Petrogenesis of Ordovician Magmatism in the Pyrenees (Albera and Canigó Massifs) Determined on the Basis of Zircon Minor and Trace Element Composition

Abstract

Each copy of any part of a JSTOR transmission must contain the same copyright notice that appears on the screen or printed page of such transmission.JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range of content in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new forms of scholarship. For more information about JSTOR, please contact support@jstor.org. A B S T R A C TZircon composition (U, Th, rare earth elements, and Hf) was tested as a tracer of petrogenetic processes in a set of metaigneous rocks from two pre-Ordovician massifs in the Pyrenees, Canigó and Albera. Two groups were differentiated after analyzing a number of elements in zircon: (1) Casemí gneiss and Marialles amphibolite and (2) subvolcanic metaporphyries and Cadí and Sureda orthogneisses. Casemí gneiss and Marialles amphibolite from the Canigó massif have high Th, Th/U, and Ce/Sm and low Yb/Gd and U/Ce that define linear trends in most of the plots used.The anomalous trend of the data in the Th/U-versus-Hf plot suggests mantle involvement in the origin of these rocks and the participation of fractional crystallization during their evolution. Zircon of the metaporphyries and the Cadí and Sureda orthogneisses exhibit similar characteristics despite a difference in age. Zircon has low Th, Th/U, Ce/ Sm, and and high Yb/Gd and U/Ce, suggesting that this mineral grew in a melt formed by anatexis of a * Eu/Eu continental crust, with stable plagioclase. These petrogenetic data are consistent with the previously studied wholerock geochemistry and Sr-Nd isotopes and confirm the use of zircon as a marker of petrogenetic processes in preference to a lithological tracer.

Magmatic evolution in the N-Gondwana margin related to the opening of the Rheic Ocean—evidence from the Upper Parautochthon of the Galicia-Trás-os-Montes Zone and from the Central Iberian Zone (NW Iberian Massif)

“…Although the onset of continental rifting may differ in age from one part of the margin to the other, the opening and subsequent widening of the Rheic Ocean is thought to have occurred before the Upper Ordovician (Cocks and Torsvik 2002;Fortey and Cocks 2003), with the Armorican Quartzite facies (c. 477 Ma; Gutiérrez- Alonso et al 2007) representing the establishment of an stable platform in the early stages of the riftdrift process (Gutiérrez-Marco et al 2002). Yet, the U-Pb ages presented in this paper confirm that the igneous activity in the autochthonous and parautochthonous domains of the margin exposed today in NW Iberia lasted at least until the Upper Ordovician, in similarity to what is described in NE Iberia (e.g., Castiñeiras et al 2010;Navidad et al 2010;Casas et al 2011;Liesa et al 2011;Martínez et al 2011), in the Armorican Massif (e.g., Ballèvre et al 2002), in the French Massif Central (Roger et al 2004;Faure et al 2010;Melleton et al 2010) and in the Mediterranean realm (e.g., Trombetta et al 2004;Helbing and Tiepolo 2005;Oggiano et al 2010;Gaggero et al 2012). Interestingly, neither of these events represents the last magmatic pulses along the continental platform, which remained magmatically active at least up to the latest Ordovician in NE Iberia (446 Ma; Casas 2010) and up to the Silurian in NW Iberia (Ancochea et al 1988;Valverde-Vaquero et al 2007).…”

“…Tilting and gentle folding of the Lower-Middle Ordovician strata, due to the rotation of individual half-grabens and horsts, create the Sardic Unconformity in Iberia. Locally in the structural highs cold-water limestone deposition occurred, sometimes with the intervention of basic magmatism and Massif Central (N-Gondwana passive margin; e.g., Roger et al 2004;Castiñeiras et al 2010;Montero et al 2007;.…”

Mesozoic multi‐stage W–Sn polymetallic mineralization in the Nanling Range, South China: An example from the Dengfuxian–Xitian ore field

“…Zircon Eu anomalies are controlled mostly by the redox state of the magma and the crystallization history of plagioclase (Burnham & Berry, ; Kong et al, ). The relationship of Hf concentrations to Eu anomalies in zircons can be applied as an index of plagioclase crystallization, since high Hf concentrations are indicative of zircons generated from more evolved melts (Castiñeiras, Navidad, Casas, Liesa, & Carreras, ; Claiborne, Miller, & Wooden, ). In the present study, the generally negative correlation between Hf concentrations and Eu/Eu* values suggests that (1) Hf became depleted in zircons from sources with less plagioclase crystallization and (2) a change from higher Hf and lower Eu/Eu* in Triassic zircons to lower Hf and higher Eu/Eu* in Cretaceous zircons reflects a shift from greater magmatic to greater hydrothermal influence (Figure d).…”

Oxygen isotope and trace element geochemistry of zircons from porphyry copper system: Implications for Late Triassic metallogenesis within the Yidun Terrane, southeastern Tibetan Plateau

“…The negligible Eu anomalies present within the PDL zircons are consistent with hydrous parental melts, as evidenced by the presence of hydrous phenocryst phases such as amphibole and biotite within bulk rock samples, a factor that probably suppressed the early crystallization of plagioclase (Blatter and Carmichael, 1998;Moore and Carmichael, 1998;Müntener et al, 2001) and resulted in weak or absent Eu anomalies. Hafnium can be used to monitor magmatic differentiation, as higher Hf concentrations are indicative of zircons generated from more evolved melts from which the early crystallized zircons have already been removed (e.g., Claiborne et al, 2006Claiborne et al, , 2010Castiñeiras et al, 2011;du Bray et al, 2011). Comparing hafnium concentrations with Eu anomalies in zircons from the same sample can therefore be used as an index of plagioclase fractionation (Castiñeiras et al, 2011;du Bray et al, 2011).…”

“…Hafnium can be used to monitor magmatic differentiation, as higher Hf concentrations are indicative of zircons generated from more evolved melts from which the early crystallized zircons have already been removed (e.g., Claiborne et al, 2006Claiborne et al, , 2010Castiñeiras et al, 2011;du Bray et al, 2011). Comparing hafnium concentrations with Eu anomalies in zircons from the same sample can therefore be used as an index of plagioclase fractionation (Castiñeiras et al, 2011;du Bray et al, 2011). In the present study, the absence of negative correlation between zircon Eu/Eu* values and Hf concentrations suggests that the latter increased while only limited plagioclase fractionation from the parental magma of PDL zircons, which is in contrast with the negative correlation observed for the RL and XWC zircons (Fig.…”