Late Paleozoic evolution of the South Tien Shan: Insights from P–T estimates and allanite geochronology on retrogressed eclogites (Chatkal range, Kyrgyzstan)

Loury, Chloé; Rolland, Yann; Cenki-Tok, Bénédicte; Lanari, Pierre; Guillot, Stéphane

doi:10.1016/j.jog.2015.06.005

Cited by 59 publications

(33 citation statements)

References 93 publications

(93 reference statements)

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“…Because of the local heterogeneities of metamorphic rocks and the compositional zoning of the rock‐forming minerals, the measured whole‐rock composition is not always adapted for modelling (e.g. Lanari et al., ; Loury et al., ; Warren & Waters, ). In this study, several examples suggest that the models based on LB provide better results (lower residuals for similar P–T conditions).…”

Section: Discussionmentioning

confidence: 99%

“…The local bulk compositions were calculated based on the mode of the petro‐textural domains (porphyroblasts with their inclusions, mineral matrix, domains showing late retrogression) observed within the thin section and their local bulk compositions determined with X MapTools ; this is somewhat equivalent to that done in other studies (Loury et al., ; Marmo et al., ; Warren & Waters, ). Mineral abundances were estimated by thin‐section optical image analysis.…”

Section: Methodsmentioning

confidence: 99%

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Exhumation of eclogite and blueschist (Cyclades, Greece): Pressure–temperature evolution determined by thermobarometry and garnet equilibrium modelling

Laurent

Lanari

Naïr

et al. 2018

Journal Metamorphic Geology

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High‐P rocks such as eclogite and blueschist are metamorphic markers of palaeo‐subduction zones, and their formation at high‐P and low‐T (HP–LT) conditions is relatively well understood since it has been the focus of numerous petrological investigations in the past 40 years. The tectonic mechanisms controlling their exhumation back to the surface are, however, diverse, complex and still actively debated. Although the Cycladic Blueschist Unit (CBU, Greece) is among the best worldwide examples for the preservation of eclogite and blueschist, the proposed P–T evolution followed by this unit within the Hellenic subduction zone is quite different from one study to another, hindering the comprehension of exhumation processes. In this study, we present an extensive petrological data set that permits refinement of the shape of the P–T trajectory for different subunits of the CBU on Syros. High‐resolution quantitative compositional mapping has been applied to support the thermobarometric investigations, which involve semi‐empirical thermobarometry, garnet equilibrium modelling and P–T isochemical phase diagrams. The thermodynamic models highlight the powerful use of reactive bulk compositions approximated from local bulk compositions. The results are also combined with Raman spectrometry of carbonaceous material (RSCM) to retrieve the metamorphic peak temperature distribution at the scale of the island. A major result of this study is the good agreement between all the independent thermobarometric methods, permitting reconstruction of the prograde and retrograde P–T trajectories. Garnet compositional zoning was used to retrieve prograde, peak and retrograde growth stages in line with the results of the P–T isochemical phase diagrams, RSCM temperature and peak‐pressure crystallization of the garnet–omphacite–phengite assemblage. Our results are consistent with previous thermobarometric estimates from other occurrences of CBU rocks (Tinos, Andros), suggesting a multistage exhumation process with (1) early syn‐orogenic exhumation within the subduction channel, (2) isobaric heating at mid‐crustal depths (~10–12 kbar) following thermal re‐equilibration of the lithosphere from a cold syn‐orogenic regime in the subduction zone to a warmer post‐orogenic regime in the back‐arc domain and (3) exhumation and cooling related to a post‐orogenic phase of extension following slab retreat. Expanding to the general aspects of subduction zones, we suggest that such metamorphic evolution of HP–LT units should be regarded as a characteristic feature of exhumation driven by slab rollback.

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Section: Discussionmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

Exhumation of eclogite and blueschist (Cyclades, Greece): Pressure–temperature evolution determined by thermobarometry and garnet equilibrium modelling

Laurent

Lanari

Naïr

et al. 2018

Journal Metamorphic Geology

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“…To the East, near the Chinese boundary, Loury et al, (2015a) described in the STS a granulitic unit composed of an assemblage of pyroxene, feldspar, quartz and garnet overthrusting towards the North a low grade (greenschist facies) metamorphic sediments unit.…”

Section: Accepted Manuscriptmentioning

confidence: 99%

New structural data on Late Paleozoic tectonics in the Kyrgyz Tien Shan (Central Asian Orogenic Belt)

et al. 2017

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The tectonic evolution of the Central Asian Orogenic Belt (CAOB) is characterized by the successive accretion of lithospheric blocks, leading to different interpretations about the polarity of subductions during the Paleozoic, the number of microplates and oceanic basins and the timing of tectonic events. This is especially the case in the Tien Shan area.In this paper, we propose new structural maps and cross-sections of Middle and South Kyrgyz Tien Shan (MTS and STS respectively). These cross-sections highlight an overall dextral strike-slip shear zone in the MTS at the crustal scale and a North verging structure in the STS. These structures are Carboniferous in age and sealed by a late Carboniferous conglomerate, later overlain by Mesozoic and Cenozoic deposits. The STS exhibits two deformation phases: (1) a top-to-the-South normal shearing that can be related to subduction or exhumation dynamics and (2) a top to the North nappe stacking that we link to the late Paleozoic collisional events between the MTS and the Tarim block.We propose a new interpretation of the tectonic evolution of the Kyrgyz Tien Shan during the Late Paleozoic collision. This model involves a partitioned collisional deformation in Late Carboniferous times, with an orthogonal collision to the south, between the Tarim and MTS, and a strike-slip regime to the north along a dextral E-W zone located between the MTS and the North Tien-Shan/ Kazakh platform, the so-called Nikolaev Line. The docking of the large Tarim Craton against the CAOB corresponds to a collision phase, which ended the longlived Paleozoic subduction history in the CAOB and was followed in the TS region by intense strike-slip deformation during the Permian.

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“…315 Ma eclogite boudins, dated at 301 ± 15 Ma by U–Pb on allanite by Loury et al. () and to 317 ± 4 Ma and 316 ± 3 Ma by Sm–Nd garnet whole‐rock ages (Mühlberg et al., ), suggesting a north‐dipping subduction (Loury et al., ). Thermo‐mechanical modelling of the STS belt is in agreement with a south‐dipping subduction model (Jourdon, Le Pourhiet, Petit, & Rolland, ), at least at the end of the Turkestan Ocean closure history.…”

Section: Geological Settingmentioning

confidence: 99%

“…HP–LT metamorphism along the STS suture zone occurs both in Kyrgyzstan (Atbashi Range) and in western China (Akeyazi area). Previous studies on the Kyrgyz Atbashi Range (Figure b,c) mainly focused on mafic eclogites, and details regarding the spatial extent and timing of HP metamorphism within the associated metasedimentary rocks and lower grade metamorphic stages at the scale of the Tien Shan belt are still lacking (Hegner et al., ; Loury, Rolland, Cenki‐Tok, Lanari, & Guillot, ; Loury et al., ; Simonov, Sakiev, Volkova, Stupakov, & Travin, ). Therefore, following these previous works, the main questions addressed in this paper are: (a) what was the timing of burial and exhumation in the Atbashi Range?…”

Section: Introductionmentioning

confidence: 99%

Tectonometamorphic evolution of the Atbashi high‐P units (Kyrgyz CAOB, Tien Shan): Implications for the closure of the Turkestan Ocean and continental subduction–exhumation of the South Kazakh continental margin

Loury

Rolland

Guillot

et al. 2018

Journal Metamorphic Geology

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The South Tien Shan (STS) belt results from the last collision event in the western Central Asian Orogenic Belt (CAOB). Understanding its formation is of prime importance in the general framework of the CAOB. The Atbashi Range preserves high‐P (HP) rocks along the STS suture, but still, its global metamorphic evolution remains poorly constrained. Several HP units have been identified: (a) a HP tectonic mélange including boudins of mafic eclogites in a sedimentary matrix, (b) a large (>100 km long) high‐P metasedimentary unit (HPMU) and (c) a lower blueschist facies accretionary prism. Raman Spectroscopy on carbonaceous material combined with phengite and chlorite multiequilibria and isochemical phase diagram modelling indicates that the HPMU recorded homogeneous P–T conditions of 23–25 kbar and 560–570°C along the whole unit. 40Ar/39Ar dating on phengite from the HPMU ranges between 328 and 319 Ma at regional scale. These ages are interpreted as (re‐) crystallization ages of phengite during Tmax conditions at a pressure range of 20–25 kbar. Thermobarometry on samples from the HP tectonic mélange provides similar metamorphic peak conditions. Thermobarometry on the blueschist to lower greenschist facies accretionary prism indicates that it underwent P–T conditions of 5–6 kbar and 290–340°C, highlighting a 17–20 kbar pressure gap between the HPMU‐tectonic mélange units and the accretionary prism. Comparison with available geochronological data suggests a very short time span between the prograde path (340 Ma), HP metamorphic peak (330 Ma), the Tmax (328–319 Ma) and the final exhumation of the HPMU (303–295 Ma). Extrusion of the HPMU, accommodated by a basal thrust and an upper detachment, was driven by buoyant forces from 70–75 km up to 60 km depth, which directly followed continental subduction and detachment of the HPMU. At crustal depths, extrusion was controlled by collisional tectonics up to shallow levels. Lithological homogeneity of the HPMU and its continental‐derived character from the North Tien Shan suggest this unit corresponds to the hyper‐extended continental margin of the Kazakh continent, subducted southward below the north continental active margin of the Tarim craton. Integration of the available geological data allows us to propose a general geodynamic scenario for Tien Shan during the Carboniferous with a combination of (a) N‐dipping subduction below the Kazakh margin of Middle Tien Shan until 390–340 Ma and (b) S‐dipping subduction of remaining Turkestan marginal basins between 340 and 320 Ma.

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Late Paleozoic evolution of the South Tien Shan: Insights from P–T estimates and allanite geochronology on retrogressed eclogites (Chatkal range, Kyrgyzstan)

Cited by 59 publications

References 93 publications

Exhumation of eclogite and blueschist (Cyclades, Greece): Pressure–temperature evolution determined by thermobarometry and garnet equilibrium modelling

Exhumation of eclogite and blueschist (Cyclades, Greece): Pressure–temperature evolution determined by thermobarometry and garnet equilibrium modelling

New structural data on Late Paleozoic tectonics in the Kyrgyz Tien Shan (Central Asian Orogenic Belt)

Tectonometamorphic evolution of the Atbashi high‐P units (Kyrgyz CAOB, Tien Shan): Implications for the closure of the Turkestan Ocean and continental subduction–exhumation of the South Kazakh continental margin

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