Isotope geochemistry evidence for Laurussian-type sources of South Portuguese Zone Carboniferous turbidites (Variscan Orogeny)
- 20 May 2020
- journal article
- research article
- Published by Geological Society of London in Geological Society, London, Special Publications
- Vol. 503 (1) , 619-642
Abstract
New Rb–Sr isotopic data from South Portuguese Zone (SPZ) turbidites show that the 87 Sr/ 86 Sr( t ) ratio increases from the basal Mértola Formation (Visean–Serpukhovian: 0.706–0.707), through the Mira Formation (Serpukhovian–Bashkirian: 0.706–0.712) to the uppermost Brejeira Formation (Bashkirian–Moscovian: 0.713–0.715). In addition, estimated Nd T DM model ages for the Mértola (1.29–1.09 Ga), Mira (1.58–1.1 Ga) and Brejeira (1.73–1.37 Ga) formations indicate inverted stratigraphy for their isotopic sources. The isotope geochemical data indicate significant changes in the sources from which the SPZ Carboniferous turbidites are derived, consistent with the progressive denudation of a continental magmatic arc built on the Laurussian margin. Mértola turbidites inherited their geochemical and isotopic characteristics from an adjacent dissected Middle–Late Devonian continental magmatic arc with an intermediate–felsic composition: that is a Laurussian (Rheic magmatic arc)-type source. The progressive erosion of its plutonic roots and older host continental basement rocks are indicated in the Mira and Brejeira formations by the increasing contribution of recycled ancient continental crust. The pronounced similarity between the Nd T DM model ages and the detrital zircon populations of the Mira and Brejeira formations (SW Iberia) suggest that they share a common Laurussian (West Avalonia/Meguma terrane)-type source but a contribution from Gondwanan (Ossa-Morena)-type sources cannot be discarded.Keywords
Funding Information
- Ministerio de Ciencia, Innovación y Universidades (CGL2016-76438-P)
- Ministerio de Ciencia, Innovación y Universidades (PGC2018-096534-B-I00)
- Fundação para a Ciência e Tecnologia (SFRH/BPD/99550/2014)
- Fundação para a Ciência e a Tecnologia (ICT-UID/GEO/04683/2019)
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