INTERPRETATION OF VOLCANIC STRUCTURES, ICE SPRINGS COMPLEX, BLACK ROCK DESERT, UTAH

The Ice Springs Complex is an area of recent (>600 ya) volcanism within the Black Rock Desert west of Fillmore, Utah, that has been influenced by E-W crustal extension and subsequent vertical crustal thinning related to the formation of the Basin and Range Province. The Complex is made up of several large cinder cones. The area has been subjected to both the regional stress field of the Basin and Range and local stress field of the cones, and to the processes of inflation and deflation of the lava flows. These processes created a number of previously unexplained structures.

The cones have been disturbed due to mining in the area, so the field site was constrained to the flows from Miter Crater for the purpose of this study. The regional stress field resulted in the creation of a normal fault oriented 015° and with a minimum displacement of 17.2 m out of the northern edge of the Miter flows, prior to flow emplacement. A flow that breached west out of Miter Crater resulted in the creation of a N-S trending scarp that shows morphology characteristic of inflation. The scarp marks the western boundary of the flow and indicates a stagnation point in the flow’s advance. The resulting inflation was responsible for creating a monoclinal boundary between the inflated flow and an older, chemically distinct flow. A breach at the western scarp of the inflated flow allowed pulses of magma to spill out past the stagnation point, which then cooled and inflated to create anastomosing fractures seen on the lower side of the scarp. Fractures seen on the upper side of the scarp are associated with the stresses of inflation of the original flow. The drainage of lava through the breach also led to the collapse of a large central area of the inflated flow. This process of collapse left a flat, depressed area bounded by scarps that show vertical lineations, and that houses several large basalt mounds that share similar columnar jointing patterns to small tumuli in the area. We theorize the different characteristics of the mounds are the result of tumuli that have been subjected to deformation of the subsidence of the area. This study demonstrates that analysis of structures found at Ice Springs provides valuable insight into the processes that affect the flow during and after emplacement, and what stresses are the dominant actors in creating structures within the lava flows.