Duration and periodicity of kimberlite volcanic activity in the Lac de Gras kimberlite field, Canada and some recommendations for kimberlite geochronology

摘要

Establishing the emplacement ages and distribution pattern of Central Slave kimberlites has played a key role in diamond exploration within the Lac de Gras kimberlite field. Nonetheless, emplacement age information is lacking for approximately 80% of the known kimberlites in this field making the assessment of emplacement age patterns difficult. This study expands the number and geographic coverage of kimberlite emplacement ages within the Lac de Gras field to re-assess the absolute timing, duration, and possible number of pulses of kimberlite eruption. U-Pb perovskite ages for eight previously undated kimberlites and an additional thirteen kimberlites, which were previously dated by either the Rb-Sr or U-Pb methods, fall within the age range of 75-45 Ma, as previously suggested for kimberlite magmatism in this area. We report the first Carboniferous age kimberlite in the Central Lac de Gras field - the Eddie kimberlite - with a U-Pb perovskite age of 321.0 +/- 3.0 Ma. A compilation of 57 kimberlite emplacement ages from the central Lac de Gras field was evaluated using probability density and mixture modeling methods. Five short-duration (4-5 Ma) periods of kimberlite magmatism are recognized at 48, 54, 61, 66 and 72 Ma; the three younger pulses have been previously recognized and remain relatively unchanged. The 54 Ma pulse represents the major kimberlite eruption event containing similar to 40% of the currently dated kimberlites in Lac de Gras field. A detailed evaluation of the temporal-spatial evolution of Lac de Gras kimberlites reveals that the oldest diamond-poor kimberlites (75-60 Ma) were emplaced in the northern and eastern parts of the field whereas the younger (55-48 Ma) economic kimberlites are concentrated in the center of the field. (C) 2015 Elsevier B.V. All rights reserved.