Mesozoic geologic evolution of the Xolapa migmatitic complex north of Acapulco, southern Mexico: implications for paleogeographic reconstructions
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.
| Main Authors: | , , , |
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| Format: | Digital revista |
| Language: | English |
| Published: |
Universidad Nacional Autónoma de México, Instituto de Geología
2009
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| Online Access: | http://www.scielo.org.mx/scielo.php?script=sci_arttext&pid=S1026-87742009000100017 |
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