TECTONIC CONTROLS ON VOLCANIC STYLES OF A SUPERVOLCANO FIELD: THE TEMORIS – CEROCAHUI REGION OF THE COPPER CANYON, NORTHERN SIERRA MADRE OCCIDENTAL (MEXICO)
In a recent summary of all LIPs on Earth, Bryan and Ernst (2008) listed the SMO as the only one that did not form atop an extensional terrane. However, our new work shows that, in the Temoris-Cerocahui region of Copper Canyon, the underlying andesite arc rocks (referred to in the region as “Lower Volcanic Complex”, LVC) were offset hundreds of meters on syndepositional normal faults immediately prior to the ignimbrite flareup (Upper Volcanic Complex, UVC). These mainly NNW-SSE trending normal faults and ENE-WSW-trending transfer zones were then partially reactivated during eruption of the UVC, and served to localize lines of plugs and fissure-like intrusions several kilometers long and 100’s of meters wide. Some of these linear intrusions pass upward into lava flow belts, and are fringed by linear belts of proximal ignimbrite. The fissure-proximal ignimbrite belts have abundant andesite blocks in cross-stratified units with set heights of 5 – 20 m. We infer that the blocks were derived from intensely fractured LVC andesites along the fissures; the distinctive mega-surge-like character of the lithic ignimbrite may reflect a higher flux for explosive eruption along fissures, relative to central vents.
Bryan, S., and Ernst, R.E., 2008, Revised definition of Large Igneous Province (LIP): Earth and Planetary Science Letters, v. 86, p. 175-202.