Thermochronological Evidence of Early Orogenesis, Eastern Pyrenees, France

Abstract

In collisional orogens, distinguishing the thermal signature of early orogenesis from the preceding rift or from subsequent thermal events is a major challenge. We present an integrated geological and low‐temperature thermochronology study of the Paleozoic Agly‐Salvezines crustal block in the retrowedge of the eastern Pyrenees (France). The northern Pyrenees preserves one of the best geological records of a rift‐to‐collision transition. The Agly‐Salvezines block represents the inverted distal European margin of an Aptian–Cenomanian rift system. Seventeen samples were collected throughout the external orogenic massif and analyzed for low‐temperature thermochronology: zircon (U‐Th)/He dating documents the cooling history of the massif during the initiation and early phase of Pyrenean convergence, while apatite (U‐Th)/He dating completes the record of plate collision. Using inverse and forward modeling of new low‐temperature thermochronology data, we show that the Pyrenean retrowedge records two clear phases of orogenic cooling, Late Campanian–Maastrichtian and Ypresian–Bartonian, which we relate to early inversion of the distal rifted margin and main collision, respectively. An earlier, late Aptian–Turonian cooling history is detected, possibly related to rifting and/or postrift. No cooling is evidenced during the Paleocene during which tectonic quiescence is recorded in the adjacent Aquitaine retroforeland basin. Using our low‐temperature thermochronology data and geological constraints, we propose a crustal‐scale sequentially restored model for the tectonic and thermal transition from extension to peak orogenesis in the eastern Pyrenees, which suggests that both thrusting and underplating processes contributed to early inversion of the Aptian–Cenomanian rift system.

Thermotectonic Evolution of the North Pyrenean Agly Massif During Early Cretaceous Hyperextension Using Multi‐mineral U‐Pb Thermochronometry

“…The formation of concave‐up, lithospheric‐scale “exhumation faults” marks the onset of crustal separation, eventual mantle exhumation, and possible oceanic breakup (e.g., Lavier & Manatschal, ; Manatschal, ; Masini et al, ; Péron‐Pinvidic et al, ; Reston & McDermott, ; Tugend et al, ). The mechanical coupling of the two structural units (upper crust pluton and middle‐lower crust high‐grade gneisses) is supported by the shared thermal histories of the two units beginning in the Albian recorded by zircon and apatite (U‐Th)/He analysis and thermal modeling (Ternois et al, ).…”

“…Furthermore, the eastern NPZ has been proposed as an example of a “hot paleomargin” with ductile crustal boundinage (Clerc et al, ; Clerc, Lahfid, et al, ; Vauchez, Clerc, et al, ). Apatite U‐Pb data along with zircon (U‐Th)/He data (Odlum & Stockli, ; Ternois et al, ) demonstrate that the lower‐ and upper‐crustal basement gneisses and granites had rapidly cooled to <<450 °C by the early Albian and were subsequently never reheated to >300 °C. The exposed gneisses and granites had cooled below the brittle‐ductile transition by the early Albian and could not have undergone ductile crustal‐scale boudinage after the early Albian.…”

Formation of the Iberian‐European Convergent Plate Boundary Fault and Its Effect on Intraplate Deformation in Central Europe

“…Sequentially restored cross sections indicate that the NPFB developed in front of basement blocks that were inverting along rift‐inherited normal faults (Figure c; Ford et al, ; Grool et al, ; Rougier et al, ). The Late Cretaceous inversion of basement blocks is recorded by zircon fission track ages and zircon (U‐Th)/He ages recording exhumation related cooling of the basement blocks around ~80–65 and ~75–60 Ma, respectively (Figure c; Ternois et al, ; Yelland, ).…”

“…Modified after Ford et al (). Zircon fission track ages (ZFT) and Zircon (U‐Th)/He ages from Yelland () and Ternois et al (), respectively.…”

Innovations in (U–Th)/He, Fission Track, and Trapped Charge Thermochronometry with Applications to Earthquakes, Weathering, Surface‐Mantle Connections, and the Growth and Decay of Mountains

“…FT and (U–Th)/He data can be acquired on crystals previously analyzed for U–Pb geochronology, aided by analytical advances of laser ablation and noble gas mass spectrometry analyses. This approach includes “double” U–Pb and FT or He analysis of apatite or zircon (Campbell et al, ; Carter & Moss, ; Fosdick et al, ; Lease, Haeussler, & O'Sullivan, ; Odlum & Stockli, ; Rahl et al, ; Reiners et al, ; Ternois et al, ; Thomson et al, ) or U–Pb, FT, and (U–Th)/He “triple” dating (e.g., Carrapa et al, ; Danišík, ; Danišík et al, ). Integration of data from two or more thermochronometric systems with different temperature sensitivities in the same mineral permits a more detailed reconstruction of the thermal history in these settings.…”