Sedimentary basins provide a deep time archive of tectonic and Earth-surface processes that can be leveraged by detrital mineral U-Pb dating and geochemistry to track paleogeography, magmatism, and crustal evolution. Zircon preserves the long-term (billions of years) record of supercontinent cycles; however, it is biased toward preserving felsic crustal records. Detrital rutile complements the detrital zircon record by providing constraints on the time and temperature of rifting and mafic magmatism, metamorphism, exhumation of the middle and lower crust, subduction, and amagmatic orogenesis. We use detrital zircon U-Pb and detrital rutile U-Pb geochronology and trace element analysis of Permian to Eocene siliciclastic rocks in the southern Pyrenees to capture supercontinent cycles of ocean basins opening and closing. Detrital rutile age spectra show peaks at ca. 100 Ma associated with rifting and hyperextension in the Pyrenean realm, 200 Ma associated with the Central Atlantic Magmatic Province, and 330 Ma, 375 Ma, and 400 Ma associated with subduction and Rheic Ocean crust formation. Zr-in-rutile thermometry and rutile Cr-Nb systematics provide further insight into metamorphic facies (peak metamorphic temperatures) and source rock lithology (mafic versus felsic affinity). Detrital zircon age spectra have peaks at ca. 300 Ma, 450 Ma, and 600 Ma associated with major orogenic events and felsic magmatism, and Th/U ratios provide information on relative zircon formation temperatures. Comparison of these independent records shows that detrital rutile reflects rifting, magma-poor orogenesis, and oceanic lithospheric processes, while detrital zircon detects continental lithospheric processes. Integrated detrital zircon and rutile data sets archive past geological events across multiple Wilson cycles.

Zircon and rutile are stable heavy minerals and nearly ubiquitous in clastic sedimentary rocks. Detrital zircon (DZ) and detrital rutile (DR) are amenable to U-Pb geo- and thermochronology, with different Pb closure temperatures that reflect different geodynamic processes. Compilations of bedrock and DZ U-Pb ages constrain the long-term (billions of years) history of supercontinent formation, and generation and preservation of felsic crust (e.g., Condie et al., 2011). However, gaps in the zircon record correlate with times of supercontinent break-up, highlighting that zircon alone fails to capture the full scope of past geological events. Rutile has the potential to complement the DZ record by filling the gaps and preserving processes occurring during supercontinent break-up, including periods of rifting and mafic magmatism, metamorphism, exhumation of middle and lower crust, and amagmatic orogenesis (e.g., O'Sullivan et al., 2016).

We compare DZ U-Pb and DR U-Pb and trace element data from clastic sedimentary rocks in the southern Pyrenees to construct a more complete record of Iberian thermo-tectonic events over the past 850 m.y. The Pyrenees are the modern orogen between the Iberian microplate and Eurasian plate and have a well-studied and complex thermal and tectonic history that spans multiple Wilson cycles. The Pyrenean foreland basins provide a wealth of DZ U-Pb data (e.g., Whitchurch et al., 2011; Vacherat et al., 2017; Thomson et al., 2017; Odlum et al., 2019), as do the Alps foreland basins (Krippner and Bahlburg, 2013; Mark et al., 2016), which show that geologic events younger than ca. 275 Ma are not captured in the DZ record. This study highlights that DR U-Pb captures thermal and tectonic events that are underrepresented by DZ, including rifting and mafic magmatism, magma-poor hyperextension, and oceanic subduction. Integrating detrital U-Pb age information from DZ and DR has potential to elucidate geodynamic histories involving both continental and oceanic lithosphere preserved in the sedimentary record.

The Iberian-Pyrenean basement assemblages and associated basin strata contain a protracted thermal-tectonic history spanning the Pyrenean (Alpine), Pangean, and Gondwanan continental cycles. The Axial Zone is the structurally thickened core of the Pyrenees characterized by a south-vergent antiformal stack of thrust sheets composed of Neoproterozoic and Paleozoic metasedimentary rocks, Neoproterozoic to Ordovician metamorphic rocks, and Carboniferous granitic plutons (Fig. 1). Neoproterozoic to Ordovician metamorphic rocks reflect two main episodes of magmatism and subsequent metamorphism, including Ediacaran–early Cambrian magmatism between 580 and 540 Ma and Early Ordovician magmatism and metamorphism dated between 475 and 460 Ma, which are attributed to the final stages of the Cadomian orogen and transition to the opening of the Rheic Ocean (e.g., Castiñeiras et al., 2008; Guille et al., 2019; Javier Álvaro et al., 2020). The Neoproterozoic and Paleozoic metasedimentary units can be broadly divided into two groups: Neoproterozoic to Ordovician metasedimentary rocks whose protoliths were deposited in Cadomian back-arc basins, and Silurian to Carboniferous metasedimentary rocks that were deposited in passive margin to foreland basin settings. These units were intruded by dominantly felsic plutons during the Carboniferous that are dated between 298 and 315 Ma (e.g., Fernández-Suárez et al., 2000; Vacherat et al., 2017) and crop out in the Pyrenees Axial Zone, Ebro Massif, and Catalan Coastal Ranges (Fig. 1). The Permian–Triassic sedimentary strata are mostly nonmarine siliciclastic units overlain by Jurassic–Lower Cretaceous predominantly carbonate strata that were deposited in isolated rift basins.

In the French retrowedge, the North Pyrenean Zone is an inverted hyperextended rift system characterized by steep north-verging reverse faults, which exhumed Paleozoic basement massifs that have similar lithologies as the Axial Zone basement, and highly deformed and partially high-temperature low-pressure (HT-LP) metamorphic Mesozoic siliciclastic and carbonate strata (e.g., Lagabrielle et al., 2010). The Spanish prowedge South Pyrenean Zone is a south-verging thin-skinned fold-thrust belt that translated Upper Cretaceous to Eocene foreland basin deposits above a Triassic evaporitic décollement during the Late Cretaceous to Miocene Pyrenean orogeny (e.g., Muñoz, 1992; Puigdefàbregas et al., 1992; Vergés et al., 2002).

Fifteen medium-grained sandstone samples were collected from Permian to Eocene units in the southern Pyrenees (Fig. 1; File S1 in the Supplemental Material1). DZ and DR U-Pb and trace element analyses were performed by laser ablation–inductively coupled plasma–mass spectrometry (LA-ICP-MS) at the University of Texas at Austin following the approach of Odlum et al. (2019). Detailed methodology, data visualization, and geochronology and geochemistry data sets can be found in Files S1, S2, and S3 in the Supplemental Material.

Zircon is a high-refractory accessory mineral that most commonly forms in intermediate to felsic igneous assemblages and high-grade metamorphic rocks. Experimental data for diffusion of Pb in zircon indicate a closure temperature >900 °C, well above its crystallization temperature (Cherniak and Watson, 2001). The Th/U ratios in zircon can be used as a proxy for crystallization temperatures, where high Th/U indicates magmatic zircon and high crystallization temperatures, and low Th/U is indicative of metamorphic zircon growth and lower crystallization temperatures (Watson and Harrison, 1983).

Composite zircon U-Pb age distributions of the samples (Fig. 2A) are characterized by pre-Alpine ages with distributions that include a prominent 280–335 Ma component with an age peak at 304 Ma, subordinate components of 450–520 Ma and 530–675 Ma, and minor age populations of 350–375 Ma and 725–825 Ma. The Th/U values of zircon with Devonian to Permian U-Pb ages cluster between 0.25–0.75. The Th/U values of zircon >550 Ma are high and dispersed between 0–1.5, whereas zircon aged 450–500 Ma have lower and less-dispersed Th/U values between 0–0.5 (Fig. 2B).

Rutile predominantly forms in metamorphic rocks and has a Pb closure temperature between ~500–650 °C, making it sensitive to thermal processes in the middle to lower crust (Vry and Baker, 2006; Kooijman et al., 2010). Rutile trace elements retain information on source rock protolith and metamorphic conditions, including the Cr-Nb discrimination index to differentiate between metamafic and metafelsic protoliths (Triebold et al., 2012) and the Zr-in-rutile thermometer to determine peak metamorphic temperatures (e.g., Triebold et al., 2012; Kohn, 2020).

Rutile U-Pb ages and geochemistry from the compiled samples (Figs. 2C and 2D) exhibit major age components of: (1) 80–135 Ma with a peak at ca. 105 Ma with both mafic and felsic affinities and Zr-in-rutile temperatures 400–600 °C; (2) 180–240 Ma with a peak at ca. 200 Ma and a minor shoulder peak at ca. 220 Ma that have high Zr-in-rutile temperatures between 800–1000 °C from predominantly mafic lithologies; and (3) Paleozoic ages between 320–425 Ma with peaks at ca. 348–400 Ma with both mafic and felsic affinities and dominant Zr-in-rutile temperatures between 500–750 °C. Detrital rutile grains with Devonian to Ordovician U-Pb ages (375–450 Ma) display two clusters, with metamorphic temperatures clustered around 700–750 °C and around 500–600 °C. Minor age components include a broad distribution of 550–750 Ma grains with highly variable crystallization temperatures and predominantly felsic lithologies (Fig. 2D).

Our composite detrital data set is interpreted to show that integrating DZ and DR data provides a holistic record of thermal and tectonic processes along the Iberian margin during the Alpine (20–275 Ma), Pangean (275–525 Ma), and Gondwanan (525–725 Ma) continental cycles. The composite detrital data set demonstrates that DZ U-Pb data record felsic arc magmatism and/or metamorphism during ocean-continent subduction and orogenesis (e.g., Condie et al., 2011), whereas DR U-Pb data record rifting and mafic magmatism, middle to lower crustal exhumation, and subduction metamorphism.

The composite DZ age distribution is characterized by pre-Alpine (>275 Ma) ages. The 280–335 Ma and 350–375 Ma zircon age components with Th/U >0.1 reflect magmatism associated with the Variscan orogenic cycle (Fig. 2A). The Variscan cycle had three phases of magmatism, including an early phase of intermediate and mafic magmatism from 330–350 Ma (Gutiérrez-Alonso et al., 2018), synextensional collapse magmatism and intrusion of granitoids from ca. 315–325 Ma (e.g., Fernández-Suárez et al., 2000; Díez Fernández and Pereira, 2016), and postorogenic granitoids interpreted to be associated with lithospheric delamination from ca. 290–305 Ma (e.g., Fernández-Suárez et al., 2000; Gutiérrez-Alonso et al., 2011). The DZ ages capture the two latter felsic phases that were sourced from the granite plutons in the Axial Zone, Ebro Massif, and Catalan Coastal Ranges (Fig. 1).

The 530–580 Ma and 450–520 Ma DZ ages with increasing proportions of low-Th/U grains (and decreasing mean and median Th/U) across the Ediacaran into the Cambrian–Ordovician (Fig. 2C) reflect Andean-type continental magmatism that was driven by the subduction of the Iapetus oceanic crust below Gondwana during the Cadomian orogenic cycle (Stampfli et al., 2002; von Raumer et al., 2002). The broad DZ peak from 450–500 Ma records the Early Ordovician magmatic event that is recognized throughout the Pyrenees and Alps and may be related to back-arc rifting (Deloule et al., 2002; Cocherie et al., 2005). The 600–675 Ma DZ are derived from igneous and metamorphic rocks formed during the Pan-African orogeny in the core of Gondwana. The large scatter in DZ Th/U values indicates coeval felsic and mafic magmatism with a decrease in proportion of low-Th/U grains from Pan-African magmatism (600–700 Ma) to Rodinian break-up (725–850 Ma).

The composite DR age distribution has notable differences from the DZ age distribution, especially post-Variscan (<250 Ma) where there are age peaks associated with phases of Permian–Jurassic rifting (170–240 Ma) and Early Cretaceous rifting and HT-LP metamorphism (80–135 Ma). The 80–135 Ma DR record greenschist to amphibolite facies temperatures (400–600 °C) and have both felsic and mafic affinities. We interpret the ages of these grains to be cooling ages that record Early Cretaceous exhumation of greenschist to amphibolite grade metamorphic rocks of the North Pyrenean Zone, high-temperature synrift metamorphism, and potentially some minor preservation of mafic alkaline magmatism associated with rifting (Montigny et al., 1986). In the North Pyrenean Zone, bedrock samples and modern river sediment contain rutile and apatite U-Pb ages between 95–120 Ma recording Early Cretaceous exhumation (Capaldi et al., 2022). The 180–240 Ma DR have dominantly mafic affinities and >800 °C Zr-in-rutile temperatures (Fig. 2C) and are interpreted to record coeval HT metamorphism during Atlantic rifting (220 Ma peak) and Central Atlantic Magmatic Province (CAMP; 200 Ma peak) magmatism. CAMP intrusions in Iberia have been previously dated at ca. 200 Ma (e.g., Marzoli et al., 2018, and references therein), overlapping with the peak DR U-Pb ages.

The 325–390 Ma DR record closing of the Rheic Ocean through the subduction of Rheic oceanic lithosphere along the external edge of Gondwana (Arenas et al., 1995). The mafic 320–350 Ma DR are likely associated with the early Variscan phase of intermediate to mafic magmatism and metamorphism (Gutiérrez-Alonso et al., 2018), whereas the felsic 320–380 Ma rutile likely record lower-crustal metamorphism and exhumation during Variscan continental collision and HP metamorphism during subduction and exhumation of HP rocks beginning ca. 375 Ma (Paquette et al., 2017). The 390–425 Ma DR peak reflects Rheic Ocean opening, which initiated between 450 Ma and as young as 395 Ma (Nance et al., 2012), and coeval early subduction of oceanic crust beneath Iberia and associated arc magmatism. The record of ocean opening is reflected by a significant component of 390–425 Ma DR that have Zr-in-rutile temperatures >650 °C (Fig. 2D) and a lack of DZ U-Pb ages in this range (Fig. 2A), whereas the coeval early subduction of oceanic lithosphere is recorded by DR with overlapping ages but lower Zr-in-rutile temperatures of 500–550 °C interpreted as lower-temperature subduction metamorphic origin (Fig. 2D). The minor DR at 450–475 Ma record an Early Ordovician magmatic event that is recognized throughout the Pyrenees (Deloule et al., 2002; Cocherie et al., 2005) and likely record the intermediate to mafic phases of Ordovician back-arc magmatism and metamorphism. DR and DZ display similar detrital age distributions of 550–850 Ma that were initially derived from the igneous and metamorphic rocks formed during the Pan-African orogeny in the core of Gondwana and recycled out of amphibolite-eclogite grade (600–800 °C) metapelitic units within the present-day Axial Zone.

The detrital rutile record preserves evidence of events that are absent from the detrital zircon record. In the Pyrenean realm, these include ca. 100 Ma, 200 Ma, and 220 Ma rifting events that are associated with the break-up of Pangea and opening of the Atlantic Ocean and Bay of Biscay, as well as 450–390 Ma mafic rutile interpreted to reflect Rheic Ocean opening. The detrital zircon preserve evidence of felsic magmatism associated with arc magmatism and orogenesis that are mostly absent in detrital rutile age distributions, including the ca. 300 Ma Variscan magmatism, 450–525 Ma felsic Peri-Gondwanan–Cadomian magmatism, and 600–700 Ma Pan-African orogeny. Though the detrital rutile record captures much of the post-Variscan history of Iberia that is missed by detrital zircon, signatures of the Late Cretaceous to Miocene Pyrenean orogeny are not archived by zircon nor rutile U-Pb geo- and thermochronology because the orogeny was amagmatic and any rocks metamorphosed during this period have not been exhumed to the surface. The two complementary detrital records are more powerful together than in isolation and together can detect complete cycles of continental break-up and assembly, where detrital rutile records rifting and ocean opening while detrital zircon is sensitive to ocean closing and collision.

This manuscript benefited from scientific discussions with M. Roigé, A. Fildani, J. Clark, C. Puigdefàbregas, D. Barber, and F. Galster. We thank Robert Holder, Teresa Schwartz, and two anonymous reviewers for their thoughtful reviews that improved this manuscript, and Andrew Barth for editorial handling. Any use of trade, firm, or product names is for descriptive purposes only and does not imply endorsement by the U.S. Government.

1Supplemental Material. Detailed methods and U-Pb and TREE data tables. Please visit https://doi.org/10.1130/GEOL.S.25209425 to access the supplemental material; contact editing@geosociety.org with any questions.
Gold Open Access: This paper is published under the terms of the CC-BY license.