Tracking the timing of subduction and exhumation using 40Ar/39Ar phengite ages in blueschist- and eclogite-facies rocks (Sivrihisar, Turkey)

Fornash, Katherine F.

doi:10.1007/s00410-016-1268-2

Cited by 36 publications

(22 citation statements)

References 65 publications

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“…These studies demonstrated that the thermal conditions in subduction zones varied through time (e.g., Agard et al, 2009;Plunder et al, 2015;Angiboust et al, 2016), but also along-strike. For instance, in the Franciscan complex of California (Wakabayashi and Dumitru, 2007), in the Sulawesi mélange in SE Asia (Parkinson, 1996) and in the sub-ophiolitic mélanges of Guatemala versus Cuba (Garcia-Casco et al, 2007), (garnet) amphibolites (high-temperature and mid-pressure conditions) are coeval with eclogite or blueschist (low-temperature and high-pressure conditions) along-strike in the same subduction complex. Taking the pressure (simply assumed to represent depth) of metamorphism into account, these may suggest along-strike temperature differences of ca.…”

Section: Oblique Subduction: Present and Past Examplesmentioning

confidence: 99%

“…Both units were metamorphosed around 80-90 Ma (e.g., Whitney and Hamilton, 2004;Fornash et al, 2016;van Hinsbergen et al, 2016;Pourteau et al, 2018) within the same subduction system but under dramatically different metamorphic conditions. In the Tavşanlı zone peak metamorphic conditions were estimated to be around 24 ± 2 kbar and 500 ± 50 • C (Okay et al, 2002;Plunder et al, 2015), whereas peak metamorphism was estimated at around 800 ± 100 • C and 8 ± 1 kbar in the Kırşehir block (Whitney and Hamilton, 2004;Lefebvre et al, 2015).…”

Section: Oblique Subduction: Present and Past Examplesmentioning

confidence: 99%

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The effect of obliquity on temperature in subduction zones: insights from 3-D numerical modeling

2018

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Abstract. The geotherm in subduction zones is thought to vary as a function of the subduction rate and the age of the subducting lithosphere. Along a single subduction zone the rate of subduction may strongly vary due to changes in the angle between the trench and the plate convergence vector, i.e., the subduction obliquity, due to trench curvature. We currently observe such curvature in, e.g., the Marianas, Chile and Aleutian trenches. Recently, strong along-strike variations in subduction obliquity were proposed to have caused a major temperature contrast between Cretaceous geological records of western and central Turkey. We test here whether first-order temperature variation in a subduction zone may be caused by variation in the trench geometry using simple thermo-kinematic finite-element 3-D numerical models. We prescribe the trench geometry by means of a simple mathematical function and compute the mantle flow in the mantle wedge by solving the equation of mass and momentum conservation. We then solve the energy conservation equation until steady state is reached. We analyze the results (i) in terms of mantle wedge flow with emphasis on the trench-parallel component and (ii) in terms of temperature along the plate interface by means of maps and the depth–temperature path at the interface. In our experiments, the effect of the trench curvature on the geotherm is substantial. A small obliquity yields a small but not negligible trench-parallel mantle flow, leading to differences of 30 °C along-strike of the model. Advected heat causes such temperature variations (linked to the magnitude of the trench-parallel component of velocity). With increasing obliquity, the trench-parallel component of the velocity consequently increases and the temperature variation reaches 200 °C along-strike. Finally, we discuss the implication of our simulations for the ubiquitous oblique systems that are observed on Earth and the limitations of our modeling approach. Lateral variations in plate sinking rate associated with curvature will further enhance this temperature contrast. We conclude that the synchronous metamorphic temperature contrast between central and western Turkey may well have resulted from reconstructed major variations in subduction obliquity.

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Section: Oblique Subduction: Present and Past Examplesmentioning

confidence: 99%

Section: Oblique Subduction: Present and Past Examplesmentioning

confidence: 99%

The effect of obliquity on temperature in subduction zones: insights from 3-D numerical modeling

2018

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“…In such systems, 40 Ar/ 39 Ar dating of mica is commonly used to determine the timing of metamorphic cooling following the traditional interpretation of Dodson's diffusion theory (Dodson, 1973), due to the ubiquity of mica and its importance as a geobarometer. However, the concentration of Ar incorporated in, or lost from a grain, is not only dependent on the cooling history and the grain size (as suggested by the Dodson, 1973 formulation) but also on the effectiveness of the grain boundary fluid network in removing Ar (the "openness" of the system) and the variation of the rates of fluid-induced replacement mineral reactions (Cenki-Tok, Darling, Rolland, Dhuime, & Storey, 2014;de Sigoyer et al, 2000;Di Vincenzo, Ghiribelli, Giorgetti, & Palmeri, 2001;Fornash, Cosca, & Whitney, 2016;Mulch & Cosca, 2004;Villa, 2010Villa, , 2016Warren, Hanke, & Kelley, 2012;Warren, Smye, Kelley, & Sherlock, 2012). Therefore, since many tectonic time-scale estimates rely on the interpretation of metamorphic ages (Lanari, Rolland, et al, 2014;Sanchez et al, 2011) and associated cooling rates (e.g.…”

Section: Introductionmentioning

confidence: 99%

Influence of dissolution/reprecipitation reactions on metamorphic greenschist to amphibolite facies mica ⁴⁰Ar/³⁹Ar ages in the Longmen Shan (eastern Tibet)

Airaghi

Warren

Sigoyer

et al. 2018

Journal Metamorphic Geology

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Linking ages to metamorphic stages in rocks that have experienced low‐ to medium‐grade metamorphism can be particularly tricky due to the rarity of index minerals and the preservation of mineral or compositional relicts. The timing of metamorphism and the Mesozoic exhumation of the metasedimentary units and crystalline basement that form the internal part of the Longmen Shan (eastern Tibet, Sichuan, China), are, for these reasons, still largely unconstrained, but crucial for understanding the regional tectonic evolution of eastern Tibet. In situ core‐rim 40Ar/39Ar biotite and U–Th/Pb allanite data show that amphibolite facies conditions (~10–11 kbar, 530°C to 6–7 kbar, 580°C) were reached at 210–180 Ma and that biotite records crystallization, rather than cooling, ages. These conditions are mainly recorded in the metasedimentary cover. The 40Ar/39Ar ages obtained from matrix muscovite that partially re‐equilibrated during the post peak‐P metamorphic history comprise a mixture of ages between that of early prograde muscovite relicts and the timing of late muscovite recrystallization at c. 140–120 Ma. This event marks a previously poorly documented greenschist facies metamorphic overprint. This latest stage is also recorded in the crystalline basement, and defines the timing of the greenschist overprint (7 ± 1 kbar, 370 ± 35°C). Numerical models of Ar diffusion show that the difference between 40Ar/39Ar biotite and muscovite ages cannot be explained by a slow and protracted cooling in an open system. The model and petrological results rather suggest that biotite and muscovite experienced different Ar retention and resetting histories. The Ar record in mica of the studied low‐ to medium‐grade rocks seems to be mainly controlled by dissolution–reprecipitation processes rather than by diffusive loss, and by different microstructural positions in the sample. Together, our data show that the metasedimentary cover was thickened and cooled independently from the basement prior to c. 140 Ma (with a relatively fast cooling at 4.5 ± 0.5°C/Ma between 185 and 140 Ma). Since the Lower Cretaceous, the metasedimentary cover and the crystalline basement experienced a coherent history during which both were partially exhumed. The Mesozoic history of the Eastern border of the Tibetan plateau is therefore complex and polyphase, and the basement was actively involved at least since the Early Cretaceous, changing our perspective on the contribution of the Cenozoic geology.

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Section: Oblique Subduction: Present and Past Examplesmentioning

confidence: 99%

answers to R1

Plunder¹

2018

Preprint

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Interactive comment on "The effect of obliquity on temperature in subduction zones: insights from 3D numerical modeling" by Alexis Plunder et al.Alexis Plunder et al. alex.plunder@gmail.com Received and published: 20 April 2018 Answers to the interactive review of the paper: "The effect of obliquity on temperature in subduction zones: insights from 3D numerical modeling" by Alexis Plunder et al. Dear Editor, dear reviewers,First of all, we wish to thanks the reviewer for their time considering our work. Below you can find answers the questions asked by the referees. C1 SED Interactive commentPrinter-friendly version Discussion paper Answers to first referee: M. Faccenda (Referee)

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Tracking the timing of subduction and exhumation using 40Ar/39Ar phengite ages in blueschist- and eclogite-facies rocks (Sivrihisar, Turkey)

Cited by 36 publications

References 65 publications

The effect of obliquity on temperature in subduction zones: insights from 3-D numerical modeling

The effect of obliquity on temperature in subduction zones: insights from 3-D numerical modeling

Influence of dissolution/reprecipitation reactions on metamorphic greenschist to amphibolite facies mica ⁴⁰Ar/³⁹Ar ages in the Longmen Shan (eastern Tibet)

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Tracking the timing of subduction and exhumation using 40Ar/39Ar phengite ages in blueschist- and eclogite-facies rocks (Sivrihisar, Turkey)

Cited by 36 publications

References 65 publications

The effect of obliquity on temperature in subduction zones: insights from 3-D numerical modeling

The effect of obliquity on temperature in subduction zones: insights from 3-D numerical modeling

Influence of dissolution/reprecipitation reactions on metamorphic greenschist to amphibolite facies mica 40Ar/39Ar ages in the Longmen Shan (eastern Tibet)

answers to R1

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Influence of dissolution/reprecipitation reactions on metamorphic greenschist to amphibolite facies mica ⁴⁰Ar/³⁹Ar ages in the Longmen Shan (eastern Tibet)