The influence of mantle plume in the genesis of the Cache Creek oceanic igneous rocks: implications for the geodynamic evolution of the inner accreted terranes of the Canadian Cordillera

West of Prince George, British Columbia, the Cache Creek Terrane is compose d of mafic lavas interlayered with both mid-Permian pelagic limestones and Upper Triassic siliceous shales and greywackes. Gabbro, basalt, dolerites, and foliated clinopyroxene-rich ultramafic rocks are exposed within the Pin chi Fault system. The mid-Permian lavas show affinities of oceanic island t holeiites. Among the Triassic lavas, three types of rocks have been disting uished. Type 1 is geochemically similar to the mid-Permian volcanic rocks. Type 2 differs from type 1 by higher TiO2 abundances and convex rare earth element patterns. Type 3 has the highest Zr, Nb, and Ta abundances and the greatest light rare earth element enrichment. The mafic rocks within the Pi nchi Fault system are similar to N-type mid-ocean-ridge basalt (N-MORB), an d the foliated ultramafic rocks are characterized by very low trace element contents, similar to extremely depleted harzburgites. Permian lavas and Tr iassic type 1 and igneous rocks from the Pinchi Fault system have the highe st epsilon(Nd(i)) ratios (+7.4 to +9.6) and those of type 3 alkali have the lowest ratios (+2.0 to +5.3). The epsilon(Nd(i)) values of type 2 are inte rmediate between those of type 1 (similar to +7) and type 3 (similar to +4. 9). This suggests that the Triassic rocks generated from a heterogeneous pl ume source or the mixing between depleted N-MORB and enriched oceanic islan d basalt sources. If the mafic igneous rocks sampled in central British Col umbia are representative of the preserved parts of an oceanic crust, within the Cache Creek Terrane, then that crust was dominated by oceanic plateau components, perhaps due to the difficulty of subducting thick crust.