生至南美地台（South American Platform）之上。