Jennifer Lindline

THE CERRO COLORADO CINDER CONE, CERROS DEL RIO VOLCANIC FIELD: A STUDY OF MELT EVOLUTION AND PLUMBING SYSTEM DYNAMICS

Cerro Colorado is a 2.5-2.6 Ma dissected cinder cone in the Cerros del Rio volcanic field, west of Santa Fe, NM. The volcano stands 2225 m high and includes a well-defined 325 m diameter central vent characterized by inward dipping beds of moderately to strongly welded and highly oxidized scoria deposits and effusive lava flows. These transition sharply to periclinally dipping wall facies composed of vesiculated fragments, oxidized and unoxidized cinders, spatter agglutinate, and lava flows. While Cerro Colorado units follow general cinder cone facies patterns (central crater facies, proximal and distal wall facies) and granularity trends (decreasing cinder size away from summit), exposed sections deviate from the idealized cinder cone models. Several wall facies outcrops show multiple and regular alternations between explosive (pyroclastic falls) and effusive (lava flows) cycles. Pyroclastic deposits are highly vesiculated while lava flows are noticeably non-vesicular. These observations indicate that Cerro Colorado eruptions fluctuated from undegassed to degassed events, implying the existence of a shallow magma storage reservoir and challenging the simple feeder-dike plumbing system cinder cone model.