Detrital-zircon geochronology and provenance of the El Oro Metamorphic Complex, Ecuador: Geodynamic implications for the evolution of the western Gondwana margin
Detrital-zircon geochronology and provenance of the El Oro Metamorphic Complex, Ecuador: Geodynamic implications for the evolution of the western Gondwana margin
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厄瓜多尔埃尔奥罗变质杂岩的碎屑-锆石年代学和物源：对西冈瓦纳边缘演化的地球动力学影响
DOI：
10.1016/j.jsames.2018.12.010
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发表时间：
2019
影响因子：
1.8
通讯作者：
Mertz-Kraus
中科院分区：
文献类型：
--
作者：
Rojas-Agramonte;Villagómez-Díaz;Toulkeridis;Mertz-Kraus
厄瓜多尔西南部的El Oro变质杂岩（EOMC）几十年来一直是争论的主题。虽然以前的研究集中在变质和变形历史的复杂的，以确定其地球动力学演化，前变质历史和它的协会在中北部的安第斯山脉的单位仍然知之甚少。在这里，我们提出了一个U-Pb碎屑锆石源区的研究提供深入了解的沉积历史和地球动力学背景的EOMC。我们的研究结果表明，EOMC的南部（Tahuín分区）是由南部（El Tigre单元; c. 525-510 Ma），以及塔温区中部和北方较年轻的古生代（后法马丁期）沉积物（La维多利亚和La Bocana单元; c. 370-360 Ma）。沉积序列的物源与秘鲁东科迪勒拉和厄瓜多尔南科迪勒拉真实的的本土后法马蒂尼期单元（440-340 Ma）相关。重要的是，我们的数据提供了证据的遗传联系之间的最北端（比龙复杂）和南部（La维多利亚和La Bocana单位）序列的EOMC。在比隆复合体（帕伦克梅兰热分区; c.）中发现了后法马丁沉积物。400-390 Ma），并来自相同的沉积物源南部EOMC的沉积物。因此，在EOMC的后法马丁沉积物的沉积范围被限制为c。400-360毫安。此外，我们确定了一个中上三叠世沉积序列在比隆复合体（利蒙普拉亚单位; c。240-215 Ma），可能与c.秘鲁Mitu群240-217 Ma同裂谷大陆碎屑岩。结合，这些新的碎屑锆石数据表明，现有的岩石地层方案是错误的，三个时间上不同的序列存在于复杂的，最古老的单位在南部和最年轻的在北部。南部EOMC（Tahuín分区）与安第斯山脉中北部的冈瓦纳边缘的分离可能是由于c. 140 Ma，南部EOMC以顺时针方向旋转到现在的东西方向。这种旋转也可能是对第一次原加勒比海海礁（英语：Proto-Caribbean Islands）增生的反应，例如c时的Alao-Quebradagrande Islands。120 Ma，最大旋转年龄受最早期沉积物的制约（早（？）到中阿尔布安，c. 113-105 Ma）到达Celica-Lancones盆地，不整合地覆盖在EOMC南部的Tahuín群上。
The El Oro Metamorphic Complex (EOMC) in SW Ecuador has been the subject of debate for several decades. While previous studies have focused on the metamorphic and deformation history of the complex to determine its geodynamic evolution, the pre-metamorphic history and its association to units in the north-central Andes remains poorly understood. Here we present a U-Pb detrital zircon provenance study to provide insights into the depositional history and the geodynamic setting of the EOMC. Our results imply that the southern portion of the EOMC (the Tahuín division) is composed of an older Palaeozoic (pre-Famatinian) sequence in the south (El Tigre unit; c. 525-510 Ma), and younger Palaeozoic (post-Famatinian) sediments in the central and northern parts of the Tahuín division (La Victoria and La Bocana units; c. 370-360 Ma). The provenance of the sedimentary sequences correlates with autochthonous post-Famatinian units (440–340 Ma) in the Eastern Cordillera of Peru and the southern Cordillera Real of Ecuador. Importantly, our data provide evidence for a genetic link between the northernmost (the Birón Complex) and the southern (La Victoria and La Bocana units) sequences of the EOMC. Post-Famatinian sediments were identified in the Birón Complex (Palenque Mélange division; c. 400-390 Ma) and are derived from the same sedimentary sources as the sediments of the southern EOMC. The depositional range of post-Famatinian sediments in the EOMC is therefore constrained to c. 400-360 Ma. Furthermore, we identified a Middle to Upper Triassic sedimentary sequence in the Birón Complex (Limón Playa unit; c. 240-215 Ma) that likely developed contemporaneously with c. 240–217 Ma syn-rift continental epiclastics of the Mitu Group in Peru. Combined, these new detrital zircon data demonstrate that the existing lithostratigraphic scheme is erroneous and that three temporally distinct sequences are present in the complex, with the oldest units in the south and the youngest in the north. Separation of the southern EOMC (the Tahuín division) from the autochthonous Gondwanan margin of the north-central Andes was likely due to a change in the regional subduction direction from SE to ENE at c. 140Ma, with the southern EOMC rotating in a clockwise direction into its present-day E–W orientation. This rotation also could have been a response to the first accretion of proto-Caribbean terranes, such as the Alao–Quebradagrande terrane at c. 120 Ma, with a maximum age for rotation constrained by the earliest sediments (Early (?) to Middle Albian, c. 113-105 Ma) arriving into the Celica-Lancones Basin, which unconformably overlie the Tahuín Group in the southern EOMC.
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