Thermochronology in Orogenic Systems

Hodges, Kip

doi:10.1016/b978-0-08-095975-7.00308-9

Cited by 30 publications

(33 citation statements)

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“…However, the oldest single zircon cooling age and oldest cooling component in each sample increase in age upsection (Figure ). This trend in the old DZ (U‐Th)/He age components is opposite of the expected trend for a classic unroofing sequence, where it is expected that all cooling ages will get younger as unroofing taps deeper structural levels [ Garver et al , ; Hodges , ; Reiners and Brandon , ]. Two hypotheses can be invoked to describe this trend, a provenance shift in the non‐Pyrenean source region tapping catchments with progressively older cooling histories, or a reverse unroofing [ Colombo , ; Garver et al , ] sequence in which the sediments are unroofed from shallow sedimentary basins containing unreset zircons resulting in an inversion of the upsection unroofing signature in the original sedimentary basin.…”

Section: Discussionmentioning

confidence: 99%

Detrital zircon (U‐Th)/(He‐Pb) double‐dating constraints on provenance and foreland basin evolution of the Ainsa Basin, south‐central Pyrenees, Spain

Thomson

Stöckli

Clark³

et al. 2017

Tectonics

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South central Pyrenean foreland basin fill preserves the eroded remnants of the early stages of fold‐thrust belt evolution and topographic growth. Specifically, the Eocene Hecho Group in the Ainsa Basin contains a succession of turbiditic channels and levees deposited in the transition zone between the fluvial‐deltaic and deep marine depozones. Detailed isotopic provenance analyses allow for the reconstruction of sediment sources of the ancient sediment routing systems. This study presents 2332 new detrital zircon (DZ) U‐Pb ages and 246 new DZ double‐dated (U‐Th)/(He‐Pb) ages from 19 turbiditic and fluvio‐deltatic sandstones in the Ainsa Basin. These data indicate a progressive provenance shift from Cadomian/Caledonian plutonic and metamorphic rocks of the eastern Pyrenees to Variscan plutonic rocks in the central Pyrenees. Minor sediment contributions from sources located to the S and SE of the basin are seen throughout the section. New DZ (U‐Th)/He results identify four main cooling events: Pyrenean orogenesis (~56 Ma), initial basin inversion (~80 Ma), Cretaceous rifting (~100 Ma), and pre‐Mesozoic cooling ages related to earlier tectonic phases. This study imposes new constraints on the paleogeographic evolution of the Pyrenees and illustrates that high‐frequency fluctuations in sediment delivery processes and sediment routing introduce superimposed noise upon the basin‐scale long‐term provenance evolution during orogenesis.

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Section: Discussionmentioning

confidence: 99%

Detrital zircon (U‐Th)/(He‐Pb) double‐dating constraints on provenance and foreland basin evolution of the Ainsa Basin, south‐central Pyrenees, Spain

Thomson

Stöckli

Clark³

et al. 2017

Tectonics

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“…Continental collision exerts a first‐order control on the evolution of mountain belts and orogenic plateaus; it affects the rate and style of mass wasting and the topography that ultimately influences local and regional climate (Hodges, and references therein). Deeply buried continental terranes now exposed in the core of mountain belts provide a unique opportunity to investigate and constrain the timescales involved in continental burial and exhumation and the ( U ) HP metamorphism that occurs in the interim (e.g., Kylander‐Clark et al, ).…”

Section: Introductionmentioning

confidence: 99%

Two‐Stage Cooling and Exhumation of Deeply Subducted Continents

et al. 2019

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The burial and exhumation of continental crust during collisional orogeny exert a strong control on the dynamics of mountain belts and plateaus. Constraining the rates and style of exhumation of deeply buried crust has proven difficult due to complexities in the local geology and thermochronometric methods typically used. To advance this field, we applied trace-element and U-Pb laser ablation inductively coupled plasma mass spectrometry analyses to rutile from eclogite and amphibolite samples from the Western Gneiss Complex of Norway-an archetypal continental (ultra)high-pressure (UHP) terrane. Peak temperature and timing of midcrustal cooling were constrained for samples collected along a subduction-and exhumation-parallel transect, using Zr-in-rutile thermometry and U-Pb rutile geochronology, respectively. Peak temperatures decrease from 830°C in the UHP domain to 730°C at the UHP-HP transition, remain constant at 730°C across most of the terrane, and decrease to 620°C at the eclogite-out boundary. U-Pb results show that most of the terrane cooled through 500°C at 380-375 Ma except for the lowest grade region, where cooling occurred approximately 20 million years earlier. The results indicate that exhumation was a two stage process, involving (1) flexural rebound and slab flattening at depth combined with foreland-directed extrusion, followed by (2) synchronous cooling below 500°C across the, by then, largely flat-lying Western Gneiss Complex. The latter implies and requires relatively homogeneous mass removal across a large area, consistent with erosion of an overlying orogenic plateau. The Caledonides were at near-equatorial latitudes at the time. A Caledonian paleo-plateau thus may represent a so far unrecognized factor in Devonian and Carboniferous atmospheric circulation and climate forcing.

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“…4). We assumed that the effective closure of a mineral-isotopic system is a volume diffusion process, governed by effective diffusion dimension and chemical composition (McDougall and Harrison 1988;Watson and Baxter 2007;Baxter 2010;Hodges 2014). Although studies suggest that fast diffusion pathways can complicate the geometry and rate of diffusion in minerals (Lee 1995), the effective diffusion dimension of mica crystals empirically appears to be similar to the physical grain size (Hames and Bowring 1994).…”

Section: Methodsmentioning

confidence: 99%

“…Such ranges are often interpreted in terms of a protracted cooling history, assuming reasonable closure temperatures for mineral-isotopic systems (e.g., Cliff 1985;Heaman and Parrish 1991;Hodges 1991Hodges , 2014Baxter 2010). However, studies of the mechanisms by which radiogenic isotopes are lost from mineral systems (e.g., Lee 1995) suggest that assigning an exact closure temperature to any particular mineral sample is not entirely straightforward (Watson and Baxter 2007).…”

Section: Introductionmentioning

confidence: 99%

Geological significance of ⁴⁰Ar/³⁹Ar mica dates across a mid-crustal continental plate margin, Connemara (Grampian orogeny, Irish Caledonides), and implications for the evolution of lithospheric collisions

Friedrich

Hodges

2016

Can. J. Earth Sci.

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Abstract:The Connemara region is a world-class example of a regional-scale, high-temperature metamorphic terrain. Its rock record documents formation of a bi-vergent orogenic wedge and associated calkalkaline magmatism in a an arc-continent collisional setting (Grampian orogeny), for which a protracted evolution was inferred based on a >75 Ma spread in U-Pb, Rb-Sr, and K-Ar mineral ages. In contrast, geological field observations imply a simple relationship between syntectonic magmatism, bi-vergent deformation, and Barrovian-type metamorphism. We explore the significance of the spread in apparent cooling ages using 40 Ar/ 39 Ar mica thermochronometers of varying grain sizes and composition, collected across metamorphic grades ranging from staurolite to upper sillimanite. We integrated geological and previously published geochronological evidence to identify a 32 Ma range (ca. 475-443 Ma) of permissible cooling ages and distinguished them from those dates not related to cooling after high-temperature metamorphism. Variations in 40 Ar/ 39 Ar dates at a single locality are ≤10 Ma, implying rapid cooling (≥6-26°C/Ma) following metamorphism and deformation. A distinct cooling age variation (≥15 Ma) occurs on the regional scale, consistent with spatial differences in the metamorphic, magmatic, and deformational evolution across Connemara. This cooling record relates to a lateral thermal gradient (30°C/km) in an evolving arc-continent collision, rather than to differential unroofing of the orogen. Our results imply that the large (≥50 Ma) spread in thermochronometers commonly observed in orogens does not automatically translate into a protracted cooling history, but that only a small number of thermochronometers supply permissible cooling ages.Résumé : La région de Connemara des Calédonides irlandaises est un exemple de classe mondiale de terrain métamorphique de haute température d'envergure régionale. Sa formation est reliée au magmatisme calcoalcalin dans le contexte d'une collision arc-continent, pour laquelle une évolution prolongée a été inférée à la lumière de la distribution sur plus de 75 Ma d'âges U-Pb, Rb-Sr, et K-Ar sur différents minéraux. Une telle évolution ne correspond pas aux observations géologiques sur le terrain, qui indiqueraient plutôt une relation simple entre un magmatisme, une déformation et un métamorphisme de type barrovien syntectoniques. Nous avons examiné la signification de la distribution des âges apparents de refroidissement à l'aide de thermochronomètres 40 Ar/ 39 Ar sur micas de granulométries et compositions variées, prélevés à différents degrés de métamorphisme allant de la zone à staurotide à la zone à sillimanite supérieure. Nous avons intégré les données géologiques et de l'information géochronologique déjà publiée pour délimiter une fenêtre de 32 Ma (de 475 à 443 Ma environ) pour les âges de refroidissement possibles et avons distingué ces derniers des âges non reliés au refroidissement ayant suivi le métamorphisme de haute température. La variation des âges 40 Ar/ 39 Ar en un ...

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Thermochronology in Orogenic Systems

Cited by 30 publications

References 342 publications

Detrital zircon (U‐Th)/(He‐Pb) double‐dating constraints on provenance and foreland basin evolution of the Ainsa Basin, south‐central Pyrenees, Spain

Detrital zircon (U‐Th)/(He‐Pb) double‐dating constraints on provenance and foreland basin evolution of the Ainsa Basin, south‐central Pyrenees, Spain

Two‐Stage Cooling and Exhumation of Deeply Subducted Continents

Geological significance of ⁴⁰Ar/³⁹Ar mica dates across a mid-crustal continental plate margin, Connemara (Grampian orogeny, Irish Caledonides), and implications for the evolution of lithospheric collisions

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Thermochronology in Orogenic Systems

Cited by 30 publications

References 342 publications

Detrital zircon (U‐Th)/(He‐Pb) double‐dating constraints on provenance and foreland basin evolution of the Ainsa Basin, south‐central Pyrenees, Spain

Detrital zircon (U‐Th)/(He‐Pb) double‐dating constraints on provenance and foreland basin evolution of the Ainsa Basin, south‐central Pyrenees, Spain

Two‐Stage Cooling and Exhumation of Deeply Subducted Continents

Geological significance of 40Ar/39Ar mica dates across a mid-crustal continental plate margin, Connemara (Grampian orogeny, Irish Caledonides), and implications for the evolution of lithospheric collisions

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Geological significance of ⁴⁰Ar/³⁹Ar mica dates across a mid-crustal continental plate margin, Connemara (Grampian orogeny, Irish Caledonides), and implications for the evolution of lithospheric collisions