Miocene to late Quaternary Patagonian basalts (46-47°S); geochronometric and geochemical evidence for slab tearing due to active spreading ridge subduction

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doi: 10.1016/j.jvolgeores.2005.09.002
Authors:Guivel, Christèle; Morata, Diego; Pelleter, Ewan; Espinoza, Felipe; Maury, René C.; Lagabrielle, Yves; Polvé, Mireille; Bellon, Hervé; Cotten, Joseph; Benoit, Mathieu; Suarez, Manuel; de la Cruz, Rita
Author Affiliations:Primary:
Université de Nantes, Planétologie et Géodynamique, Nantes, France
Other:
Universidad de Chile, Chile
Universite de Bretagne Occidentale, France
CNRS, France
Servicio Nacional de Geologia y Mineria, Chile
Volume Title:Journal of Volcanology and Geothermal Research
Source:Journal of Volcanology and Geothermal Research, 149(3-4), p.346-370. Publisher: Elsevier, Amsterdam, Netherlands. ISSN: 0377-0273
Publication Date:2006
Note:In English. 78 refs.; illus., incl. 5 tables, sketch map
Summary:Miocene to Quaternary large basaltic plateaus occur in the back-arc domain of the Andean chain in Patagonia. They are thought to result from the ascent of subslab asthenospheric magmas through slab windows generated from subducted segments of the South Chile Ridge (SCR). We have investigated three volcanic centres from the Lago General Carrera-Buenos Aires area (46-47°S) located above the inferred position of the slab window corresponding to a segment subducted 6 Ma ago. (1) The Quaternary Rio Murta transitional basalts display major, trace elements, and Sr and Nd isotopic features similar to those of oceanic basalts from the SCR and from the Chile Triple Junction near Taitao Peninsula (e.g., (87Sr/86Sr)o = 0.70396-0.70346 and εNd = +5.5 to +3.0). We consider them as derived from the melting of a Chile Ridge asthenospheric mantle source containing a weak subduction component. (2) The Plio-Quaternary (<3.3 Ma) post-plateau basanites from Meseta del Lago Buenos Aires (MLBA), Argentina, likely derive from small degrees of melting of OIB-type mantle sources involving the subslab asthenosphere and the enriched subcontinental lithospheric mantle. (3) The main plateau basaltic volcanism in this region is represented by the 12.4-3.3-Ma-old MLBA basalts and the 8.2-4.4-Ma-old basalts from Meseta Chile Chico (MCC), Chile. Two groups can be distinguished among these main plateau basalts. The first group includes alkali basalts and trachybasalts displaying typical OIB signatures and thought to derive from predominantly asthenospheric mantle sources similar to those of the post-plateau MLBA basalts, but through slightly larger degrees of melting. The second one, although still dominantly alkalic, displays incompatible element signatures intermediate between those of OIB and arc magmas (e.g., La/Nb>1 and TiO2<2 wt.%). These intermediate basalts differ from their strictly alkalic equivalents by having lower High Field Strength Element (HFSE) and higher εNd (up to +5.4). These features are consistent with their derivation from an enriched mantle source contaminated by ca. 10% rutile-bearing restite of altered oceanic crust. The petrogenesis of the studied Mio-Pliocene basalts from MLBA and MCC is consistent with contributions of the subslab asthenosphere, the South American subcontinental lithospheric mantle and the subducted Pacific oceanic crust to their sources. However, their chronology of emplacement is not consistent with an ascent through an asthenospheric window opened as a consequence of the subduction of segment SCR-1, which entered the trench at 6 Ma. Indeed, magmatic activity was already important between 12 and 8 Ma in MLBA and MCC as well as in southernmost plateaus, i.e., 6 Ma before the subduction of the SCR-1 segment. We propose a geodynamic model in which OIB and intermediate magmas derived from deep subslab asthenospheric mantle did uprise through a tear-in-the-slab, which formed when the southernmost segments of the SCR collided with the Chile Trench around 15 Ma. During their ascent, they interacted with the Patagonian supraslab mantle and, locally, with slivers of subducted Pacific oceanic crust that contributed to the geochemical signature of the intermediate basalts. Abstract Copyright (2006) Elsevier, B.V. [G.L.B.]
Sections:Geochemistry; Petrology
Subsections:General; Igneous rocks
Subjects:Alkali basalts; Alkaline earth metals; Ar-40/Ar-36; Argon; Basalts; Cenozoic; High-field-strength elements; Igneous rocks; Isotope ratios; Isotopes; Metals; Miocene; Neogene; Noble gases; Plate tectonics; Quaternary; Rare earths; Sea-floor spreading; Slabs; Sr-87/Sr-86; Stable isotopes; Strontium; Subduction; Tertiary; Trace elements; Upper Quaternary; Volcanic fields; Volcanic rocks; Andes; Argentina; Chile; Patagonia; Patagonian Andes; South America; Chile Margin Triple Junction
Coordinates:S500000 S450000 W0700000 W0800000
Abstract Numbers:06M/1054
Record ID:2006053282
Copyright Information:GeoRef, Copyright 2019 American Geosciences Institute. Reference includes data from CAPCAS, Elsevier Scientific Publishers, Amsterdam, Netherlands
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