https://orcid.org/0000-0001-9206-5108
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ABSTRACT
Proterozoic to lower Palaeozoic metamorphic sequences are exposed in southern Mexico providing an important geological record for Rodinia and northwestern Gondwana reconstructions. The Sierra de Juárez Complex (SJC) is an enigmatic basement block in southern Mexico that recorded Jurassic dextral strike-slip mylonitic deformation, likely instigated by Pangea break-up and opening of the Gulf of Mexico. However, the origin and pre-Mesozoic evolution of this block are poorly constrained. In this paper, we present the result of fieldwork, LA-ICP-MS U-Pb zircon geochronology, and major and trace element geochemical analyses that allow us to define the following lithological units in the SJC: (1) an anorthositic-gabbroic metamorphic unit (Viguera Suite) with protolith ages of 979–976 Ma and a thermal disturbance event at ca. 920–880 Ma; (2) a MORB-like metagabbroic unit (San Agustín Orthogneiss) with a protolith age of 441.9 ± 3.6 Ma; (3) a metamorphic supracrustal sequence (Etla Unit) that includes amphibolites and pelitic schists with maximum depositional ages of 422–414 Ma and a detrital provenance sourced in Gondwanan-type terranes; and (4) metagranitic intrusions with a protolith age of 191.9 ± 1 Ma, suspected to be syntectonic with respect to the Jurassic mylonitic event. The Silurian-Devonian San Agustín Orthogneiss and Etla Unit constitute the roots of a formerly undocumented lower Palaeozoic terrane that, together with the Viguera Suite, underwent high-pressure amphibolite facies metamorphism between 398–391 Ma, likely related to contractional tectonics. Based on these data, the SJC is proposed as a Mesoproterozoic to middle Palaeozoic crustal block with a geologic evolution coupled to NW Gondwana and a potential correlation with the Grenville-aged and peri-Gondwanan-type terranes like those currently located in southeastern Mexico, Central America, and northwestern South America.
Acknowledgments
The first author acknowledges the Consejo Nacional de Ciencia y Tecnología (CONACyT) for granting him Masters and PhD scholarships. This contribution was financed by the following projects: CONACyT 164454 “Sistemas Tectónicos de México, Origen y Evolución” and PAPIME, UNAM, PE101615 “Leyendo la Historia de la Tierra: el Poder de la Observación en el Estudio de las Rocas a Macro y Microescala”, both granted to Fernando Ortega Gutiérrez; PAPIIT-DGAPA, UNAM, IN101520, granted to Luigi A. Solari; and a DGAPA-UNAM Postdoc scholarship granted to Roberto Maldonado. We also thank J. Tomás Vázquez Ramírez for thin section preparation; Consuelo Macías Romo, Manuel Albarrán Murillo and Teodoro Hernández Treviño for helping with mineral separation; Carlos Ortega Obregón for acquisition of geochronologic data; Jazmín A. López Díaz and Ma. Concepción Arredondo de la Rosa for help in zircon CL photomicrography; Patricia Girón and Rufino Lozano for major element determinations, and Ofelia Pérez Arvizu for trace element determinations. The first author also thanks Mónica G. Ramírez Calderón and Sandra Guerrero Moreno for early comments that helped to improve this work, and to Daniel Villanueva Lascurain for language revision. The Editorial handling of Dr. R. Stern, as well as the careful journal reviews of Dr. B. Weber as well as two anonymous reviewers are also acknowledged, because they improved the clarity of the concepts described in this manuscript.
Disclosure statement
The first author and co-authors declare that they have no financial interests or personal relationships that could have influence the work reported in this paper.
Supplementary material
Supplemental data for this article can be accessed here.
Correction Statement
This article has been republished with minor changes. These changes do not impact the academic content of the article.
Highlights
- The Sierra de Juárez Mylonitic Complex (SJMC) in southern Mexico contains Neoproterozoic – lower Palaeozoic magmatic and sedimentary sequences.
- The Viguera Suite displays protolith ages ranging between 979-975 Ma.
- The Etla Unit is sourced in Neoproterozoic, Cambrian and Ordovician peri-Gondwanan and Rodinian-type terranes.
- The San Agustín Orthogneiss displays a lower Silurian magmatic age with a MORB-like signature
- lithological similarities are found in northwestern peri-Amazonian terranes, the Chiapas Massif Complex and El Triunfo Complex as well as in Guatemala Units.