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ETUDE GEOLOGIQUE DE LA SIERRA MADRE DEL SUR AUX ENVIRONS DE CHILPANCINGO ET D'OLINALA, GRO.: Une contribution à la connaissance de l'évolution géodynamique de la marge pacifique du Mexique depuis le Jurassique

Abstract : SUMMARY

The study is about Sierra Madre del Sur, has mountain belt wich lining the Pacific coast, parallel to the Acapulco Trench. It is based one geological mapping of two representative areas situated in Guerrero state (the first around Olinalà, the second near the capital Chilpancingo), and one carring out transects (scale 1/1). Its goal is to individualize the significant geological sets and to characterize the structures related to the various stages of deformation; this in order to reconstitute the evolution of the sierra since the Jurassic inferior, by putting it within the geodynamic framework of the southern part of Mexico currently located at the crossroads of the North America plates, Caribbean and Coconuts.

The first part relates to the architecture and the history of the sierra, approached by the stratigraphic and petrographic approaches and the retrotectonic structural analysis. The Jurassic pre continental – base (part of the block of Oaxaca) includes/understands a base – born of the assembly of the "terranes" Oaxaca and Mixtèque with the Paleozoic inferior – equipped locally with his sedimentary cover of the Paleozoic superior little deformed; the Xolapa Complex which levels along the coast, is a lower part of this crust, migmatized and granitized as a root of the arcs Jurassic and the Paleogene, and recently exhumed. In the whole of the Middle Jurassic, the volcanic rocks and volcanoclastic are recognized with dominant acid (Chapolapa Formation) of an arc with which the basin back-arc with Tecocoyunca is associated. Both are tectonised and metamorphised (green schist) by the compressive Nevadien phase of the Jurassic superior. In connection with the eustatic rise, the lower Cretaceous is marked by the marine invasion and the deposit in discordance of the neritic formations with recifs formations of the thick carbonated platform of Guerrero – Morelos. It is on the "peaceful" edge of this one that is carried out, at the base of the higher Cretaceous, the haulage of the "terrane" Guerrero (intra-oceanic arc generated during the Jurassic superior and the lower Cretaceous) by collision unintermitting – arc. A major consequence of this event is the formation, with before crown, of a basin flexural in which a powerful terrigenous series (flysch Mexcala) accumulates, during the higher Cretaceous and the Paleocene one. This basin, affected by the Laramide phase, undergoes, with the Paleocene lower – Eocene superior, a strong East-West shortening, adapted by the crumpling of the separated cover and the chipping of the base. The unmatched unit, the Paleogene and lower miocene, include/understand post-Laramide continental molasses (Formation Balsas) passing laterally and vertically to the volcanic drill plate with dominant ignimbritic generated by the subduction of the old Farallon plate; it is deformed by basic folds south-eastern – southern – north-western – north of lower Miocène. Since Miocène and following the departure of the Chortis block the evolution, still in progress, Sierra Madre del Sur is under the dependence of the subduction of the Cocos plate: it is it which induces and maintains the exhumation the lower continental crust of the block of Oaxaca (between the surface of subduction and a major surface of detachment crustal in normal fault) with update of the Complex Xolapa and deformation in antiforme of the Sierra Madre del Sur, parallel to the pit of subduction of Acapulco and thus very obliquely compared to the mesozoïc and tertiary former structures recut.

The second part is initially the occasion to specify, by the placement of the pétro-geochemical tool, the geodynamic environments of the genesis of two geological sets present in the Sierra Madre del Sur and which are essential markers of the evolution of the Mexican margin: the volcanic arc Chapolapa of the Middle Jurassic whose importance has, until now, been underestimated and the higher Jurassic arc volcanic – cretaceous lower of the "terrane" Guerrero.
The petrographic characteristics, the geochemistry of the major elements, the geochemistry of the elements traces and the isotopic geochemistry of the generally acid volcanic rocks of the arc Chapolapa, indicate that they are connected with the calc-alkali series of an old arc of the Andean type. They derive from the fusion of a coat asthenospheric contaminated by the fluids of the hydrothermalized paleo-pacific oceanic crust, by sediments involved in the subduction and, probably, by the North-American continental crust (block of Oaxaca) on which they rest.
The volcanic rocks (acid lava and andesites of the lower Cretaceous) of the "terrane" Guerrero present in this part of the Sierra Madre del Sur are also calco-alkalin. But the geochemical indicators confirm that their context of installation was that of an insular arc the intra-Pacific
These results, thereafter, are integrated in the presentation, in 2d, of an evolutionary model of the Sierra Madre del Sur This one, built, in six stages according to the calendar established in the first part, schematizes the evolution of this building, from the Jurassic one to the current one.

In the third part and on the basis of library search, a synthesis is carried out on the Jurassic components present, as in the Sierra Madre del Sur, with before "terrane" Guerrero on the old edge of the North-American continent. By finding characteristics petrologic, geochemical, stratigraphic and structural comparable, the presence of an old preliminary Nevadien chain is highlighted, from California to Honduras, even if its shifted initial continuity at summer in a sinistral way and on several hundred kilometers by transforming faults, on the one hand in the north of Mexico to the lower Jurassic – superior Crétacé, on the other hand in the south of Mexico and Guatemala since the Paleogene. This essential data is integrated in a model of palinspathic evolution of Mexico, presented since the Jurassic one in six charts.
Complete list of metadatas

https://tel.archives-ouvertes.fr/tel-00006638
Contributor : José Luis Garcia-Diaz <>
Submitted on : Wednesday, August 4, 2004 - 5:18:50 PM
Last modification on : Thursday, November 19, 2020 - 3:54:26 PM
Long-term archiving on: : Friday, April 2, 2010 - 8:59:20 PM

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  • HAL Id : tel-00006638, version 1

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José Luis Garcia-Diaz. ETUDE GEOLOGIQUE DE LA SIERRA MADRE DEL SUR AUX ENVIRONS DE CHILPANCINGO ET D'OLINALA, GRO.: Une contribution à la connaissance de l'évolution géodynamique de la marge pacifique du Mexique depuis le Jurassique. Géologie appliquée. Université de Savoie, 2004. Français. ⟨tel-00006638⟩

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