Lithos | 2019
Thermal history of the Donjek harzburgite massif in ophiolite from Yukon, Canada with implications for the cooling of oceanic mantle lithosphere
Abstract
Abstract We examine the partial melting and the cooling history of a ~5\u202fkm section of mantle lithosphere preserved in the Donjek massif, part of a Permian ophiolite in the northern Cordillera of Yukon, Canada. The mantle rocks are depleted spinel harzburgite containing Mg exchange (solvus) temperatures (TBKN) of 900–970\u202f°C. The harzburgite represents lithosphere formed at an initial melting temperature of ~ 1350\u202f°C that cooled at rate of 10−1 to 10−4\u202f°C/year as deduced by TREE values with cation diffusion and grain size data. The TREE temperatures and cooling rates for the Donjek massif show a regular systematic variation with depth from the crust-mantle transition along a trend similar to the Samail ophiolite of Oman, consistent with conductive heat transfer beneath a cool lower crust. High near-solidus temperatures and the cooling rates in the massif were a consequence of rapid obduction against oceanic crust along either a transform or low angle detachment soon after melt extraction. Final emplacement of the ophiolite as klippen on underlying continental crust occurred ~ 40\u202fm.y. later.