During the Triassic, continental breakup started in western equatorial Pangea, while active continental margins developed along North and South America’s Pacific borders. Besides many uncertainties about how -Gondwanan terrains of Mexico evolved during and after Pangea’s amalgamation, the apparent absence of Late Triassic magmatism has been an enigmatic feature of Mexico’s geology. Here, we present the first documented occurrences of Late Triassic igneous rocks and a coeval high-grade metamorphic event in southern Mexico, as well as evidence for subsequent Early Jurassic ductile deformation and magmatism. Samples come from the Chiapas Massif Complex (CMC), a crystalline basement of the southern Maya Block. Field evidence suggests that garnet-bearing leucogranitic stocks intruded a former structural boundary between different Precambrian-Paleozoic basement units. High-precision Sm-Nd garnet-whole-rock ages (ID-TIMS partial dissolution techniques) and U-Pb geochronology on zircon rims (LA-ICPMS) revealed Norian igneous crystallization ages for the leucogranites (∼221–213 Ma). Isotope and geochemical data indicate that these granites originated from crustal reworking by anatexis. A garnet-bearing leucosome from a migmatite yielded a slightly younger Sm-Nd age (∼204 Ma), indicating cooling soon after the peak conditions of the anatectic event. Additionally, monazite from a mylonitized leucogranite yielded an Early Jurassic U-Pb age (∼179 Ma), indicating ductile deformation. Nearly coeval zircon ages from an undeformed pink granite and a nearby volcaniclastic sequence (∼184–189 Ma) further imply contrasting erosion levels during the Early Jurassic. The new data support models for regional stretching of eastern and southern Mexico, where crustal extension during the gravitational collapse of a collisional orogen in paleo-northern Mexico led to continental rifting and the breakup of Pangea. In the CMC, crustal extension is reflected by Norian anatectic crustal melts and migmatites, as well as Early Jurassic plutonic and extrusive magmatism that are localized in certain fault-bounded blocks with different erosion levels compared to adjacent blocks.

中文翻译：

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墨西哥南部恰帕斯地块杂岩中的晚三叠世至早侏罗世深熔岩浆作用：赤道西盘古大陆地壳伸展的起始和模式的新证据


三叠纪期间，大陆分裂始于西赤道盘古大陆，而活跃的大陆边缘则沿着北美和南美的太平洋边界发展起来。除了关于墨西哥冈瓦纳地形在盘古大陆合并期间和之后如何演变的许多不确定性之外，晚三叠世岩浆活动的明显缺失一直是墨西哥地质学的一个神秘特征。在这里，我们首次展示了晚三叠世火成岩的记录和墨西哥南部同时代的高级变质事件，以及随后的早侏罗世韧性变形和岩浆作用的证据。样本来自恰帕斯地块复合体 (CMC)，这是南部玛雅地块的一个结晶基底。现场证据表明，含石榴石的淡色花岗岩群侵入了不同前寒武纪-古生代基底单元之间的前构造边界。高精度 Sm-Nd 石榴石全岩年龄（ID-TIMS 部分溶解技术）和锆石边缘 U-Pb 地质年代学（LA-ICPMS）揭示了淡色花岗岩的诺里安火成岩结晶年龄（∼221–213 Ma）。同位素和地球化学数据表明这些花岗岩起源于地壳深熔改造。来自混合岩的含石榴石隐色体产生了稍微年轻的 Sm-Nd 年龄（~204 Ma），表明在深熔事件的峰值条件之后不久就发生了冷却。此外，来自糜棱岩化淡色花岗岩的独居石产生了早侏罗世 U-Pb 年龄（∼179 Ma），表明存在延性变形。来自未变形的粉红色花岗岩和附近火山碎屑序列（~184-189 Ma）的近乎同时代的锆石年龄进一步暗示了早侏罗世期间侵蚀水平的对比。 新的数据支持墨西哥东部和南部区域拉伸的模型，其中墨西哥古北部碰撞造山带重力塌陷期间的地壳扩张导致大陆裂谷和盘古大陆的分裂。在 CMC 中，地壳伸展由诺里安深熔地壳熔体和混合岩以及早侏罗世深成岩和喷出岩浆作用反映，这些岩浆作用位于某些断层边界块体中，与邻近块体相比，其侵蚀程度不同。