Relation between structural evolution of the Longmenshan orogenic zone and sedimentation of its foreland basin

Liao, Taiping; Zhang, Qikun; Zhang, Furong; Chen, Hongkai; Sun, Hongquan

doi:10.1016/s1674-5264(09)60147-2

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“…In the internal metasedimentary cover, the occurrence of a greenschist facies event during the Early Cretaceous is consistent with the 40 Ar/ 39 Ar ages recorded in the Wenchuan fault zone (119–114 Ma, Arne et al., ) and with 123–120 Ma 40 Ar/ 39 Ar biotite ages from the Danba area (Xu et al., ). The Early Cretaceous also marks a change in the type and rate of sedimentation of the autochthonous units in the western Sichuan basin that become characteristic of a flexural basin forming in response to a rapid uplift of the belt (Liao, Hu, Zhang, Chen, & Sun, ). In order to explain the decreasing age of the Early Cretaceous event approaching the front of the belt, we propose that the related deformation phase firstly affected sediments in the northwest of the Tonghua area (lm147) at 160–147 Ma, and then propagated to the southeast at 150–135 Ma (to13‐4), and to the basement in the Tonghua and Pengguan crystalline massifs at 140–118 Ma (lm09‐52) and 145–130 Ma respectively (Figure ).…”

Section: Discussionmentioning

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: Discussionmentioning

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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The Mesozoic Along‐Strike Tectonometamorphic Segmentation of Longmen Shan (Eastern Tibetan Plateau)

et al. 2018

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The Longmen Shan belt (eastern border of the Tibetan plateau) constitutes a tectonically active region as demonstrated by the occurrence of the unexpected 2008 Mw 7.9 Wenchuan and 2013 Mw 6.6 Lushan earthquakes in the central and southern parts of the belt, respectively. These events revealed the necessity of a better understanding of the long‐term geological evolution of the belt and its effect on the present dynamics and crustal structure. New structural and thermobarometric data offer a comprehensive data set of the paleotemperatures across the belt and P‐T estimates for low‐grade metamorphic domains. In the central Longmen Shan, two metamorphic jumps of 150–200 °C, 5–6 kbar and ~50 °C, 3–5 kbar acquired during the Early Mesozoic are observed across the Wenchuan and Beichuan faults, respectively, attesting to their thrusting movement and unrevealing a major decollement between the allochtonous Songpan‐Garze metasedimentary cover (at T > 500 °C) and the autochtonous units and the basement (T < 400 °C). In the southern Longmen Shan, the only greenschist facies metamorphism is observed both in the basement (360 ± 30 °C, 6 ± 2 kbar) and in the metasedimentary cover (350 ± 30 °C, 3 ± 1 kbar). Peak conditions were reached at ca. 80–60 Ma in the basement and ca. 55–33 Ma in the cover, ca. 50 Ma after the greenschist facies metamorphic overprint observed in the central Longmen Shan (ca. 150–120 Ma). This along‐strike metamorphic segmentation coincides well with the present fault segmentation and reveals that the central and southern Longmen Shan experienced different tectonometamorphic histories since the Mesozoic.

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Relation between structural evolution of the Longmenshan orogenic zone and sedimentation of its foreland basin

Cited by 2 publications

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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)

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

The Mesozoic Along‐Strike Tectonometamorphic Segmentation of Longmen Shan (Eastern Tibetan Plateau)

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Relation between structural evolution of the Longmenshan orogenic zone and sedimentation of its foreland basin

Cited by 2 publications

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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)

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

The Mesozoic Along‐Strike Tectonometamorphic Segmentation of Longmen Shan (Eastern Tibetan Plateau)

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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)

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