Abstract In central Mexico, remnants of the early volcanic activity in the Trans-Mexican Volcanic Belt (TMVB) are exposed at Sierra de Guadalupe in the northern part of the Mexico City Basin and to the south in the Tepoztlan, Malinalco, Tenancingo, and Chiltepec areas. A few published studies indicate a general early to middle Miocene age for some of these volcanic centers. We present new geologic, geochronologic and geochemical data that refine the timing of this early volcanic activity and its geochemical character, shedding light on the geodynamic evolution during this period. The Sierra de Guadalupe is a volcanic complex with effusive and explosive activity that generated andesitic lavas with plagioclase, ortho- and clinopyroxene plus amphibole phenocrysts, as well as dacitic lava flows and domes with plagioclase, orthopyroxene, amphibole and/or biotite phenocrysts. Pyroclastic and epiclastic (lahars) deposits are also observed in the northern slopes of this volcanic complex. The chemical composition of the Sierra de Guadalupe rocks is calc-alkaline andesitic to dacitic. New 40Ar/39Ar and U-Pb zircon ages demonstrate that volcanic activity at Sierra de Guadalupe lasted ca. 5.0 Ma from ca. 20.1 Ma to 14.8 Ma. Remnants of volcanic centers found in the Tepoztlan, Malinalco, Tenancingo, and Chiltepec areas ~80 km to the south show similar compositions and eruptive styles, with 40Ar/39Ar ages ranging between 21 and 16 Ma. Rocks with similar ages and lithologies were also described in deep wells drilled in the Mexico City Basin. As a whole, the age distribution shows that early to middle Miocene volcanism, making up the initial activity of the TMVB, migrated toward the north from Tepoztlan (310 km from the trench) up to Pachuca (445 km from the trench), and is likely associated with a shallowing the subducting Cocos slab underneath this region. Our results confirm that magmatism in the TMVB began in the early Miocene by dehydration of the Cocos slab as attested by high Ba/La and Th/Yb ratios.

中文翻译：

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墨西哥城盆地早中新世弧火山活动：跨墨西哥火山带的开始

摘要 在墨西哥中部，墨西哥城盆地北部的瓜达卢佩山脉和南部的 Tepoztlan、Malinalco、Tenancingo 和 Chiltepec 出露了跨墨西哥火山带 (TMVB) 早期火山活动的遗迹。领域。一些已发表的研究表明，其中一些火山中心的一般早到中新世时代。我们提供了新的地质、地质年代学和地球化学数据，这些数据完善了这一早期火山活动的时间及其地球化学特征，揭示了这一时期的地球动力学演化。Sierra de Guadalupe 是一个火山复合体，具有喷发性和爆炸性的活动，产生了带有斜长石、正斜辉石和角闪石斑晶的安山岩熔岩，以及带有斜长石、正辉石、闪石和/或黑云母斑晶。在这个火山复合体的北坡也观察到了火山碎屑和外碎屑（火山泥）沉积物。Sierra de Guadalupe 岩石的化学成分为钙碱性安山质至英安质。新的 40Ar/39Ar 和 U-Pb 锆石年龄表明，瓜达卢佩山脉的火山活动持续了大约 10 年。约 5.0 Ma 20.1 毫安至 14.8 毫安。在南部约 80 公里的 Tepoztlan、Malinalco、Tenancingo 和 Chiltepec 地区发现的火山中心遗迹显示出相似的成分和喷发风格，40Ar/39Ar 年龄介于 21 到 16 Ma 之间。在墨西哥城盆地钻探的深井中也描述了具有相似年龄和岩性的岩石。总的来说，年龄分布表明，早到中新世火山活动，构成了 TMVB 的初始活动，从 Tepoztlan（距海沟 310 公里）向北迁移至 Pachuca（距海沟 445 公里），并且可能与该地区下方俯冲的 Cocos 板块变浅有关。我们的结果证实 TMVB 中的岩浆活动始于中新世早期，由高 Ba/La 和 Th/Yb 比率证明的 Cocos 板片脱水。