Re^Os evidence for replacement of ancient mantle lithosphere beneath the North China craton Shan Gao a;b , Roberta L. Rudnick c ; Ã , Richard W. Carlson d , William F. McDonough c ; 1 , Yong-Sheng Liu b a Key Laboratory of Continental Dynamics, Department of Geology, Northwest University, Xi’an 710069, PR China b Faculty of Earth Sciences, China University of Geosciences, Wuhan 430074, PR China c Department of Earth and Planetary Sciences, Harvard University, Cambridge, MA 02138, USA d Department of Terrestrial Magnetism, Carnegie Institution of Washington, 5241 Broad Branch Road, N.W., Washington, DC 20015, USA Received 25 July 2001; received in revised form 7 January 2002; accepted 23 January 2002 Abstract Re^Os data for peridotite xenoliths carried in Paleozoic kimberlites and Tertiary alkali basalts confirm previous suggestions that the refractory and chemically buoyant lithospheric keel present beneath the eastern block of the North China craton (and sampled by Paleozoic kimberlites) is indeed Archean in age and was replaced by more fertile lithospheric mantle sometime after the Paleozoic. Moreover, lithospheric mantle beneath the central portion of the craton (west of the major gravity lineament) formed during the last major Precambrian orogeny, around 1900 Ma ago. This age is significantly younger than the overlying crust (2700 Ma), suggesting that the original Archean lithosphere was replaced in the Proterozoic. The timing of lithospheric replacement in the eastern block of the North China Craton is constrained only to the Phanerozoic by the Re^Os results. Circumstantial geologic evidence suggests this new lithosphere is Jurassic or Cretaceous in age and formed after collision of the Yangtze and North China cratons in the Triassic, an event that was also responsible for the subduction and uplift of ultrahigh-pressure metamorphic rocks. Collectively, these data suggest that lithosphere replacement occurred in response to two continent collisional events widely separated in time (V1900 and V220 Ma). Coupled with observations from other Archean cratons we suggest that wholesale replacement of lithospheric mantle ( þ lower crust) may require large-scale continental collision. ß 2002 Elsevier Science B.V. All rights reserved. Keywords: Re/Os; isotope ratios; Archean; Mantle; North China Platform; delamination 1. Introduction Cratons are ancient continental regions that have been tectonically quiescent for billions of years. They are characterized by low surface heat £ow (average = 40 mW/m 2 [1,2]) and are underlain by mantle that is seismically fast to depths on the order of 250^300 km [3,4]. These 0012-821X / 02 / $ ^ see front matter ß 2002 Elsevier Science B.V. All rights reserved. PII:S0012-821X(02)00489-2 * Corresponding author. Present address: Geochemistry Laboratory, Department of Geology, University of Maryland, College Park, MD 20742, USA. Fax: +1-301-314-9661. E-mail address: rudnick@geol.umd.edu (R.L. Rudnick). 1 Present address as corresponding author. Earth and Planetary Science Letters 198 (2002) 307^322 www.elsevier.com/locate/epsl