Provenance Evolution During Progressive Rifting and Hyperextension Using Bedrock and Detrital Zircon U-Pb GEOSPHERE; V

Research Paper THEMED ISSUE: Anatomy of Rifting: Tectonics and Magmatism in Continental Rifts, Oceanic Spreading Centers, and Transforms

GEOSPHERE Provenance evolution during progressive rifting and hyperextension using bedrock and detrital zircon U-Pb GEOSPHERE; v. 12, no. 4 geochronology, Mauléon Basin, western Pyrenees doi:10.1130/GES01273.1 Nicole R. Hart1, Daniel F. Stockli1, and Nicholas W. Hayman2 12 figures; 1 supplemental file 1Department of Geological Sciences, Jackson School of Geosciences, University of Texas at Austin, 2275 Speedway C9000, Austin, Texas 78712, USA 2Institute for Geophysics, Jackson School of Geosciences, University of Texas at Austin, 10100 Burnet Road, Austin, Texas 78712, USA

CORRESPONDENCE: hartnic4@utexas.edu ABSTRACT nental rifted margins and their transition to passive margins. For magma-poor CITATION: Hart, N.R., Stockli, D.F., and Hayman, margins in particular, the processes that occur during continental extension, N.W., 2016, Provenance evolution during progressive rifting and hyperextension using bedrock and The responses of sedimentary systems to rifting at continental margins break-up, and margin development have long been debated and modeled on detrital zircon U-Pb geochronology, Mauléon Basin, are three-dimensional and involve the mixing of various sediment sources the basis of observations from rifted margins such as the Iberia-Newfound- western Pyrenees: Geosphere, v. 12, no. 4, p. 1166– through tectonic drivers and sediment response. Such sedimentary responses land or northwest Australian margins, and exhumed fossil rifted margins 1186, doi:10.1130/GES01273.1. have not been well studied along magma-poor, hyperextended margins where such as in the eastern Alps, as well as numerical models (e.g., Froitzheim and the crust is stretched and thinned to ≤10 km. The asymmetric Mauléon Basin Eberli, 1990; Driscoll and Karner, 1998; Whitmarsh et al., 2001; Pérez-Gussinyé Received 24 September 2015 Revision received 22 April 2016 of the western Pyrenees is the product of such magma-poor hyperextension and Reston, 2001; Huismans and Beaumont, 2002; Lavier and Manatschal, Accepted 24 May 2016 resulting from lateral rift propagation from the Bay of Biscay during Cretaceous 2006; Osmundsen and Ebbing, 2008; Péron-Pinvidic and Manatschal, 2009; Published online 23 June 2016 time. After rifting, limited shortening during Cenozoic Pyrenean inversion up- Unternehr et al., 2010). These geological and numerical models have focused lifted the basin, resulting in preservation of outcrops of rift basin fill, upper and on the processes accommodating lithospheric break-up as well as structural lower crustal sections, serpentinized lithospheric mantle, and basic rift-fault evolution during progressive strain localization from diffusive rifting, crustal relationships. In this study ~5800 new zircon U-Pb ages were obtained from necking (extension and thinning that leads to a zone of crustal thinning from prerift, synrift, and postrift strata; the ages constrain the proximal to distal ~30 km to ≤10 km and an inflection point in the seismic Moho), hyperextension evolution of the Mauléon Basin and define a general model for sediment rout- (crustal thinning to ≤10 km), mantle exhumation, and eventual lithospheric ing during rifting. Zircon U-Pb analyses from lower crustal granulites indicate separation to seafloor spreading (Péron-Pinvidic and Manatschal, 2009; that granulite plutons crystallized at 279 ± 2 and 274 ± 2 Ma, and paragneissic Mohn et al., 2010). While this structural and geometric evolution has been granulites yielded zircon rim ages of ca. 295 Ma. Detrital zircon U-Pb ages from discussed (e.g., Whitmarsh et al., 2001), the spatial and temporal complexi- western Pyrenean prerift strata show age modes of ca. 615 and ca. 1000 Ma, ties of tectonically controlled sedimentation, such as the relative amounts of suggesting continual recycling and/or well-mixed Gondwanan-sourced sedi- mixing between proximal and distal sources, recycling between subbasins, ments throughout the Paleozoic and early Mesozoic; additional Paleozoic age spatial and temporal basin compartmentalization, and subbasin reintegration components (ca. 300 and ca. 480 Ma) are also observed. The variation of detri- during progressive rifting remain unknown. Such sedimentary routing vari- tal zircon U-Pb ages in synrift and postrift strata illustrates that during rifting, ations could have implications for stratigraphic models of basin evolution, provenance varied spatially and temporally, and sediment routing switched structural controls on subsidence, and the progressive geometric evolution from being regionally, to locally, and then back to regionally derived within of rifted margins. individual structurally controlled subbasins. Where preserved and exposed, hyperextended systems offer a window into the synrift and early postrift sedimentary records of rifted continental margins that are generally inaccessible due to their submarine locations and INTRODUCTION burial by thick passive margin sediments (e.g., Iberian-Newfoundland margin and the Gulf of Mexico). This has restricted tectonic sedimentation studies to Stratigraphy at rifted and passive continental margins is an important re- reflection and refraction seismic surveys and/or sparse boreholes that gener- corder of continental extension and breakup. The stratigraphic record can be ally do not penetrate the synrift sedimentary sections within the necking do- used to reconstruct the temporal variations in the interplay between exten- main or the distal rifted margin. In contrast, fossil rifted margins preserved in For permission to copy, contact Copyright sional tectonics and sedimentation, and to provide a more complete under- orogens offer the opportunity to explore and characterize the complexities of Permissions, GSA, or [email protected]. standing of the tectonic, climatic, thermal, and geomorphic evolution of conti- the tectonic and stratigraphic evolution of hyperextended margins. Such fossil

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margins, such as in the Eastern Alps, tend to be variably tectonized and over- Matte, 1986; Ziegler, 1990). Permian extension and orogenic collapse was fol- printed by later orogenic deformation, and often preserve only a fragmented lowed first by the northward propagation of North Atlantic rifting, resulting in synrift basin record (e.g., Masini et al., 2012). The Early Cretaceous Mauléon rift Jurassic to Early Cretaceous exhumation and marine incursion, and then later basin in the western Pyrenees is therefore noteworthy because it offers access by the initiation of Cretaceous rifting and seafloor spreading in the Bay of Bis- to a relatively complete synrift to postrift sedimentary record in a setting where cay (Jammes et al., 2009; Filleaudeau et al., 2011; Vacherat et al., 2014). While the postrift inversion and shortening-related structural and thermal overprint- diffuse extensional faulting has been suggested in the northern and southern ing seem to be relatively modest (e.g., Teixell, 1998; Lagabrielle and Bodinier, Pyrenees during Early Cretaceous time from 145 to 132 Ma, which may rep- 2008; Jammes et al., 2009; Masini et al., 2014; Tugend et al., 2014; Vacherat resent early stages of Cretaceous extension (Vergés and García-Senz, 2001; et al., 2014), making it an ideal locality for the reconstruction of synrift and Jammes et al., 2009; Vacherat et al., 2014), the future Mauléon Basin area was postrift sedimentation and for the understanding of rift-related basin evolution characterized by stable carbonate platforms with some evidence for limited at hyperextended rift margins. Early Cretaceous salt mobility. The onset of dramatic synrift subsidence, how- To better understand the evolution of the Mauléon Basin during rifting, we ever, clearly postdates the deposition of lower Aptian carbonates (Ducasse and apply a combination of bedrock and detrital zircon (DZ) U-Pb dating. DZ U-Pb Velasque, 1988; Canérot et al., 2001; Masini et al., 2014). analyses have evolved over the past decade into a powerful tool in process-ori- Continental extension in the Bay of Biscay, leading to break-up and sea- ented provenance analyses (e.g., Gehrels, 2014, and references therein) and floor spreading, propagated eastward and resulted in large-magnitude re- studies have employed these techniques to focus on source-to-sink problems gional crustal extension (~120%) in southwestern France and northern Spain, at passive margins and in intercontinental rifts (e.g., Cawood and Nemchin, local thinning of the crust to 0–10 km, and local exhumation of sublithospheric 2000; Lamminen and Köykkä, 2010; Craddock et al., 2013; Lamminen et al., mantle rocks (Lagabrielle and Bodinier, 2008; Jammes et al., 2009; Masini 2015); however, no systematic study has focused on a high-resolution interpre- et al., 2014). Such dramatic crustal thinning is now widely referred to as hyper tation of sedimentary provenance at hyperextended continental rifted margins extension (e.g., Sutra and Manatschal, 2012). One of these areas of western with the emphasis on source-to-sink changes during progressive rifting. This Pyrenean hyperextension is the Mauléon-Arzacq rift system, which is charac- study aims to fill this gap by presenting zircon U-Pb data from the western terized north to south by four separate domains. The northernmost domain Pyrenean tectonic hinterland and prerift strata, as well as a systematic detrital is the Arzacq Basin, where the European continental crust beneath the basin provenance analysis for synrift and postrift strata from the south Mauléon shows southward thinning, and the sedimentary sequences show southward subbasin (SMB) and north Mauléon subbasin (NMB). By defining the major thickening, approaching the hyperextended region (Teixell, 1990; Daignières DZ age components of Paleozoic to Mesozoic prerift strata, it is possible to et al., 1994; Biteau et al., 2006). To the south, the Grand Rieu high was a barrier fingerprint and deconvolve the DZ age distributions of basin-fill deposits and between the Arzacq Basin and the Mauléon Basin until the end of active hyper- reconstruct the lateral and temporal variations in sedimentation within and extension. The third domain is the Cretaceous Mauléon Basin (Fig. 1), which between structural domains and subbasins during rifting. Note that previous formed over hyperextended crust and can be subdivided into the NMB and studies have applied zircon dating to define geochronological and thermo- SMB. The Mauléon Basin is bounded by fault zones to the east and west, by chronological constraints for the development of the Pyrenees (e.g., Vacherat the Grand Rieu high to the north, and by the Axial domain (western equivalent et al., 2014), but many of these studies mainly focused on the evolution of of the Axial Zone of the central and eastern Pyrenees or the Pyrenean hinter- the central and eastern Pyrenees from extension to early continental conver- land) to the south. gence (e.g., Whitchurch et al., 2011; Filleaudeau et al., 2011; Mouthereau et al., 2014). In contrast, the data presented here serve to illuminate the spatial and temporal variations in sedimentation in the western Pyrenees during synrift Prerift and Synrift Stratigraphy and postrift time and provide constraints on sedimentary processes during progressive extension and rifting. The stratigraphy of the Mauléon Basin can be subdivided into two groups, western Pyrenean prerift strata and basin-fill strata (Fig. 2). The western Pyrenean prerift units include lower crustal granulite, Paleozoic metasedimen- GEOLOGIC BACKGROUND tary strata, and late Paleozoic to early Mesozoic sedimentary strata. The basin- fill units include synrift and postrift sedimentary basin deposits. The following Regional Geology is a brief description of these units; see Masini et al. (2014) and references therein for a detailed discussion of Mauléon Basin stratigraphy. Western Pyrenean moderate-grade metamorphic thrust sheets and lower Vielzeuf (1984) identified two lower crustal granulite units: the lower unit is amphibolite to granulite facies basement resulted from the collision of Gond- a metabasic granulite and the upper unit is a quartzofeldspathic metasedimen- wana and Baltica-Laurentia during the late Paleozoic Variscan orogeny (e.g., tary granulite with a Cambrian to Ordovician protolith (Boissonnas et al., 1974).

1°20′ W 1°10′ W 1°00′ W

13WPY06 12WPY13 12WPY54 12WPY11 12WPY10 12WPY55 13WPY07 12WPY56 43°20 ′

N 12WPY12 13WPY05 12WPY48 N 43°20 ′

12WPY44 12WPY43 12WPY57 12WPY42 12WPY18 12WPY41 12WPY08 12WPY47 12WPY46 12WPY45 12WPY49 12WPY58

12WPY07 Figure 1. Geologic map of the Mauléon 12WPY06 12WPY05 12WPY59 Basin in the western Pyrenees created from Bureau de Recherches Géologiques et Minières map sheets (1:50,000) of Iholdy, 12WPY01 12WPY19 St. Jean Pied de Port, Tardets-Sorholus, Espelette, Hasparren, Larrau and obser- 43°1 0 ′ N vations described by Masini et al. (2014). N 13WPY02 Zircon U-Pb sample locations are super- 12WPY30 imposed. Inset: Regional map of Europe; 43°10 ′ 12WPY31 12WPY32 the black box indicates the location of the study area. 13WPY01 12WPY36 13WPY04 12WPY38 12WPY33 12WPY35

12WPY27 12WPY26 12WPY28 12WPY25 12WPY24 12WPY21

12WPY23 12WPY20

Alluvium and Colluvium Jurassic Granulitic Basement south Mauléon detachment 1 : 50,000

Paleogene Triassic Sample locations north Mauléon detachment

Cretaceous Paleozoic France-Spain Border 0 2 4 6 8 10 km

Paleogene Pyrenean inversion Limestone, calcareous flysch, marl Postrift

Upper Limestone, calcarenite, marl Basin-fill Cretaceous Conglomerate, sandstone and shale Synrift Limestone and Spicula Marl Lower Limestone

Cretaceous Limestone and marl

Sandstone, shale, bauxite

Limestone and marl Jurassic

Late Paleozic Limestone to early Mesozoic Evaporite and shale strata Triassic Limestone and dolomite Figure 2. Simplified stratigraphic column of Conglomerate the western Pyrenees indicating sampled intervals, modified after Masini (2011). Col- Sandstone, silt, pelite ored rock units correspond to the colored Permian rock units in Figure 1. Conglomerate

Sandstone, silt, turbidite Carboniferous Limestone western Pyrenean prerift strata Devonian Sandstone, pelite Paleozoic Limestone metasedimentary Pelite Silurian strata Sandstone Conglomerate Cambrian Ordovician Sandstone and pelite

Gneiss Lower crustal Precambrian granulites Granulite pluton

Collected Sample Interval

Both of these units underwent granulite facies metamorphism during the Vari 1982; Jammes et al., 2009; Masini et al., 2014). Due to lack of exposure of the scan orogeny, with peak temperatures and pressures of 775 ± 50 °C and 6 ± stratigraphic record, Masini et al. (2014) noted that it is difficult to determine 0.5 kbar (Masini et al., 2014, and references therein). Reported biotite 40Ar/39Ar the timing of cessation of activity along the NMD. ages indicate that these strata had been exhumed to middle crustal depths of ~10 km by Late Triassic to Early Jurassic time (Masini et al., 2014). Stratigraphi Pyrenean Inversion cally above the granulites are lower Paleozoic sedimentary strata (Fig. 2) that underwent low-grade anchizonal to lower greenschist facies metamorphism Estimates of shortening that occurred in the west-central Pyrenees during during the Variscan orogeny (Heddebaut, 1973). Pyrenean orogenesis between Late Cretaceous and early Miocene time range The deformed and metamorphosed lower Paleozoic strata are overlain from ~75–165 km (~30%), on the basis of north-south balanced cross sec- by undeformed Permian conglomerate, sandstone, silt, and pelite. As is the tions, to ~180 km of total convergence from plate reconstructions (Teixell, case across much of central and western Europe, the Permian section is over- 1998; Beaumont et al., 2000; Rosenbaum et al., 2002; Mouthereau et al., 2014; lain by Buntsandstein, a group of Triassic continental deposits consisting of Teixell et al., 2016). This variability may stem from balanced cross-section as- shale, sandstone, and conglomerate (e.g., Germanic facies; Curnelle, 1983; sessments underestimating shortening by not taking into account the role of Fréchengues, 1993; Masini et al., 2014), which are in turn overlain by Late Tri- hyperextended domains at the early stages of convergence (Mouthereau et al., assic transgressive Muschelkalk platform carbonate, Keuper evaporites, and 2014). While the shortening values vary, balanced cross sections and surface a second carbonate platform (see Fig. 2). These deposits are cut by a major structure restorations show that the amount of shortening decreases from east erosional unconformity due to a Late Jurassic regression (Curnelle, 1983; to west across the Pyrenees (Seguret and Daignieres, 1986; Teixell, 1998). Fréchengues, 1993; Masini et al., 2014). The final prerift deposits are Barremian In the western Pyrenees, shortening caused the Mauléon Basin to be par- to lower Aptian carbonate and marl (Masini et al., 2014). tially inverted as a tectonic pop-up block. The North Pyrenean frontal thrust Mauléon Basin synrift deposition (Fig. 2) began with upper Aptian and system to the north of the Mauléon Basin and the Igountze-Mendibelza or Albian carbonate and marl (Masini et al., 2014). Toward the Axial domain, Lakora thrust to the south of the Mauléon Basin accommodated most of this these grade into Albian and Cenomanian delta-derived siliciclastic turbidite shortening as the basin was thrust northward over the former Grand Rieu high and conglomerate (Boirie and Souquet, 1982). These megasequences and and Arzacq domains and southward onto the Axial domain (Casteras, 1969; flysch were deposited concurrently and diachronously in the SMB and NMB Teixell, 1990, 1998; Muñoz, 1992; Daignières et al., 1994). Masini et al. (2014) as rifting occurred (Souquet et al., 1985; Masini et al., 2014). Postrift deposition noted that within the Mauléon Basin these thrust systems cut through the (Fig. 2) began during Cenomanian time as siliciclastic sedimentation ended basement while east of the basin the thrusts cut the sedimentary cover. They with another transgression that covered the Axial domain, which led to the suggested that this lateral change in structural level of thrusting may have deposition of platform carbonate in a calc-turbidite and hemipelagic system caused more of the deformation to be accommodated at a deeper crustal level (Masini et al., 2014). in the Mauléon Basin, allowing for greater preservation of prerift, synrift, and postrift structures as compared to the central and eastern Pyrenees. Formation of the Mauléon Basin

The opening of the SMB was accommodated by the south Mauléon de- ZIRCON U-Pb SAMPLING STRATEGY AND METHODOLOGY tachment (SMD), which exhumed upper crustal Paleozoic section, as shown in Figure 1 (Masini et al., 2014). From Albian to Cenomanian time, the Axial do- In this study we seek to systematically define the DZ U-Pb age distributions main and the Jara-Arbailles ridge were the southern and northern extents, re- of Paleozoic to Mesozoic prerift strata and thereby to fingerprint and decon- spectively, of the SMB (Boirie and Souquet, 1982; Souquet et al., 1985; Claude, volve the DZ U-Pb age distributions of basin-fill deposits, with the objective 1990; Masini et al., 2014). The current model envisions that from late Aptian of reconstructing the lateral and temporal variations in sedimentation within to early Albian time, progressive strain associated with crustal thinning was and between structural domains and subbasins during continental extension transferred from the SMD along a mid-crustal detachment to the lower crust of and rifting. To pursue this goal, samples were taken from various stratigraphic the Arzacq Basin, leading to an asymmetric rift geometry (Masini et al., 2014). intervals within the necking, hyperthinned, and exhumed mantle domains (as During mid-Albian time, the locus of extension shifted northward with the mapped by Tugend et al., 2014). Zircon was then separated from a total of 47 inception of the north Mauléon detachment (NMD), forming the NMB (Jammes samples: 30 Paleozoic and Mesozoic metasedimentary prerift samples, 2 felsic et al., 2009; Masini et al., 2014). The Jara-Arbailles ridge became a breakaway granulite samples from the Labourd Massif, and 15 sedimentary synrift and block separating the SMB and NMB (Fig. 1). On the basis of crosscutting rela- postrift samples from the Mauléon subbasins (Fig. 1). tions, the NMD was active during the deposition of the second megasequence Standard mineral separation techniques were applied, including crushing, and exhumed the already thinned lower crust and mantle (Boirie and Souquet, grinding, water table concentration, heavy-liquid density, and magnetic sus-

ceptibility separation techniques. Zircon separates were then sprinkled onto Western Pyrenees Prerift Strata Zircon U-Pb Results double-sided tape on 1 in (~2.54 cm) epoxy resin mounts, and at least 120 zircon grains were randomly chosen to be analyzed using laser ablation–induc We analyzed 32 samples to identify the western Pyrenean prerift strata sig- tively coupled plasma–mass spectrometry (LA-ICP-MS) U-Pb geochronology to natures and characterize the bedrock source terranes. These include 9 granu- obtain provenance data sets that resolve any age component >5% (Vermeesch, lite samples from the hyperthinned domain that yielded 1123 individual U-Pb 2004). The analyses were completed using a PhotonMachine Analyte G.2 ages (Figs. 1 and 3A). A total of 19 samples (15 Ordovician, 3 Devonian, and excimer laser with a large-volume Helex sample cell and a Thermo Element2 1 Carboniferous) from the Paleozoic metasedimentary units (metamorphosed ICP-MS. GJ1 was used as the primary reference standard (Jackson et al., 2004) during the Variscan orogeny) yielded 1843, 378, and 139 individual DZ U-Pb and Pak1 (in-house zircon standard, 42 Ma, from Pakistan) was used as second- ages, respectively (Figs. 1 and 4). A total of 4 samples (1 Permian and 3 Trias- ary reference standard. A 30 mm laser spot was used to ablate ~16 mm deep sic) from unmetamorphosed (post-Variscan) late Paleozoic to early Mesozoic pits on the flat prism plane of the nonpolished, tape-mounted zircons, provid- prerift strata yielded 117 and 368 individual DZ U-Pb ages, respectively (Figs. ing a depth profile of each analyzed grain. This technique enables the resolu- 1 and 4). These results are presented in stratigraphic order and displayed as tion of multiple zircon growth zones evident from core and rim ages (Stockli KDE plots (Figs. 3A and 4). The KDE plots for each individual sample (Fig. 4) and Stockli, 2013). The data from the analyses were then reduced using Iolite are combined into a single KDE to illustrate the DZ U-Pb signature for each data reduction software and VizualAge (Paton et al., 2011; Petrus and Kamber, stratigraphic interval (Fig. 5). 206 238 Mauléon Basin sample locations 2012). For increased precision the ages presented are Pb/ U ages for zircons 207 206 Sample Latude (N) Longitude (E) Elevaon (m) younger than 1200 Ma, and Pb/ Pb ages for zircons older than 1200 Ma 12WPY0143°12'19.8'' 01°19'38.1" 125 12WPY0543°13'50.0'' 01°18'06.7"113 (Gehrels et al., 2008). All ages reported use 2s absolute propagated uncertain- Lower Crustal Granulites 12WPY0643°13'04.8'' 01°19'24.6" 268 ties, 207Pb/206Pb ages are <30% discordant, and 206Pb/238U ages are <10% discor- 12WPY0743°13'32.5'' 01°15'20.4" 375 12WPY0843°18'08.7'' 01°14'25.5" 305 dant (Gehrels, 2011). The discordance reported is calculated with the 206Pb/238U Nine granulite samples from the Labourd Massif were analyzed to define 12WPY1043°21'11.9'' 01°20'11.8" 379 12WPY1143°21'36.9'' 01°19'30.8" 274 and 207Pb/235U ages if younger than 1200 Ma and the 206Pb/238U and 207Pb/206Pb the DZ signature of the lower crustal units exposed in the distal hyperthinned 12WPY1243°20'18.8'' 01°19'52.8" 430 12WPY1343°21'48.66" 01°17'32.33" 103 ages if older than 1200 Ma. Mineral separation and LA-ICP-MS analyses were domain of the NMB (Figs. 1 and 3A). The granulites of the Labourd Massif 12WPY1843°18'54.5'' 01°15'35.7" 203 12WPY19 43°11'59.4'' 01°17'30.7" 807 completed at the UTChron facilities at the Jackson School of Geosciences at can be subdivided in terms of their protolith composition into orthogneissic 12WPY2043°02'16.3'' 01°01'39.4" 1295 12WPY2143°02'24.3'' 01°01'39.2" 1363 the University of Texas at Austin. and paragneissic granulites. We obtained ~200 zircon U-Pb ages from ortho 12WPY2343°02'41.5'' 01°01'25.5" 1221 12WPY2443°03'04.4'' 01°00'55.9"1169 For the presentation and discussion of the detrital zircon U-Pb results, we gneissic granulite samples 12WPY08 and 12WPY48, which only display a 12WPY2543°03'31.1'' 01°01'08.3"1180 12WPY2643°04'08.0'' 01°01'19.8" 1035 adhere to the following terminology in accordance with common use in pub- single magmatic age mode (Fig. 3B); these samples yielded concordant U-Pb 12WPY2743°04'19.7'' 01°01'16.6"898 12WPY2843°04'20.5'' 01°01'12.0"900 lished literature (e.g., Davis et al., 2003; Vermeesch, 2004; Gehrels et al., 2008; ages of 279 ± 2 Ma and 274 ± 2 Ma, respectively (Fig. 3C). 12WPY3043°09'01.3'' 01°17'16.6" 373 12WPY3143°09'02.0'' 01°17'38.8" 467 Castiñeiras et al., 2008; Filleaudeau et al., 2011; Whitchurch et al., 2011; Malusà We obtained 923 U-Pb ages from 7 paragneissic granulite samples, which 12WPY3243°08'52.2'' 01°17'44.6" 538 et al., 2013; Mouthereau et al., 2014; Pullen et al., 2014). The entire spectrum of display multimodal DZ age distributions (Fig. 3B). All of these samples (except 12WPY3343°08'29.3'' 01°17'30.5" 744 12WPY3543°08'21.4'' 01°17'48.7" 806 U-Pb ages is referred to as an age distribution. Specific groups of age modes 12WPY12) show distinct zircon rim ages similar to the orthogneissic magmatic 12WPY3643°08'27.4'' 01°18'06.5"903 12WPY3843°07'56.2'' 01°19'06.3"902 for samples or stratigraphic intervals that reflect a particular provenance are zircons (Fig. 3D). These zircon overgrowth ages (n = 378) cluster ca. 295 Ma. 12WPY4143°17'28.2'' 01°17'31.9" 881 12WPY4243°17'41.1'' 01°17'28.9" 803 referred to as signatures, and the individual modes of the age distribution Given their paragneissic detrital nature, samples 12WPY12, 12WPY18, and 12WPY4343°17'51.6'' 01°17'47.8"596 12WPY4443°18'00.4'' 01°17'37.9" 534 are discussed as age components. 13WPY05 show significant DZ core ages that range from 778 to 453 Ma (n = 12WPY4543°15'26.2'' 01°19'09.3"96 12WPY4643°16'11.9'' 01°18'59.2" 416 325, 35% of all U-Pb ages obtained from these samples) with a distinct mode 12WPY4743°16'34.5'' 01°19'02.2" 316 12WPY4843°19'37.6'' 01°23'21.7"67 of ca. 590 Ma. In addition, sample 12WPY12 shows a significant secondary 12WPY49 43°15'20.4'' 01°15'38.1" 179 12WPY5443°20'55.6'' 01°14'15.3" 153 SAMPLES AND RESULTS DZ core age that ranges from 1071 to 806 Ma (n = 60, 7%) and has a mode of 12WPY5543°20'20.1'' 01°14'36.2" 466 12WPY5643°20'14.2'' 01°14'31.0" 466 ca. 955 Ma. 12WPY5743°18'27.6'' 01°00'33.2"64 All DZ U-Pb analyses are displayed as kernel density estimation plots (KDE; 12WPY5843°15'28.4'' 01°02'30.9" 100 12WPY59 43°12'49.8'' 01°07'55.1"199 Vermeesch, 2012) and tabulated in Supplemental File S11. The subsequent 13WPY0143°09'08.5'' 01°24'55.0" 1089 13WPY0243°09'13.2'' 01°24'33.8"952 presentation of the data focuses primarily on DZ U-Pb ages younger than Paleozoic Metasedimentary Strata 13WPY0443°07'44.9'' 01°19'41.6"939 13WPY0543°19'33.2'' 01°16'10.3" 212 1200 Ma because that is the age range where the most diagnostic variations in 13WPY0643°21'40.1'' 01°14'12.4" 178 13WPY0743°20'39.5'' 01°19'56.3" 666 ages are observed, and the aim of the bedrock DZ analyses is to identify age All 15 Ordovician samples were collected from greenschist to amphibo- components in each of the prerift strata to ultimately fingerprint the synrift lite facies metasedimentary rocks: 5 from Mount Monoa in the distal neck- 1Supplemental File S1. Excel file containing eight tabs and postrift strata. Residual DZ ages older than 1200 Ma, which make up only ing domain, 1 near the base of Mount Jara in the proximal hyperthinned do- that detail the Mauléon Basin sample location data ~15%–25% of the ages obtained, generally do not show distinct age variations main, 7 from Mount Baygoura in the hyperthinned domain, and 2 from Pic and the collected zircon U-Pb data. Please visit http:// dx.doi .org /10 .1130/GES01273 .S1 or the full-text article that would be useful in discerning differences in sedimentary provenance or de Garralda in the distal hyperthinned domain (Fig. 1). These samples exhibit on www.gsapubs.org to view the Supplemental File. routing between synrift and postrift basin samples. two distinct DZ U-Pb age components (Fig. 5), one ranging from 748 to 521 Ma

A 12WPY12 n=105 13WPY05 n=152 12WPY18 n=129 12WPY13 n=139 13WPY07 n=111 12WPY11 n=116 12WPY10 n=171 12WPY48 n=118 12WPY08 n=82 GRANULITES Ʃ n=1,123

0 400 800 1200 1600 2000 2400 2800 3200 3600 Age (Ma)

B 12WPY12 n=77 C 340 13WPY05 n=138 0.054 12WPY48 12WPY18 n=123 274.1 ± 2 Ma 320 12WPY13 n=130 0.050 13WPY07 n=107 MSWD = 12 12WPY11 n=111 300 12WPY10 n=166 U 0.046 Ʃ n=852 280 Figure 3. Zircon U-Pb results from para 23 8 / 0.042 gneiss and orthogneiss units. (A) Kernel

GNEISS 260 Pb density estimation (KDE) plots for all of RA 20 6 0.038 240 the analyzed granulite samples. Different PA colored curves represent each different 220 0.034 analyzed sample, and the number of grains data-point error ellipses are 2σ analyzed from each sample is indicated. 0.030 0.20 0.24 0.28 0.32 0.36 0.40 (B) KDE plots for each of the lower crustal 207Pb/235U granulite samples analyzed. Each sam- 12WPY48 n=117 ple is separated into one of two groups, 12WPY08 n=82 orthogneiss or paragneiss. Each group Ʃ n=199 0.054 340 12WPY08 shows the number of grains analyzed from 279.2 ± 2 Ma 320 each sample and the sum of grains ana- S 0.050 MSWD = 50 lyzed from each group. (C) Concordia plots 300 of the zircon U-Pb analyses for the two

U 0.046 280 orthogneissic granulites. MSWD—mean 23 8 / square of weighted deviates. (D) Zircon 0.042 260 Pb U-Pb rim and inherited core ages from ORTHOGNEIS 20 6 0.038 240 paragneissic lower crustal granulite samples, shown as kernel density estimation 220 0.034 plots. data-point error ellipses are 2σ 0.030 0 200 400 600 800 1000 1200 0.20 0.24 0.28 0.32 0.36 0.40 Age (Ma) 207Pb/235U

D Rims Ʃ n=191 Cores Ʃ n=165 GRANULITES GNEISSI C RA PA

0 200 400 600 800 1000 1200 Age (Ma)

12WPY01 n=126 13WPY01 n=118 12WPY19 n=124

Ʃ n=368 TRIASSIC

12WPY35 n=117 13WPY02 n=117 12WPY36 n=144

N 12WPY41 n=115 A

I 12WPY42 n=131 C

I 12WPY43 n=127

N V

A Ʃ n=634

O P TE LA

Figure 4. Detrital zircon U-Pb results from the western Pyrenean prerift strata shown 12WPY20 n=139 12WPY46 n=129

N 12WPY47 n=115 with kernel density estimation plots for A

I Ʃ n=244 each sample analyzed. The different col- C

I ored curves represent different analyzed V

O samples and the vertical gray bars indicate

D the depositional age of the unit as defined R

O by the Bureau de Recherches Géologiques et Minières (BRGM) geologic maps. Each unit shows the number of grains analyzed CARBONIFEROUS from each sample and the sum of grains MIDDLE analyzed from each stratigraphic interval. The Ordovician samples are separated into 13WPY04 n=127 12WPY05 n=128 Early, Middle, and Late Epochs as defined 12WPY38 n=126 12WPY31 n=124 by the BRGM geologic maps. Note: No 12WPY06 n=125 12WPY32 n=116 Silurian samples were analyzed.

Ʃ n=378 12WPY33 n=116

N A

I Ʃ n=484

O D Ʃ n=1,843 R 12WPY44 n=117 O 12WPY45 n=123 12WPY55 n=119

N 12WPY56 n=122

A I

EAR LY Ʃ n=481

R O

0 400 800 1200 1600 2000 2400 2800 3200 3600 0400 8001200160020002400280032003600 Age (Ma) Age (Ma)

Ʃ n=285 (n = 678 ages, 37%) with a mode of ca. 626 Ma and the second ranging from 1189 to 850 Ma (n = 480 ages, 26%) with a mode of ca. 994 Ma. Only one sample, 12WPY42 from Mount Baygoura, shows a significant deviation in DZ age spectrum from the other samples with an additional DZ age component that ranges from 497 to 423 Ma (n = 29 ages, <1%) with a mode of ca. 470 Ma

TRIASSIC (Fig. 4). Two Devonian samples were collected from greenschist to amphibolite facies metasedimentary strata, one from Mount Monoa in the distal necking domain and one near the base of Mount Jara in the proximal hyperthinned Ʃ n=88 domain (Fig. 1). Both samples yielded two distinct DZ age components (Fig. 5). One ranges from 731 to 525 Ma (n = 125 ages, 33%) and has a mode of ca.

675 Ma. The second ranges from 1187 to 846 Ma (n = 100 ages, 27%) and has

N A

I a mode of ca. 999 Ma. These samples also show a less prominent DZ age M

R component that ranges from 834 to 740 Ma (n = 38 ages, 10%), with a mode E P of ca. 768 Ma. The single Carboniferous sample was collected from a Namuro-West phalian greenschist facies metasedimentary rock in the proximal necking domain of Mendibelza (Fig. 1). This sample shows three distinct DZ age compo- Figure 5. Kernel density estima- Ʃ n=125 nents (Fig. 5). The first ranges from 364 to 267 Ma (n = 22 ages, 16%) and has a tion (KDE) plots of the zircon U-Pb signatures for each of the prerift mode of ca. 334 Ma, the second ranges from 509 to 399 Ma (n = 26 ages, 19%) S units analyzed; individual samples and has a mode of ca. 472 Ma, and the third ranges from 734 to 526 Ma (n = 49 from each unit are combined to ages, 35%) and has a mode of ca. 610 Ma. This sample also has two less promi show a single KDE unit signature. nent DZ age components. The first ranges from 847 to 767 Ma (n = 9 ages, 7%) The vertical gray bars indicate the depositional age of the unit as de- and has a mode of ca. 801 Ma. The second ranges from 1134 to 904 Ma (n = 19

CARBONIFEROU fined by the Bureau de Recherches ages, 14%) and has a mode of ca. 998 Ma. Géologiques et Minières geologic maps. Each unit shows the sum of grains analyzed from each strati- Ʃ n=270 graphic interval. Note: No Silurian Late Paleozoic to Early Mesozoic Prerift Strata samples were analyzed.

The single Permian sample was collected from sandstone interbedded

N A

I with conglomerate near the top of Mount Hautza (Fig. 1). This Permian sample N

O shows three distinct DZ age components, one ranging from 373 to 275 Ma (n =

V E

D 13 ages, 11%) with a mode of ca. 300 Ma, a second ranging from 727 to 531 Ma (n = 43 ages, 37%) with a mode of ca. 606 Ma, and a third ranging from 883 to 739 Ma (n = 19 ages, 16%) with a mode of ca. 780 Ma. This sample also has another less prominent DZ age component that ranges from 1027 to 940 Ma Ʃ n=1,370 (n = 11 ages, 9%) with a mode of ca. 1002 Ma (Fig. 5). Two Triassic samples were collected from sandstone, one near the base

and one near the top of Mount Jara, in the proximal hyperthinned domain.

N A

I A third sample was collected from sandstone near the top of Mount Hautza

C I

V (Fig. 1). These samples show one significant DZ age component (Fig. 5), which

O D

R ranges from 719 to 534 Ma (n = 168 ages, 46%) and has a mode of ca. 597 Ma. O These samples also display three minor DZ age components (Fig. 5). The first ranges from 388 to 263 Ma (n = 15 ages, 4%) and has a mode of ca. 328 Ma, the second ranges from 512 to 437 (n = 22 ages, 6%) and has a mode of ca. 0 200 400 600 800 1000 1200 475 Ma, and the third ranges from 1039 to 931 Ma (n = 39 ages, 13%) and has Age (Ma) a mode of ca. 948 Ma.

Detrital Zircon U-Pb Ages from the Proximal to Distal Mauléon Basin Hyperthinned to Exhumed Mantle Domain

We analyzed 15 samples from synrift and postrift strata across the Mauléon Seven samples from the NMB characterize the hyperthinned to exhumed Basin and its different rift domains to constrain the spatial and temporal varia- mantle domain (Fig. 1). These samples were collected from Albian to Ceno- tions in sediment provenance during continental extension and rifting. The DZ manian sedimentary rock near the Abarratia quarry (n = 2), Cenomanian to U-Pb results are presented from the proximal to distal domains of the Mauléon Turonian turbidite (n = 3) and sandstone (n = 1), and Coniacian to Santonian hyperextended region. All ages obtained are displayed in KDE plots (Fig. 6). conglomerate (n = 1). Similar to samples from the Mendibelza area and the SMB, DZ analysis indicates five main age components, as shown in Figure 7: Carboniferous–Permian (mode ca. 325 Ma, n = 195 ages, 23%), early Paleozoic Proximal Necking Domain (mode ca. 485 Ma, n = 90 ages, 11%), Cryogenian–Ediacaran (mode ca. 617 Ma, n = 259 ages, 31%); Tonian (mode ca. 776 Ma, n = 40 ages, 5%), and Stenian– Seven samples from the Mendibelza area characterize the synrift to postrift Tonian (mode ca. 980 Ma, n = 121 ages, 15%). stratigraphic evolution of the proximal necking domain (Fig. 1). These samples During Albian to Cenomanian time, the Carboniferous–Permian DZ age stratigraphically transition upsection from Albian Spicula Marls (n = 1) to Albian component (mode ca. 325 Ma) dramatically increased in abundance from to Cenomanian turbidite (n = 1), conglomerate (n = 4), and sandstone (n = 1). The ~34% to ~70%. In Cenomanian time, this DZ age component decreased to DZ analyses show five distinct age components (see Fig. 7 for graphical presen- ~15%, before it increased to ~29% during Turonian time, and finally decreased tation of the distributions): Carboniferous–Permian (mode ca. 311 Ma, n = 142 to ~4% during Coniacian to Santonian time. The early Paleozoic DZ age com- ages, 16%), early Paleozoic (mode ca. 469 Ma, n = 89 ages, 10%), Cryogenian– ponent (mode ca. 485 Ma) indicated a decrease in abundance from ~12% to Ediacaran (mode ca. 606 Ma, n = 326 ages, 37%), Tonian (mode ca. 801 Ma, n = ~7% during Albian to Cenomanian time, increased to ~21% during Ceno- 46 ages, 5%), and Stenian–Tonian (mode ca. 961 Ma, n = 128 ages, 15%). manian to Turonian time, and finally decreased to ~8% during Coniacian to In the proximal necking domain, DZ provenance signatures exhibit a sys- Santonian time. The Cryogenian–Ediacaran DZ age component (mode ca. tematic provenance shift from Albian through Cenomanian time (Fig. 7). The 617 Ma) decreased from ~35% to ~17% during Albian to Cenomanian time, Carboniferous–Permian DZ age component (mode ca. 311 Ma) increased in and increased to ~44% during Cenomanian time. During Turonian time this abundance from ~5% to ~37% with minor fluctuations and then decreased to DZ age component decreased again to ~30%, before it increased to ~51% ~30% in the stratigraphically highest sample (Fig. 7). Across the stratigraphic during Coniacian to Santonian time. The Tonian DZ age component (mode section, the early Paleozoic DZ age component (mode ca. 469 Ma) had a rela- ca. 776 Ma) abundance was consistently <~10%. The Stenian–Tonian DZ tively constant abundance (~7%) until it increased to ~24% toward the top of age component (mode ca. 980 Ma) decreased in abundance from ~12% the section. The Cryogenian–Ediacaran DZ age component (mode ca. 606 Ma) to ~4% during Albian to Cenomanian time, and later during Cenomanian showed the highest abundance of any of the age components but decreased time the abundance increased to ~27%. This DZ age component then de- in abundance from ~50% to ~33% upsection. The Tonian DZ age component creased during Cenomanian to Turonian time to ~14% and increased again to (mode ca. 801 Ma) was consistently the least abundant, remaining relatively ~33% during Coniacian to Santonian time. constant at <10%. The Stenian–Tonian DZ age component (mode ca. 961 Ma) showed a decrease in abundance from 27% to <10% with minor fluctuations. Overall the samples from the Mendibelza area indicate a general increased DISCUSSION amount of younger zircon ages and a decrease in the older zircon ages upsection through the Albian to Cenomanian stratigraphy. Through comparing the prerift DZ U-Pb signatures with the synrift and postrift DZ age distributions, we are able to interpret and reconstruct the basin sedimentary evolution during progressive rifting. These findings are Distal Necking Domain then used to construct a basin evolution model for hyperextended rift margins. In order to do this, DZ U-Pb age components are separated into those Due to limited exposure and preservation of the SMB, only one sample was that are diagnostic and those that are nondiagnostic in defining the prove- collected and analyzed from sandstone at the base of Mount Monoa. This sam- nance signature of the samples. Diagnostic DZ age components are defined ple characterizes synrift deposition in the distal necking domain (Fig. 1). Here as those that were not found in all of the analyzed samples and therefore can there are only three main DZ age components (Fig. 7): Cryogenian–Ediacaran help to distinguish between stratigraphic units. In contrast, nondiagnostic (mode ca. 645 Ma, n = 48 ages, 40%), Tonian (mode ca. 786 Ma, n = 11 ages, DZ age components are defined as those that are present in all of the prerift 9%), and Stenian–Tonian (mode ca. 995 Ma, n = 23 ages, 19%). intervals.

Mendibelza south Mauléon subbasin north Mauléon subbasin

12WPY21P n=122 N 12WPY07 n=98

O C

12WPY23 n=118 12WPY49 n=132

TURONIAN

TO TO

12WPY24P n=118 12WPY58P n=115 CENOMANIAN CENOMANIAN

N Figure 6. Detrital zircon U-Pb results from A

I 12WPY25P n=117 12WPY59P n=108

N synrift and postrift strata with kernel A

M density estimation plots for each of the O

N detrital samples analyzed. Each curve E

C represents one sample, and the number O

T of grains analyzed from each sample is

N noted. The curves are separated into three

A I

B groups based on their location: Mendi- L A belza, south Mauléon subbasin, and north

12WPY26 n=129 12WPY57 n=124 Mauléon subbasin.

E C

12WPY27 n=128 12WPY54 n=118

12WPY28 n=139 12WPY30P n=120 13WPY06P n=145

L A

TO CENOMANIA N

L A

0 1200 2400 3600 0 1200 2400 3600 0 1200 2400 3600 Age (Ma) Age (Ma) Age (Ma)

Necking domainHyperthinned to exhumed mantle domain Mendibelza south Mauléon subbasin north Mauléon subbasin 8% 4% 12WPY21 n=100 4% 12WPY07 n=76 8% 30% 33% 34% 51% 24% 4%

5% 12WPY23 n=110 1% 12WPY49 n=117 4% 15% 29% 33% 37% 30% 24% 22%

12WPY24 n=103 12WPY58 n=107 4% 14% 23% 18% 15% 9% 7% 21% Figure 7. Proximal to distal comparison of 43% 46% detrital zircon U-Pb age components using kernel density estimation plots for each of the detrital samples analyzed. The three 12WPY25 n=89 12WPY59 n=80 locations, Mendibelza, south Mauléon 17% 14% 18% 27% 8% subbasin, and north Mauléon subbasin, 10% 6% represent the proximal necking domain 10% to distal hyperthinned and exhumed 49% 41% mantle domain. Each curve represents one sample and the age distributions are sepa 12WPY26 n=103 12WPY57 n=99 rated into five age components. The per- 18% 20% 22% 15% cent of ages in each component is shown SYNRIFT TO LATE POSTRIFT SYNRIFT TO EARLY POSTRIFT 7% in the pie chart to the right of each curve. 6% 6% 11% 50% 45%

8% 2%4% 12WPY27 n=110 7% 12WPY54 n=111 23% 17% 9% 7% 53% 70%

5% 2% 12WPY28 n=116 12WPY30 n=91 13WPY06 n=116 12% 8% 7% 9% 25% 27% 34% 8% 12% 51% 53% 35%

SYNRIFT 12%

0 400 800 1200 0 400 800 1200 0 400 800 1200 Age (Ma) Age (Ma) Age (Ma)

Definition of Bedrock Zircon U-Pb Provenance Signatures cled into Paleozoic metasedimentary and prerift sedimentary units, producing these common provenance signatures. Although the age range and mode exhibit some minor variations between While these nondiagnostic DZ age components are inadequate when charac- samples and between stratigraphic intervals, all of the prerift samples share terizing differences between prerift strata, they illustrate a signature that is vital nondiagnostic age components of ca. 615 Ma, ca. 780 Ma, and ca. 1000 Ma, in determining the provenance of the prerift units. This DZ signature is similar predominantly the ca. 615 Ma and ca. 1000 Ma components (Fig. 5). Thus, we to those that are found in Ediacaran to Carboniferous age deposits throughout suggest that zircons with these nondiagnostic DZ ages were continually recy- parts of Iberia (Fernández-Suárez et al., 2002; Bea et al., 2010; Fernández-Suárez

0.5 Triassic Permian 12WPY48 Carboniferous 0.4 Devonian Ordovician Granulite 12WPY08 Paragneiss 0.3 Orthogneiss

Figure 8. Multidimensional scaling (MDS) 0.2 plot of western Pyrenean prerift strata 12WPY38 12WPY32 detrital zircon data. Plot shows the com- 12WPY46 12WPY31 parison of bedrock families that are high- 12WPY44 12WPY45 lighted by different colors. *12WPY12 0.1 12WPY47 12WPY06 plots significantly different than the gran- 12WPY41 12WPY36 12WPY56 13WPY04 ulite family and may not actually be a 12WPY05 granulite sample. 12WPY43 12WPY55 12WPY33 12WPY35 0 12WPY12* 13WPY02 12WPY13 12WPY01 12WPY10 13WPY01 12WPY42 13WPY07 –0.1 12WPY19 12WPY20

13WPY05 –0.2 12WPY18 –0.2 0 0.2 0.4 0.6 0.8

et al., 2013; Gutiérrez-Alonso et al., 2015). Zircon grains corresponding to this 1994). In the paragneissic granulites the DZ age of ca. 295 Ma represents a zir- signature likely originated from the East African orogen, northern Egypt, and the con rim age (Fig. 3B). Given that all but one paragneiss sample contained this Sinai Peninsula, and thus Iberia, and consequently the western Pyrenees, were zircon rim age, it is clear that granulite facies metamorphism was widespread much closer to eastern Gondwana than previously expected (Fernández-Suárez throughout the Labourd Massif during the Variscan orogeny. et al., 2002, 2013; Bea et al., 2010; Gutiérrez-Alonso et al., 2015). The paragneissic granulites yielded two separate trends in terms of inherited zircon core ages. The first trend is observed in the paragneiss sample that Lower Crustal Granulites does not display the ca. 295 Ma rim age, 12WPY12 (Fig. 3B). This sample has significant ca. 480 Ma, ca. 600 Ma, and ca. 955 Ma age components, which are The key diagnostic DZ ages collected from the orthogneissic and para similar to the DZ ages found in the Ordovician samples (Fig. 5). This implies that gneissic granulites from the Labourd Massif are ca. 274, ca. 279 Ma, and ca. the protolith for this paragneiss sample may have been deposited during Ordo- 295 Ma (Fig. 3). For the orthogneissic granulites, this magmatic component vician time and later underwent metamorphism during the Variscan orogeny. dates early to middle Permian zircon crystallization, which is within the 304 The other six paragneiss samples in Figure 3B show a less abundant ca. 615 Ma to 266 Ma age range, and more specifically resulted from a magmatic event DZ age component and are lacking the ca. 1000 Ma DZ age component. It is ranging from 276 to 266 Ma, established elsewhere by Pereira et al. (2014) on possible that the U-Pb depth profiling approach might not have penetrated all the basis of zircon U-Pb analyses from the southern Pyrenees. These plutons of the inherited cores, leading to a decrease in the abundance of these inherited are therefore related to Variscan magmatism; similar early to middle Permian zircon core ages. Alternatively, the protoliths of these six samples may not have magmatic events are also preserved in the southern, western, and northern been derived from Ordovician, but rather from Cambrian units (Boissonnas Pyrenees. In addition, the ages of the orthogneissic granulites are similar to et al., 1974). Fernández-Suárez et al. (2013) noted that there is a general a lack the defined age (278 Ma) of felsic lavas from the Ossau massif (Innocent et al., of the ca. 1000 Ma DZ age component in some Cambrian age units in north-

ern Iberia, and because no Cambrian samples were analyzed from the western stead, the source terrane must have contained nondiagnostic DZ age com- Pyrenean prerift strata, it is possible that the Cambrian samples in this area ponents, such as in the Ordovician and Devonian strata. The ca. 300 Ma age may also lack this ca. 1000 Ma DZ age component; additional analysis from component is the only diagnostic component in this unit (Fig. 5). These zircons Cambrian samples from the western Pyrenees would be needed to verify this. are interpreted to be derived from late Variscan volcanic rocks, which crop out in the southern Pyrenees (Lago et al., 2004, and references therein). Paleozoic Metasedimentary Strata One of the diagnostic aspects of the Triassic samples is the significant decrease in abundance of ca. 300 Ma and ca. 330 Ma DZ age components Most of the samples from Ordovician and Devonian metasedimentary observed in Permian and Carboniferous units, respectively. This indicates units show little variation in the DZ signature between samples and all dis- minimal recycling of these units into the Triassic units (Fig. 5). The second play two (nondiagnostic) age components of ca. 625 Ma and ca. 1000 Ma; only diagnostic DZ age component is a minor ca. 475 Ma age component that is one Ordovician metasedimentary sample shows a diagnostic DZ age compo- only found in the Carboniferous and Ordovician units, which may indicate mini nent with an age mode of ca. 470 Ma (Fig. 4). These zircons are interpreted to mal recycling from these units as well. be from magmatism that occurred during the transition from the Cadomian orogeny to the Variscan orogeny (Deloule et al., 2002; Cocherie et al., 2005; Western Pyrenees Prerift Strata Multidimensional Scaling Castiñeiras et al., 2008; Denèle et al., 2009; Gutiérrez-Alonso et al., 2015). Expo- sures of these igneous bodies can currently be found in the eastern Axial zone All of the western Pyrenean prerift samples were plotted using a standard and also north of the North Pyrenean fault (Whitchurch et al., 2011; Filleaudeau statistical technique, multidimensional scaling (MDS), to highlight provenance et al., 2011; Mouthereau et al., 2014). trends during prerift time (Vermeesch, 2013). The resulting MDS plot can be Many of the same nondiagnostic DZ age components (ca. 610 Ma, ca. separated into two patterns. The first is illustrated by granulite samples that 800 Ma, ca. 1000 Ma) are present in the Carboniferous units, likely due to the trend nearly perpendicular to the other prerift samples (Fig. 8). In addition, recycling of sediments during the Variscan orogeny. These units also display the paragneissic granulites plot closer to the other prerift samples; the para two diagnostic DZ age components. The first, one of the most abundant, has gneissic samples share inherited DZ core ages similar to age components an age mode of ca. 472 Ma. The only other unit bearing this DZ age component found in the other prerift strata. The second pattern shows nearly identical is a single sample from the Ordovician metasedimentary unit (Fig. 4). One pos- Ordovician and Devonian bedrock families that evolve in a diagonally linear sible explanation for these grains being deposited in the Carboniferous unit trend to Carboniferous, Permian, and Triassic bedrock families, and nearly would be exhumation of Ordovician units, with this age component, during the intersect the paragneissic granulites (Fig. 8). This linear trend observed in Variscan orogeny and recycling of these grains into Carboniferous units. The Paleozoic to early Mesozoic prerift strata does not represent a significant shift second diagnostic DZ age component has an age mode of ca. 330 Ma (Fig. 5), in detrital provenance, but simply reflects the addition of younger detrital U-Pb which is likely associated with synorogenic Variscan magmatism between 350 age components in progressively younger stratigraphic intervals. and 315 Ma (Schaltegger et al., 1996; Castro et al., 2002; Gutiérrez-Alonso et al., 2011). If these zircons are magmatic, the similarity in the age mode (ca. 330 Ma) Mauléon Basin Evolution from the Proximal to Distal Margin and the depositional age of the unit (326–304 Ma) could possibly indicate rapid denudation during late Carboniferous time. Alternatively, this similarity could With the signatures of the western Pyrenean prerift strata characterized, indicate that these zircons are volcanic in origin, but late Variscan volcanism it is now possible to use the diagnostic DZ age components from the prerift appears to be sparse until the latest Carboniferous time and only well docu- units to interpret the Mauléon Basin DZ data. The significant variations in the mented for Permian time (Bixel, 1988; Innocent et al., 1994; Pereira et al., 2014). DZ signatures of synrift and postrift sedimentary rocks from the proximal neck- By the end of Carboniferous time the Variscan orogeny had come to an apex ing domain to the exhumed mantle domain of the NMB and SMB are used in the western Pyrenees with magmatism as well as the low-grade anchizonal to determine the synrift to postrift basin evolution. We discuss the data from to lower greenschist facies metamorphism of Ordovician–Carboniferous strata proximal to distal in the following. (Heddebaut, 1973). The Mendibelza transect crosses the Albian to Cenomanian proximal necking domain and the synrift to postrift deposits exhibit a classic unroofing se- Late Paleozoic to Early Mesozoic Prerift Strata quence (Fig. 7). Due to the presence of significant ca. 600 Ma and ca. 960 Ma, and lack of ca. 300 Ma DZ age components in the stratigraphically lowest While the Permian sample shares many of the same nondiagnostic charac- Albian synrift samples, the source terrane for these samples is likely Paleozoic teristics with the Carboniferous sample (ca. 606 Ma, ca. 780 Ma, ca. 1002 Ma), to early Mesozoic strata such as Ordovician, Devonian, and/or Triassic units it completely lacks the ca. 472 Ma DZ age component, which indicates that (Figs. 5 and 7). Upsection, these samples show a significant increase in abun- the Carboniferous units were not recycled into Permian units (Fig. 5); in- dance of Carboniferous–Permian detrital zircons as the Cryogenian–Ediacaran

and Stenian–Tonian detrital zircons generally decrease in abundance (Figs. 7 hyperextension, the SMB was either isolated and disconnected from the and 9). This upsection variation in basin deposits as rifting progressed during Mendibelza basin, strongly implying locally sourced fault-controlled subbasins Albian to Cenomanian time can be accounted for by the addition of a source (SMB was sourced from the metamorphosed Paleozoic units exposed in the terrane with ample ca. 300 Ma zircons, while the Paleozoic source terrane be- immediate footwall of the SMD), or the subbasins were not isolated, indicating came buried or depleted. In the proximal and necking domains, only Variscan that sediments eroded from Axial domain plutons would have accumulated in plutons that are present throughout the Pyrenean Axial Zone in the central Albian–Cenomanian strata in the NMB (Mendibelza and the SMB would show and eastern Pyrenees have been dated as ca. 300 Ma (e.g., Denèle et al., 2014). distinct provenance signatures due to significant sediment bypassing). Therefore, Carboniferous–Permian detrital zircons in Albian to Cenomanian de- The NMB is located within the hyperthinned to exhumed mantle domain posits in the Mendibelza area may have originated from similar Variscan-aged that is characterized by synrift and postrift sedimentation from Albian to Conia- plutons that continued west from the Axial Zone into the Axial domain of the cian–Santonian time (Fig. 7). Similar to the Mendibelza transect, these samples western Pyrenees, but are no longer exposed or have been completely eroded. show a progressive tectonic unroofing sequence (Figs. 7 and 9). During Albian This implies that from Albian to Cenomanian time, during the evolution from extension, Carboniferous–Permian (ca. 300 Ma) detrital zircons dominated the synrift to postrift, the proximal necking domain may have been sourced re- DZ signature of the NMB, but appear to be absent in the intervening SMB. Un- gionally from Axial domain Variscan plutons rather than locally from Paleozoic less early synrift sediment routing completely bypassed the SMB, it appears to early Mesozoic strata. that ca. 300 Ma Variscan-aged detrital zircons from Mendibelza and the NMB Due to limited exposure and preservation of the SMB or distal necking were derived from different sources in Albian time (Figs. 7 and 9). Consequently, domain, only one Albian sample was collected and analyzed from the SMD this requires an additional, non–Axial Zone–derived ca. 300 Ma DZ source in hanging wall in Irouleguy Valley (Fig. 7). While SMB sediments were deposited the NMB. During early hyperextension, NMB strata were deposited in immedi- synchronously with Albian deposits from the Mendibelza transect, the sample ate proximity of fault-bound lower crustal granulites of the Labourd Massif; it from the SMB lacks Carboniferous–Permian detrital zircons that are prevalent is therefore likely that ca. 300 Ma detrital zircons from the NMB were derived throughout the Mendibelza transect (Fig. 7). This suggests that during Albian from these granulites as they were exhumed during Albian to Cenomanian

north Mauléon subbasin: Mendibelza: Necking domain

N Hyperthinned to exhumed mantle domain

A S

N 12WPY07

O C 12WPY49

Figure 9. Synrift to postrift detrital zircon

TURONIAN 12WPY58 spatial and temporal age component variations. The percentages in each age com- 12WPY21 ponent shown in Figure 7 are plotted on 12WPY59 the x-axis. Each sample is arranged on the 12WPY23 y-axis to display the upsection evolution for the synrift and postrift deposits and

CENOMANIAN 12WPY24 compare temporal and spatial variations 12WPY57 of the Mendibelza and north Mauléon 12WPY25 subbasin samples.

12WPY26 12WPY54 12WPY27 13WPY06

ALBIAN 12WPY28 0102030405060708090 100 0102030405060708090 100 Grains within agebins(%) Grains within age bins (%)

time. The MDS analysis of the samples from the NMB (Fig. 10) shows that In the NMB, the abundance of the granulite-derived zircons dramatically the stratigraphically lowest sample (13WPY04) plots between the bedrock and decreased from a maximum of 70% to 15% in Cenomanian to early Turonian granulites trends and then clearly evolves into the granulite field (12WPY54), synrift to postrift strata (Figs. 7 and 9). The MDS plot also indicated that by indicating a potential unroofing sequence and that sample 12WPY54 is likely Cenomanian time the subbasins became increasingly integrated, because derived directly from granulites. This trend is significantly different than 12WPY57 and 12WPY59 from the NMB are not distinguishable from Mendi- Albian–Cenomanian samples from Mendibelza (12WPY24–12WPY28) that are belza samples 12WPY24–12WPY28, and therefore have identical provenance generally clustered on the MDS plot (Fig. 10). While 13WPY04 is not as clearly (Fig. 10). These samples evolve in a linear fashion that represents a mixing differentiated from the Mendibelza samples on the MDS plot as 12WPY54, the line between Paleozoic strata and ca. 300 Ma Variscan metamorphosed strata rim KDE plot (Fig. 11) clearly indicates that 13WPY04 lacks the multimodal rim and granulite plutons. As rifting progressed, fault-bound granulites of the age distribution that is present in Albian to Cenomanian Mendibelza samples, distal hyperextended margin were buried and no longer contributed detritus indicating that 13WPY04 and the Mendibelza samples were likely derived from to fault-controlled subbasins, which became increasingly sourced from a different source. Instead, 13WPY04 shows rim and core distributions that Ordovician, Devonian, and/or Triassic units that are characterized by Cryo- are more similar to the rim and core distributions from the Labourd Massif genian–Ediacaran detrital zircons (Figs. 5 and 7). As the basin continued to granulites. While trace element analyses could be used in the future to fur- fill, the input from the Axial domain increased and the Mendibelza samples ther characterize the similarities and differences between sedimentary strata (12WPY21 and 12WPY23) and the NMB samples (12WPY58 and 12WPY49) at Mendibelza, SMB, NMB, and granulites, the differences illustrated through evolved similarly, again indicating similar provenance (Fig. 10). In the NMB, MDS and core and rim age analyses strongly suggest that the ca. 300 Ma DZ the Carboniferous–Permian DZ age component increased again to ~30% in age component in the NMB is significantly different from Mendibelza, and was late Turonian time, indicating that sediments may have been increasingly likely derived from the granulitic basement of the underlying distal rift margin regionally sourced from the Axial domain Variscan plutons in the hinterland rather than from sediment bypass and Variscan plutons in the Axial domain. (Figs. 7 and 9).

0.2

0.1

12WPY07 12WPY59 0 12WPY30 12WPY57 12WPY28 12WPY25 Figure 10. Multidimensional scaling (MDS) 12WPY26 plot of the Cretaceous detrital zircon data, 12WPY24 comparing the south Mauléon subbasin, north Mauléon subbasin (NMB), and –0.1 12WPY27 13WPY06 Mendibelza. The smaller colored arrows show the upsection progression through 12WPY54 time. The general trends from Mendibelza 12WPY58 12WPY49 and the NMB sections are indicated by Mendibelza large colored arrows. –0.2 south Mauléon subbasin Cretaceous 12WPY21 north Mauléon subbasin Triassic Devonian 12WPY23 –0.3 Ordovician Granulite Paragneiss

–0.2 0 0.2 0.4 0.6

Rims Ʃ n=45 Rims Ʃ n=23 Cores Ʃ n=44 Cores Ʃ n=20 NMB ALBIAN-CENOMANIAN

MENDIBELZA ALBIAN-CENOMANIAN Figure 11. Comparison of kernel density 0 200 400 600 800 1000 1200 0 200 400 600 800 1000 1200 estimation plots from zircon U-Pb rim and Age (Ma) Age (Ma) inherited core ages from lower crustal granulites, Mendibelza Albian–Cenomanian Rims Ʃ n=191 samples (12WPY24–12WPY28), and north Cores Ʃ n=165 Mauléon subbasin (NMB) Albian–Ceno- manian sample (13WPY04). GRANULITES

0 200 400 600 800 1000 1200 Age (Ma)

The stratigraphically highest samples from the proximal Mendibelza (late Hyperextended Margin Sediment Dispersal Model Cenomanian) and the distal NMB (Coniacian–Santonian) exhibited a marked decrease in ca. 300 Ma detrital zircons, by 7% and 25%, respectively (Fig. 7 and These new constraints on the stratigraphic and sedimentary provenance 9). This abrupt change appears to signal a diachronous shift in postrift prove- evolution of the Mauléon Basin can be integrated with models for the de- nance across the hyperextended rift margin and is characterized by decreased velopment of magma-poor hyperextended continental margin structural Carboniferous–Permian detrital zircons and increased contribution of Paleozoic domains to reconstruct the evolution and architecture of the region. The DZ to Mesozoic prerift-related detrital zircons from Ordovician, Devonian, and/or U-Pb signatures of Paleozoic and Mesozoic strata deposited prior to Creta- Triassic strata (Figs. 5 and 7). This marked shift in postrift provenance could ceous extension documented continual recycling of metasedimentary rocks potentially be explained by the formation of salt-walled basins during Ceno- of Gondwanan affinity. While the timing of diffuse and protracted extension manian time, such as the Chaînons bérnais (e.g., Canérot, 1989; Jammes et al., is difficult to determine, the DZ U-Pb signatures indicated a dominance of re- 2009). Alternatively, late Santonian inversion tectonics could have triggered gional sourcing through Triassic time without any major provenance shifts or this provenance switch due to promotion of axial drainage along the northern significant fault-controlled local sourcing. During strain localization and the Pyrenees (e.g., Rosenbaum et al., 2002; Vissers and Meijer, 2012; Metcalf et al., progressive onset of crustal necking, sedimentary provenance underwent 2009; López-Mir et al., 2014). Whitchurch et al. (2011) pointed to regional oro- an abrupt transition to locally derived sediment within individual structurally gen-parallel, axial sediment routing from east to west during initial orogenesis controlled subbasins and an upsection transition back to regional hinterland- in the south-central Pyrenees from Late Cretaceous to Paleogene time. If the derived sedimentation in the proximal necking domain. In the Mauléon Basin western Pyrenees were affected by this initial orogenesis, it is possible that the this is apparent in the proximal necking domain of the Mendibelza area, where Mauléon Basin area could have been affected by similar orogen-parallel east- Albian early synrift sediments were derived locally from Paleozoic to early west sediment routing, providing sediments potentially recycled from early Mesozoic strata, with increasing input of regionally sourced sediments derived Paleozoic strata and deposited into Late Cretaceous strata. from Variscan plutons of the Axial domain of the western Pyrenean hinterland

(Fig. 12, gray arrow). As strain continued to localize and the necking and hyper- crustal necking begins an abrupt change occurs. At this stage of rifting, the thinned domains developed, sedimentation in fault-controlled subbasins was proximal and distal parts of the margin are isolated from hinterland sedimen- locally sourced from adjacent exhumed footwall units and appeared to be iso- tary supply and become locally sourced. During the progression from synrift lated from hinterland-derived sediment supply. This effect manifested in the to postrift, the proximal margin has an increase in hinterland sedimentary sup- distal necking domain in the SMB in the sourcing of Albian units from meta- ply, and as the subbasins fill-and-spill they become reintegrated as the margin morphosed Paleozoic units from the immediate footwall of the SMD and, in the transitions to a passive continental margin (Nottvedt et al., 1995; Anderson hyperthinned domain of the NMB, by local sourcing of Albian to Cenomanian et al., 2000; Mohn et al., 2010; Masini et al., 2013). strata from exhumed granulite facies lower crust (Fig. 12, white arrows). As rifting progressed, these distal, isolated subbasins were filled by progressively more regionally sourced synrift and postrift sediments until these subbasins CONCLUSIONS became reintegrated and hinterland-derived sediments spilled into the distal necking domain, and eventually the hyperthinned and exhumed mantle do- The Mauléon Basin offers a unique opportunity to apply DZ U-Pb prove- mains. This fill-and-spill integration of subbasins occurred throughout the nance techniques to an exhumed, fossil, magma-poor, hyperextended margin diachronous evolution of the Mendibelza area and the NMB as illustrated by to gain insight into the interplay between tectonics and sedimentation during Albian to Cenomanian deposits in the Mendibelza area that were isolated and the progression of rifting. New bedrock U-Pb age data from lower crustal gran- did not reach the distal hyperextended domain of the NMB until Cenomanian ulites from the Labourd Massif in the western Pyrenees indicate that the ortho to Turonian time (Fig. 12, black arrows). On the basis of provenance data, it is gneissic granulite plutons crystallized at 279 ± 2 Ma and 274 ± 2 Ma during late not possible to differentiate late synrift from postrift strata, because the transi- Variscan magmatism. Paragneissic granulites yielded zircon rim ages of ca. tion was gradual and not abrupt. During late synrift to postrift sedimentation, 295 Ma that indicated widespread Variscan granulite facies metamorphism of provenance returned to a regionally sourced, hinterland-dominated sediment the Labourd Massif. Inherited zircon core ages from these paragneissic granu- supply until the region became influenced by subsequent events. lites point to a Cambrian or Ordovician aged metasedimentary protolith. The generalities of this sediment dispersal model from the western DZ U-Pb signatures of the western Pyrenees prerift Paleozoic and Mesozoic Pyrenees give insight into observations that are transferable to other hyper strata indicate a Gondwanan signature, typical for Precambrian to Paleozoic extended basins. The model indicates that during the early stages of rifting, strata from Iberia, that was likely sourced from the East Africa orogen, northern while extension is diffuse, there is little to no change in provenance, but once Egypt, and the Sinai Peninsula of Gondwana. The western Pyrenean Paleozoic

Axial Domain Mendibelza south Maulééon subbasin north Maul on subbasin

Postrift Variscan Pluton Prerift Synrift Figure 12. Simplified two-dimensional model of hyperextended margin sediment dispersal developed on the basis of zircon Upper continental crust U-Pb analyses from the Mauléon Basin. Granulite facies White arrows indicate locally sourced syn- lower crust rift deposits. The gray arrow indicated late synrift to postrift regionally derived deposits. The black arrow represents regionally derived units deposited diachronously Middle continental crust across the basin.

Subcontinental mantle Lower continental crust

Proximal domain Necking domain Hyperthinned to exhumed mantle domain

and Mesozoic prerift strata all exhibit common age components with modes of Beaumont, C., Muñoz, J.A., Hamilton, J., and Fullsack, P., 2000, Factors controlling the Alpine evo- ca. 615 Ma, ca. 780 Ma, and ca. 1000 Ma, suggesting either continual recycling lution of the central Pyrenees inferred from a comparison of observations and geodynamical models: Journal of Geophysical Research, v. 105, p. 8121–8145, doi:10 .1029 /1999JB900390 . and/or a supply of well-mixed Gondwanan-sourced zircons throughout the Biteau, J.J., Le Marrec, A., Le Vot, M., and Masset, J.M., 2006, The Aquitaine Basin: Petroleum Paleozoic and early Mesozoic. Ordovician, Carboniferous, and Permian strata Geoscience, v. 12, p. 247–273, doi:10.1144/1354-079305-674. also contain major diagnostic DZ U-Pb age components that differentiate their Bixel, F., 1988, Le volcanisme stéphano-permien des Pyrénées Atlantiques: Bulletin des Centres de Recherches Exploration-Production Elf-Aquitaine, v. 12, p. 661–706. unit signatures, with age modes of ca. 300 Ma in Carboniferous and Permian Boirie, J., and Souquet, P., 1982, Les Poudingues de Mendibelza: dépôts de cônes sous-marins strata and ca. 480 Ma in Ordovician and Carboniferous strata, which are inter- du rift albien des Pyrénées: Bulletin des Centres de Recherches Exploration-Production preted to be related to Variscan and Cadomian magmatism, respectively. Elf-Aquitaine, v. 6, p. 405–435. Boissonnas, J., Destombes, J., Heddebaut, C., Le Pochat, G., Lorsignol, S., Roger, P., and Ternet, DZ U-Pb analyses have confirmed a diachronous multibasin rifting evolu- Y., 1974, Feuille d’Iholdy: Bureau de Recherches Géologiques et Minières, scale 1:50,000. tion of the Mauléon-Arzacq rift system in the western Pyrenees, and provided Canérot, J., 1989, Early Cretaceous rifting and salt tectonics on the Iberian margin of the western a general model for sediment dispersal processes at hyperextended continen- Pyrenees (France). Structural consequences: Bulletin Technique Exploration-Production Elf tal margins. DZ provenance analyses of synrift and postrift sedimentary rocks Aquitaine, v. 13, p. 87–99. 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During the late synrift to postrift time, the proximal margin (SHRIMP) for Cadomian and Early Ordovician magmatism in the Eastern Pyrenees: New had an increase in hinterland sedimentary supply, and as the subbasins filled insights into the pre-Variscan evolution of the northern Gondwana margin: Tectonophysics, v. 461, p. 228–239, doi:10.1016/j.tecto.2008.04.005. and spilled, they became reintegrated and the hinterland sediments reached Castro, A., Corretgé, L., De La Rosa, J., Enrique, P., Martínez, F., Pascual, E., Lago, M., Arranz, E., the distal hyperthinned and exhumed mantle domains. At that point, sedi- Galé, C., and Fernández, C., 2002, Palaeozoic magmatism, in Gibbons, W., and Moreno, T., mentation returned to a regionally sourced hinterland drainage system until eds., The geology of Spain: London, Geological Society of London, p. 117–153. the region became influenced by subsequent events. In addition, tracking the Cawood, P.A., and Nemchin, A.A., 2000, Provenance record of a rift basin: U/Pb ages of detrital zircons from the Perth Basin, Western Australia: Sedimentary Geology, v. 134, p. 209–234, presence of the ca. 300 Ma age component spatially and temporally across doi:10.1016/S0037-0738(00)00044-0. the basin in synrift and postrift strata showed that the lower crustal granulites Claude, C., 1990, Etude stratigraphique, sédimentologique et structurale des dépôts méso- were exhumed during Albian to Cenomanian time. This is a key constraint in zoïques au Nord du massif du Labourd. Rôle de la faille de Pamplona (Pays Basque) [Ph.D. thesis]: Pessac, France, Université de Bordeaux III, 437 p. defining the activity along the NMD, as the detachment must have been active Cocherie, A., Baudin, T., Autran, A., Guerrot, C., Fanning, C.M., and Laumonier, B., 2005, U-Pb and the hyperthinned domain must have been formed prior to these granulites zircon (ID-TIMS and SHRIMP) evidence for the Early Ordovician intrusion of metagranites being exhumed. in the late Proterozoic Canaveilles Group of the Pyrenees and the Montagne Noire (France): Bulletin de la Société Géologique de France, v. 176, p. 269–282, doi:10.2113 /176 .3 .269. Craddock, J.P., Konstantinou, A., Vervoort, J.D., Wirth, K.R., Davidson, C., Finley-Blasi, L., Juda, N.A., and Walker, E., 2013, Detrital Zircon Provenance of the Mesoproterozoic Midcontinent ACKNOWLEDGMENTS Rift, Lake Superior Region, U.S: The Journal of Geology, v. 121, p. 57–73, doi:10 .1086 /668635 . This project was financially supported by American Association of Petroleum Geologists Foun- Curnelle, R., 1983, Evolution structuro-sédimentaire du Trias et de l’Infra-Lias d’Aquitaine: Bulle- dation Arthur A. Meyerhoff Memorial Grants-In-Aid, a Jackson School of Geosciences off-cam- tin des Centres de Recherches Exploration-Production Elf-Aquitaine, v. 7, p. 69–99. pus research award, and Petrobras. We thank Emily Cooperdock, Gavin Wagoner, and Jacqueline Daignières, M., Seguret, M., Specht, M., and ECORS Team, 1994, The Arzacq-Western Pyrenees Reber for their assistance in the field, and Lisa Stockli and Spencer Seman for their assistance ECORS deep seismic profile, in Hydrocarbon and petroleum geology of France: European with data acquisition, data reduction, and interpretation. We also acknowledge invaluable insights Association of Petroleum Geoscientists Special Publication 4, p. 199–208, doi:10 .1007 /978-3 and discussions with Luc Lavier, Edgardo Pujols-Vazquez, Anna Eliza Svartman Dias, Gianreto -642-78849-9_15. Manatschal, Victor Hugo, Emmanuel Masini, Suzon Jammes, and Antonio Teixell. We thank Davis, D.W., Williams, I.S., and Krogh, T.E., 2003, Historical development of zircon geochronol- one anonymous reviewer and M.E. Bickford and F. Mouthereau, editor S. de Silva, and associate ogy: Reviews in Mineralogy and Geochemistry v. 53, p. 145–181, doi:10 .2113 /0530145 . editor Derek Keir for their thorough and thoughtful comments that clarified and improved the Deloule, E., Alexandrov, P., Cheilletz, A., Laumonier, B., and Barbey, P., 2002, In-situ U-Pb zircon manuscript. ages for Early Ordovician magmatism in the eastern Pyrenees, France: The Canigou ortho gneisses: International Journal of Earth Sciences, v. 91, p. 398–405, doi:10 .1007 /s00531-001 -0232-0. 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