2 research outputs found
The Mesozoic along-strike tectono-metamorphic segmentation of Longmen Shan (eastern Tibetan plateau)
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 longâterm geological evolution of the belt and its effect on the present dynamics and crustal structure. New structural and thermobarometric data offer a comprehensive dataset of the paleoâtemperatures across the belt and PâT estimates for lowâgrade metamorphic domains. In the central Longmen Shan, two metamorphic jumps of 150â200°C, 5â6 kbar and ~50 °C, 3â5 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 SongpanâGarze metasedimentary cover (at T > 500°C) and the autochtonous units and the basement (T < 400°C). In the southern Longmen Shan, the only greenschistâfacies 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 c. 80â60 Ma in the basement and c. 55â33 Ma in the cover, c. 50 Ma after the greenschistâfacies metamorphic overprint observed in the central Longmen Shan (c. 150â120 Ma). This alongâstrike metamorphic segmentation coincides well with the present fault segmentation and reveals that the central and southern Longmen Shan experienced different tectonoâmetamorphic histories since the Mesozoic