PRELIMINARY PETROLOGY AND GEOTHERMOMETRY OF PYROXENITE AND PERIDOTITE XENOLITHS FROM STIKINIA LITHOSPHERE, CRAVEN LAKE VOLCANIC CENTER, NORTHERN CORDILLERAN VOLCANIC PROVINCE, BC

This research documents textures and mineral compositions of ultramafic xenoliths from the Pleistocene Craven Lake volcanic center, in north-central British Columbia. The samples are the most southerly documented occurrence of peridotite xenoliths found within the northern Cordilleran volcanic province (NCVP). The mineral textures and compositions were documented with a standard petrographic microscope and JEOL 5900 Scanning Electron Microscope with an Oxford Energy Dispersive Spectrometer. Four different types of ultramafic xenoliths have been identified based on mineralogical and textural differences. Type 1 comprises 50% olivine (Ol) with maximum dimensions (MD) ranging from 1.0 mm - 1.5 mm, 20% clinopyroxene (Cpx) with MD ranging from 1.0 mm – 2.0 mm, 10% orthopyroxene (Opx) with MD ranging from 1.0 mm – 2.0 mm, 5% spinel (Spl) with MD ranging from 0.025 mm – 2.0 mm, and 15 % hornblende (Hrn) with MD ranging from 0.25 mm – 2.5 mm. The average density for Type 1 is 3.10 g/cm3. Type 1 also contains a vein of Hrn and apatite (Ap), which varies from 1.0 mm - 3.0 mm in thickness. Type 2 comprises 60% Ol with MD ranging from 0.25 mm -1.0 mm, 25% Opx with MD ranging from 0.5 mm – 1.5 mm, 10% Cpx with MD ranging from 0.5 mm – 2.0 mm, and 5% Spl with MD ranging from 0.2 mm – 1.0 mm. The average density for Type 2 is 3.21 g/cm3. Type 2 is unique in the suite because it has a smaller grain size and more Opx than Cpx. About one-third of the Ol grains exhibit deformation twins. Type 3 comprises 70% Ol with MD ranging from 0.5 mm – 3.0 mm, 15% Cpx with MD ranging from 0.5 mm – 1.25 mm, 10% Opx with MD ranging from 0.5 mm - 1.5 mm, and 5% Spl with MD ranging from 0.25 mm – 2.0 mm. The average density for Type 3 is 3.26 g/cm3. Type 4 comprises 60 % Cpx with MD ranging from 0.25 mm - 6.5 mm, 40 % Opx with MD ranging from 0.5 mm - 3.0 mm, and < 5% Spl with MD ranging from 0.25 mm - 2.0 mm. The average density for this type was 3.24 g/cm3. Type 4 is unique to this suite because of its lack of Ol. Preliminary two pyroxene QUIlF geothermometry yields temperature estimates of 1050 to 1100 deg C at pressures of 10 kb.