Paleocene to Miocene migmatization and kinematics of the deformation at the northern boundary of the Xolapa Complex: implications for the Chortís Block-southern Mexico connection

ABSTRACT

The Xolapa Complex of southern Mexico preserves evidence of its connection with the Chortís Block of Central America. Orthogneisses yielded U-Pb protolith ages from 172 to 169 Ma and paramigmatites are dated at 217 Ma. El Salitre and the Amatlán granitoids show crystallization ages of 65 and 59–57 Ma, respectively. In central Xolapa, diatexites have ages from 38 to 31 Ma, and granites were dated from 30 to 29 Ma. In the southeastern Xolapa, crystallization ages of 45 Ma and 23 to 21 Ma were obtained from migmatites and anatectic granites, respectively. Previous data indicate three diachronous stages of crustal melting along the Xolapa block. Structural data reveal that the Xolapa Complex is tectonically juxtaposed against the Acatlán Complex through ductile zones. Two mylonitic foliations are predominant in the northern boundary of the Xolapa Complex: (i) a sub-vertical NW-SE foliation with subhorizontal or low-plunging stretching lineation and left-lateral kinematics; and (ii) a subhorizontal NE-SW foliation with normal plunging stretching lineation and top-to-NE kinematics. The first mylonitic event related to the sinistral eastward motion of the Chortís Block occurred between 58 and 54–50 Ma. The second event took place in central Xolapa after or synchronous with the 38–31 Ma emplacement of diatexites. This event is related to an extensional phase that uplifts the Xolapa Complex with concerning the Acatlán Complex. In the southeastern region, deformation occurred after or synchronous with the emplacement of anatectic granites dated at 23–22 Ma. Our geochronological and structural data delineated an eastward decreasing age trend of migmatization, whereas the mylonitic deformation reported through the Xolapa Complex is consistent with a diachronous migration and detachment of the Chortís Block relative to the Acatlán Complex from Paleocene to early Miocene times.

KEYWORDS:

• Diachronous migmatization
• U-Pb geochronology
• mylonitic deformation
• Xolapa Complex
• Chortís Block

Acknowledgments

Some aspects of this contribution formed part of a Master of Science thesis by Sarmiento-Villagrana. English version of this manuscript was improved by Isaac Neri Gómez-Sarmiento and Travis Ashworth. Thanks to Jazmin A. López-Díaz from Universidad Autónoma de Guerrero for assistance with CL images. Thanks for the reviews and improvements done by Peter Schaaf, editor-in-Chief Robert J. Stern and an anonymous reviewer. This work was conducted during a Postdoctoral Fellowship provided to the first and third authors by the Consejo Nacional de Ciencia y Tecnología (CONACyT).

Disclosure statement

No potential conflict of interest was reported by the authors.

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Funding

This work was supported by the Consejo Nacional de Ciencia y Tecnología.