The anatomy of a cinder cone: preliminary paleomagnetic, rock magnetic, structural, and petrologic data from the La Cienega volcano, Cerros del Rio volcanic field, northern New Mexico
Abstract
The Cerros del Rio volcanic field is one of several middle Pliocene to Pleistocene basaltic volcanic fields of the axial Rio Grande Rift in central and northern New Mexico. It is a monogenetic volcanic field that comprises about 60 cinder-spatter cones, occupies ~ 700 km2, and ranges in age from 2.7 Ma to 1.1 Ma. Eruptive centers are typically central vent volcanoes, ranging from low-relief shields to steep-sided, breached cinder and spatter cone remnants. They represent short eruptive events that likely were derived from rapidly evolving reservoir-conduit systems. Mining activity has exposed the volcanic plumbing system of the Cienega Mine cinder cone, just west of Santa Fe, NM. Here, geologists from France and USA have been investigating the exposed roots of this eviscerated Pliocene volcano to investigate magma conduit geometry, magma flow structures, and eruption patterns. We are testing models for magma transport and volcano construction using a variety of field and laboratory tools. Common models of volcanic construction envision the magma feeder as a dike or pipe-like conduit transporting molten rock from a deep reservoir to the eruptive vent. We posit that small volcanic pluming systems are inherently more complex and actually involve numerous feeder geometries throughout the volcano lifespan. Our preliminary work suggests that the simple exteriors of some cinder cones hide a long life and complex history, both of which would change the appreciation of the related volcanic hazards in active systems. The Cienega Mine cinder cone consists of several meter- to decimeter-wide intrusions that connect to eruptive centers. These intrusions show a continuity of brittle to ductile structures from their margins to interiors. We have collected samples across each intrusion as well as along strike for anisotropy of magnetic susceptibility (AMS) and petrographic analysis in order to establish magma flow patterns. AMS results yield a remarkably consistent dataset that coincides with shear-related structures (e.g., tension gashes, Riedel shears, elongate vesicles) and shows that magma flowed towards the remnant spatter cone. Ongoing paleomagnetic analysis is assessing the emplacement sequence. We postulate that as each dike was emplaced, it shouldered aside earlier dikes or the dikes may have been displaced by localized slumping of the edifice. Integrative petrofabric, field mapping, paleomagnetic, and AMS studies are providing important information about magma flow patterns and improving our understanding of the kinematics of magma flow beneath a volcano and the dynamic evolution of the volcanic construct and the potential hazards associated with magma migration beneath active volcanic centers on Earth and beyond.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2011
- Bibcode:
- 2011AGUFMGP23A1036P
- Keywords:
-
- 1518 GEOMAGNETISM AND PALEOMAGNETISM / Magnetic fabrics and anisotropy;
- 1527 GEOMAGNETISM AND PALEOMAGNETISM / Paleomagnetism applied to geologic processes;
- 1540 GEOMAGNETISM AND PALEOMAGNETISM / Rock and mineral magnetism;
- 8486 VOLCANOLOGY / Field relationships