Strong Variability in the Thermal Structure of Tibetan Lithosphere. Issue 3 (15th March 2023)

• Record Type: Journal Article
• Authors: Xia, B.; Artemieva, I. M.; Thybo, H.; Klemperer, S. L.
• Is Part Of: Journal of geophysical research. Volume 128:Issue 3(2023)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2023-03-15
• Subjects: Geomagnetism -- Periodicals; Geochemistry -- Periodicals; Geophysics -- Periodicals; Earth sciences -- Periodicals; 551.1
• DOI: 10.1029/2022JB026213
• Languages: English
• ISSNs: 2169-9313

Abstract

Abstract: We present a model of thermal lithospheric thickness (the depth where the geotherm reaches a temperature of 1300°C) and surface heat flow in Tibet and adjacent regions based on a new thermal‐isostasy method. The method accounts for crustal density heterogeneity, is free from any assumption of a steady‐state lithosphere thermal regime, and assumes that deviations from crustal Airy‐type isostasy are caused by lithosphere thermal heterogeneity. We observe a highly variable lithospheric thermal structure which we interpret as representing longitudinal variations in the northern extent of the subducting Indian plate, southward subduction of the Asian plate beneath central Tibet, and possible preservation of fragmented Tethyan paleo‐slabs. Cratonic‐type cold and thick lithosphere (200–240 km) with a predicted surface heat flow of 40–50 mW/m 2 typifies the Tarim Craton, the northwest Yangtze Craton, and most of the Lhasa Block that is likely refrigerated by underthrusting Indian lithosphere. We identify a "North Tibet anomaly" with thin (<80 km) lithosphere and high surface heat flow (>80–100 mW/m 2 ). We interpret this anomaly as the result of removal of lithospheric mantle and asthenospheric upwelling at the junction of the Indian and Asian slabs with opposite subduction polarities. Other parts of Tibet typically have intermediate lithosphere thickness of 120–160 km and a surface heat flow of 45–60 mW/m 2, with patchy anomalies in eastern Tibet. While different uplift mechanisms for Tibet predict different lithospheric thermal regimes, our results in terms of a highly variable thermal structure beneath Tibet suggest that topographic uplift is caused by an interplay of several mechanisms. Plain Language Summary: The world's highest and largest plateau in Tibet has a unique topography with an average elevation of >4 km and is often named "the Roof of the world." Continental collision between the Indian and Eurasian plates created Tibet and the Himalaya, and the dynamics of plateau growth and related large‐scale regional geological processes present a series of intriguing geoscience problems. Several geodynamic models involving modification of the entire lithosphere have been proposed as mechanisms for the Tibetan uplift. Two end‐member models involve either a "cold" or a "hot" Tibetan lithosphere. As different uplift mechanisms predict different lithospheric thermal regimes, knowledge of the thermal structure is key to understanding the driving forces of the Tibetan uplift. However, the thermal regime of Tibet is poorly known from surface heat‐flow measurements as high‐quality observations are almost absent. To bypass the problem of limited geophysical data coverage, we use a new thermal isostasy method to constrain the lithospheric thermal structure of Tibet and adjacent areas. Our results show a strongly variable lithospheric thermal structure beneath Tibet and suggest that topographic uplift is caused by an interplay of several mechanisms. Key Points: Thick Tibetan lithosphere defines the longitudinally variable northern extent of the Indian plate The "North Tibet Anomaly" with a hot mantle marks the junction of the Indian and Asian slabs Tethyan paleo‐slabs explain variable lithosphere thickness in eastern Tibet