U-Pb zircon (ID-TIMS and SHRIMP) evidence for the early ordovician intrusion of metagranites in the late Proterozoic Canaveilles Group of the Pyrenees and the Montagne Noire (France)

Abstract

Depending on the quality of the zircon grains available for analysis, two methods may be used to date igneous rock emplacement, namely U-Pb TIMS with isotope dilution or in situ U-Pb SIMS (SHRIMP). Both methods have been used to determine, in a precise and accurate manner, the emplacement age of the granitic protolith of the various orthogneisses in the Pyrenean Axial Zone. More specifically, four representative samples of G1, G2 and a “transition gneiss” yielded reliable datings with an average age of 473 ± 4 Ma for each sample. The surrounding sediments of the Canaveilles Group were constrained by zircon grains from interlayered metarhyodacite and dated at 581 ± 10 Ma using the SHRIMP method, clearly giving this group a late Proterozoic (Vendian) age. Finally, the Somail orthogneiss of the Montagne Noire, equivalent to that of the Canigou, yielded an age of 471 ± 4 Ma with the in situ U-Pb method, which is identical to the dating of the Pyrenean samples. In addition, most of the studied orthogneisses recorded a wide range of significant concordant inherited ages spanning from early Archaean (3.5 Ga) to Pan-African/Cadomian (600–800 Ma). Bearing in mind the calc-alkaline affinity of the studied rocks, this work demonstrates the huge contrast between the active Gondwana margin in the north (“South European terrane”) and the remarkably homogeneous continental plate that existed from Arabia to Morocco during the Ordovician.

Cadomian volcanosedimentary complexes across the Ediacaran–Cambrian transition of the Eastern Pyrenees, southwestern Europe

“…These granitic plutons were recently dated as Ordovician, among others, by Cocherie et al (2005), Castiñeiras et al (2008), Denele et al (2009), Casas et al (2010, Liesa et al (2011), Martínez et al (2011 and Mezger and Gerdes (2016). In the Canigó and Roc de Frausa units, they intrude the base of the Canaveilles Group, the so-called Nyer Formation after Álvaro et al (in press).…”

“…Their facies and sedimentological interpretations are documented below. Finestrelles Member at Pic de la Clape summit (542.9 + 5/− 1.3 Ma, this work), PC11 Fabert metarhyolite at Pic de la Clape summit (532.9 ± 6 Ma, this work), RF3 548.4 ± 8.4 Ma (Castiñeiras et al 2008); TG Finestrelles Member at Tregurà (575 ± 4, 570 ± 10 and 568 ± 6 Ma; Casas et al 2015) recalculated at 565 ± 9, 559 ± 9 and 552 ± 10 Ma, respectively (this work); PC, Pir, Pyr samples referred to in the text and selected for geochemical analyses, cB col de Banyuls marble, cN Cap Norfeu marble; sample GRA1 from the Vallespir unit (580 ± 10 Ma, Cocherie et al 2005) in need of revision and not represented here 1 3…”

“…1). The dominance of unfossiliferous fine-grained siliciclastic sediments interrupted by marbles and scattered igneous rocks has rendered correlation and dating difficult b Geological map of the study area; modified from Baudin et al (2008), Laumonier et al (2015a, b) and Casas et al (2015) 1 3 (Guitard et al 1998;Deloule et al 2002;Laumonier et al 2004;Cocherie et al 2005;Castiñeiras et al 2008).…”

“…Despite the recent publication of numerous U-Pb zircon ages (e.g. Cocherie et al 2005;Castiñeiras et al 2008;Casas et al 2015;Laumonier et al 2015a, b, c), the age of some Cadomian-related volcanosedimentary complexes included in the Canaveilles Group remains contentious. In addition, many of their correlations are still exclusively based on lithostratigraphic comparisons.…”

“…Unfortunately, zircon U-Pb dating of these rocks yielded some confusion in what was considered a handful of correlatable stratigraphic marker beds encompassing a geochronological interval of ca. 32 my (580-548 Ma; Cocherie et al 2005;Castiñeiras et al 2008;Casas et al 2015;Laumonier et al 2015a, b, c). Therefore, a reassessment of available radiometric ages, completed with new U-Pb dating of zircon obtained by LA-ICP-MS, appears to be necessary for better understanding the volcanogenic record preserved in the Eastern Pyrenees across the Ediacaran-Cambrian transition.…”