Journal of Petrology, Volume 40, Issue 1: January 1999.

Petrology of Peridotite and Pyroxenite Xenoliths from the Jericho Kimberlite: Implications for the Thermal State of the Mantle beneath the Slave Craton, Northern Canada

M. G. KOPYLOVA¹, J. K. RUSSELL¹ AND H. COOKENBOO²

¹DEPARTMENT OF EARTH AND OCEAN SCIENCE, THE UNIVERSITY OF BRITISH COLUMBIA, VANCOUVER, B.C., CANADA, V6T 1Z4
²CANAMERA GEOLOGICAL LTD, 399 MOUNTAIN HIGHWAY, NORTH VANCOUVER, B.C., CANADA, V6B 2M9

We report comprehensive petrological and thermobarometric data for the following types of mantle xenoliths from the Jericho kimberlite in the Slave craton: (1) coarse peridotite; (2) porphyroclastic peridotite; (3) megacrystalline pyroxenite; (4) ilmenite-garnet wehrlite and clinopyroxenite. The varieties of the upper-mantle xenoliths, and their proportions, petrography and mineralogy, mainly resemble those from kimberlites of other cratons. Unique characteristics of the north-central Slave mantle include the presence of high-temperature megacrystalline pyroxenite and an unusually high proportion of pyroxenitic magmatic rocks related in origin to megacrysts. Other unique aspects of Jericho peridotitic mantle are: (1) a pronounced Cr enrichment in mineral chemistry within high-temperature peridotite; (2) an anomalously high proportion of chemically unequilibrated samples; (3) an uncommon pattern in silicate mineral chemistry in spinel-bearing peridotite that reflects equilibration with spinel. The central Slave mantle is colder than the mantle beneath the rest of the North American craton and the mantle beneath Kaapvaal and Siberian cratons. Thermobarometric data are fitted to a model steady-state geotherm with an exponential decrease in heat production with depth using a geologically constrained value of surface heat production at Jericho. The estimated model values of surface heat flow (Q₀ = 52-53 mW/m²) show an excellent agreement with two heat flow measurements available for the Slave craton (53-55 mW/m²). Thus, the cool upper mantle here coexists with a highly radiogenic crust.

Keywords: mantle xenolith;peridotite;pyroxenite;Slave craton;thermal state

Pages 79-104

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