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首页> 外文期刊>Journal of Volcanology and Geothermal Research >Eruptive chronology and tectonic context of the late Pleistocene Tres Virgenes volcanic complex, Baja California Sur (Mexico)
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Eruptive chronology and tectonic context of the late Pleistocene Tres Virgenes volcanic complex, Baja California Sur (Mexico)

机译：晚下更新世Tres Virgenes火山群，下加利福尼亚州苏尔（墨西哥）的喷发年代和构造背景

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摘要

Based on a detailed geological map and stratigraphy aided by new Th-230/U-238 and P-206/U-238 age determinations we established the eruptive chronology of the Tres Virgenes Volcanic Complex (TVVC). The complex consists of three northeast-southwest aligned stratovolcanoes, which from older to younger are El Viejo, El Azufre, and La Virgen and associated cinder cones and domes. The alignment was fed from fissures that mark the southern trace of the left-lateral Cimarron Fault. The TVVC was built upon the basement rocks of the Peninsular Ranges Batholith (similar to 99 Ma), the Santa Lucia Formation (21.6 Ma), the Esperanza basalt (7.6 Ma), and the 1.1 Ma ignimbrite of El Aguajito caldera. The TVVC began its formation at ca. 300 ka mainly with dacitic lava flows and domes that formed El Viejo volcano (4.2 km(3)). At around 173 ka, activity migrated to the southwest to build El Azufre volcano (3.8 km(3)) with the emission of dacitic lavas and several phases of dome construction and destruction with the generation of pyroclastic density currents. El Azufre's activity ended similar to 128 ka with the extrusion of the summit dome. At about 112 ka, volcanism migrated 42 km to the southwest to begin the construction of La Virgen Volcano through the emission of andesitic and dacitic lavas that built the largest cone of the complex until similar to 22 ka (31.2 km(3)). This volcano was built upon several stages of cone construction with the emission of lava flows and peripheral dacitic domes and cinder cones. Between 128 and 112 ka six cinder cones vented along the Cimarron Fault between the La Virgen and El Azufre volcanoes. By assuming a constant emission of magma the total volume of the TVVC (39 km(3)) was erupted at an average rate of 0.13 km(3)/kyr. Of this volume, effusive eruptions dominated the evolution of the complex (89%) of which 62% are dacites and 38% andesites. The TVVC rocks have compositions of 50-67 wt% in silica, and low-medium K (0.5-2.5 wt% K2O). Trace element signatures of the TVVC rocks (Sr/Y 40, La/Yb 10, Nb-Ti negative anomalies and relative enrichments of LILE and LREE) suggest a post-subduction mixture between adakitic and calc-alkaline magmas. Xenoliths of granodiorites hosted in lavas and La Virgen tephra suggest that magma chambers feeding the complex have stagnated at depths 2 km within the Peninsular Ranges Batholith as confirmed by geobarometry, aeromagnetic data, and the drill-holes of the geothermal field. Today, the Tres Virgenes geothermal field generates 10 MW of electricity although future exploration of several nearby areas may increase such capacity. (C) 2018 Elsevier B.V. All rights reserved.
机译：根据详细的地质图和地层学，并根据新的Th-230 / U-238和P-206 / U-238年龄确定，我们建立了特雷斯维吉涅斯火山群（TVVC）的喷发年代。该建筑群由三个东西向排列的平流层火山组成，从大到小分别是El Viejo，El Azufre和La Virgen以及相关的煤渣锥和穹顶。对准是从裂缝开始的，裂缝标志着左侧西马龙断层的南部。 TVVC建立在半岛山脉基岩（类似于99 Ma），圣卢西亚组（21.6 Ma），Esperanza玄武岩（7.6 Ma）和El Aguajito火山口的1.1 Ma火成岩的基底岩石上。 TVVC的成立始于大约300 ka主要是由高铁熔岩流和穹顶组成的El Viejo火山（4.2 km（3））。在大约173 ka时，活动迁移到西南部，形成El Azufre火山（3.8 km（3）），并散发着高铁熔岩，形成了几个圆顶阶段，并形成了火山碎屑密度流，破坏了圆顶。 El Azufre的活动由于顶峰穹顶的挤压而结束，类似于128 ka。在大约112 ka时，火山活动向西南方向迁移了42 km，开始通过散发安第斯山脉和大溪流熔岩而建造La Virgen火山，直到形成22 ka（31.2 km（3））为止，该熔岩才构成了该复合体的最大圆锥体。这座火山建立在圆锥构造的几个阶段，散发着熔岩流，外围的大圆顶和煤渣圆锥。在128到112 ka之间，沿着维马根火山和El Azufre火山之间的Cimarron断层排放了六个煤渣锥。通过假设恒定的岩浆排放，TVVC的总体积（39 km（3））以0.13 km（3）/ kyr的平均速率喷发。在这个体积中，喷发性喷发占了该复合体的演化的主要部分（89％），其中62％是水母和38％的安山岩。 TVVC岩石的二氧化硅成分为50-67 wt％，低钾含量为K（0.5-2.5 wt％）。 TVVC岩石的痕量元素特征（Sr / Y <40，La / Yb <10，Nb-Ti负异常以及LILE和LREE的相对富集）表明了浆状岩浆和钙碱性岩浆之间的俯冲后混合物。熔岩和La Virgen tephra中所含的花岗闪长岩的异型岩表明，由地层气压法，航空磁数据和地热场的钻孔所证实，在该岩床内的岩浆腔停滞在岩溶岩半岛范围> 2 km的深度内。今天，Tres Virgenes地热田可发电10兆瓦，尽管未来在附近几个地区的勘探可能会增加这种能力。 （C）2018 Elsevier B.V.保留所有权利。

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