CRATER MORPHOLOGIES IN MONOGENETIC VOLCANIC FIELDS OF WESTERN

CRATER MORPHOLOGIES IN MONOGENETIC VOLCANIC FIELDS OF WESTERN NEW MEXICO R. A. De Hon 2011 GSA Annual Meeting

Rebranded THE SIGNIFICANCE OF MAARS ON EARTH AND MARS R. A. De Hon 2011 GSA ANNUAL MEETING

THIS PRESENTATION • As original title states… Morphology of landforms in three monogenic volcanic fields in western New Mexico • Specifically, the morphology of… Maar craters Tuff cones Cinder cones • Located in …New Mexico: Red Hill-Quemado Volcanic Field Bandera Volcanic Field Mt. Taylor-Mesa Chivato Volcanic Field

WITH SPECIAL ATTENTION TO MAAR CRATERS • Maar craters are formed when magma encounters groundwater. The resultant steam explosion 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.

CREDITS – PREVIOUS WORKERS • Jayne C. Aubele • Larry S. Crumpler • A. W. Laughlin • P. W. Lipman • C. Maxwell • And many others

WHY DO WE CARE? • Early ejecta in maar craters contain accidentals from underlying strata. • Occasionally the ejecta incudes mantle xenoliths. • Maare on Mars may be unique sites to obtain deep crustal samples. Mantle xenolith Kilbourne Hole, NM

ULTIMATE OBJECTIVES • Volcanic morphometry with attention to explosive craters and transitional forms • Early ejecta as sampling of subjacent rock materials • Magma, vapor, country rock interactions and final crater morphology • Application to Mars volcanic craters and possibility of maar craters as crustal sampling sites

This talk

Mesa Chivato Bandera (Malpias) Red Hill MAAR CRATERS in Northeast New Mexico

N 100 km

CHAIN OF CRATERS BANDERA FIELD Maar

ZUNI SALT LAKE 1 km

CERRO AMERICO 1 km

EXAMPLE: CINDER CONE—CERRO AMERICO Basal Diameter 1 237 meters Crater Diameter 269 Cone Height 118 Crater Depth 41

1 km BANDERA CRATER

EXAMPLE: TUFF RING—BANDERA CRATER Basal Diameter Crater Diameter Rim Height Crater Depth 1156 556 128 156

HEUCO CRATER 1 km

EXAMPLE: MAAR—HUECO Basal Diameter 1150 meters Crater Diameter 718 Rim Height 75 Crater Depth 98

Scoria mound

Curve is best fit to Red Hill and Mesa Chivato data CD Cd

Depth vs. Height gs ff Tu n Ri

Base surge and Air Fall— Reworked shallow sublacent material Vent Opening Breccia— Most of the subcrater xenoliths are found here.

VOLCANIC CENTRAL VENT VARIATIONS PRISTINE Constituents of the eruption changes as eruption progresses… Lava Variation in size is chiefly due to the duration of eruptions and volume of material ejected. Cinder cone Scoraceous cinders Tuff Ring Epiclastic tuff Maar 1 km All profiles to same scale. Early xenolith-rich breccia

VENT MORPHOLOGY A FUNCTION OF • Composition of magma and volatile content of magma • Depth of magma and groundwater interaction • Volatiles in country rock • Connate water • Ground ice • Continuing activity • Pyroclastic • Lava • Resistance of country rock • Slumping during eruptive phase • Degradation following eruption

Highly eroded -or. Blew its top?

Crater-in-crater

Rimless depression

RED HILL MAAR with internal cinder cones

Cone filling maar

VOLCANIC CENTRAL VENT VARIATIONS Renewed activity Explosion crater? Pristine Cinder cone Cone filling maar Tuff Ring Cone-in-maar Maar 1 km All profiles to same scale. Degraded Scoria Mound Breached crater Rimless depression

SO, THE POINT IS… • Earliest maar ejecta provide a sampling of substrate materials. • Those materials may be preserved in a variety for subsequent structures. • Some day, in future exploration of Mars, maare will be important sites to visit and sample.

THANK YOU Mars Volcanic field