ABSTRACT

Several plutonic bodies are distributed along the northern and eastern margins of the Mesa Central province, intruding mainly clastic and carbonate sedimentary sequences from the Triassic and Cretaceous. In this work, U-Pb ages in zircon and apatite have been obtained using the LA-ICPMS technique in samples from six of these plutons and some possibly related volcanic rocks. In general, intrusive rocks are porphyritic, suggesting a relatively shallow intrusion and are mostly monzogranite to quartz-monzodiorite in composition, displaying biotite and amphibole. According to the geochronological results, the plutonic rocks can be divided into two groups; a group that varies in age from Campanian-Maastrichtian limit up to Paleocene, and a second group that essentially corresponds to the Oligocene, specifically the Rupelian. Unfortunately, the geochronological data on apatites were not conclusive to establish a trajectory or cooling rate and the ages obtained in this mineral phase for several of these bodies are very similar to the age of zircons, which suggests a relatively rapid cooling, very probably associated with shallow depths of emplacement. The statistical analysis of obtained and published ages suggests two periods of significant magmatic activity that occurred essentially during the Late Cretaceous (Campanian) and during the late Eocene (Bartonian and Priabonian). Notably, the plutonic bodies, particularly those of the group of ancient granites (Paleocene-Late Cretaceous) are very far from the ancient subduction zone to which they have been associated, in addition to being spatially close to plutonic rocks of the Eocene and Oligocene. In this sense, the traditional model of magmatic migration originated by the flat subduction of the Farallon plate is not very consistent, so it will be necessary to evaluate or reconsider the geodynamic evolution associated with magmatism for this region, in view to these new data and to those that could be generated later.

摘要

几个深成体分布在中部梅萨省北部和东部边缘，主要侵入三叠纪和白垩纪的碎屑和碳酸盐沉积序列。在这项工作中，锆石和磷灰石的 U-Pb 年龄已经使用 LA-ICPMS 技术在来自其中六个岩体和一些可能相关的火山岩的样品中获得。侵入岩总体呈斑状，表明侵入体较浅，成分多为二长花岗岩至石英-二长闪长岩，呈黑云母和闪石。根据年代学结果，深成岩可分为两类；一个年龄从坎帕尼亚-马斯特里赫特界到古新世不等的组，第二组基本上对应于渐新世，特别是鲁佩尔。很遗憾，磷灰石的年代学数据不能确定轨迹或冷却速率，并且在该矿物阶段中获得的其中几个体的年龄与锆石的年龄非常相似，这表明冷却相对较快，很可能与较浅的深度有关的安置。对获得和发表的年龄的统计分析表明，两个重要的岩浆活动时期主要发生在白垩纪晚期（坎帕纪）和始新世晚期（巴托纪和普里雅本纪）。值得注意的是，除了在空间上接近始新世和渐新世的深成岩外，深成体，特别是古花岗岩群（古新世-晚白垩世）的深成体离它们相关的古代俯冲带非常远。在这个意义上说，