Present state of knowledge and new geochemical constraints on the central part of the Mexican Volcanic Belt and comparison with the Central American Volcanic Arc in terms of near and far trench magmas

Authors: SURENDRA PAL VERMA

Abstract: Abstract: A brief critical review is presented of the geological, geophysical, geochemical, and plate tectonic evidence for the origin and evolution of the central part of the Mexican Volcanic Belt (C-MVB). Databases were constructed for the C-MVB from new and published data as well as for the Central American Volcanic Arc (CAVA), other continental and island arcs, continental rifts or extensional areas, and collision zones. Conventional procedures as well as statistical techniques of multidimensional tectonic discrimination diagrams and significance tests were used to interpret the data. A subdivision of the databases for the C-MVB and CAVA into near the trench or front-arc and far from the trench or back-arc magmas helped to demonstrate the lack of slab input for the C-MVB and the presence of a classic arc-trench system for the CAVA. The use of software IgRoCS, DODESSYS, UDASYS, TecD, and TecDIA provided the following conclusions: 1) basic magmas in the C-MVB that originated in the mantle without the involvement of the subducted slab represent a continental rift setting; 2) C-MVB acid and intermediate magmas that originated, respectively, from the crust and mixed mantle-crustal sources do not show a clear influence of the present subducted slab and represent the tectonic setting of the older crustal and mixed mantle-crustal source rocks; and 3) all rocks in the CAVA were derived from the involvement of the subducted slab and represent a classical continental arc system related to the subduction of the Cocos plate beneath the Caribbean plate, whereas CAVA back-arc rocks originated mainly in the mantle, probably with much less involvement of the subducted slab. Reinterpretation of the Sr, Nd, Pb, and Hf isotopic data supports these inferences. I propose a new tectono-petrogenetic model based on the continuation of the extensional tectonics related to the triple rift system in the western part of the MVB.

Keywords: Southern Mexico, Central America, log-ratio transformations, significance tests, extension or rift, subduction

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