Decoupling of zircon U–Pb and trace-element systematics driven by U diffusion in eclogite-facies zircon (Monviso meta-ophiolite, W. Alps)

Dating Continental Subduction Beneath the Samail Ophiolite: Garnet, Zircon, and Rutile Petrochronology of the As Sifah Eclogites, NE Oman

“…Mafic eclogite zircons with similar morphologies and sector zoningand in similar rocks and tectonic settingsgenerally give punctuated dates (<1 Myr) representing discrete fluid pulses [e.g., Rubatto and Hermann, 2003;Rubatto and Angiboust, 2015;Garber et al, 2020b]. Further, the single-population zircon U-Pb TIMS date from Warren et al [2003] on the same zircons (that is within uncertainty of our average LA-ICPMS date) further suggests that the zircons do form a single age population.…”

“…Alternatively, the amount of garnet may not have been sufficient to deplete the whole‐rock HREE budget by the time zircon crystallized, or the zircon may have grown during an initial phase of exhumation‐related garnet breakdown immediately postdating garnet growth. However, it is as likely that the REE did not entirely achieve chemical equilibrium during zircon (re)crystallization, which has frequently been observed in other high‐ P altered zircons that retain a trace‐element “memory” of their precursors, even in the presence of garnet (Chen et al., 2010; Štípská et al., 2016; Garber, Smye, et al., 2020). We therefore suggest that—such as those in the eclogites—the metafelsite zircons record (re)crystallization during the growth of the peak metamorphic assemblage (garnet‐phengite‐quartz), which slightly preceded garnet and zircon (re)crystallization in the eclogites.…”

“…Rutile U‐Pb systematics from the mafic eclogites are also disturbed (Figures 8a–8c; see below), and it is difficult to conceive of continuous, protracted precipitation of individual sector‐zoned zircons from a metamorphic fluid over ∼10 My (as the entire range in date is observed within single crystals). Mafic eclogite zircons with similar morphologies and sector zoning—and in similar rocks and tectonic settings—generally give punctuated dates (<1 Myr) representing discrete fluid pulses (e.g., Rubatto & Hermann, 2003; Rubatto & Angiboust, 2015; Garber, Smye, et al., 2020). Furthermore, the single‐population zircon U‐Pb TIMS date from Warren et al.…”

Protracted Subduction of the European Hyperextended Margin Revealed by Rutile U‐Pb Geochronology Across the Dora‐Maira Massif (Western Alps)

“…The Monviso complex is interpreted to be a former oceanic core complex in a slow‐spreading ocean (Festa et al., 2015; Lagabrielle & Cannat, 1990). Its main unit (Lago Superiore unit), just above the Dora‐Maira complex, was metamorphosed at 2.7 GPa and 580°C (Angiboust et al., 2011, 2012; Groppo & Castelli, 2010; Locatelli et al., 2018); it reached its peak between 53 and 45 Ma (Duchêne et al., 1997; Garber et al., 2020; Monié & Philippot, 1989; Rubatto & Angiboust, 2015; Rubatto & Hermann, 2003) and was retrogressed at lower crustal depths at 42–36 Ma (Angiboust & Glodny, 2020; Cliff et al., 1998). The timing of peak metamorphism of the overlying Monviso unit, metamorphosed at 2.2 GPa and 490°C (Angiboust et al., 2012; Schwartz, Lardeaux, Guillot, & Tricart, 2000) is unknown, but retrogression occurred at the same time as in the Lago Superiore unit (Angiboust & Glodny, 2020).…”

Along-dip variations of subduction fluids: The 30–80 km depth traverse of the Schistes Lustrés complex (Queyras-Monviso, W. Alps)

“…After peak burial between 62 and 55 Ma for LPU and LPM (Agard et al, 2002) and around 50-45 Ma for the Monviso LPL (Rubatto and Hermann, 2003;Rubatto and Angiboust, 2015;Garber et al, 2020), the four units of the Queyras-Monviso transect were exhumed from late Eocene to Miocene times (Schwartz et al, 2007(Schwartz et al, , 2020Angiboust and Glodny, 2020)…”