Multi-stage construction of the Little Cotton wood stock, Utah, USA: Origin, intrusion, venting, mineralization, and mass movement

Abstract Many porphyry molybdenum deposits are hosted in multi-phase plutons, but it is unclear some how these magmas originated and whether the pluton intruded as fractionated or was by new batches of magma. New mapping has clarified field relationships between units White Pine Mo system Little Cottonwood stock, Utah (western United States), including intrusion, Red porphyry, rhyolite dikes, phreatomagmatic pebble dikes. Geologic relations geochemistry show formed a continental arc setting during rollback subducting Farallon slab rather than extension related to orogenic collapse. Whole-rock shows distinct fractionation trends for each major intrusive composite pluton, suggesting they separately, which supported U-Pb zircon laser ablation–inductively coupled plasma–mass spectrometry (LA-ICP-MS) ages ca. 30 Ma 27 26 previously undated porphyry. Mineral textures, cross-cutting relationships, alteration mineralogy indicate that intrusion youngest phase led fluid-saturated magmatic triggered venting, emplacement In adjacent east Traverse Mountains, dikes contain clasts have similar mineral assemblages, igneous deposit. This indicates Mountains upper lower parts same magmatic-hydrothermal system, decapitated mega-landslide likely facilitated Oligocene hydrothermal later Basin Range faulting.