Transtensional deformation and structural control of contiguous but independent magmatic systems: Mono-Inyo Craters, Mammoth Mountain, and Long Valley Caldera, California

摘要

The Long Valley region of eastern Californian(United States) is the site of abundantnlate Tertiary–present magmatism, includingnthree geochemically distinct stages of magmatismnsince ca. 3 Ma: Mammoth Mountain,nthe Mono-Inyo volcanic chain, and LongnValley Caldera. We propose two tectonicnmodels, one explaining the Mammoth Mountain–nMono-Inyo magmatism and the othernexplaining the presence of Long Valley Caldera.nFirst, the ongoing Mammoth Mountain–nMono-Inyo volcanic chain magmatismnis explained by a ridge-transform-ridge system,nwith the Mono-Inyo volcanic chain actingnas one ridge segment and the South Moatnfault acting as a transform fault. Implicit innthis fi rst model is that this region of easternnCalifornia is beginning to act as an incipientnplate boundary. Second, the older Long ValleynCaldera system is hypothesized to occurnin a region of enhanced extension resultingnfrom regional fault block rotation, specifincally involving activation of the sinistralnfaults of the Mina defl ection. The tectonicnmodels are consistent with observed spatialnand temporal differences in the geochemistrynof the regional magmas, and the westwardnprogression of magmatism since ca. 12 Ma.