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www.postersession.com Conclusions Acknowledgements D. Robillard , C. Taylor, T. Smith, J . Brousseau , J. Lofto , B . Johnston Supervised by Sandra Johnstone, as part of GEOL 300: Igneous & Metamorphic Petrology course requirements, Spring 2015 Nanoose Geology Geochemistry Petrography In order to determine the nature of metamorphism, 9 thin sections (7 from 2015; 2 from 2009) were analyzed using petrographic microscopes. Photomicrographs of basalt from each site are shown below in plane polarized light (PPL) and cross polarized light (XPL). Predictions or Comments Similar anomaly at Nankivell Point (as outlined in the 2009 study)? Results show a Karmutsen signature within mapped Sicker Group territory Evidence of contact metamorphism? Hornblende-hornfels-type (contact ) metamorphism adjacent to intrusion Different geochemical signatures proximal to the intrusion? Basalt at Sites 1 & 2 display variable and inconsistent geochemical affinites Sincere thanks to the following contributors: • Acme Labs in Vancouver, BC, for geochemical analysis. • Vancouver Petrographics in Langley, BC, for thin sections. • Students of GEOL300 for their participation in field studies. • Sandra Johnstone for her guidance in completing this research. Results suggest that geochemical anomalies at Nankivell Point may be explained through contact metamorphism. Based on geochemical and petrographic observations, we interpret that the basalt as Nankivell Point may represent metamorphosed Sicker Group basalt. However, further sampling is necessary. Recommendations for future research: 1. Produce detailed geologic maps for all three sites. 2. Collect more samples and analyze metamorphic variability closer to and further from the intrusive contact at Nankivell Point 3. Investigate the validity of mapped Karmutsen Fm. at Site 1. Fig. 1. Current BCGS geology map of the Nanoose Peninsula study area. Note the location of 3 sample sites. Site 1 is located at “Ainsley Beach” where Karmutsen Fm. basalt shares a suspected fault-related contact with a quartz-diorite “Island Intrusion” of the Bonanza Arc. Site 2 is located at Nankivell Point where quartz-diorite shares an intrusive relationship with basalt interpreted as part of the Sicker Group [8] . Site 3 is located along Dolphin Beach where Sicker Group pillow basalt is most dominant. Sicker-type-rocks associate with the Nanoose Complex (mapped in blue); however, stratigraphic relationships are unclear; age constraints are broadly Paleozoic [8] . Map derived from BCGS data available at mapplace.ca. Base map modified by Robillard et al. (2015). Field Photos Regional Geology • Vancouver Island is mostly of the exotic Wrangellia terrane, which formed during three major volcanic episodes [2] : 1. Sicker Group island - arc volcanism ( 380 - 360 Ma) [8] . These rocks comprise the basement of Wrangellia and are overlain by limestone of the Buttle Lake Group. 2. Karmutsen Fm . ocean - island volcanism ( 230 - 225 Ma) [3] . Karmutsen basalt represents the most widespread unit on Vancouver Island and is overlain by Quatsino Fm. limestone. 3. Bonanza island - arc volcanism ( 202 - 168 Ma) [1] . Bonanza rocks represent the final episode of Wrangellian volcanism and commonly intrude older Wrangellian rocks. • Wrangellia collided with North America ~100 Ma [8] . Thus, rock units comprising Wrangellia are commonly folded and faulted. The geology of Nanoose is not well understood [8] . Mafic volcanic rock (i.e., basalt) is currently mapped as Sicker Group in the northeast and Karmutsen Formation (Fm.) in the southeast (Fig. 1). However, a 2009 study by VIU students suggests that Sicker Group basalt at Nankivell Point may actually be part of the Karmutsen Fm. The goal of this research is to investigate an anomalous geochemical result from the 2009 study at Nankivell Point in order to determine if (a) basalt is incorrectly mapped as Sicker Group, or (b) if metamorphism is causing this anomaly. If basalt at Nankivell Point is incorrectly mapped as Sicker Group (and is in fact Karmutsen Fm.), we expect a lack of contact metamorphism in addition to Karmutsen signatures on AFM, MnO/TiO 2 /P 2 O 5 , TAS, and Harker diagrams. If, however, metamorphism is responsible for geochemical anomalies reported in 2009, we expect contact metamorphic mineral assemblages and different geochemical signatures in samples closer to and further from a local intrusive body. 1. Canil, D., Styan, J., Larocque, J., Bonnet, E., & Kyba, J. (2010). Thickness and composition of the Bonanza arc crustal section, Vancouver Island, Canada. Geological Society of America Bulletin, B26578-1. 2. DeBari, S.M., Anderson, R.G., & Mortensen, J.K. (1999). Correlation among lower to upper crustal components in an island arc: the Jurassic Bonanza arc, Vancouver Island, Canada. Canadian Journal of Earth Sciences, 36(8), 1371-1413. 3. Greene, A.R., Scoates, J.S., Weis, D., Nixon, G.T., & Keiffer, B. (2009). Melting history and magma evolution of basalts and picrites from the accreted Wrangellia ocean plateau, Vancouver Island, Canada. Journal of Petrology. 4. Le Maitre, R. W., Streckeisen, A., Zanettin, B., Le Bas, M. J., Bonin, B., & Bateman, P. (Eds.). (2002). Igneous rocks: a classification and glossary of terms: recommendations of the International Union of Geological Sciences Subcommission on the Systematics of Igneous Rocks. Cambridge University Press. 5. Massey, N.W.D. (1995). Geology and mineral resources of the Alberni-Nanaimo Lakes sheet, Vancouver Island: 92F/1W, 92F/2E, 92F/7E. British Columbia, Geological Survey. 6. Massey, N.W.D. (1995). Geology and mineral resources of the Cowichan Lake sheet, Vancouver Island: 92C/16. British Columbia, Geological Survey. 7. Winter, J.D. (2010). Principles of igneous and metamorphic petrology, 2nd Ed. Prentice Hall. 8. Yorath, C.J., Sutherland, A., and Massey, N.W.D. (1999). Lithoprobe, Southern Vancouver Island, British Columbia: Geology, Geological Survey of Canada Bulletin 498. Whole-rock geochemistry for 7 basalt samples (5 from 2015; 2 from 2009 study) was analyzed using inductively coupled plasma mass spectrometry (ICP-MS). These data are compared with published geochemical data [3,5,6,8] on Karmutsen Fm. and Sicker Group rocks. Site 1 hosts 2 different varieties of altered basalt. Further from the intrusion, sulphide-bearing “basalt” is heavily altered and contains some clastic material of unknown composition (Fig. 6). Closer to the contact, typical fine-grained basalt is less oxidized and contains some 2 mm amygdules of calcite and cubic pyrite (Fig. 2). Site 2 also hosts 2 types of altered basalt. Further from the intrusion, brown-hornblende-rich basalt (Fig. 3) contains mineral assemblages that may suggest hornblende-hornfels-facies metamorphism. Close to the intrusion, clinopyroxene is more dominant and overprints twinned plagioclase phenocrysts (Fig. 4). Site 3 showcases dark-green, opaque-rich, plagiophyric pillow basalt (Fig.6). Mineral assemblages (Fig. 5) resemble those characteristic of prehnite-pumpellyite to lower-greenschist-facies metamorphism [7] . Fig. 6. ( ) Alteration and clasts noted in basalt at Site 1. Clastic material is not characteristic of Karmutsen Fm. basalt. ( ) Intrusive contact at Site 2, marked by abundant dykes and felsic veins. ( ) Green pillow basalt at Site 3 is interpreted as part of the Sicker Group. Photos by Sandra Johnstone. Na 2 O + K 2 O Fe 2 O 3 T MgO Derived from more-evolved magma MnO*10 TiO 2 P 2 O 5 *10 0 2 4 6 8 10 12 14 37 42 47 52 57 62 67 72 77 Na 2 O + K 2 O (wt. %) SiO 2 (wt. %) 0 1 2 3 4 5 6 7 8 42 47 52 57 62 67 72 77 Na 2 O (wt. %) SiO 2 (wt. %) 0 5 10 15 20 42 47 52 57 62 67 72 77 Al 2 O 3 (wt. %) SiO 2 (wt. %) 0 2 4 6 8 10 12 14 16 18 20 42 47 52 57 62 67 72 77 CaO (wt. %) SiO 2 (wt. %) 0 5 10 15 20 25 42 47 52 57 62 67 72 77 Fe 2 O 3 T (wt. %) SiO 2 (wt. %) 0 2 4 6 8 10 12 14 16 18 20 42 47 52 57 62 67 72 77 MgO (wt. %) SiO 2 (wt. %) (a) (b) (c) (d) (e) (f) (g) (h) (a) AFM diagram. Sicker Group plots dominantly calc-alkaline, while Karmutsen Fm. plots tholeiitic. Note considerable signature overlap. (b) MnO/TiO 2 /P 2 O 5 diagram. Note distinct separation between Sicker Group and Karmutsen Fm data. Site 1 & 2 samples vary with location. (c) TAS diagram. Boundaries define specific volcanic rock types [4] . Sicker Group data spans various rock types; Karmutsen Fm. plots strongly within the basalt category [4] . No genetic significance implied. (d-h) Harker diagrams. Major oxides are plotted against SiO 2 . Plots show consistent trends. However, notice that overlap is significant. Introduction References Fig. 2. Fine-grained basalt in PPL (left) and XPL (right). Clinopyroxene overprints feldspar laths. Opaques represent Fe-Ti oxides and cubic pyrite. 50 μ m 50 μ m 200 μ m 200 μ m 50 μ m 50 μ m Sicker affinity: Karmutsen affinity: Sicker affinity: Karmutsen affinity: Sicker affinity: Karmutsen affinity: Sicker affinity: Karmutsen affinity: Fig. 3. Brown-hornblende-rich basalt in PPL (left) and XPL (right). Hornblende dominates and crystallizes with glomeroporphyritic style. 50 μ m 50 μ m Fig. 4. Typical fine-grained basalt in PPL (left) and XPL (right). Plagioclase is overprinted by abundant clinopyroxene. Note similarities with Fig. 2. Fig. 5. Quartz-epidote vein in PPL (left) and XPL (right). Also note fibrous pumpellyite—an indicator mineral for prehnite-pumpellyite metamorphism [7] . Calc-alkaline Tholeiitic Basalt Data Legend *Note the location of each sample relative to the intrusion Published Data: Sicker Group Karmutsen Formation WELCOME TO NANOOSE PENINSULA Nankivell Point “Ainsley Beach” Dolphin Beach 1 2 3 1:30,000 1 km Bonanza Arc “Island Intrusions” Sicker-related “Nanoose Complex” Karmutsen Fm. Fault structure Ocean Site number Nanoose Study Area Lantzville Nanaimo Schooner Cove Sicker Group Karmutsen Fm. e pidote a ltered plagioclase hornblende clinopyroxene
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