Conuma River and Leagh Creek intrusive complexes: windows into mid-crustal levels of the Jurassic Bonanza island arc, Vancouver Island, British Columbia

The Conuma River and Leagh Creek intrusive complexes are examples of mid-crustal portions of the Jurassic Bonanza island arc, located on Vancouver Island, British Columbia, Canada. The Conuma River locality exhibits layered intrusions, consisting of alternating hornblenditic and hornblende gabbroic cumulates, occurring with numerous, contemporaneous small volume mafic to intermediate intrusions in tonalitic rocks. The Leagh Creek intrusions exhibit extensive silicic and basaltic magma mingling. Both complexes are interpreted as products of multiple magma pulses into the solidifying host intrusions. Two new radiometric hornblende Ar-Ar ages suggest Early to Middle Jurassic ages for two intrusions from each of the complexes. Geochemical crystallization modeling shows a genetic link between the Conuma River cumulate hornblenditic and non-cumulate hornblende gabbroic intrusions via dominantly olivine fractionation. Conversely, most of the intrusions of both complexes cannot be related by simple crystallization modeling, suggesting a complex history, involving magma mingling and assimilation processes.