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The Xolapa Complex (XC) is the largest plutonic and metamorphic mid-crustal basement unit in Mexico and represents an ancient continental magmatic-arc. A complete range from metatexite to diatexite migmatitic structures has been produced during a single high-grade metamorphic event. However, structural relics reveal the existence of early Cpx + Pl + Qtz ± Opx and Grt + Opx + Pl + Qtz ± Cpx pre-migmatitic metamorphic assemblages. Field relationships and microstructural observations allow us to constrain five pre-, syn-and post-migmatitic deformational phases. It is argued that migmatitic structures and minor anatectic granites were developed during ductile recumbent folding and shear structures related to the D2-D3 phases. Late post-migmatitic ductile-brittle deformation is evidenced by the development of NNE trending transpressional thrusting (D4), and E-W left-lateral mylonitic shear zones (D5). Biotite-breakdown melting in felsic rocks and amphibole-breakdown melting in mafic rocks, as well as geothermobarometric results, indicate that metamorphism took place at temperatures from 830 to 900°C and pressures ranging from ‡6.3 to 9.5 kbar. Late migmatitic assemblages equilibrated in the highest temperature range along a clockwise P-T path. The relationships between the large diversity of migmatitic structures and the progressive production of melt suggest that feedback relations prevailed as a time-marker during a contractional regime. Deformation, metamorphism, and plutonism of the XC show that this terrane evolved as a north-east-verging thrust system with synkinematic metamorphism and partial melting, during the Late Cretaceous -Palaeogene. The tectonothermal history of XC is analogous to a Cordilleran metamorphic magmatic-arc formed in an accretionary tectonic framework. This new model provides constraints on the exhumation mechanism and thermal evolution of southern Mexico.

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A new geological map at 1:50,000 scale of La Reforma Caldera Complex has been produced applying modern survey methodologies to volcanic areas. This map aims to represent a reliable and objective tool to understand the geological evolution of the region. La Reforma Caldera Complex is a Pleistocene nested caldera located in the central part of the Baja California peninsula, Mexico. The twelve formations defined within the Quaternary volcanic record were grouped into three phases (pre-caldera, caldera, and post-caldera). The pre-caldera phase (>1.35 Ma) is characterized by scattered eruptions, mostly occurred in submarine environment. The caldera phase (1.35-0.96 Ma) groups several distinct explosive and effusive eruptions that formed the present-day caldera depression. The post caldera phase includes scattered effusive eruptions (ended at 0.28 Ma) and resurgence, characterized by several hundred meters of uplift of the central block within the caldera depression.

El sistema de fallas Morelia-Acambay (MAFS) consiste en una serie de fallas normales de dirección E-W y NE-SW que cortan la parte central del Cinturón Volcánico Transmexicano. El sistema de fallas se asocia a la formación de las depresiones lacustres de Chapala, Zacapu, Cuitzeo, Maravatio y Acambay. Las fallas E-W de MAFS aparecieron hace 7-9 millones de años durante Mioceno temprano. Las fallas NNW-SSE son más viejas y se han reactivado en el tiempo, desplazando y controlando a las depresiones lacustres E-W. Se estimaron las magnitudes sísmicas de las estructuras E-W de la región de Morelia-Cuitzeo asumiendo una ruptura cosismica. Cartografía, geología estructural y paleosismología sugieren que las estructuras de MAFS en la región de Morelia-Cuitzeo han estado activas durante el Holoceno, controlando los terremotos históricos que afectan a paleosuelos con cerámica de las culturas Pirinda-Purepecha. Estos terremotos históricos también están registrados en las fallas E-W del campo geotérmico de Los Azufres. En la región de Pátzcuaro, las estructuras E-W de MAFS también se ligan a sismos fuertes ocurridos durante épocas prehistóricas e históricas. Por ejemplo, la secuencia lacustre de Jarácuaro, en el sector meridional del lago Pátzcuaro ha registrado por lo menos tres sismos importantes (Período de PostClassic, 1845 y 1858). El sismo de 1858 (Magnitud estimada de ~7.3) generó un tsunami de 2 m de altura descrito en los archivos históricos. Un sismo similar en la actualidad devastaría esta zona del estado de Michoac’an, la cual está ocupada por las poblaciones de más alta densidad. De hecho, el 17 de octubre de 2007 mientras que este articulo era escrito, ocurrieron tres sismos en la ciudad de Morelia que fueron ligados a la falla normal derecha de la Central o de La Paloma. Este hecho corroboraba la sismicidad potencial de las fallas E-W y NE-SW del TMBV.

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