Presentation on theme: "R. A. De Hon 2011 SWAAG, Austin, TX CRATER MORPHOLOGIES IN MONOGENETIC VOLCANIC FIELDS OF WESTERN NEW MEXICO."— Presentation transcript:
R. A. De Hon 2011 SWAAG, Austin, TX CRATER MORPHOLOGIES IN MONOGENETIC VOLCANIC FIELDS OF WESTERN NEW MEXICO
THIS PRESENTATION As title states… Morphology of landforms in three monogenic volcanic fields in western New Mexico Specifically, the morphology of… Maar craters Tuff rings Cinder cones and modification of these forms Located in … Red Hill-Quemado Volcanic Field Bandera Volcanic Field Mt. Taylor-Mesa Chivato Volcanic Field
Mesa Chivato Bandera (Malpias) Red Hill MAAR CRATERS Arizona New Mexico
WITH SPECIAL ATTENTION TO MAAR CRATERS Maar craters are formed when magma encounters groundwater. The resultant venting to the surface excavates a bowl-shaped pit surrounded by a tuff ring that resembles a meteorite crater. The term maar comes from a Franconian dialect for lake derived from the Latin “mare” (sea). In the type locality—the Efiel Region of Germany— the craters extend below the water table and are occupied by lakes. Maar craters range in size from a few hundred meters to several kilometers in diameter. Their eruptive history consists of repeated venting over a period of weeks or months.
ULTIMATE OBJECTIVES Volcanic morphometry with attention to craters and their modification by later eruption or erosion Early ejecta as sampling of subjacent rock materials Application to Martain volcanic craters.
WHY SHOULD YOU CARE? The earliest ejecta in maar craters provide a sampling of subjacent strata. At some localities the ejecta incudes mantle xenoliths. Mantle Xenolith Kilbourne Hole, NM
ZUNI SALT LAKE 1 km
Air Fall Lapilli Tuff, Zuni Salt Lake Maar
Base surge and Air Fall Vent Opening Breccia Breccia contain blocks of subjacent rocks including basement granites and in some localities mantle xenoliths
Base Surge and Air Fall Bedded Deposits Vent Opening Breccia RIM DEPOSITS AT KILBOURNE HOLE
Base Surge Beds Bomb Sag Accretionary Lapilli
N 100 km Location of volcanic vent structures in western New Mexico
EXAMPLE: MAAR—HUECO CRATER Basal Diameter1150 meters Crater Diameter 718 Rim Height (h) 75 Crater Depth (d) 98 d h
La Jolla Maar, Mesa Chivato 1 km Many maare in the region are characterized by concentration of scrub vegetation on raise tuff rings.
LA JOLLA MAAR, MESA CHIVATO Basal Diameter1200 Crater Diameter 930 Rim Height 15 Crater Depth 36
Tuff Rings Depth vs. Height
PRISTINE Tuff Ring Maar Cinder cone VOLCANIC CENTRAL VENT VARIATIONS 1 km All profiles to same scale. Variation in size and morphology is chiefly due to the duration of eruptions and volume of material ejected. Composition of ejecta changes as eruption progresses… Lava Scoriaceous cinders Epiclastic bedded tuff Early xenolith-rich breccia
VENT MORPHOLOGY Magma and ground-water interaction Duration of activity Accidental ejecta Pyroclastic Lava Resistance of country rock Slumping during eruptive phase Degradation following eruption
Highly eroded -or- Blew its top? Floor above surface
RED HILL MAAR Maar with floor cinder cones
Cone filling maar
Rimless depression (erosional remnant of maar crater )
Renewed activity Pristine Degraded Cone filling maar Tuff Ring Breached crater Cone-in-maarMaarRimless depression Explosion crater?Cinder cone Scoria Mound VOLCANIC CENTRAL VENT VARIATIONS 1 km All profiles to same scale. Morphological variations corresponding to renewed eruptions or by erosional degradation
SO, WHAT? THE POINT IS… Earliest maar ejecta provides a sample of substrate materials. Those early materials may be preserved in a variety for subsequent volcanic structures. Someday…maar craters and their variants will be important sites to visit on Mars.
CREDITS PREVIOUS WORKERS IN WESTERN NEW MEXICO VOLCANIC FIELDS Jayne C. Aubele Larry S. Crumpler A. W. Laughlin P. W. Lipman C. Maxwell And many others