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A xenolith-derived geotherm and the crust-mantle boundary at Qilin, southeastern China

Authors
Journal
Lithos
0024-4937
Publisher
Elsevier
Publication Date
Volume
38
Identifiers
DOI: 10.1016/0024-4937(95)00043-7
Disciplines
  • Earth Science
  • Geography

Abstract

Abstract Pressure-temperature estimates on a group of well-equilibrated garnet pyroxenites from the Qilin locality, southeastern China have been used to construct the first detailed, locality-specific paleogeotherm for eastern China. This xenolith-defined geothermal gradient is comparable to that for northwestern Spitsbergen, Norway, and higher than that derived for southeastern Australia. The strong curvature of this geotherm between 20 and 50 km depth indicates that advection, rather than conduction was the dominant heat-transfer mechanism in the lower crust and upper mantle at that time. Underplating and overplating of basaltic magmas at the crust-mantle boundary is the likely cause of the advective heat transfer. Temperature estimates on two-pyroxene granulites suggest they were entrained from the lower crust. The crust-mantle boundary, defined from the lowest temperature estimates for spinel lherzolites, lies at ca 27 km depth in this locality. This is shallower than the Moho ( ~ 31 km) defined by seismic refraction. Calculation of V p for the xenolith rock types, and comparison with observed V p data, allow definition of a stratigraphie sequence. From 27 to 31 km depth, garnet granulites, spinel lherzolites and garnet pyroxenites may be interlayered in a transitional zone. Comparison with present-day heat flow measurements and seismic results suggest that this lithospheric section has undergone cooling since the Cenozoic volcanism.

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