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Les formations orogéniques mésozoiques du Guerrero (Mexique méridional) : Contribution à la connaissance de l'évolution géodynamique des cordillères mexicaines

Abstract : In the Teloloapan-Zihuatanejo area (southern Mexico), are exposed six volcano-sedimentary and/or volcanopiutonic arc séquences ranging in âge from Late Jurassic to Early Cretaceous which accreted to the North American plate at the end of the Cretaceous. The Taxco-Taxco Viejo is composed of calc-alkaline andésites, dacites and rhyolites interbedded in detrital sédiments. This séquence is affected by a syn-kinematic low grade metamorphism (221-276°C). This séquence Iikely represents the remnants of an island arc built on a continental crust. The Telolopan séquence consists of a highly deformed succession of Tithonian to Albian basalts and andésites of calc-alkaline affinity, which are highly enriched in LREE [QLa/Yb)N=5.5-10.5] and HFSE. Their eNd = +1.6 to +4.6 ratios, rather low for intra-oceanic calc-alkaline melts, suggest that they dérive from an enriched mantle source. Sedimentary cover includes volcaniclastic turbidites, reefal and bioclastic limestones and sandstones and shales of Aptian-Albian âge. The Arcelia séquence is a deformed succession of Albian-Cenomanian mafic pillow basalts and dykes of tholeiitic afinity [(La/Yb)N= 1.0-2.6, eNd = +5.5 to +8.0]. Sedimentary cover consists of radiolarian cherts and black shales. Locally plutonic rocks are thrusted on the volcanic rocks. The Huetamo séquence is formed of a more than 5000 m thick, slightly deformed succession of: (1) Tithonian volcaniclastic conglomérâtes and turbidites, which contain at the base uncommon intra-oceanic tholeiitic pillow basalts [(La/Yb)N = 1.0-1.2; eNd = +7.5]; (2) Neocomian volcaniclastic turbidites; (3) Aptian-Albian reefal limestones and volcanic conglomérâtes; and, (4) upper Cretaceous red beds. Geochemical characteristics of volcanic pebbles within conglomérates vary from tholeiitic [(La/Yb)N = 1.9] basalts in the Jurassic levels through calc-alkaline [(La/Yb)N = 2.6-3.5] andésites and dacites in the Neocomian strata to shoshonitic [(La/Yb)N = 10.3-10.4] andésites and dacites in the Aptian-Albian levels. The Zihuatanejo séquence includes an undeformed succession of calc-alkaline [(La/Yb)N = 2.5-9.8] andésites and dacites, volcaniclastic turbidites and Albian-Cenomanian limestones. Andésites are uncommonly depleted in HFSE and enriched in isotopic Nd (eNd = +7.4 to +9.7). The Las Ollas subduction complex contains a variety of exotic including limestones, quartzites and island-arc tholeiitic [(La/Yb)N = 0.7-1.4; eNd = +7.9 to +8.1] mafic and ultramafic rocks recristallized under médium to high P/T conditions which are included in a sheared matrix of flysch and serpentine. The magmatic affinities of these aforementioned arc séquences which belong to the Guerrero terrane are diversified from one sequence to another and within each sequence. However, two main suites can be recognized : (1) a tholeiitic suite composed of basalts and their feeder dykes, depleted to slightly enriched in LREE which is exposed at Arcelia and Las Ollas; (2) a calcalkaline suite enriched or depleted in High Field Srengh Eléments. In the tholeiitic suite, ultramafic and mafic cumulates are tectonically associated with the basalts and ail these igneous rocks derived from the partial melting of depleted source (eNd ranging between +5.5 to +8; Spinel Lherzolite). In the HFS-enriched calc-alkaline suite of Teloloapan, basalts and mafic andésites predominate and Iikely derived from the partial melting of an enriched source (eNd ranging between +1.6 to +4.6; Garnet Lherzolite). The HFS-depleted calc-alkaline suite (eNd ranging between 7.5 to +9) is represented by the Zihuatanejo andésites and the Aptian-Albian pebbles from Huetamo. These rocks derived probably from the a Spinel Lherzolite depleted source but with a partial melting ratio lower than in the tholeiites. These constrasting arc suites suggest that during the Late Jurassic-Early Cretaceous, the western margin of Mexico was characterized by an intense and diversified magmatic activity Iikely produced in more than one arc-trench System.
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Submitted on : Wednesday, August 29, 2012 - 12:45:11 PM
Last modification on : Friday, March 25, 2022 - 11:08:45 AM

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Oscar Talavera Mendoza. Les formations orogéniques mésozoiques du Guerrero (Mexique méridional) : Contribution à la connaissance de l'évolution géodynamique des cordillères mexicaines. Tectonique. Université Joseph-Fourier - Grenoble I, 1993. Français. ⟨tel-00726204⟩

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