Abstract

PEREZ-GUTIERREZ, Rosalva; SOLARI, Luigi A.; GOMEZ-TUENA, Arturo  and  MARTENS, Uwe. Mesozoic geologic evolution of the Xolapa migmatitic complex north of Acapulco, southern Mexico: implications for paleogeographic reconstructions. Rev. mex. cienc. geol [online]. 2009, vol.26, n.1, pp.201-221. ISSN 2007-2902.

The Xolapa Complex in the Acapulco-Tierra Colorada area, southern Mexico, is made up of orthogneisses and paragneisses, both affected by a variable degrees of migmatization. These rocks are intruded by several episodes of Jurassic-Oligocene, calc-alkaline granitic magmatism. Three phases of ductile deformation affected the gneisses and migmatites. D₁ produced an amphibolite-facies metamorphic banding (M₁) and a penetrative S₁ foliation, axial planar to isoclinal, recumbent F₁ folds with axes parallel to a NE to NW, gently plunging, L₁ stretching lineation. D₂ consists of a S₂ foliation defined by hornblende, biotite and garnet, synchronous with M2 migmatization that generated leucosomes, which are generally parallel to S₁. D₃ is made up of asymmetric, chevron F₃ folds that deform the composite S₁/S₂ foliation during greenschist to lower amphibolite metamorphism (M3). U-Pb SHRIMP (Sensitive High-Resolution Ion Micropobe) geochronology carried out on zircon separated from two orthogneisses yielded an Early Jurassic magmatic event (178.7 ± 1.1 Ma) and the age of migmatization (133.6 ± 0.9 Ma). Two episodes of Pb loss were also recognized, the first at 129.2 ± 0.4 Ma, and the second during the earliest Paleocene (61.4 ± 1.5 Ma); they are probably associated with two episodes of magmatism. The Early Jurassic magmatic arc may be correlated with a magmatic arc in the eastern Guerrero terrane. The Early Cretaceous migmatization is inferred to have resulted from shortening, possibly due to the accretion of an exotic block, such as the Chortís block along whose northern margin contemporaneous, high-pressure metamorphism has been recorded.

Keywords : migmatization; U-Pb; Mesozoic; Xolapa Complex; southern México.

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