Abstract The Xolapa Complex (XC) is a high-grade metamorphic belt exposed along the southern margin of the North American plate in Mexico. Its evolution includes an episode of widespread anatexis related to crustal thickening and subsequent uplift to upper crustal levels, which culminated in the Paleocene. On the basis of field and petrographic work, this study integrates a petrological modelling approach with LA-ICP-MS U–Pb zircon and monazite geochronology to elucidate the tectonothermal evolution of this metamorphic belt. The study area in central XC includes a suite of alternating migmatitic paragneiss and garnet-bearing mafic schist. Petrological evidence and phase equilibria calculations demonstrate that a staurolite–kyanite grade metamorphism occurred at ~640–670 °C and 8–9 kbar before extensive migmatization took place. Differential anatexis of fertile and refractory layers occurred progressively via biotite and amphibole dehydration-melting reactions, and continued during peak metamorphism at granulite-facies conditions of ~800–820 °C and ~5–7 kbar. According to Ti-in-zircon thermometry, melt generation/mobilization progressed during cooling until crystallize at ~700 °C. The age of prograde metamorphism was likely recorded by monazite cores that give mid- to Late Cretaceous ages. Cooling and melt crystallization could be constrained by leucosome zircon dated at 61.8±0.6 Ma. Both zircon and low-Y monazite from whole rock and melanosome portions, respectively, are consistent with an episode of growth around 60.9±0.5 Ma. Monazite, however, would have continued its crystallization process for a period of ca. 10 Ma. Thin zircon and high-Y monazite rims show ages between ~34–25 Ma and are interpreted to reflect a stage of reheating by magmatic advection related to large Oligocene plutonism in the region. Age and nature of central XC basement show good correlation with other Early-Cretaceous volcano-sedimentary basins of central and southern Mexico. A period of crustal thickening would have buried the sequence at depths of ~30 km, causing Barrovian-type metamorphism during mid- to Late Cretaceous time and eventually, anatexis that evolved at granulite-facies conditions during orogenic collapse in the Paleocene (≥62 Ma). The time span from leucosome crystallization to late-stage reheating in central XC would imply a protracted high-temperature evolution indicating a middle- to upper-crustal residence time of at least ca. 30 Ma.

中文翻译：

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墨西哥南部 Xolapa Complex 中部高品位变质火山沉积岩的岩石学和 U-Pb 年代学

摘要 Xolapa Complex (XC) 是墨西哥北美洲板块南缘出露的高等级变质带。它的演化包括与地壳增厚和随后抬升到上地壳水平相关的广泛的退热期，在古新世达到顶峰。本研究在实地和岩石学工作的基础上，将岩石学建模方法与 LA-ICP-MS U-Pb 锆石和独居石年代学相结合，以阐明该变质带的构造热演化。XC 中部的研究区包括一套交替混合的副片麻岩和含石榴石的镁铁质片岩。岩石学证据和相平衡计算表明，在发生广泛混合之前，在约 640-670 °C 和 8-9 kbar 下发生了十字石-蓝晶石级变质作用。通过黑云母和角闪石脱水熔化反应逐渐发生肥沃层和耐火层的差异化，并在约 800-820 °C 和约 5-7 kbar 的麻粒岩相条件下的峰值变质作用期间继续进行。根据 Ti-in-zircon 测温法，在冷却过程中熔体生成/流动进行，直到在 ~700 °C 结晶。顺行变质作用的年龄可能是由独居石岩心记录的，这些岩心给出了中至晚白垩世的年龄。冷却和熔融结晶可能受到年龄为 61.8±0.6 Ma 的无色体锆石的限制。分别来自全岩和黑素体部分的锆石和低 Y 独居石都与 60.9±0.5 Ma 左右的生长事件一致。然而，独居石将继续其结晶过程约一段时间。10 马。薄锆石和高 Y 独居石边缘显示年龄在~34-25 Ma 之间，被解释为反映了与该地区大型渐新世深成体相关的岩浆平流重新加热的阶段。XC中部基底的年龄和性质与墨西哥中南部其他早白垩世火山-沉积盆地具有良好的相关性。一段地壳增厚会将层序掩埋在约 30 公里的深度，在中至晚白垩世期间引起巴罗式变质作用，并最终在古新世造山崩塌期间在麻粒岩相条件下演化（≥62 Ma ）。从白质体结晶到中央 XC 后期再加热的时间跨度意味着长期的高温演变表明中至上地壳的停留时间至少为大约 30 马。