Thermal history and petrology of wood and other organic inclusions in kimberlite pipes at Lac de Gras, Northwest Territories
L D Stasiuk, Walter W. Nassichuk · 1995
Dispersed peatified to coalified wood and other macerals within the crater and diatreme facies of kimberlite pipes at Lac de Gras have been studied using reflected light microscopy. The coalification levels fall into two categories: i) cellulose-bearing, lignitic peat (<0.20 %Ro); and ii) lignite to sub-bituminous (0.33-0.44 %Ro). The latter are from the diatreme facies whereas most of the low rank samples are from the crater facies. The average temperature of lignitic peat never exceeded 30°C. Huminite from the diatreme facies was subjected to higher temperatures but none of the huminites display microscopic features attributable to pyrometamorphism. If the wood in the diatreme is primary, a short heating event (about 100°C) may have enhanced coalification without altering peat in the crater facies. Alternatively, if huminite in the diatreme represents pre-intrusion burial, coalification and pre-Paleocene erosion may have occurred. The preservation of primary, asphalt bitumen supports a maximum temperature of less than 110°C.